– SPECIAL FOUNDATION WORKS –

Support material

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Contents:

1. Diaphragm walls

2. Sheet piles walls

3. Ground anchors

4. Reinforced fills

5. Soil nailing

6. Bored piles

7. Displacement piles

8. Micropiling

9. Deep mixing

10. Deep vibration

11. Deep drainage

12. Grouting

13. Jet grouting

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1. DIAPHRAGM WALLS

Glossary Clamshell (or grab): Excavation tool with two jaws to remove soil, rock or debris from an

excavation by an intermittent operation. Jaws are attached to a steel frame. There are two main

types of clamshells.

— mechanical grabs using steel cables to open/close the jaws;

— hydraulic grabs using hydraulic circuits to open/close the jaws.

Hydrofraise (or cutter or mill): Excavation tool with rotating wheels fitted with steel picks to

remove soil, rock or debris from an excavation by a continuous operation.

Chisel: Heavy steel tool used to break up obstructions, boulders and hard strata encountered in the

excavation or for socketing into hard soil or rock. There are particular types of chisels used to

rectify an excavation trajectory, to extract stop ends, etc.

Kelly (bar): Shaft, often telescopic, connected between the power drive and the digging tool which

allows deep excavation.

Cable(s): Steel cable(s) suspending the digging tool which allows deep excavation.

Excavation crane: Crane used to handle the excavation tool (clamshell or hydrofraise).

Handling crane: Crane used to handle the reinforcement cages and other equipment.

Water stop: Special flexible element attached longitudinally to a stop end in such a way that half

of the water stop is embedded in concrete in a panel after the concreting and stop end extracting

operations. When constructing the adjacent panel, the other half of the water stop is released and

also becomes embedded in concrete. As a result, the water stop surrounded in concrete at the

contact zone between two panels helps to limit water leakage through this critical surface. Two

water stops can be installed at a same joint if required.

Overlap: The distance of a panel excavation into the material of an adjacent panel to ensure

diaphragm wall continuity when no stop ends are used. The overlapping technique (no stop ends) is

always used for hardening slurry walls, often used for plastic concrete walls and sometimes used

for cast-in situ concrete walls where a hydrofraise (mill) can be employed to breakdown hard

concrete at joints.

Filter cake: Thin pastelike deposit formed by bentonite particles aggregating as water drains from

the suspension to the ground through the edge walls of the excavation during its progress. This

filter cake allows the bentonite suspension pressure to be maintained above the ground water

pressure such that the excavation edge walls remain stable.

Cutting back: Removal of surplus concrete (protrusions, etc) and bentonite cake when exposing

the diaphragm wall panels.

Trimming: Removal of surplus concrete above the cut-off level

Capping beam: Reinforced concrete beam built above the cut-off level to connect the cast-in situ

diaphragm wall panels together and/or to connect to overlying structural elements.

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Air lift: Pumping technique in which air is pumped into the base of a suction pipe to cause reduced

density of material in the pipe and induce upward flow to evacuate solids and fluids (flushing). The

air lift technique may be used to clean/replace the bentonite suspension before concreting.

Pre-blasting: Preliminary operation consisting in drilling holes along the alignment of a diaphragm

wall to place explosives in very hard material and blast it before commencing the diaphragm wall

excavation.

Lean concrete: Very low strength, low fines concrete poured in a panel excavation to stop

bentonite loss, to fill voids or to fill panel excavation deviation. The characteristics of the lean

concrete should allow its re-excavation with normal tools.

Concreting curve: Diagram representing the volume of poured concrete versus depth.

Excavation curve: Diagram representing the excavation depth versus time.

Desanding unit: Plant to remove sand and silt in order to clean the support fluid during excavation

and before concreting.

Specific materials and products used for the execution of diaphragm walls

Bentonite

Bentonite is a clay containing mainly the mineral montmorillonite.

Bentonite is used in support fluids, either as a bentonite suspension or as an addition to polymers. It

is also used as a constituent part of hardening slurries and of plastic concrete.

Bentonite can contain additives (i.e. polymers) in aqueous suspension.

Bentonite used in bentonite suspensions shall not contain harmful constituents in such quantities as

can be detrimental to reinforcement or concrete.

Polymers

Polymers can be used as rheological additive to bentonite suspensions with a content of 0,1 – 1,5

mass % in relation to bentonite dry weight or as sole constituent.

Polymers are materials formed of molecules from chained monomeric units.

There are different types of polymers ranging from natural gums to specially tailored blends of

synthetic products.

Support fluids

Bentonite suspensions

A bentonite suspension shall be prepared with either natural or activated sodium bentonite.

In certain cases, e.g. when the density of the suspension has to be increased, suitable inert materials

may be added.

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Others than in exceptional circumstances, the fresh bentonite suspension shall meet the conditions

shown in Table 1 and the "re-use" or "before-concreting" bentonite suspension shall meet the

conditions shown in Table 2.

At the stage "before concreting", an upper limit value between 4 % and 6 % for sand content may

be used in special cases (e.g.: non load bearing walls, unreinforced walls).

The values in Tables 1 and 2 may be modified in special circumstances, for example in the case of:

– soils or rock with high permeability or cavities where loss of bentonite can occur;

– high piezometric ground water levels (confined or artesian conditions);

– very soft soils;

– salt water conditions.

A bentonite suspension with sufficient flow limit can be required by the design, e.g in order to

reduce penetration into the ground.

Table 1 — Characteristics for fresh bentonite suspensions

(1) see Table 2 , notes 1 to 3 for the test procedures

Table 2 — Characteristics for bentonite suspensions

Notes (1) The Marsh value, the fluid loss, the sand content and the filter cake can be measured, for

example, using the tests described in the American Petroleum Institute document "Recommended

Practice Standard Procedure for Field Testing Water-Based Drilling Fluids" (reference: American

Petroleum Institute Recommended Practice 13B-1, June 1, 1990).

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(2) The Marsh value is the time required for a volume of 946 ml to flow through the orifice of the

cone. A volume of 1 000 ml may be used, but in this case, the Marsh values given in tables 1 and 2

should be adjusted.

(3) The duration of the fluid loss test may be reduced to 7,5 min. for routine control tests. However,

in this case, the values for fluid loss and filter cake shall be adjusted. The fluid loss for the 7,5 min.

test will be approximately half of the value obtained in the 30 min test.

(4) Indicative values

Polymer solutions

Polymers may be designed to work in conjunction with bentonite or to be used as stand alone

support fluid.

Its use shall be based on full-scale trial trenches on the site or on the basis of comparable

experience in similar geotechnical conditions.

NOTE: EN 1997-1 defines comparable experience as an experience which relates to similar works

in similar conditions and is well documented or otherwise clearly established.

Fresh hardening slurries

The characteristics of the slurry shall be suitable to ensure satisfactory performance during

execution.

A hardening slurry may be prepared with calcium bentonite or activated sodium bentonite.

NOTE 1 Hardening slurries are generally used in the precast concrete diaphragm wall technique

and for slurry walls.

NOTE 2 Hardening slurries serve as support fluid during excavation, and, together with the fines

from the natural ground, form the final, hardened material.

Admixtures may be used to adjust setting time of the slury and its consistency during excavation

and during any subsequent insertion of elements.

Concrete

Unless otherwise stated, the concrete used in cast in situ concrete diaphragm walls or in precast

concrete diaphragm walls shall comply with SR EN 206.

For correct execution, the cast in situ concrete shall be designed to avoid segregation during

placing, to flow easily around the reinforcement, and when set, to provide a dense and low

permeability material.

The specified properties of the hardened cast in situ concrete, related to strength and durability,

shall be compatible with the consistency requirements.

In the case of a maximum aggregate particle size of 32 mm, the concrete mix shall have the

following characteristics:

– sand content (d ≤ 4 mm) greater than 40 % by weight of the total aggregate ;

– fine particles (d ≤ 80 µm) in the concrete mix (including cement and other fine

materials) between 400 kg/m3 and 550 kg/m3.

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The minimum cement content shall be related to the maximum aggregate size in accordance with

Table 3.

Table 3 — Minimum cement content for concrete

The water/cement ratio shall not exceed 0,6.

The admixtures allowed for concreting using tremie pipe(s) may be:

– water reducing/plasticizing;

– high range water reducing/super-plasticizing; and

– set retarding.

Admixtures may be used:

– to give a mix of high plasticity;

– to avoid bleeding, honeycombing or segregation that might otherwise result from a high

water content ;

– to prolong the consistency as required for the duration of the placement ;

– to cater for any interruptions in the placement process.

Fresh concrete

Concrete used for diaphragm walls shall:

– have a high resistance against segregation ;

– be of high plasticity and good cohesiveness ;

– have good flow ability ;

– have the ability to self-compact ; and

– be sufficiently workable for the duration of the placement procedure.

The slump test or the flow table test may be used to evaluate the consistence of the fresh concrete.

The consistence ranges of the fresh concrete in different conditions of use shall comply with Table

4.

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Table 4 — Consistency ranges for fresh concrete in different conditions

Consistency of the concrete should be monitored with time. A minimum slump of 100 mm after

four hours is recommended.

Plastic concrete

Plastic concrete shall be designed in order to obtain the required deformability and permeability,

together with adequate workability and strength.

Plastic concrete is used for cut-off walls when, in addition to low permeability, high deformability

is required.

Their constituent parts are:

fine grain material (e.g. silt, clay or bentonite);

cement or another binder;

well-graded aggregates;

water;

and possibly additions and admixtures.

For plastic concrete limiting w/c ratio does not apply.

Considerations related to design of diaphragm wall made of panels The panel dimensions should take into account the dimensions of available excavating equipment,

the method and sequence of excavation, panel stability during excavation and concrete supply.

The terminology used to define the dimensions and details of panels is shown on Figures 1 and 2.

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Key: 1 Wall thickness 7 Guide-wall

2 Horizontal length of reinforcement cage 8 Cut off level

3 Cage width 9 Vertical length of reinforcement cage

4 Length of panel 10 Reinforcement cage

5 Platform level 11 Depth of excavation

6 Casting level 12 Concave portion of curved joints

Figure 1 — Geometry of a panel

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Key: P Primary

S Secondary

1 Starter

2 Intermediate

3 Closure

Figure 2 — Schematic examples of different types of panels and joints (plan view)

The width of the excavating tool shall be at least equal to the design wall thickness.

The design of the wall shall take into account the discontinuity of the reinforcement at the joints

between the panels and between adjacent cages in the same panel.

Space shall be allowed between reinforcement cages of adjacent panels to accommodate the type of

joints to be made and to take account of the construction tolerances.

Space shall be allowed in the reinforcement cage for the installation of the tremie pipe.

A reinforced concrete capping beam should be constructed along the top of reinforced concrete

diaphragm walls, where it is necessary to distribute loads or minimize differential displacements.

In exceptional cases where it is necessary to provide structural continuity across the joints, special

techniques are available.

Design shall consider that diaphragm walls cannot be expected to be completely watertight, since

leakage can occur at joints, at recesses or through the wall material. Damp patches and droplets of

water on the surface of the wall cannot be avoided under normal circumstances.

Design should not normally consider continuity of reinforcement between the cages and across the

joints but it may be constructed in exceptional circumstances.

Panel stability during excavation The length of the panels and the level of the support fluid shall ensure the stability of the trench

during excavation.

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The excavation tools or procedures, especially where chiselling or blasting are used, can have an

influence on the trench stability.

Special precautions in chiselling and blasting have to be taken e.g in loose soil overlying a hard

rock.

To ensure trench stability the level of the support fluid shall be adjusted with respect to the highest

piezometric ground water level anticipated during excavation, and the support fluid level shall

always remain at least 1 m above the highest piezometric level.

In the case of loose sand or soils with cu < 15 kPa, it can be necessary to stabilise the soil by

increasing its strength or by raising the level of the support fluid and/or to increase its density

during excavation, and to minimize the time during which the trench is left open.

In case where a loss of support fluid can occur (e.g highly permeable, coarse soils or where there

are voids in the ground), special measures may be adopted, for example :

– increasing the flow limit of the fluid by increasing the bentonite content in the

suspension;

– adding a filler material to the bentonite suspension, either at the mixing plant or directly

in the trench;

– in the case of voids, filling the trench to an appropriate depth with lean mix concrete or

other suitable material, and reexcavating;

– grouting the layers concerned before excavating the trench.

The ground water level can change in relation with execution (e.g case of closing a box). Risk on

trench stability in relation with change in water level due to construction should be considered.

Also possible mitigation measures (e.g. dewatering as a way to reduce pore pressure) should be

considered.

The stability considerations shall take account of the following factors:

– stabilizing forces due to the support fluid ;

– groundwater pressures ;

– earth pressures, including the three-dimensional geometry of the problem ;

– shear strength parameters of the soils ;

– effects of adjacent loads ;

– constructions details of adjacent structures.

The trench stability during excavation includes two aspects:

– the local stability of the soil at the walls of the trench;

– the overall stability of the excavation.

The trench remains stable as a result of the stabilizing forces of the support fluid acting against the

walls of the trench:

– in case of bentonite suspensions, the support effect in fine-grained soils is due to the

formation of a filter cake. In coarser soils, this effect is due to a limited penetration into

the pores of the soil;

– in the case of polymer solutions, the support effect is caused by the seepage pressure of

the liquid flowing into the soil.

The penetration depth, which increases with time, is significant in the case of silty or sandy soils,

but remains small in the case of clayey soils.

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Reinforcement cages

The reinforcement within a panel may comprise one or more cages within the panel length.

Multiple cages and joints

The minimum clear distance between two cages in the same panel shall be at least 200 mm.

The maximum clear distance between two cages in the same panel should be 400 mm

The minimum clear distance between the ends of the cages and the joints formwork including

water-stop if any, shall be 100 mm and shall take into account the verticality tolerances, the shape

of the joints and the possible use of water stops.

A clear distance of 200 mm is recommended between the ends of the cages and the joints formwork

including water-stop if any.

In the case of the concave portion of curved joints, except special cases, the cage should not enter

into the concave portion of the joint.

This does not apply to the case of diaphragm walls with continuous horizontal reinforcement across

the joints.

Execution of diaphragm walls

Construction sequence

The phases of execution differ with the type of wall and support fluid used.

In the general case a support fluid is used.

The basic sequences for cast in situ concrete diaphragm walls are:

– excavation, generally with a bentonite suspension or other support fluid;

– cleaning the excavation including recirculation of bentonite;

– placing the reinforcement;

– concreting;

– trimming.

The basic sequences for precast concrete diaphragm walls are:

– excavation, generally with a hardening slurry, sometimes with a bentonite suspension ;

– cleaning the excavation. When a bentonite suspension is used, it is replaced by a

hardening slurry. If required by the design, a stronger material such as mortar or

concrete may be placed at the bottom of the excavation, to support the precast panel and

applied loads ;

– placing the precast element.

The basic sequences for cut-off slurry walls are :

– excavation with a hardening slurry. In some cases (e.g. excavations of long duration), a

different support fluid may be used, which has then to be replaced by the hardening

slurry;

– when required, placing elements such as membranes, reinforcement or sheet piles;

– trimming and protective capping.

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The basic sequences for plastic concrete walls are:

– excavation, generally with a bentonite suspension;

– cleaning the excavation;

– concreting;

– trimming.

Preliminary works

Working platform

The working platform shall be stable, above the water table, horizontal and be suitable for traffic of

heavy equipment and lorries.

The area along the line of the wall shall be clear of underground obstructions.

Special care is to be taken for excavating and backfilling trenches in case of removal of disturbed

soil or underground obstructions.

Excavation and backfilling are to be done symmetrically along the axis of the wall, to a depth

corresponding at least to the level of undisturbed soil, with sufficient width and depth with regard

to the guide-walls.

The top of the working platform should be at least 1,5 m above the highest water-table anticipated

during excavation, taking into account possible fluctuations.

Guide-walls

Guide-walls shall be designed and constructed:

– to ensure alignment of the diaphragm wall,

– to serve as a guide for the excavating tools,

– to secure the sides of the trench against collapse in the vicinity of the fluctuating level of

the support fluid,

– to serve as a support for the reinforcement cages or prefabricated panels or other

elements inserted in the excavation until the concrete or hardening slurry has hardened,

– to support the reaction forces of stop end extractors when necessary.

Guide-walls are usually made of reinforced concrete with a depth normally between 0,7 m and 1,5

m depending on ground conditions.

In the case of cut-off walls excavated continuously, if ground conditions should permit, guide-walls

may not be necessary.

Guide-walls should be propped apart until the excavation of the panel takes place.

The distance between the guide-walls should normally be 20 mm to 50 mm greater than the width

of the excavating tool.

The top of the guide-walls should normally be horizontal and have the same elevation on both sides

of the trench.

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Excavation

Supporting the walls of the excavation

Except special ground and site conditions, a support fluid shall be used during excavation.

In some cases, it can be possible to excavate using water as a support fluid.

In certain soils with cohesive properties or in rock, dry excavation may be used, provided the

ground strength is sufficient to ensure stability of the sides of the trench.

In soils where no comparable experience is available, a trial excavation should be made.

During excavation, the level of the support fluid will fluctuate, but it shall not be allowed to

drawdown below the level required for excavation stability.

The level of the support fluid shall remain above the base of the guide-walls, unless there is no risk

of caving of the soil below the guide-walls.

Excavation sequence

The excavation may be carried out continuously or in panels.

The sequence of excavation, panel lengths and distances between panels being excavated, depend

on the ground conditions, the type of wall, and the type of excavating tools.

The excavation of a panel shall not be started before the concrete, the plastic concrete or the

hardening slurry in the adjacent panel or panels has gained sufficient strength.

The use of chisels, other tools, or blasting, which affect the nearby panels already filled with

concrete or hardening slurry shall not be made before the material in these panels has sufficient

strength to resist the stresses developed during these operations.

Loss of support fluid

When a sudden and significant loss of the support fluid occurs during excavation, the excavation

shall be refilled immediately with an additional volume of support fluid, possibly containing

sealing materials.

If this procedure is insufficient, the excavation shall be backfilled as quickly as possible with lean

concrete or other material which can be readily re-excavated.

In situations where significant loss of support fluid can occur (e.g. highly permeable soils, cavities),

an additional volume of support fluid, and possibly sealing materials or suitable fill, shall be stored

in a readily accessible area.

Forming the joints

Stop ends shall be of adequate strength and properly aligned throughout their length.

The joints are normally formed either by using steel or concrete stop ends or by cutting into the

concrete or hardened material of the previously cast adjacent panel. In some cases, waterstops can

be incorporated into the joints.

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In the case of stop ends which are extracted laterally, the extraction shall be made upon completion

of the excavation of the adjacent panel.

In the case of stop ends which are extracted vertically, the extraction shall be made gradually

during the setting of the concrete.

Placing the reinforcement or other elements

Reinforcement cages, precast concrete panels or other elements (such as sheet piles, membranes)

shall not rest on the bottom of the excavation, but shall be suspended from the guide-walls.

Concreting and trimming

Concreting in dry conditions

Particular care shall be observed when concreting in dry conditions, to avoid segregation.

Direct pumping may be used in dry excavations.

Vibration of the concrete shall not be used.

Specific slump values are required for dry conditions.

Concreting under support fluid

The time elapsing between the start of excavation and commencement of concreting shall be kept

as short as possible.

The tremie pipe shall be clean and watertight. Its inner diameter shall be at least 0,15 m and 6 times

the maximum aggregate size. Its outer diameter shall be such that it passes freely through the

reinforcement cage.

The number of tremie pipes in a panel shall be adjusted to limit the horizontal distance the concrete

has to travel.

In normal circumstances, the horizontal distance the concrete has to travel should be less than 3,0

m.

Where there is more than one cage per panel, at least the same number of tremie pipes should be

used.

When several tremie pipes are used, they shall be arranged and supplied with concrete in such a

way that a reasonably uniform upward flow of the concrete is assured.

When starting concreting, the support fluid and the concrete in the charged tremie pipe shall be

kept separate by a plug of material or by other suitable means.

To start concreting, the tremie pipe shall be lowered to the bottom of the trench and then raised

approximately 0,1 m.

After concreting has started, the tremie pipe shall always remain immersed in the fresh concrete.

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The tremie pipe shall remain immersed into the fresh concrete for at least 6 m at the beginning of

concreting and before the first section of the pipe is drawn. Immediately after extracting the first

section, the immersion depth shall not fall below 3 m.

The immersion depth may have to be reduced when the concrete approaches ground level to

facilitate concrete flow.

An adequate supply of concrete shall be available throughout the whole placement process to

enable a controlled smooth operation.

In order to ensure concrete integrity, the rate of concrete rising over the full height of the panel

should not be less than 3 m/h.

Since the top of the cast concrete may not be of the required quality, sufficient concrete shall be

placed in the panel to ensure that the concrete below the cut-off level has the specified properties.

The required quality of the concrete at the cut-off level is achieved by providing a height of

concrete above the cut-off level.

The height of concrete above the cut-off level depends on the cut-off level, the wall dimensions and

the number of tremie pipes.

Trimming

Trimming of the concrete to cut-off level shall be carried out using equipment and methods which

will not damage the concrete, reinforcement or any instrumentation installed in the panels.

Where possible, some trimming above cut-off level may be carried out before the concrete has set.

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2. SHEET-PILE WALLS

Legend

a tubes + sheet piles

b U box piles + U sheet piles

c Z box piles + Z sheet piles

d H beams + Z sheet piles

Fig. 1 – Examples of combined walls

Legend

a sheet piles e tie rod

b strut f anchor plate or screen

c waling g variable angle

d rock dowel h ground anchor or tension pile

Fig. 2 – Example of a sheet pile wall structures

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Legend

a hammer

b driving cap

c sheet pile

d leader

e pile guide

Fig. 3 – Examples of a sheet pile driving rig with fixed leader

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Legend

a hammer

b cushion

c leader

d sliding guide

e driving cap

f leader slide

Fig. 4 – Example of a driving cap

Legend

a claw b tongue c driving direction

Fig. 5 – Driving direction for Z-sheet piles with tongue and claw interlocks

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Legend

a sheet pile b waling c strut d support bracket e bag filled with concrete

Fig. 6 – Bags filled with concrete or cement mortar in order to obtain a good connection

between waling and sheet piles

Driving of sheet pi les

Sheet piles are installed in the ground by one or a combination of the following methods:

– impact ;

– vibration ;

– pressing.

Vibrating is in many circumstances the most efficient method. In combination with leader guiding

it is also a very accurate method of driving sheet piles to the required depth. However, if very

dense sands and gravel above groundwater level or stiff clay layers have to be driven through,

vibrating may be ineffective. In these cases either driving assistance or impact driving may be

required. When obstacles are present and cannot be removed, either predrilling or careful impact

driving are the best methods to be used.

Generally driving with a vibrator causes a higher level of vibration in the surrounding ground than

impact driving. High frequency vibrators, where the eccentricity of the rotating mass can be varied

during the start up and stop phases of the driving process, can considerably reduce the adverse

vibrations of the process on the surrounding ground.

Vibrations from impact hammers and vibratory drivers are normally considerable and can travel

over relatively long distances. Foundations which are subjected to vibration will pick up part of

these vibrations and transfer them to the various elements of the supported structure. As a result

damage can be caused to sensitive buildings near to the source of the vibrations. Special care is

necessary if such structures are founded on loose sand, especially if it is saturated, because it is

subject to sudden settlement resulting from vibrations in the ground.

Where vibration or noise is considered a problem, pressing the sheet piles into the ground may

be a solution. Normally pressing is effective in cohesive soils. In difficult soil conditions pre-

boring and sometimes water jetting can be effective in assisting the sheet pile to reach the

required depth.

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Different types of pile driving equipment suitable for the installation of the sheet piles are

available. The most common types are:

– free falling hammers ;

– diesel hammers ;

– hydro hammers ;

– air hammers ;

– high and low frequency vibrators ;

– high frequency vibrators with a variable eccentricity of rotating mass;

– high frequency vibrator with continuously variable excentricity and resonance free start and

stop phases ; pressing systems.

Installation and driving assistance

Driving method

In the 'pitch and drive' method a single or double sheet pile, is driven to full depth before pitching the

next one. This simple procedure has the advantage that the top of the sheet pile has only to be lifted a

distance equal to the length of the pile above the ground surface. Moreover it easily can be guided

manually into the interlock of the sheet pile which has already been driven.

In the case of dense sands, stiff cohesive soils and in soils containing obstructions, the 'pitch and

drive'method can lead to de-clutching problems in the free leading interlock and occasionally to rather

large deviations from the required position.

"Panel driving"and "staggered panel driving", enables better control of the position of the sheet piles

along the wall length. At the same time the danger of declutching is minimised.

As a whole panel is pitched it is not necessary to drive all the sheet piles to full depth in order to

maintain sheetpiling operations. If obstructions are encountered, individual sheet piles can be left

high without disruption to the installation process.

"Staggered driving" is a particular form of "panel driving" which may be applied when difficult soil

conditions are encountered. The sheet piles in the panel are driven in a sequence indicated in figure

7.

The disadvantage of the "panel driving" method is that interlocking the sheet piles requires

individual piles to be lifted to twice their length.

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Legend

a direction of sheet pile installation

b driving direction (1 3 5)

c driving direction (4, 2)

d upper guide

e lowerguide

Fig. 7 - Example of staggered driving of sheet piles D.2

Driving assistance

It is often necessary to loosen very dense sand layers.

Normally applied methods are

a) low pressure jetting with low water volumes

– pressure : 1,5 Mpa to 2,0 MPa ;

– discharge : 2 I/s to 4 1/s per tube ;

– diameter of pipes : approx. 25 mm ;

– number of pipes : 1 to 2 per sheet pile.

The pipes are welded to the sheet piles and left in situ.

b) high pressure jetting

– pressure : 25 Mpa to 50 MPa (at pump outlet)

– discharge : 1 1/s to 2 1/s ;

– pipe diameter : 20 mm to 30 mm ;

– nozzle diameter : 1,5 mm to 3,0 mm.

c) predrilling, with or without cement bentonite.

d) blasting in special cases.

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Low pressure jetting is mainly used in dense non-cohesive soils.

Low pressure jetting with low water volumes, in combination with a vibrator, enables sheet piles

to penetrate very dense soils. In general the soil characteristics are only slightly modified and there

is practically no settlement, although special care has to be taken when the sheet piles have to

carry vertical loads.

In addition, low pressure jetting is sometimes used for pre-treatment of the soil prior to pile

driving.

High pressure jetting or fluidisation can be very effective in very dense soil layers.

Limited amounts of jetting fluid, water or sometimes cement-bentonite, are introduced into the

ground through nozzles fixed to the sheet pile at a short distance above its tip. As a result of the

limited water consumption this method permits effective control of the pile. The soil properties

are only adversely effected in a limited area around the sheet piles. The overall performance will

not be significantly influenced.

Pre-drilling is sometimes carried out prior to the sheet pile driving. The soil is locally loosened by

this process. Normally flight auger drills are used.

Facturing by blasting is normally carried out if the sheet piles have to pass hard obstructions in the

soil or if they must penetrate bedrock.

Timber sheet piles and walings

Timber for sheet piles and walings in permanent sheet pile wall structures is normally of high

durability.

Tropical hardwood normally meets this requirement without any preservation. However

coniferous species when used in waterfront structures, need to be impregnated by a preservation

fluid pressed into the wood under vacuum conditions.

Cutting, boring and similar operations should preferably be carried out in the factory before the

timber is impregnated. When impregnated timber is subsequently cut, bored or similarly re-

shaped, it is necessary to treat the affected area with special protecting liquid.

Joints

Normally timber sheet piles are jointed by tongue and groove type interlocks of a trapezoidal

shape. However a rectangular shape is also used.

The dimensions of the tongue determine the size of the groove as shown in figure 8.

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Legend A Tongue and groove with trapezoidal shape B Tongue and groove with rectangular shape

Fig. 8 – Shape and dimensions of tongue and groove interlocks of timber sheet piles

Corner sheet piles

Corner sheet piles generally have a square crosss section with grooves to conne the

adjacent sheet piles (see figure 9.)

Fig. 9 – Example of a timber corner pile with grooves

Execution

Normally timber sheet piles are only used in retaining structures with a limited retained height.

Typical uses are:

– vertical or nearly vertical embankments along canals and ditches;

– small quays in yachting harbours and similar.

Driving is usually carried out with light driving equipment. If a free falling mass is used the

height of the drop should not exceed 2,5 m.

When a vibrator is used, panels of several piles are driven as units.

In order to keep the sheet piling in the correct position, a guide frame is used. Low pressure water

25

jetting is often used to assist driving work in sand layers.

In order to ascertain a proper tongue and groove connection, the sheet piles are often bevelled at

the "free" side of the toe as shown in figure 10.

Legend

a driving direction

b bevel width

c ground pressure

Fig. 10 – Bevelling at the toe and driving direction

3. GROUND ANCHORS

Ground anchors are covered by EN 1537.

Scope

— — to support a retaining structure;

— — to provide the stability of slopes, cuts or tunnels;

— — to resist uplift forces on structures,

by transmitting a tensile force to a load bearing formation of soil or rock.

Two types of ground anchors:

— pre-stressed anchorages consisting of an anchor head, a tendon free length and a tendon bond

length bonded to the ground by grout (figure 1);

— non pre-stressed anchorages consisting of an anchor head, a tendon free length and a restraint

such as a fixed anchor length bonded to the ground by grout, a deadman anchorage, a screw

anchor or a rock bolt.

Key 1 Anchorage point at jack during stressing 6 SoiI Urock

2 Anchorage point at anchor head in service 7 Borehole

3 Bearing plate 8 Debonding sleeve

4 Lold transfer black 9 Tendon

5 Structural element 10 Grout body

Figure 1 - Sketch of a ground anchor

Drilling methods

The drilling method shall be chosen with due regard to the ground conditions so as to

cause either minimum ground modification or the modification most beneficial to the

anchor capacity and to allow the design anchor

resistance (Rd) to be mobilised.

Reasons for minimum ground modification are:

- to prevent collapse of the borehole wall during drilling and tendon installation (where

necessary a casing should be utilised) ;

- to minimise loosening of the surrounding ground in cohesionless soils ;

- to minimise change of ground water levels ;

- to minimise softening of the surface of the borehole wall in cohesive soils and degradable

27

rocks.

Techniques to counteract the water pressure and to prevent any blow-out, hole collapse and

erosion during drilling, installation and grouting operations shall be identified in advance and

implemented as and when required. In high water table situations it may be appropriate to use

heavy drilling fluids.

Possible preventative measures include

- the use of special auxiliary drilling equipment such as seals or packers;

- the lowering of the water table, after the risks of general settlement of the ground have been

assessed;

- pre-grouting of the ground.

Grouting

Grouting meets one or more of the following functions:

a. to form the fixed anchor length in order that the applied load may be transferred

from the tendon to the surrounding ground ;

b. to protect the tendon against corrosion ;

c. to strengthen the ground immediately adjacent to the fixed anchor in order to

enhance ground anchor capacity ;

d. to seal the ground immediately adjacent to the fixed anchor length in order to limit

the loss of grout.

If a grout volume injected is in excess of three times the borehole volume at pressures not exceeding

total overburden pressure, then general void filling is indicated which is beyond routine anchor

construction. In such cases general void filling may be necessary before grouting the anchor. For

functions c) and d) above only nominal grout consumptions should be expected.

Anchor grouting

Placement of grout should be carried out as soon as possible after completion of drilling.

When grouting by the tremie method, the end of the tremie pipe shall remain submerged in

grout within the fixed anchor length and grouting shall continue until the consistency of the

grout emerging is the same as that of the injected grout.

The grouting process should always start at the lower end of the section to be grouted. For

horizontal and upward inclined holes, a seal or packer is required to prevent loss of grout from

either the fixed anchor length or the entire hole.

Stressing

Stressing is required to fulfil the following two functions

- to ascertain and record the load carrying behaviour of the anchor ;

- to tension the tendon and to anchor it at its lock-off load.

Stressing and recording shall be carried out by experienced personnel under the control of a

suitably qualified supervisor, provided preferably by a specialist anchor contractor or stressing

equipment supplier.

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Investigation test

Investigation tests may be required to establish for the designer, in advance of the installation

of the working ground anchors, the ultimate load resistance in relation to the ground conditions

and materials used, to prove the competence of the contractor and/or to prove a new type of

ground anchor by inducing a failure at the grout/ground interface.

Acceptance test

Each working anchor shall be subjected to an acceptance test.

The objectives of the acceptance test are as follows:

a) to demonstrate that a proof load, which will depend on the test method, can be sustained by

the anchor ;

b) to determine the apparent tendon free length ;

c) to ensure that the lock-off load is at the designed load level, excluding friction ;

d) the creep or load loss characteristics at the serviceability limit state, when necessary.

Definitions

permanent anchorage anchorage with a design life of more than two years

temporary anchorage anchorage with a design life of less than two years

acceptance test load test on site to confirm that each anchorage meets the design requirements

suitability test load test on site to confirm that a particular anchor design will be adequate in particular ground

conditions

investigation test load test to establish the ultimate resistance of an anchor at the grout/ground interface and to

determine the characteristics of the anchorage in the working load range

4. REINFORCED FILLS

Reinforced fill, covered by EN 14475, is an engineered fill reinforced by the inclusion of horizontal

or subhorizontal reinforcement placed between layers of fill during construction.

The scope of reinforced fill applications includes (Figure1):

- earth retaining structures, (vertical, battered or inclined walls, bridge abutments, bulk

storage facilities), with a facing to retain fill placed between the reinforcing layers;

- reinforced steep slopes with a facing, either built-in or added or wrap-around, reinforced

shallow slopes without a facing, but covered by some form of erosion protection without a

facing, reinstatement of failed slopes;

- embankments with basal reinforcement and embankments with reinforcement against

frost heave in the upper part.

30

Definitions

fill natural or man made material formed of solid particles, including certain rocks, used to construct

engineered fill

engineered fill fill which is placed and compacted under controlled conditions

reinforced fill engineered fill incorporating discrete layers of soil reinforcement, generally placed

horizontally, which are arranged between successive layers of fill during construction

reinforcement generic term for reinforcing inclusions placed within fill

fill reinforcement reinforcement which enhances stability of the reinforced fill mass by mobilising the axial tensile

strength of the fill reinforcement by soil interaction over its total length

31

geosynthetics for the purpose of this European standard "geosynthetics" stands for "geotextiles and geotextile

related products"

foundation foundation of a reinforced fill structure is the total area of the surface upon which the lowest layer

of reinforcement is installed

facing covering to the exposed face of a reinforced fill structure which retains the fill between layers of

reinforcement and protects the fill against erosion

full height facing unit facing unit equal to the height of the face of the structure

discrete facing unit partial height facing unit used to construct incrementally a reinforced fill structure

hard facing unit panel or block usually of precast concrete with intrinsically low vertical compressibility and high

bending stiffness.

deformable facing unit preformed steel grid section, a preformed solid steel section or a rock filled gabion with

intrinsically vertical compressibility and low bending stiffness.

soft facing unit soil fill encapsulated in a geogrid or a geotextile facing with no bending stiffness.

facing system assemblage of facing units used to produce a finished reir forced fill structure

rigid facing system facing system with no capacity to accommodate vertical differential settlement between fill and

facing.

semi-flexible facing system facing system with some capacity to accommodate differential settlement between fill and facing

flexible facing system pliant, articulated, facing system with capacity to accommodate differential settlement between fill

and facing

green facing vegetative cover or infill used without facing units or as an adjunct to reinforced fill structures

constructed using facing units

cladding false facing added in front of the facing to improve the aesthetics of a finished reinforced fill

structure

32

design life service life, in years, required by the design

temporary structures structures with a design life of 1 - 5 years (Class 1)

permanent structures structures with a design life of more than 5 years (Class 2 - 5)

Materials and products

Construction of reinforced fill involves the use of the following major components:

- fill material;

- fill reinforcement, and if required;

- facing system.

Fill materials The fill used within the reinforced zone shall be selected to meet the properties required by the

design and the project specification.

The suitability of a reinforced fill material is dependent on a number of factors that shall be

considered when selecting the material:

- fill workability;

- function and environment of the structure and long term behaviour;

- fill layer thickness and maximum particle size;

- facing technology;

- vegetation;

- drainage properties;

- aggressivity of the fill;

- fill - reinforcement interaction;

- fill - internal friction and cohesion;

- frost susceptibility.

Fill workability

The fill workability shall be such that it can be placed and compacted to produce the properties

required by the design.

Function and environment of the structure and long term behaviour

Some types of structure have a critical function where post construction settlement is very

important. e.g. bridge abutments, walls supporting railway tracks and buildings, or high earth

retaining structures etc. In these cases fill material which is easy to compact and which will have

subsequent low compressibility shall be selected.

Where a structure is exposed to flooding and subsequent rapid drawdown the drainage properties

of the fill shall be checked for compatibility with the design assumptions.

33

Reinforcement products

Fill reinforcements can be made from metals, generally steel, or polymeric materials.

Facings Facings can be produced in a variety of materials and configurations with a variety of facing-

reinforcement connections and a variety of joint fillers and bearing devices.

Facing units and systems

Reinforced fill is constructed using successive layers of compacted, selected fill incorporating

intervening layers of horizontal or sub-horizontal fill reinforcement placed at spacing required by

the design.

Reinforced fill earth retaining structures, with a vertical, battered or inclined face (see Figure 2),

require a facing to retain the fill between the reinforcing layers. Depending on the particular

system, certain layers of fill reinforcements may however not be connected to the facing.

On shallow reinforced slopes, facing is generally not necessary. Such slopes are usually protected

by vegetation with / without erosion control materials.

The facing can be constituted of either hard units (typically made of concrete), or deformable units

(typically made from metal, steel grid or mesh, or gabion baskets), or soft units (typically made

from geosynthetic sheets or grids, or woven wire mesh).

Where hard or deformable facing units are used, these serve as a formwork against which the

selected fill is placed and compacted. Where soft facing units are used, it is generally necessary to

employ temporary formwork to maintain the face alignment during the construction of walls or

steep slopes.

Key: 1 Earth retaining structures

2 Reinforced slopes

3 Vertical

4 Vertical wall

5 Battered wall

6 Inclined wall Steep slope

7 Shallow slope

8 Some specific types of facings : panels, blocks, V2 elliptical

steel units, gabions

9 Specific types of sloping panel, eg for bulk storage

10 Some common types of facings: planter units, wire mesh,

wrapped around

11 No facing, erosion protection may be required

12 Line of 4:1 face slope angle

13 Line of 1:1 face slope angle

Figure 2 - Reinforced fill earth with a vertical, battered or inclined face

34

Facing units Hard facing units: Hard facing units are usually produced in precast concrete, either un-

reinforced or reinforced.

Concrete facing units may be full height panels, partial height panels, sloping panels, planter units, or

segmental blocks. Many types of concrete facing units are proprietary and form part of proprietary

systems.

The reinforcements are connected to the units either by means of devices embedded or

inserted into the concrete units, or they are simply clamped between the units.

Full height panels: As the name suggests, full height panels (see Figure 3) are precast to the

required full height of the specific reinforced fill wall to be constructed. The breadth of full

height panels is typically in the range 1 to 3 m and the thickness in the range 100 to 200 mm.

Figure 3 - Full height panels

Partial height panels: Partial height panels (See Figure 4) are the most common and typically

have heights in the range 1 to 2 m and thickness in the range 100 to 200 mm. Distinctive shapes

correspond to specific ways of fitting panels together, and to particular construction

procedures. Simple rectangular shapes are also available. The panels are fitted with connecting

devices embedded into the back face. The edges are usually provided with nibs and recesses, or

tongues and grooves.

Figure 4 - Partial height panels

35

Segmental blocks: Facing units in the form of precast or dry cast un-reinforced concrete blocks

(see Figure 5) are usually referred to as modular blocks or segmental blocks. Units may be

manufactured solid, or with cores. The mass of these units commonly ranges from 20 and 50 kilos.

Unit heights typically range from 150 mm to 250 mm, exposed face length usually varies from

200 mm to 500 mm. Depending on the type of reinforcement, blocks may be provided with

connecting accessories (pins, rake). Otherwise the reinforcement is clamped between successive

courses of blocks.

Figure 5 - Segmental blocks

Figure 6 - King post and concrete planking

Deformable facing units

Semi elliptical steel units: facing elements of steel sheet (see Figure 7) formed into elliptical or

U-shaped half cylinders. Such units, placed horizontally, are typically 2 to 4 mm thick, 250 mm to

400 mm high and a few metres long. They are fitted with holes along the horizontal edges for

connection to the reinforcements.

Figure 7 - Semi elliptical steel units

Steel welded wire mesh: Facing units may be formed of open-backed welded wire mesh sections

(see Figure 8), either flat or pre-bent to the required slope angle. These units serve as a formwork

during construction. When used for inclined faces, such units may be vegetated to prevent long

36

term erosion of the face. When used for vertical or battered faces, such units may have an inner

layer of stone or crushed rock, or be backed with a geosynthetic liner, especially for temporary

applications.

Figure 8 - Steel welded wire mesh

Gabion baskets: Facing units may also be formed using polymeric geogrid or woven steel wire,

galvanized or plastic coated, or galvanized welded wire mesh gabion baskets (See Figure 9) which

are filled with stone or crushed rock. The size of such gabion baskets is usually in the range of

0,5 m to 1,0 m in height, 2 m to 3 m in length and 0,5 m to 1,0 m in depth. The gabion baskets may

be supplied with an extended tail that forms a frictional connection to the main reinforcement

Figure 9 - Gabion baskets

Tyres: Facing units may also be formed with tyres. These tyres are of similar size and are generally

stacked in a staggered arrangement to form the facing.

Soft facings units

The most widely used soft facing unit is the so called wrapped facing (See Figure 10) in which

full width reinforcement, such as polymeric grid or geotextile, or woven wire mesh, is extended

forward from the reinforced fill to wrap around the face of each intervening layer of fill. Where

polymeric grids or woven wire meshes are used these may be faced, or backed, with a suitable

geotextile to guard against erosion of the face.

To construct such slopes to an acceptable alignment it is common practice to use temporary

formwork.

37

Key 1 Bags

Figure 10 - Soft facing units

Some typical reinforcement forms

38

Figure 11 – Steel reinforcement

Figure 12 – Polymeric reinforcements

5. SOIL NAILING

The objective of soil nailing is to improve the stability of the soil in cases where the stability

conditions are adverse. The stability is achieved by inserting soil nails, consisting of reinforcing

bars, into the soil. Soil nailing is generally applied in connection with excavations, slopes and

occasionally tunneling and for improvement of soil stability. The soil nails mobilise frictional

forces along their entire length, which contributes to increasing the stability condition. The amount

of nails and the length of installation of the nails have to be adjusted in relation to the stability

conditions, encountered during the ongoing activities. Protection against corrosion in case of long-

term stability problems is required in aggressive soil conditions.

A soil nail construction can involve the following material components for:

a) soil nail system;

b) facing system;

c) drainage system.

Terms and definitions

bearing plate plate connected to the head of the soil nail to transfer a component of load from the facing or

directly from the ground surface to the soil nail

drainage system series of drains, drainage layers or other means to control surface and ground water

facing covering to the exposed face of the reinforced ground that may provide a stabilising function to

retain the ground between soil nails, provide erosion protection and have an aesthetic function

facing drainage system of drains used to control water behind the facing

facing system assemblage of facing units used to produce a finished facing of reinforced ground

facing unit discrete element used to construct the facing

flexible facing flexible covering which assists in containing soil between the nails

hard facing stiff covering, for example sprayed concrete, precast concrete section or cast in-situ concrete

production nail soil nail which forms part of the completed soil nail structure

reinforcing element generic term for reinforcing inclusions inserted into ground

40

reinforced ground ground that is reinforced by the insertion of reinforcing elements

sacrificial nail soil nail installed in the same way as the production nails, solely to establish the pullout capacity

but not forming part of the soil nail structure

soft facing soft facing has only a short-term function to provide topsoil stability while vegetation becomes

established

soil nail reinforcing element installed into the ground, usually at a sub-horizontal angle, that mobilises

resistance with the soil along its entire length

soil nail construction any works that incorporates soil nails, and can have a facing and/or a drainage system

soil nail system consists of a reinforcing element and may include joints and couplings, centralisers, spacers, grouts

and corrosion protection

test nail nail installed by the same method as the production nails for the purpose of verifying the pullout

capacity and durability, and could be forming a part of the structure

proof load load applied in the testing

Examples of uses of soil nailing

Soil nail systems are produced using a wide range of materials and configurations.

Vertical walls Slopes

Figure 1 - Safeguarding stability of excavations by the use of soil nailing

41

Tunnel excavation

Key 1 ground surface

2 soil nails

3 tunnel advances

Figure 2 — Safeguarding tunnelling operations by the use of soil nailing

In the case of excavations, the sequence of excavation and soil nailing has to be adjusted in order

not to comprise the stability conditions of the site. Typical methods of excavation in combination

with soil nailing operations are illustrated in Figures 3 and 4.

Key 1 excavation

2 installing the nails

3 reinforced shotcrete (or prefabricated facing panels)

4 next excavation

Figure 3 — Typical sequences of excavation and installation

Key 1 bulk excavation to proposed formation

2 berm

3 installed nails

4 existing ground

5 local trimming of face required to achieve agreed tolerances prior to nail installation of nail row "N"

N Nth row

Figure 4 — Bulk excavation to form benches and face for row "N" of soil nails

42

Reinforcing element

The reinforcing element of the nail is usually produced from metals (typically steel) and to a lesser

extent from other materials, such as fibre reinforced plastics, geo-synthetics or carbon fibre.

NOTE: The reinforcing element may be a solid bar, a hollow bar, an angle bar or some other form

of cross-section.

When nails are to be grouted, they may be ribbed or profiled to improve the effective bond with the

grout.

Examples of soil nail systems

The soil nail systems include reinforcement bars, usually steel bars, inserted into and bonded with

the ground to the depth required with regard to safety conditions, and often provided with a head

plate and a facing system to ensure stability between the nails and also to avoid erosion problems.

There is a number of different soil nailing systems. Typical examples are given in Figure 5.

a) Pre-bored and grouted b) Self-boring

Key 1 facing 6 coupler

2 head plate 7 inner spacer

3 locking nut 8 grout annulus

4 outer spacer 9 reinforcing element

5 duct 10 drill bit

Figure 5 — Typical components of soil nail system, pre-bored & grouted shown

with hard/flexible facing

FACING SYSTEMS

Facing systems are constructed using a variety of materials, configurations and connections to the

reinforcement. Facings exposed to frost should be protected by frost insulation and extra drainage.

The facing system shall be able to sustain differential settlements required by the design without

structural damage to the facing.

The suitability of the facing system shall be proven by comparable experience or by tests, proving

the serviceability of the system and the durability of the materials used for the design life of the soil

nail construction.

43

Examples of facing systems used in a soil nail structure

Hard facing

The combination of soil nails and facing has to fulfill the function of stabilising the slope between

the nails, and shall therefore be dimensioned to sustain the expected maximum destabilising forces.

Figure 6 — Constructed hard facing with concrete (either sprayed or placed or precast)

(should be improved)

Figure 7 — Strengthening of existing retaining structures (should be improved)

Flexible facing

Flexible facings are designed to provide the necessary restraint to the areas of slope face between

the bearing plates, as well as erosion control. The selection of type of flexible facing is dependent

upon slope angle, soil friction angle value, slope height and predicted loading. The common

flexible facings include geogrids steel fabrics and geosynthetic.

Figure 8 — Wire mesh

44

Soft facing

The primary function of soft facing is erosion control and protection against surface ravelling. In

many cases, the soft facing has to reinforce the vegetation layer, either in the temporary or the

permanent situation. In some instances, nails serve only to retain the facing and not to stabilise the

slope.

Without facings

Nailing in case of critically inclined sliding surfaces (e.g. rock strata with reduced shear resistance),

however with a stable surface.

DRAINAGE SYSTEMS

Water is detrimental to slope stability and has to be drained away from the surface as much as

possible. In this way, general or local erosion etc. and critical water pressures behind facings may

be minimised (specially important in case of a full cover or with a vegetation layer.

Three essential measures have to be distinguished:

a) prevention of surface runoff water;

b) surface drainage;

c) subsurface drainage.

Interception of surface water run off

Figures 9 and 10 show examples of drainage above the soil nailing structure.

Figure 9 — Trenched drains above the soil nail structure guided to the sides of the slope

Key 1 e.g. Y-drains

Figure 10 — Surface drainage above the soil nail structure

(e.g. in case of stratum water)

45

Surface drainage

Systems for flexible and soft facings with vegetation layers but also possible behind hard facings

(sprayed concrete).

Key 1 foot drainage

Figure 11 — Seepage

Drainage systems for hard and impermeable facings

In case of concrete walls, prefabricated or cast in place, spread filters made of drainage material

and collector drains can be applied.

In any case, with impermeable facings, sufficient leakage holes have to be placed.

Key 1 drainage material

2 collector drain

3 “weep-hole” drain

Figure 12 — Hard and impermeable facings

Subsurface drainage

Subsurface drainage will be required if water-bearing strata are predicted or encountered.

Subsurface drainage may be required if the groundwater table has to be lowered. Drainage

boreholes normally contain slotted or perforated pipes. They are normally wrapped with a

geotextile filter to prevent the ingress of fines. The characteristic opening size of the geotextile

should be chosen to minimise clogging while permitting water into the pipe.

46

The number, length and pattern of the drainage pipes depend on the expected amount and regime of

water. The inclination of the boreholes is typically ≥ 5 %.

Figure 13 — Subsurface drainage

6. BORED PILES

The construction of bored piles is covered by EN 1536.

Definitions

The term pile is used for circular section structure and the term barrette for other shapes. Both are

bored piles.

bored pile pile or barrette formed with or without a pile casing by excavating or boring a hole in the ground

and filling with plain or reinforced concrete (Fig. 1) Designation for bored pile are given fig.8

barrette discrete length of diaphragm wall, usually short, or a number of interconnecting lengths cast

simultaneously (e.g. L-, T- or cruciform shapes), used to support vertical and/or lateral loads. (fig.

2)

end bearing pile bored pile transmitting actions to the ground mainly by compression on its base.

friction pile bored pile transmitting actions to the ground mainly by friction and adhesion between the lateral

surface of the pile and the adjacent ground.

skin friction frictional and/or adhesive resistance on the bored pile surface

negative skin friction frictional and/or adhesive action by which surrounding soil or fill transfers downward load to a

bored pile when the soil or fill settles relative to the bored pile shaft

continuous flight auger pile (CFA-pile) pile formed by means of a hollow stemmed continuous flight auger through the stem of which

concrete or grout is pumped as the auger is extracted (see figure 11, figure 12)

prepacked pile pile where the completed excavation is filled with coarse aggregate which is subsequently injected

with cement mortar from the bottom up.

pile base grouting pressure injection of grout below the base of an installed bored pile base in order to enhance

performance

under load

pile shaft grouting injection of grout carried out after bored pile concrete has set for the enhancement of skin friction

by the use of grouting pipes which are installed down the shaft, normally placed with the bored pile

reinforcement

48

enlarged base base of a bored pile formed to have an area greater than that of its shaft. For bored piles, normally

constructed by the use of special underreaming or belling-out tools (see figure 3).

integrity test test carried out on an installed bored pile for the verification of soundness of materials and of the

pile geometry.

sonic test integrity test where a series of sonic waves is passed between a transmitter and a receiver through

the concrete of a bored pile and where the characteristics of the received waves are measured and

used to infer the state of continuity and section variations of the bored pile shaft.

sonic coring sonic integrity test carried out from core drillings in a bored pile shaft or from a pre-placed tube

system

test pile bored pile to which loads are applied to determine the resistance deformation characteristics of the

pile and the surrounding ground

trial pile bored pile installed to assess the practicability and suitability of the construction method for a

particular application.

static pile test loading test where a bored pile is subjected to chosen static axial and/or lateral actions at the bored

pile head for the analysis of its capacity.

maintained load test static loading test in which a test pile has loads applied in incremental stages, each of which is held

constant

for a certain period or until pile motion has virtually ceased or has reached a prescribed limit (ML -

test).

constant rate of penetration test static loading test in which a test bored pile is forced into the ground at a constant rate and the force

is measured (CRP-test).

dynamic pile test loading test where a dynamic force is applied at the pile or the barrette head for assessment of pile

capacity.

socket bottom part of a bored pile in hard ground (usually rock)

grout fluid mixture of a binding and/or setting agent (usually cement), fine aggregate and water that

generally hardens after being placed in position.

49

Shapes

Bored piles can be of two kind of shapes: – with circular shape (see figure 1) and – barrettes (see figure 2), provided the section is concreted in a single operation.

Bored piles can have:

– uniform cross-section (straight shaft);

– telescopically changing shaft dimensions;

– excavated base enlargements; or

– excavated shaft enlargements

Te European Standard EN 1536 applies to bored piles with the following dimensions:

– depth to width ratio larger or equal to 5 ;

– shaft diameter : 0,3 ≤ D ≤ 3,0 m (see figure 1, figure 3);

– dimension for barrettes :

Wi ≥ 0,4 m (see figure 2);

ratio between the dimensions : Li / Wi ≤ 6

where:

Li is the largest dimension of the barrette and

Wi is the least dimension of the barrette;

– cross-sectional area of barrettes : A ≤ 10 m² ;

50

The European Standard EN 1536 also apply to piles with the following rake (see figure 4):

– n ≥ 4 (Θ ≥ 76°) ;

– n ≥ 3 (Θ ≥ 72°) for permanently cased piles.

Shaft or base enlargements covered by the European Standard EN 1536 are:

– base enlargements in non-cohesive ground :

DB / D ≤ 2 and

in cohesive ground : DB / D ≤ 3;

– shaft enlargements in any ground : DE / D ≤ 2;

– slope of the enlargement in non-cohesive ground :

m ≥ 3 and

in cohesive ground : m ≥ 1,5

(see figure 3).

The provisions of the European Standard EN 1536 apply to:

– single bored piles;

– bored pile groups (see figure 5);

– walls formed by piles (see figure 6).

51

The bored piles which are the subject of the European Standard EN 1536 can be excavated by

continuous or discontinuous methods using support methods for stabilizing the excavation walls

where required.

Bored piles can be constructed:

– of unreinforced (plain) concrete,

– of reinforced concrete,

– of concrete reinforced by means of special reinforcement such as steel tubes, steel sections

or steel fibres,

– of precast concrete (including prestressed concrete) elements or steel tubes where the

annular gap between the element or tube and the ground is filled by concrete, cement or

cement-bentonite grout.

(see figure 7).

52

Excavation

When constructing bored piles measures shall be taken to prevent uncontrolled inflow of water

and/or soil into the bore.

An inflow of water and/or soil could cause for instance :

– a disturbance to or instability of the bearing stratum or the surrounding ground;

– loss of support by the removal of soil from beneath adjacent foundations;

– unstable cavities outside the bored pile;

– damage to the unset concrete in the bored pile or bored piles recently installed nearby;

– voids in the shaft during concreting;

– washing out of cement.

There are increased risks in :

– loose granular ground;

– soft cohesive ground; or

– ground which is variable.

53

In soils liable to flow into the bore or where there is a risk of collapse, means of support shall be

used to maintain stability and thereby prevent the uncontrolled entry of soil and water.

Common means of support of bore walls are :

– casings;

– support fluid;

– soil-filled auger flights.

Bored pile bores shall be excavated until they reach :

– the specified bearing stratum, or

– the anticipated founding level,

and shall be socketed into the founding material where and as required by the design.

In cases of

– unfavourable stratification of the bearing layers,

– founding on bedrock, or

– sloping surface of the bearing layers

the excavation shall be carried down to provide full face contact.

Bored piles can be excavated in an intermittent or continuous process :

— tools for intermittent excavation are for example: grabs, shells, augers, boring buckets and

chisels ;

— tools for continuous excavation are for example: augers, drilling or percussion tools for

excavation combined with

augering or flushing methods for soil removal.

The employment of

– temporary or permanent casings

– support fluids, or

– soil-filled flights of a continuous flight auger

can be necessary to support the excavation walls.

The type of boring tool shall

– be appropriate to the given soil, rock, groundwater or other environmental conditions,

– be selected with a view to preventing loosening of material outside the bored pile and below

its base, and

– allow the bores to be excavated quickly.

It can be necessary to change the method or tool employed to meet the requirements.

Special tools and/or techniques other than those used for excavation may be used for the cleaning

of bases.

In situations where water or support fluid is present inside the bore, the choice and operation of

tools shall not impair bore walls stability.

A piston effect with negative influence on the stability of the bored pile walls can occur and the

operating speed of the tool should be adapted accordingly.

Excavations supported by casings

Raking piles shall be cased over their entire length if their inclination is: n ≤15 (θ≤86°) unless it can

be shown that uncased bores will be stable (see figure 4).

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Casings may be installed during the excavation process using :

– oscillating or

– rotating equipment

or they may be driven prior to the excavation using :

– piling hammers or

– vibrators or other.

Where a bored pile is excavated

– below the groundwater table in permeable ground, or

– in artesian conditions

an internal excess pressure shall be provided within the casing by a head of water or other suitable

fluid of not less than 1,0 m which shall be maintained until the bored pile has been concreted.

In unstable bores the casing shall be maintained in advance of boring.

The advancement in relation to the excavation shall be adjusted to suit the ground and groundwater

conditions.

The insertion of the casings ahead of boring is necessary to prevent an inflow of soil and

disturbance below the bored pile base which can affect the bored pile performance ("caving in",

"bottom heave"). The creation of a cavity outside the casing can endanger the integrity of a

concreted bored pile if and when the casing is withdrawn ("necking").

Zones of loosening can also move upwards to the surface and can there cause subsidence.

Excavations supported by fluids

The properties of a support fluid shall be in accordance with previously given conditions.

There are two types of excavations supported by fluids:

– direct circulation boring system (fig. 9)

– reverse circulation boring system (fig. 10)

The upper part of an excavation shall be protected by a lead-in tube or guide wall

– to guide the boring tools;

– to protect the bore walls against collapse of upper loose soils; and

– for the safety of site personnel.

At all times during boring and concrete placement the level of support fluid shall be maintained :

– within the lead-in tube or the guide wall, and

– at least 1,5 m above the external ground-water level.

Boring with continuous flight augers

Piles may be formed without other means of support of the bore, by using a continuous flight auger

in such a way that the stability of the bore is preserved by the material on the flights (fig.11, fig.12).

Continuous flight auger piles shall not be constructed with inclinations of n ≤10 (θ≤84°), unless

measures are taken to control the direction of the excavation and the installation of the

reinforcement.

Boring with continuous flight augers shall be carried out as fast as possible and with the least

practical number of auger rotations in order to minimize the effects on the surrounding ground.

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Where layers of unstable soil are encountered with a thickness of more than the pile diameter, the

feasibility of the construction shall be demonstrated by means of trial piles or local experience

before the commencement of the works.

Unstable soils are considered to be :

– uniform non-cohesive soils (d60/d10 < 1,5) below the groundwater table;

– loose non-cohesive soils with relative density Dr < 0,3;

– clays with high sensitivity;

– cohesive soils with undrained shear strength cu < 15 kPa.

Uniform non-cohesive soils with 1,5 < d60/d10 < 3,0 below the groundwater table can be sensitive.

During excavation the advance and speed of rotation of the auger shall be adjusted in accordance

with the soil conditions so that soil removal is limited to such an extent that :

– the lateral stability of the bore wall will be preserved, and

– over-excavation will be minmized.

For this the boring tool shall be provided with sufficient torque and traction power.

The pitch of the flights shall be constant over the whole length of the auger.

A system of closure shall be provided in the hollow auger stem to prevent the entry of soil and

inflow of water during drilling.

When the required depth has been reached, the auger shall be lifted from the bore only if

– the surrounding ground is stabilized by the rising concrete, or

– the surrounding ground remains stable.

If a pile can not be completed and the auger has to be removed, the auger shall be withdrawn by

back-screwing and the bore hole shall be back-filled with soil or support fluid.

Unsupported excavation

Excavation without the provision of support to bore walls is permissible in ground conditions

which remain stable during excavation and where a collapse of ground material into the bore is not

likely.

The stability of the unsupported excavation shall be demonstrated by means of trial bored piles or

comparable experience before the commencement of the works.

The upper part of the excavation shall be protected by a lead-in tube unless

– the excavation is carried out in firm soil, and

– the diameter D is smaller than 0,6 m.

Concreting and trimming

The interval between completion of excavation and commencement of concrete placement is

required to be kept as short as possible.

Prior to concrete placement the cleanliness of the bore shall be checked.

The bored pile trimming operation:

– shall be carried out only when the concrete has obtained sufficient strength,

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– shall remove all concrete which is contaminated or of lower quality than required from the

top of the bored pile, and

– shall continue until sound concrete over the whole cross section is revealed.

Concreting in dry conditions

The procedure for placing concrete in dry conditions shall not be followed if there is standing water

at the base of the bore.

A check shall be carried out immediately before the placement.

If water is recognized concrete should be placed as for submerged conditions.

Concreting shall be carried out in such way as to avoid segregation. The concrete shall be directed

vertically into the centre of the bore by means of a funnel and an attached length of pipe so that the

concrete does not hit

– the reinforcement, or

– the walls of the bore.

The internal diameter of the concreting pipe shall not be less than 8 times the maximum size of the

aggregate.

Concreting in submerged conditions

In order to avoid mixing between concrete and bentonite, the instantaneous velocity of concrete

rising should not be less than 3 m/h.

The main purpose of the tremie pipe is the prevention of segregation of the concrete during

placement or its contamination by the fluid inside the bore.

Submerged concrete shall not be compacted by internal vibration.

Compaction is dependent on the flow characteristics of the concrete in relation to its self weight

and the surcharge of the fluid above the concrete column.

The tremie pipe, including all its joints, shall be water tight.

It shall be equipped at its upper end with a hopper to receive the fresh concrete and prevent spillage

of concrete which otherwise could fall freely into the bore, segregate or become contaminated.

The tremie pipe shall be smooth to allow free flow of concrete and have a uniform internal

diameter of at least

– 6 times the maximum size of the aggregate, or

– 150 mm

whichever is the greater.

The external shape and dimension of the tremie pipe, including its joints, shall allow its free

movement inside the reinforcement cage.

The maximum outside diameter of the tremie pipe including its joints should be not more than:

– 0,35 times the pile diameter D or the inner diameter of a casing ;

– 0,6 times the inner width of the reinforcement cage for piles; and

– 0,8 times the inner width of the reinforcement cage for barrettes.

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The immersion of the tremie pipe into the concrete should be not less than 1,5 m, particularly when

disconnecting sections of the pipe and when recovering and disconnecting sections of temporary

casing.

For piles with a diameter D ≥ 1,2 m the immersion should be at least 2,5 m and for barrettes at least

3,0 m, particularly when two or more tremie pipes are used.

When concrete is placed under support fluid:

– a sample of the fluid shall be taken from the base of the bore, and

– any major filtercake or debris shall be removed from the bottom of the bore

immediately before the start of the placement.

Extraction of casings

The extraction of temporary casings shall not begin until the concrete column has reached a

sufficient height inside the casing to generate an adequate excess pressure.

– to protect against inflow of water or soil at the tip of the casing; and

– to prevent the reinforcement cage from being lifted.

The extraction shall be carried out while concrete is still of the required consistency.

During the continued extraction a sufficient quantity and head of concrete shall be maintained

inside the casing to balance the external pressure so that the annular space vacated by the removal

of the casing is filled with concrete.

The supply of concrete, and the speed of extraction of the casing shall be such that no inflow of soil

or water occurs into the freshly placed concrete, even if a sudden drop of concrete level should

occur when a cavity outside the casing is uncovered.

Concreting of continuous flight auger piles

Concreting of piles excavated with continuous flight augers may be carried out by placing concrete

through the hollow central stem of the auger, the stem being closed at its base, to avoid entry of

water or soil until concrete placing commences.

Once boring has reached the final depth, concrete shall be placed through the stem to fill the pile as

the auger is withdrawn.

External grouting of bored piles

Shaft and/or base grouting shall be carried out only after the cast-in-situ concrete has set.

Only permanent grouting pipes are allowed and their arrangement shall be appropriate to the zones

and materials to be grouted.

Base grouting can be carried out:

– through steel pipes attached to cages;

– by means of a flexible box structure (see Figure 13) installed with the reinforcement,

allowing the spread of grout over the whole base area of the bored pile; or

– with sleeved perforated cross pipes arranged at the bored pile bottom.

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Shaft grouting shall be carried out through grouting pipes fixed to the reinforcement cage or tube or

a precast concrete element as applicable (see figure 14).

Pile walls

A template of steel or concrete should be installed at the working platform for the maintenance of

the pile positions where specified accuracy requires.

Excavations should be supported by temporary casings in the construction of secant pile walls.

Normally in the construction of secant pile walls, alternate piles only should be reinforced. These

reinforced piles should be constructed after the initially installed unreinforced piles on either side

are in place.

Where all piles are to be reinforced, the primary piles shall be constructed so as not to impair the

later alternate pile installation.

The construction sequence of secant and contiguous pile walls, and the concrete composition

employed, shall be chosen as such that the concrete of the primary piles has achieved sufficient

strength for stability but has not developed a strength that would be too high for an intersection to

be achieved.

In the construction of secant pile walls, hardening slurry may be used for primary piles instead of

concrete.

Bored pile testing The principal requirements for bored pile testing shall comply with EN 1997-1. The following

notes contain general remarks, which may be supplemented by national application documents, as

applicable (as long as respective European Standards are not available).

Bored pile tests may be used for proof of :

- resistance/deformation characteristics in the general range of specified actions;

- the soundness and proper construction of a pile.

Bored pile tests can consist of :

- maintained load tests;

- constant rate of penetration tests;

- dynamic pile tests for the determination of the pile capacity; and

- integrity tests which measure the acoustic or vibration properties of the bored pile in order

to determine the presence of possible anomalies within its body.

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Fig. 8 - Bored pile: Designations

60

Fig. 9 - Direct circulation boring system

Fig. 10 – Reverse circulation boring system

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Fig. 11 - Auger

Fig.12 - Continuous flight auger drilling

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Fig. 13 - Pile base grouting (examples)

Fig. 14 - Shaft grouted pile

7. DISPLACEMENT PILES

Displacement piles are covered by EN 12699.

Terms

displacement pile pile which is installed in the ground without excavation or removal of material from the ground

except for limiting heave, vibration, removal of obstructions or to assist penetration (see Figure 1,

2, 3)

prefabricated (displacement) pile pile or pile element which is manufactured in a single unit or in pile segments before installation

(see Figure 9b)

cast in place (displacement) pile pile installed by driving a closed ended concrete shell or permanent or temporary casing, and

filling the hole so formed with plain or reinforced concrete(see Figure 5 and 9a)

screw pile pile in which the pile or pile tube comprises a limited number of helices at its base and which is

installed under the combined action of a torque and a vertical thrust. By the screwing-in

and/or by the screwing-out, the ground is essentially laterally displaced and virtually no soil is

removed

jacked pile pile pressed into soil by means of static force

grouted pile prefabricated pile fitted with an enlarged shoe to create along a part or the full perimeter of the

pile a space which is filled during driving with grout, mortar or microconcrete. See Figure 7

post grouted pile pile where shaft and/or base grouting is performed after installation through pipes fixed along or

incorporated in the pile. See Figure 8

driving method to bring the piles into the ground to the required depth, such as hammering, vibrating,

pressing, screwing or by a combination of these or other methods

leader steel sections used for guiding driving equipment and/or pile during driving. See Figure 6

impact hammer tool of construction equipment for driving piles by impact (striking or falling mass)

vibrator (vibrating hammer) tool of construction equipment for driving or extracting piles, drive tubes or casing by the

application of vibratory forces

helmet device, usually steel, placed between the base of the impact hammer and the pile or drive tube so

as to uniformly distribute the hammer impact to the top of the pile. See Figure 6

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hammer cushion device or material placed between the impact hammer and the helmet to protect the hammer

and the pile head from destructive direct impact. The hammer cushion material shall have

enough stiffness to transmit hammer energy efficiently into the pile.

pile cushion material, usually softwood, placed between the helmet and the top of a precast concrete pile.

follower a temporary extension, used during driving, that permits the driving of the pile top below

ground surface, water surface, or below the lowest point to which the driving equipment can

reach without disengagement from the leaders

driving criteria driving parameters used to be fullfilled when driving a pile

jetting use of pressurised water to facilitate the driving of a pile by means of hydraulic displacement of

parts of the soil

preboring (preaugering, predrilling) boring through obstructions or materials too dense to penetrate with the planned pile type and

driving equipment

set mean permanent penetration of a pile in the ground per blow measured by a series of blows

drive tube steel tube used to displace the ground during the formation of a driven cast in place pile. Drive

tube is withdrawn during concreting

casing steel tube used temporarily or permanently to support shaft walls during the construction of a pile.

In permanent situation the casing can act as a protective or load bearing unit

mandrel a steel core for driving that is inserted into a closed-end tubular pile. After installation the mandrel

is withdrawn

test pile pile to which a load is applied to determine the resistance deformation characteristics of the pile

and surrounding ground

trial pile pile installed to assess the practicability and suitability of the construction method for a particular

application

preliminary pile pile installed before the commencement of the main piling works or section of the works for the

purpose of establishing the suitability of the chosen type of pile, driving equipment and/or for

confirming the design, dimensions and bearing capacity

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driven pile pile which is forced into the soil by driving, the soil being displaced by the pile or drive tube

maintained load pile test static loading test in which a testpile has loads applied in incremental stages, each of which is

held constant for a certain period or until pile motion has virtually ceased or has reached a

prescribed limit (ML - test)

constant rate of penetration pile load test static loading test in which a test pile is forced into the ground at a constant rate and the force is

measured (CRP - test)

dynamic pile load test loading test where a pile is subjected at the pile head to a dynamic force for analysis of its load

bearing capacity

sonic test , low strain integrity test integrity test where a series of waves is passed between a transmitter and a receiver through the

concrete of a pile and where the characteristics of the received waves are measured and used

to infer continuity and section variations of the pile shaft

sonic coring sonic integrity test of pile concrete carried out from core drillings in a pile shaft or from a pre-

placed tube system

working level level of the piling platform on which the piling rig works.

Classification and examples

Figure 1 – Family tree chart for displacement piles

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Figure 2 – Examples of shafts and bases of displacement piles

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Figure 3 – Examples of cross sections for displacement piles

68

Figure 4 – Examples for toe protection for prefabricated displacement piles

69

Figure 5 – Examples of construction of cast in place displacement piles

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Figure 6 – Examples of piling rig with impact hammer

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Figure 7 – Example of grouted pile

72

Figure 8 – Example of post grouted pile

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Figure 9 – Displacement piles, termes and levels

8. MICROPILES

Micropiles are covered by EN 14199

Classification, domains of use

There are two types of micropiles from execution stand point:

- drilled micropiles with a shaft diameter not greater than 300 mm;

- driven micropiles with a shaft diameter or a maximum shaft cross sectional extension not

greater than 150 mm

Micropiles are structural members to transfer actions to the ground and may contain bearing

elements to transfer directly or indirectly loads and or to limit deformations. Their shaft and base

resistance may be improved (mostly by grouting) and they may be constructed with (see Figure 1):

- uniform cross section (straight shaft); or

- telescopically changing shaft dimensions;

- shaft enlargements; and/or

- base enlargement.

Other than practical considerations, there are no limitations regarding, length, rake

(definition of rake, see Figure 2), slenderness ratio or shaft and base enlargements.

Micropiles can act as (see Figure 3):

single micropiles;

micropile groups;

reticulated micropiles;

micropile walls.

The material of micropiles can be:

steel or other reinforcement materials;

grout, mortar or concrete;

a combination of above.

Micropiles may be used for:

- working under restricted access and/or headroom conditions;

- foundations of new structures (particularly in very heterogeneous soil or rock formations);

- reinforcing or strengthening of existing structures to increase the capacity to transfer load

to depth with acceptable load settlement characteristics, e.g. underpinning works;

- reducing settlements and/or displacements;

- forming a retaining wall;

- reinforcing of soil to form a bearing and/or retaining structure;

- improving slope stability;

- securing against uplift;

- other application where micropiles technicques are appropriate.

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Figure 1 – Example of micropile shafts and bases

Figure 2 – Definition of rake

Key 1 Single micropile

2 Micropile groups

3 Reticulated micropiles

4 Micropile walls

Figure 3 – Examples of micropile structures

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Terms and definitions

micropiles piles which have a small diameter (smaller than 300 mm shaft diameter for drilled piles and

not greater than 150 mm shaft diameter or maximum shaft cross sectional extension for driven

piles).

drilling method of removing the soil or rock in an intermittent or continous process

drilling fluid/ mud water or a suspension of bentonite, polymers or clay, in water with or without cement and

other additions, for stabilization of borehole walls and for flushing

driving method to bring the micopile into the ground to the required depth, such as hammering,

vibrating, pressing screwing or by a combination of these or other methods

casing tube used to support the micropile hole during the construction of a micropile. The casing can

be permanent or temporary. Permament casing may act as a load bearing element and/or as a

corrosion protection

drive tube steel tube used to displace the ground during the formation of a driven cast in place micropile.

The drive tube is withdrawn during grouting or concreting

grout a setting material, usually cement and water, containing sometimes additives or a limited

amount of fine aggregates, which transfers load from the bearing element or the micropiles

shaft to the ground and/or contributes to corrosion protection

mortar concrete with very small aggregates(< 8 mm)

grouting pumping of grout or concrete into the borehole with a pressure which is higher than the

hydrostatic pressure

tube-à-manchettes a regularly slotted sleeved tube through that grout injections are possible using a packer device

filling grouting under no applied fluid pressure other than the height of grout fluid. Sometimes

referred to as gravity grouting or as tremie grouting

test micropile micropile to which a load is applied to determine the resistance and deformation

characteristics of the micropile and the surrounding ground

preliminary micropile micropile installed before the commencement of the main piling works or section of the works

for the purpose of establishing the suitability of the chosen type of micropile and/or for

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confirming the design, dimensions are bearing capacity

trial micropile micropile installed to assess the practicability and suitability of the construction method for a

particular application

working micropile micropile which is part of a structure

integrity test test carried out on an installed micropile for the verification of soundness of micropile

components

static load test loading test where a micropile is subjected to chosen axial and/or lateral forces at the

micropile head for the analysis of its capacity and deformation characteristics

maintained load test (ML test) static loading test in which a test micropile has loads applied in incremental stages, each of

which is held constant for a certain period or until micropile motion has virtually ceased or has

reached a priscrebed limit

constant rate of penetration test (CRP test) static load test in which a test micropile is forced into the ground at a constant rate and the

force is measured

Execution of micropiles

The micropiles shall be executed and supervised by trained and experienced personnel.

A method statement should be provided before starting the execution of micropiles. This method

statement should contain (but is not limited to) the following information:

- identification , objective and scope of the micropiles;

- soil description; (possibly by reference to site investigation report);

- environmental issues;

- technical requirements;

equipment and working procedure for:

- drilling and/or driving;

- installation of reinforcement or bearing element;

- filling, grouting or concreting;

- measures to ensure the boring accuracy:

- grouting parameters;

- site installation and working areas;

- spoil management;

- quality control procedures.

Special care shall be taken for the execution of tangent or secant micropiles for the formation

of walls (spacing, deviation, sequence of drilling, constitutive material).

Where possible the preliminary, trial or test micropiles should be installed close to positions of

soil investigation.

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Drilling When constructing micropiles by drilling, continuous drilling with flushing for the removal of soil is the

most common method.

Micropile boreholes shall be drilled until they reach:

- the specified embedment in the bearing stratum; or

- the anticipated founding level; or

- the prescribed length.

When uncontrolled inflow of water and soil into the borehole can occur or when there is a

risk of collapse, special measures shall be taken to maintain the stability and thereby prevent

the uncontrolled entry of soil and water. An inflow of water and/or soil could cause for instance:

- a disturbance to or instability of the bearing stratum or the surrounding ground;

- loss of support by the removal of soil from beneath underpinned or adjacent foundations;

- damage to the unset grout, mortar or concrete in the micropile or micropiles recently installed nearby; - defaults

in the shaft;

- washing out of cement.

There are increased risks in:

- loose granular soil;

- soft cohesive soil;

- ground which is variable;

- when using air as drilling fluid with direct circulation under the groundwater table.

Use of flushing

Drilling can be performed with water, air and drilling fluids.

When drilling methods with air as flushing medium are used for underpinning works, special

care should be taken to avoid disturbance or fracturing of the ground.

Boreholes supported by casings

Casings should be used when the borehole is unstable or there is a significant fluid loss or when

filling or grouting is performed through the casing.

Drilling with continuous flight augers

No special limitations exist concerning the inclination on the basis that the direction of

excavation is controlled and the installation of the reinforcement can be achieved correctly.

Normally grout or mortar is used for the execution of micropiles with continuous flight augers.

Driving

When impact or vibrating driving methods are applied for underpinning works, their feasibility shall

be proven (e.g. with comparable experience taking into account the soil type and the condition

of the structures to be underpinned).

Enlargements

Micropile enlargements may be formed:

- by excavation;

- by driving compacted quantities of concrete below the bottom of the drive tube or permanent

casing;

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- by installing an expanded body.

Grouting

The following methods may be employed for filling and grouting the borehole:

- filling the borehole with grout;

- grouting:

- single step grouting through a temporary casing;

- single step grouting through a bearing element;

- grouting during driving and/or drilling;

- single or multiple step grouting through tubes-ă-manchettes, special valves or

post-grouting tubes (= multi-stage grouting).

Filling or grouting meets one or more of the following functions:

- to create or improve the bond between the micropile shaft and the surrounding ground to

allow the design shaft bearing capacity to be mobilised;

- to protect the reinforcement against corrosion;

to improve the bearing capacity of the micropile;

to strengthen and seal the ground immediately adjacent to the micropile in order to enhance the

micropile bearing capacity.

Filling the borehole with grout

The interval between the completion of the borehole drilling and the filling up of the borehole

with grout shall be kept as short as possible.

Measures shall be taken to ensure that the micropile length is completely filled with grout.

When filling the borehole with the tremie pipe or through the drill rods or tubular bearing elenients,

the end of the tremie pipe or drill rods shall remain submerged in the grout and grouting shall

continue until the consistency of the grout emerging on top is almost the same as that of the injected

grout (Figure 5).

When filling the borehole, air and drilling fluid shall be able to escape to permit complete grout

filling.

For drilled boreholes the remaining cuttings shall be able to escape when filling the borehole.

Single step grouting through a temporary casing

The reinforcement shall be placed before the temporary casing is extracted.

During extraction of the temporary casing the grout level within the casing shall be brought back

up to ground level before the next length of casing is removed (Figure 6).

The grouting pressure should be applied at least every 2 m during the extraction of the casing.

Single step grouting through a load bearing element

When tubes are used as bearing element, single step grouting can be applied at the bottoni of the

bearing element (Figure 7).

When the specified grouting pressure cannot be applied, re-grouting shall be performed after a

certain waiting period until the specified grouting pressure can be applied.

Grouting during drilling

When grouting is applied during drilling, the bearing elements are fitted with a drill bit and they are

drilled into the ground.

For grouting during drilling, the grout pressure and flow rate should be adjusted depending on the

grout susceptibility to penetrate the ground loosened by the drilling process and contained within

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the annulus around the reinforcing element.

When grouting during drilling, grout flushing should be carried out at a constant rate and the

flush should be re-established each time a new section of bearing element are added prior to

advancing the drill bit.

Multi-stage grouting

Multi-stage grouting may be executed by single step grouting through tube-ă-manchettes

(Figure 8) or by multiple step grouting through tube-ă-manchettes or special valves (Figure 9) or

by single step grouting through several post-grouting tubes staggered in length (Figure 10).

The multi-stage grouting phase(s) shall take place only after the grout placed into the borehole

has set.

The grouting shall be carried out either in single or multiple step(s) and in single or multiple stage(s),

according to the project specifications.

When the specified grouting pressure cannot be applied additional step(s) of grouting shall be

performed after a certain waiting period until the specified grouting pressure can be applied.

The grouting tubes shall be flushed with water after each grouting step and filled with grout

at the end of the whole grouting process.

Micropile testing

Tests on micropiles can be performed on preliminary micropiles and/or working micropiles.

Static load tests

Static load tests on micropiles may consist of:

a) maintained load tests;

b) constant rate of penetration tests.

Static load tests on preliminary micropiles

Static load tests on preliminary micropiles shall be performed when:

a) new techniques are used for the execution of the micropiles;

b) micropiles have to be installed in ground conditions for which previous tests are not

available;

c) higher working loads are applied than those already adopted in similar ground

conditions;

d) when the results of static load tests are used to determine the design load.

Static load tests on working micropiles

In the project specifications it shall be specified if static load tests have to be performed on

working micropiles.

For micropiles working in compression static load tests on at least two micropiles should be

performed for the first 100 micropiles and 1 for each next 100 micropiles.

For micropiles working in tension static load tests on at least two micropiles should be

performed for the first 25 micropiles and 1 for each next 25 micropiles.

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Dynamic load tests and integrity tests

The use of dynamic load tests and integrity tests can not be generalised for micropiles because the

interpretation of the results concerning the bearing capacity and integrity may be difficult due to the small

diameter andlor shape of the micropile and the presence of a bearing element. So the use of dynamic load

tests and integrity tests has to be limited to cases where experience or comparison with static load tests has

demonstrated that the results can he interpretated in a confident way.

For dynamic load tests the micropile shall be allowed to gain sufficient strength after

installation and before testing.

Figure 5 – Filling up a borehole with grout

Figure 6 – Single step grouting through a temporary casing

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Figure 7 – Single step grouting through a load bearing element

Figure 8 – Single step grouting through a tube-à-manchettes

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Key 1 Packer

Figure 9 – Multiple step grouting through a tube-à-manchettes or special valves

Figure 10 – Single step grouting through several post-grouting tubes

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9. DEEP MIXING

Deep mixing works are carried out by two different methods: dry mixing and wet mixing and form

the objects of EN 14679.

Deep mixing considered in EN 14679 is limited to methods, which involve:

a) mixing by rotating mechanical mixing tools where the lateral support provided to the surrounding

soil is not removed;

b) treatment of the soil to a minimum depth of 3 m;

c) different shapes and configurations, consisting of either single columns, panels, grids, blocks,

walls or any combination of more than one single column, overlapping or not:

d) treatment of natural soil, fill, waste deposits and slurries, etc.;

e) other ground improvement methods using similar techniques exist.

Definitions

dry mixing (malaxare în uscat) process consisting of mechanical disaggregation of the soil in situ and its mixing with binders with

or without fillers and admixtures in dry powder form

wet mixing (malaxare umedă) process consisting of mechanical disaggregation of the soil in situ and its mixing with a slurry

consisting of water, binders with or without fillers and admixtures

binder (liant) chemically reactive materials (lime, cement, gypsum, blast furnace slag, fly ash, etc.)

admixture (aditiv) dispersant, fluidifier, retarding agent

filler non-reacting material (sand, limestone powder etc.)

column pillar of treated soil manufactured in situ by a single installation process using a mixing tool. The

mixing tool and the execution process govern the shape and size of the cross section of a column

mixing tool tool used to disaggregate the soil, distribute and mix the binder with the soil, consisting of one or

several rotating units equipped with several blades, arms, paddles with/without continuous or

discontinuous flight

augers

penetration (downstroke) stage/phase of mixing process cycle, in which the mixing tool is delivered to the appropriate depth

and initial mixing and fluidisation of the soil take place

retrieval (upstroke)

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stage/phase of mixing process cycle, in which the final mixing and retrieval of the mixing tool take

place

Material and products

Construction of deep mixing involves the addition of a binder and, if needed, one or more of the

following components to the soil:

a. admixture;

b. water;

c. filler;

d. structural reinforcement.

Practical aspects of deep mixing

The objective of deep mixing is to improve the soil characteristics, e.g. to increase the shear

strength and/or reduce the compressibility, by mixing the soil with some type of chemical additives

that react with the soil. The improvement becomes possible by ion exchange at the surface of clay

minerals, bonding of soil particles and/or filling of voids by chemical reaction products. Deep

mixing is classified with regard to the binder utilised (cement, lime/cement and possible additives,

such as gypsum, fly ash, etc.) and the method of mixing (wet/dry, rotary/jet-based, auger-based or

blade-based).

The development of deep mixing was started in Sweden and Japan in the late 1960's. Dry mixing,

using granular quick lime (unslaked lime) as a binder, was put into practice in Japan in the middle of

the 1970's. Approximately at the same time, dry mixing originated in Sweden as lime (powdered

lime) mixing to improve the settlement characteristics of soft, plastic clays. Wet mixing, using

cement slurry as a binder, was also put into practice in Japan in the middle of the 1970's. Deep

mixing has since spread into other parts of the world. More recently, the combination of cement and

lime with gypsum, fly ash and slag has been introduced.

Recently, hybrid techniques have been developed by combining deep mixing with other soil

improvement methods (such as jet grouting) or other machinery (surface mixing).

Fields of application

A variety of applications for deep mixing exists for temporary or permanent works and either on land

or marine, Figure 1. The main applications are reduction of settlement, improvement of stability and

containment.

Execution

The execution consists typically of positioning, penetration and retrieval. During penetration, the

mixing tool(s) cut and disaggregate the soil to the desired depth of treatment. During retrieval, the

binder is injected into the soil at a constant flow rate, as the retrieval speed is kept constant. The

mixing blades rotate in the horizontal plane and mix the soil and the binder. There are, however,

some variations of machines, in which the binder is injected during the penetration phase and both in

the penetration and retrieval phase.

Deep mixing can be carried out by two different methods: dry mixing where the binder is introduced

by air and wet mixing where the binder is in slurry form.

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In dry mixing the binder is usually a mixture of cement and lime (unslaked), or a combination of

cement, lime, gypsum, blast furnace slag or pulverized fuel ash (PFA) in granular or powdered form.

Air is used to feed (or incorporate) the binder into the soil. (The moisture content of the soil needs to

be � 20%).

Figure 1. - Applications of deep mixing for various purposes

In wet mixing the most common binder is cement.

Dry mixing is primarily utilised to improve the characteristics of cohesive soil, whereas wet

mixing is applied also in order to improve the characteristics of granular material. For certain

applications, such as prevention of liquefaction, dry mixing has also been used in loose granular soil.

Dry mixing

Dry mixing is normally carried out in accordance with some general principles.

As can be seen in the flow chart, the binder is fed into the soil in dry form with the aid of

compressed air. Two major techniques for dry mixing exist at present: the Nordic and the Japanese

techniques.

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Figure 2. - Sequence of installation

The installation is carried out according to the following procedure, from left to right (Figure 2):

1) the mixing tool is correctly positioned;

2) the mixing shaft penetrates to the desired depth of treatment with simultaneous disaggregation of

the soil by the mixing tool;

3) after reaching the desired depth, the shaft is withdrawn and at the same time, the binder in

granular or powder form is injected into the soil;

4) the mixing tool rotates in the horizontal plane and mixes the soil and the binder;

5) completion of the treated column.

Nordic technique

Equipments used in the Nordic countries are able to install columns to a depth of 25 m with a

column diameter of normally 0,6 m to 1,0 m. The columns can be inclined up to about 70' in

relation to the vertical. The machines have one mixing shaft with the injection outlet positioned at

the mixing tool. Mixing energy and amount of binder are monitored and in some cases

automatically controlled to achieve uniform treated soil.

The mixing tool is drilled down to the final depth and a predetermined amount of binder is

added through an inner tube with an opening at the mixing tool (during the retrieval phase).

During the retrieval phase, the soil and binder are mixed by continued turning of the mixing tool.

Both phases can be repeated for the same location, if required.

Japanese technique

There are several variations of execution machines, which have either one or two mixing shafts.

Each mixing shaft of these machines have several blades with a diameter of 0,8 m to 1,3 m and are

able to install columns to a depth of 33 m. The binder, usually cement powder, is brought to the

mixing machine by compressed air.

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Comparison of the Nordic and Japanese dry mixing techniques

Wet mixing

In wet mixing the binder is usually cemnt slurry. Filler (sand and additives) may be added to the

slurry when necessary. The specific quantity of slurry added can vary with depth. For machines with

the outlet below the mixing tool the slurry need not be added during the retrieval phase.

Whereas flight augers may be sufficient for predominantly granular soils, increasing fineness

and stiffness requires more complicated mixing tools provided with mixing and cutting blades of

different shapes and arrangements The rotary drives, turning the shaft, need to have enough power

to destroy the matrix of the soil for intimate mixture with the slurry.

Depending on the type of soil and slurry, a mortar-like mixture is created which hardens during

the hydration process. Strength and permeability depend strongly on the composition and

characteristics of the soil (fines content, organic content, type of clay, shape of the grains,

grain size distribution, grain hardness), the amount and type of binder and the mixing

procedure.

The wet mixing process can be interrupted on condition that the slurry has not begun to harden and

the mixing tool starts again at least 0,5 m in the soil already treated.

Pumps for transport of the slurry to the outlet need to have sufficient capacity (delivery rate and

pressure) to safely deliver the design quantity of slurry.

Wet mixing is common in Central and Southern Europe, North America and Japan.

Patterns of installation

Depending on the purpose of deep mixing, a number of different patterns of column

installations are used (Figures 3, 4, 5, 6). If the main purpose is to reduce settlement, the columns

are usually placed in an equilateral triangular or in a square pattern. If, on the other hand, the

purpose is to ensure stability of, for example, cuts or embankments, the columns are usually

placed in walls perpendicular to the expected failure surface. Overlapping of the columns is

particularly important when the columns are installed for containment purposes. Overlapping is

normal in block type, wall type and grid type installations.

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Key 1 Strip 3 Triangular

2 Group 4 Square

Figure 3 - Examples of treatment patterns in dry mixing

Figure 4 - Block type pattern in dry mixing with overlapping columns

Key

1 Wall type

2 Grid type

3 Block type

4 Area type

Figure 5 - Examples of treatment patterns in wet mixing on land

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Key

1 Wall type 5 Tangent column

2 Grid type 6 Tangent wall

3 Block type 7 Tangent grid

4 Area type 8 Tangent block

Figure 6 - Examples of treatment patterns in marine conditions

Hybrid methods

There are several methods, which use techniques reminding of deep mixing. These methods,

which in this context are named hybrid methods, are continuously under development to tackle

particular ground conditions and foundation problems. They typically combine hydraulic and

mechanical mixing.

Mass stabilisation

In cases where the soil conditions are very bad, e.g. peat, gyttja or organic clay and soft clay

deposits, mass stabilisation can be required, in which the whole soil mass is treated down to a

depth of normally 2 m to 3 m. The maximum depth of treatment presently is 5 m. The mass

stabilisation machines differ essentially from the column stabilisation machines. The binder is fed

to the mixing head while the mixer rotates and simultaneously moves vertically and horizontally.

Mostly the mass stabilisation machine is a conventional cavator but equipped with a mass

stabilisation mixer.

In Figure 7 are shown two types of mass stabilisation.

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Key

1 Stabiliser tank + scales

2 Execution machine

3 Mixing tool

4 Mass stabilised peat, gyttja or clay

5 Peat, gyttja, clay

6 Direction of mass stabilisation

7 Geotextile (reinforcement)

8 Preloading embankment

Figure 7 - Two types of mass stabilisation

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10. DEEP VIBRATION

Ground treatment by deep vibration achieved by depth vibrators and compaction probes is the

object of EN 14731.

The following types of treatment are covered by EN 14731:

� deep vibratory compaction to densify the existing ground;

� vibrated stone columns to form a stiffened composite ground structure by the insertion of

granular material which itself shall be densified. Generally, stone columns have a diameter

greater than 0,6 m and lower than 1,2 m.

The following treatment methods are covered by EN 14731:

� methods in which depth vibrators, containing oscillating weights which cause horizontal

vibrations, are inserted into the ground;

� methods in which compaction probes are inserted into the ground using a vibrator which

remains at the ground surface and which in most cases oscillates in a vertical mode.

Definitions

deep vibratory compaction type of ground treatment by deep vibration in which the main purpose is to densify the soil. The

treatment is applicable to many granular soils and normally results in increased strength and

stiffness, reduced permeability and reduced susceptibility to liquefaction

vibrated stone columns type of ground treatment by deep vibration in which a depth vibrator is used to form continuous

stone columns from the maximum depth of penetration up to the ground surface, and hence to form

a stone column/soil structure which should have an increased strength and stiffness compared with

the ground in an untreated state. The treatment is applicable to a wide range of soils and in granular

soils some densification may also be achieved. Three installation processes, the dry top-feed

process, the wet process and the dry bottom-feed process are described in Annex B

depth vibrator basic component of ground treatment equipment used in the installation of vibrated stone columns

and in vibro compaction, which vibrates horizontally by means of an eccentric weight rotating

about its longitudinal axis, and penetrates into the ground. The penetration in the ground can be

made easier by air or water flushing

top vibrator vibrator which remains above the ground surface

compaction probe tool for deep vibratory compaction which is inserted into the ground to transmit vibrations from a

top vibrator which remains at the ground surface; wings, drainage or water flushing can be provided

to facilitate the compaction process

vibrating tool item of equipment which is inserted into the ground to cause vibration at depth; commonly a depth

vibrator containing oscillating weights or a compaction probe inserted into the ground using a top

vibrator which remains at the ground surface

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wet process method of installing vibrated stone columns in which flushing water removes soft material,

stabilises the hole and allows specified granular material to reach the tip of the depth vibrator

where it is compacted (the process is described in Annex B)

dry bottom-feed process method of installing vibrated stone columns in which specified granular material is delivered

directly to the tip of the vibrator via a feed pipe attached to the vibrator, with the vibrator

remaining in the ground during the construction of the column to maintain the stability of the hole

(the process is described in Annex B)

Materials for deep vibratory compaction

Material may be added during deep vibratory compaction. This may be the natural granular material

being compacted at the site or imported material.

Added materials shall be sufficiently hard and chemically inert so as to remain stable during the

treatment process and subsequent working life in the anticipated soil and groundwater conditions.

Materials for vibrated stone columns

Material used to form stone columns shall be:

� sufficiently hard and chemically inert so as to remain stable during column construction and

subsequent working life in the anticipated soil and groundwater conditions;

� graded appropriately for compaction to form a dense column fully interlocked with the

surrounding ground and in compliance with other requirements such as drainage;

� compatible with the plant used and flow freely within bottom-feed and through-feed delivery

systems without arching which may block these systems.

Gradings typically used with the different processes are given in the following table.

Process Grading in mm

Dry top-feed process 40 to 75

Wet process 25 to 75

Dry bottom-feed process 8 to 50

Deep vibratory compaction

Deep vibratory compaction is usually restricted to granular soils; increasing fines content will

reduce the compaction efficiency. It is often found that a fines content of more than 10 % causes

difficulties. Soils exhibiting inter-particle bonding due to cementation, suction or some other

cause may not be suitable for this type of ground treatment. In some cases, compaction efficiency

can be increased by using water flushing, or in combination with vertical drains. Compaction up

to ground surface is only possible applying additional measures.

Deep vibratory compaction of granular soils can be achieved by methods which use either a

depth vibrator or a top vibrator.

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Key 1 Eccentric weight (within)

2 Extension tube

3 Isolator

4 Water or air jets

5 Motor (within)

6 Fins to prevent twist

7 Nose cone

Fig. 1 - Depth vibrator

Where a top vibrator is used, it is connected to the top of a compaction probe, which is designed

to transfer the vibrations to the soil as efficiently as possible. Several different types of

compaction probes are available including the vibro-wing (Figure 2) and other flexible probes.

Conventional vibrators for sheet-pile driving can be used, but special vibrators have been

developed. Although the top vibrator usually vibrates vertically, the probe will cause horizontal

accelerations which may locally be greater than the vertical ones. The compaction increases

when resonance is created between the vibrating system (vibrator and compaction probe) and

surrounding soil. By means of vibration sensors placed on the ground, and a vibrator with

adjustable frequency, the frequency can be adapted to amplify ground vibrations; this method is

known as resonance compaction.

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Fig. 2 - Vibro-wing

Compaction is achieved by inserting the probe at treatment points usually on a triangular or

rectangular grid. Spacings are typically from lm to 4 m depending on the type and size of the

compaction probe and vibrator capacity. At each treatment point the probe is inserted into the soil

to the depth to which compaction is required. The compaction is obtained during penetration or

during penetration and extraction. The compaction time at each point varies typically from 5 min to

40 min and the time required increases with the fine content of the soil. Compaction can be effected

using several passes, with closer spacings in the later passes.

Installation of vibrated stone columns

There are three principal methods of installing vibrated stone columns, dry top-feed process, wet

process and dry bottom-feed process, and for each method the installation of a single column is

described. With the vibrated stone column processes, column installation is repeated for further

columns at a predetermined spacing to effect the desired treatment. All three processes use a

similar type of depth vibrator, which is an eccentric weight assembly rotating rapidly within a

heavy tubular steel casing. The general arrangement of the ciepth vibrator is,'shown ,in Figure A.1.

The nose of the vibrator is tapered to aid penetration on the ground, whilst vertical fins prevent the

vibrator rotating during penetration.

The following descriptions are given as typical. In practice small differences in detail may be

noticed.

Dry top-feed process

In granular soils, this method is usually only possible above the water table. The whole

assembly is suspended from a crawler mounted crane and the vibrator is lowered onto the ground.

Penetration of the fill and/or underlying weak soil is effected by a combination of the weight of the

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vibrator, the high frequency vibration and compressed air. A compressor supplies the depth

vibrator with air, which emerges from nozzles in the main steel housing just above the vibrator tip.

The general arrangement is shown in Figure 3. After reaching the required depth, the vibrator is

held in the ground for a short time and then withdrawn. A small charge of clean, inert granular

material is tipped into the hole and the vibrator is lowered again to compact the granular material

and interlock it with the surrounding soils. By adding successive small charges of granular material

and compacting each one to chosen levels of power consumption, a dense stone column is built up

to ground level. Typically gradings for the granular material are within the range from 40 mm to 75

mm.

Key

1 Stone column being formed

2 Stockpile of granular infill

3 Vibrator

Fig. - Dry top-feed process

Wet process

The wet process is used where the dry top-feed process cannot be used because of unstable ground.

The depth vibrator is similar to that used for the dry process but is equipped with water

flushing.

The depth vibrator (Figure 4) is suspended from a suitable crane, lowered onto the ground and

the water jets are opened. The vibrator penetrates quickly through weak soils under its own

weight aided by the water flushing and vibrations. The vibrator is partially withdrawn and is

sometimes surged to flush out the weak soils accumulating in and adjacent to the bore. Following

formation of an open hole the vibrator is kept in the ground and the water flow reduced whilst

clean inert granular material is successively heaped around the top of the vibrator bore at ground

level. The granular material then passes down between the vibrator and the surrounding soils to

permit the construction of a stone column in short lifts and repenetration steps. It is important that

the water flow is maintained until the vibrator reaches ground surface. The vibrator compacts the

granular infill and interlocks it tightly with the surrounding soil. The cycle is repeated until a

compact stone column is built up to ground level. Typically gradings for the granular material are

within the range from 25 mm to 75 mm.

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Key

1 Stone column

2 Stone stockpile

3 Water flushing

4 Vibrator

Fig. 4 - Wet process

Dry bottom-feed process

As the vibrator remains in the hole during column construction, the process can operate successfully

in unstable hole conditions and can be used instead of the wet process in most cases. The bottom-

feed depth vibrator has a heavy duty supply tube located down one side and permanently fixed to

the vibrator forming a fully integrated vibrator/granular material supply. The supply tube bends

inwards at the vibrator tip to ensure a central location for the supply of granular material. The

general arrangement is shown in Figure 5.

The cycle of operations for this completely dry process is as follows. The vibrator is positioned

on the ground at the treatment point location; and the whole system is charged with granular

material. With the granular material in the supply tube acting as a plug at the tip of the vibrator,

assisted as necessary by compressed air and under the combined action of the vibrations and its

weight, using an additional pull down force if necessary, the depth vibrator penetrates the

ground to the required depth. The stone column is then formed and compacted by lifting the

vibrator, holding the lift for a short time to allow the granular material to run, and then forcing the

vibrator down on the charge of granular material to compact and tightly interlock it with the

surrounding soil. This is repeated, charging the system with granular material as necessary, until

a compact stone column is formed up to ground level. Typically gradings for the granular material

are within the range from 8 mm to 50 mm.

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Key

1 Pressure chamber

2 Vibrator

3 Stone stockpile

4 Stone feed bucket

5 Stone delivery tube

Fig. 5 - Dry bottom-feed process

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11. VERTICAL DRAINAGE

In cases where external loading of low-permeability soils, such as clay, gyttja (Decomposed plant

and animal remains; may contain inorganic constituents), decomposed peat etc., causes a stress increase

exceeding the pre-consolidation pressure of the soil, excess pore water pressure will be induced,

followed by a consolidation process in which pore water is squeezed out of the soil. The volume

decrease of the soil caused thereby is accompanied by a gradual increase in effective stress

and a corresponding decrease in excess pore water pressure. The consolidation process will

continue until the excess pore water pressure has completely dissipated and the load is carried by

effective stresses, a process whose duration depends on the consolidation characteristics of the soil

and the drainage paths (the longer the drainage paths, the longer the consolidation process). The

aim of vertical drain installation is to shorten the drainage paths and the time required for the

excess pore water pressure, induced by the loading operation, to dissipate. The time of excess pore

water pressure dissipation (the consolidation time) will be shorter the closer the drains are installed.

Vertical drainage is covered by EN 15237.

Fields of application

The installation of vertical drains is carried out as a means of speeding up Iong-term

consolidation settlements caused by loading. Another objective is to improve stability conditions by

an overall increase in shear strength. In seismic regions vertical drainage can also be used for the

purpose of mitigating liquefaction phenomena.

Examples of areas where this technique has generally been applied are: - embankments for roads and

railroads;

- construction and reinforcements of dikes;

- embankments for construction sites of housing estates, industrial estates, terminals etc.; -

preloading for landfills;

- marine constructions and near-shore applications;

- land reclamation, ports and airports.

A growing area of application is in the environmental field, remediation of contaminated ground.

Contaminated water squeezed out through the drains may have to be treated before disposal.

The required life span of vertical drains is normally limited to a maximum of about 5 years,

with the exception of drains used for liquefaction mitigation where the lifetime needs to be

significantly longer.

Execution of vertical drainage

The functional requirements of the project form the basis for the geotechnical design of vertical

drainage. The execution of a vertical drainage system includes the creation of a working

platform, the placement of a drainage blanket, positioning of the drain pattern and installation

of the drains, followed by the loading operation and monitoring.

Prefabricated drain types have gradually replaced sand drains, which previously were

frequently used. The installation of vertical drains may detrimentally affect the original

properties of the soil (e.g. decrease the shear strength and coefficient of consolidation). A

possible decrease in shear strength has to be taken into account in cases where stability under

loading conditions may be threatened. Vertical drainage and preloading are illustrated in

Figure 1. Due to the excess pore water pressure created by loading, pore water is squeezed

out of the soil in the horizontal direction towards the drains and thereafter in the vertical

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direction through the drains. A generally smaller amount of water is also squeezed out of the

soil in the vertical direction between the drains (contributory effect of one-dimensional

consolidation).

Key 1 surcharge load

2 drainage blanket

3 vertical drains

4 clay layer

5 pore water flow

Figure 1 - Sketch showing fully penetrating drains (drains in contact with drainage layers at

top and bottom), drainage blanket and surcharge load

Depending upon the installation method and procedure used, the installation of vertical drains may

affect the original properties of the soil (e.g. decrease the shear strength and coefficient of

consolidation). This should be considered in the design.

Drain types

Band drains

Prefabricated band drains consist typically of a central core surrounded by a filter sleeve, Figure

2. The width of the band drains is typically 100 mm.

a) Channel-shaped core with glued filter

b) Channel-shaped core with wrapped filter

c) Geo-mat with edge-sealed filter

d) Cusp-shaped core with wrapped filter

Figure 2 - Examples of band drains

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Band drains are installed inside a hollow mandrel with rectangular, rhomboid or circular cross-

section. The size of the mandrel is normally adapted to leave a free inside space for the band

drain during installation. Moreover, the bending rigidity of the mandrel needs to be high enough

to ensure verticality of the drain installed.

An anchor, which is fixed to the drain tip before installation, prevents the drain from being

dragged up when the mandrel is withdrawn, Figure 3. During installation the soil should be

prevented from intruding between the inside surface of the mandrel and the drain. Otherwise, the

drain will be subjected to high tensile forces upon withdrawal. The shape of the mandrel and the

anchor needs to be fitted to prevent soil intrusion into the mandrel.

The penetration of the mandrel is either performed by means of a static load or by dynamic

action, using a vibratory or impact hammer. Static installation is preferable in soils sensitive to

disturbance.

After withdrawal of the mandrel, the drains should be cut in a way to ascertain good contact with

the drainage blanket, preferably about 25 cm above the working platform.

Figure 3 - Example of band drain anchor

Prefabricated cylindrical drains

Types of drains

A prefabricated drain consists of a tubular core, typically 50 mm in outer diameter and 45 mm

in inner diameter, made of annular-corrugated perforated plastic, resistant to crushing, shocks,

rapid tension and ageing, surrounded by a filter sock made of non-woven geotextile.

Method of installation

The prefabricated cylindrical drains are installed inside a hollow, cylindrical mandrel with an

external diameter of typically 100 mm. The mandrel, which is normally pushed into the soil by

static loading, needs to have sufficient rigidity. An anchor plate is fixed to the drain tip before

installation and prevents soil from intruding into the mandrel during installation.

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Upon withdrawal of the mandrel the drains are cut in a way to ascertain good contact with the

drainage layer, preferably 25 cm above the working blanket.

Sand drains

Types of drains

Sand drains usually consist of sand columns, 18 cm to 50 cm in diameter, which are installed into

the soil and are in direct contact with the soil.

The sand used for sand drains should preferably fall within the grain size limits shown with cross-

ruled area in Figure 4. However, there are many case histories where sand drains have functioned

successfully having wider grain size distributions, falling outside the limits of the cross-ruled area.

The grain size distribution of the sand used in these case histories falls within the limits given by the

outer unbroken lines in Figure 4.

Key

1 sand

2 gravel

3 grain size d, mm

4 content of grains <d in wt, % of total mass

Fig. 4 – Grain size limits of granular material to be used in sand drains

Methods of installation

Sand drains are either installed by so-called non-displacement methods or by so-called

displacement methods.

The non-displacement methods comprise shell and auger drilling, powered auger drilling, water

jetting, flight augering and wash boring. The auger method consists in screwing the auger down to

the required depth, then pulling it upwards while sand is transferred to the hole below the auger tip

through the axis. The hollow auger method consists of screwing the auger down to the required

depth and then pulling it upwards while sand is transferred to the hole below the auger tip through

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its hollow axis. In the water jetting method, the hole, which will be filled with sand, is first created

by water jetting at a pressure and flow adjusted to the soil condition. Sand is then poured into the hole

without compaction.

The displacement methods comprise mandrel or vibro installation methods. In the mandrel method a

hollow mandrel with a flap at its lower end is driven into the ground. As the mandrel is withdrawn,

the flap opens and water-saturated sand filled into the mandrel thereby creates the sand drain. In the

vibro installation method, a mandrel with or without a flap on its lower end is inserted into the soil

to the required depth by means of a top vibrator mounted on the mandrel. After installation the

vibrator is continuously pulled upwards without compacting the sand fill exerting from the lower

end of the mandrel.

Alternatively, the drains are installed by means of a depth vibrator, which after installation is

continuously pulled upwards without compacting the sand fill.

Drainage blanket and working platform

For the efficiency of the vertical drainage system an appropriate drainage blanket (a layer of

granular material of appropriate thickness and/or a geotextile or geotextile-related products)

should be installed. The consolidation settlement causes a depression of the central part of the

drainage blanket. Temporary wells for removing drained water from the drainage blanket may

therefore be required, especially in cases where the width of the drainage blanket is large.

Protection of the drainage blanket against frost effects should be considered when relevant.

The execution of a vertical drainage project requires the presence of a working platform with an

upper surface suitable to facilitate the vertical installation of the drains. The working platform needs

to be capable of carrying the installation equipment. The presence of pockets and lenses of soft

soil in the working platform can significantly reduce the local bearing capacity and result in

overturning of the installation rig. The placement of a geotextile separation layer underneath the

working platform may be a way of avoiding the risk of heterogeneities in the working platform.

Loading

The loading operation usually consists of placing a surface load on top of the drainage blanket.

This is a critical phase of vertical drainage projects. Loading needs to be carried out in such a way

that the stability of the ground is not endangered. Therefore, the unit weight of the fill used for

loading has to be defined and controlled. The un-drained shear strength of the soil may be

detrimentally affected, not only by the drain installation in itself, but also by the loading operation

if carried out with heavy equipment. In most cases, it is important that the filling operation is

monitored by settlement and pore pressure observations.

If the shear strength of the soil is too low to permit placement of the fill to full height, loading

berms are required. Alternatively, loading has to be carried out stepwise, followed by

investigation of the gain in shear strength and dissipation of excess pore water pressure during the

consolidation process, required to permit the placement of the next load-step, and so on. In the case

of stepwise loading the specified thickness of each embankment layer need to be checked in order to

avoid excess loading and consequential failure.

Groundwater lowering in permeable strata in connection with the drains can also be used as an

alternative to, or in combination with, external loading.

At sites of drain installation where the stability conditions are unsatisfactory, the surface load can be

replaced or augmented by the vacuum method, Figure 5. In this case the drainage blanket is

overlain by an airtight cover and sealed hermetically along its outer borders. The drainage blanket

is connected to a vacuum pump, which produces under-pressure in the drains in relation to the pore

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water pressure in the soil and results in consolidation [9] [10]. The under-pressure achieved by the

vacuum method in this case is maximum 70 kPa to 80 kPa.

Key

u d. = pore water pressure in the drains

uvac = under-pressure (assumed equal to a vacuum of 70 % of atmospheric pressure)

a) pore pressure dissipation caused by the drains

b) pore pressure dissipation without drains

1 airtight cover

2 to vacuum pump

Figure 5 – Sketch of the vacuum method and its effect on power water pressure, both

for horizontal pore water flow towards the drains (a) and

for vertical pore water flow between the drains (b)

Monitoring

The effect of vertical drainage should be monitored by both settlement and pore pressure

measurements. The measured values are used to check the actual rate of consolidation and the

assumptions made in the design. It is important that the monitoring system is installed in due time

before the installation of the drains, both with regard to the effect of drain installation itself

(excess pore pressure due to disturbance caused by drain installation and its possible negative

influence on stability) and with regard to the interpretation of the results of observation subsequently

achieved.

The aim of soil improvement by vertical drainage is generally to prevent unacceptable settlement

from taking place. Therefore, settlement observations are a necessary ingredient in the monitoring

system.

Excess pore pressure observations by means of piezometers installed at different depths is

doubtless the most appropriate way of checking that the degree of consolidation has reached the

set level according to the design. The piezometers should be placed in the centre between the drains

where the rate of consolidation is a minimum.

Typical locations for observations of settlement and pore pressures for a case with homogeneous

ground of limited thickness are shown in Figure 6 and for a case with stratified ground in Figure 7.

The number of measurement profiles depends on the extent of the site and the thickness and

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layering of the compressible layers that are treated by vertical drainage.

Key 1 embankment 5 underlying permeable layer

2 drainage blanket and working platform 6 settlement gauge

3 vertical drain 7 piezometer

4 compressible soil

Figure 6 - Typical instrumentation for monitoring the efficiency of

vertical drainage (simple case)

Key 1 embankment

2 drainage blanket and working platform

3 vertical drain

4 compressible soil

5 underlying permeable layer

6 settlement gauge

7 piezometer

8 permeable sand layer

9 compressible soil

Figure 7 - Typical instrumentation for monitoring the efficiency of

vertical drainage (site with different layers)

In practice, one needs to consider the degree of consolidation achieved in the soil layers having

the lowest coefficient of consolidation (usually having also the most unfavourable compression

characteristics). In homogeneous soil condition, the lowest degree of consolidation is achieved

where the effect of vertical onedimensional consolidation is minimal, i.e. in the middle of the clay

layer. If the discharge capacity of the drains is too low this will strongly influence the degree of

consolidation achieved with increasing depth of installation. Using only surface settlement

observations as a means of checking the degree of consolidation achieved throughout the soil layer

may consequently lead to wrong conclusions.

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12. GROUTING

Grouting for geotechnical purposes (geotechnical grouting) is a process in which the remote

placement of a pumpable material in the ground is indirectly controlled by adjusting its

rheological characteristics and by the manipulation of the placement parameters (pressure, volume

and the flow rate).

The following principles and methods of geotechnical grouting are covered by EN 12715:

- displacement grouting (compaction grouting, hydraulic fracturing) ;

- grouting without displacement of the host material (permeation, fissure grouting, bulk

filling).

Definitions

grout a pumpable material (suspension, solution, emulsion or mortar), injected into soil or rock, which

stiffens and sets with time

displacement grouting injection of grout into a host medium in such a manner as to deform, compress, or displace the ground

compaction grouting a displacement grouting method which aims at forcing a mortar of high internal friction into the

soil to compact it without fracturing it

hydraulic fracturing (hydraulic fracture, claquage grouting) the fracturing of a ground initiated by the injection of water or grout under a pressure in excess of

the local tensile strength and confining pressure; also called hydrofracturing, hydrosplitting,

hydrojacking or claquage

non-displacement grouting substitution of the natural interstitial fluid in the accessible existing voids of the ground by a grout

or mortar without any significant displacement of the ground. The term includes penetration

grouting and bulk filling

permeation (impregnation) grouting the replacement of interstitial water or gas of a porous medium with a grout at injection pressures low

enough prevent displacement

penetration grouting grout injection of joints or fractures in rock, or pore spaces in soil, without displacing the ground.

The term includes permeation (impregnation), fissure and contact grouting

fissure grouting the injection of grout into fissures, joints, fractures and discontinuities, particularly in rock

contact grouting the injection of grout into the interface between man-made structures and the ground

bulk filling bulk filling is the placement of grout with a high particulate content to fill substantial voids

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Grout materiais

a. Hydraulic binders and cements

Hydraulic binders include all cements and similar products used in water suspension for

making grouts.

Microfine (ultra-fine) hydraulic binders or cements are characterised by a particle size d95 of less

than 20 µm.

The granulometric curve, especially of the microfine products used, shall be known.

b. Clay materials

Natural clays, activated or modified bentonites can be added to cement based grouts in order

to reduce bleeding and filtration under pressure, to vary the viscosity and cohesion (yield) of the

grout, or to improve the pumpability of the grout.

The mineralogy, particle size, water content, and Atterberg liquid limit of the clay should be known.

c. Sands, gravels and fillers

Grouts Grouts are classified as:

- suspensions: either particulate or colloidal suspensions ;

- solutions: either true or colloidal solutions ;

- mortars.

Figure 1 - Grout classification

The following intrinsic properties shall be considered when choosing a grout:

- rheology (viscosity, cohesion, etc.), Setting time, Stability ;

- particle size, if applicable ;

- strength and durability ;

- toxicity.

Suspensions

Suspensions are characterised by:

- the grain size distribution of the solid particles ;

- their water/solid ratio ;

- the rate of sedimentation and bleeding ;

- their water retention capacity under pressure filtration.

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Solutions

Some types of silicate grout are not stable with time and their use should be carefully assessed.

Organic silicate gels may lead to the proliferation of bacteria in the ground.

Resins are usually applied under the circumstances given in Table 2.

Table 2 - Application of resin grouts

Mortars

Mortars showing high internal friction are used for compaction grouting or for the filling of voids.

Their rheological behaviour is usually determined by slump tests.

Mortars flowing under their own weight are generally used for filling cavities, large cracks,

open fissures and voids in granular soils. They shall be stable and their rheological behaviour

(similar to suspensions) is usually characterised with suitably selected flow cones.

When used for compaction grouting, the mortar should contain a minimum of 15% of fines pass 0,1

mm.

Grouting principles and methods The introduction of grout in a host medium is achieved either wiht or without displacement of the

ground. Figure 2 illustrates the various injection methods associated with these two principles:

Figure 2 - Grouting principles and methods

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Grouting without ground displacement (non-displacement grouting)

Permeation (impregnation) grouting

Permeation grouting aims at filling the accessible interstices between grains in permeable soils

by a grout without destruction of the integrity of the ground. It reduces the permeability of the host

material and usually increases the strength and density.

In order to avoid displacement, permeation grouting shall be carried out at carefully

controlled pressures and flow rates.

Fissure and contact grouting

Fissure grouting aims at filling open fissures, fractures or joints in a rock mass with grouts

without creating new or opening existing fractures, in order to reduce the permeability and/or

increase the strength of the grouted mass.

Bulk filling

Bulk filling is used for the filling of large natural or man made openings. The term is generally

applied to the placement of large volumes of grout under gravity or at low pressures.

Bulk filling may be followed by a phase of grouting under pressure to fill the remaining voids.

Grouting with ground displacement (displacement grouting)

Displacement grouting refers to the injection of grout under pressure with the deliberate intent of

spatially displacing the host medium. The term includes injection methods such as compaction

grouting, and hydraulic fracturing (claquage). The method is used to increase the density of a

plastically deformable materiai, 3.nd the volume of the treated mass where the plastic deformation

limit is reached.

Controlled displacement grouting can be employed to strengthen the ground under existing

structures.

Hydraulic fracturing

Grouting by hydraulic fracturing is used to:

- reinforce or stabilise the ground (soil or rock) ;

- produce controlled uplift of structures ;

- achieve watertightness by creating compartments.

It is difficult to control the propagation of an hydraulic fracture plane. Hence, the grouting

objective should usually be achieved by an incremental series of injections, spread over a period of

time.

Compaction grouting

Compaction grouting refers to the intrusion of a comparatively stiff (viscous) particulate grout

into the ground to induce displacement and deformation. The grout is usually extruded from

open-ended injection tubes. The grout consistency is such that the grout remains as a

homogeneous mass and neither permeation nor hydraulic fracturing of the host medium occurs.

Compaction grouting is most often used to compact and densify loose ground and to raise and

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support structures which have settled.

The final grid of grout holes is generally defined during the grouting process, in accordance with

the results of control tests performed in the centre of the primary grid.

Grout

In soils, a groutability ratio, such as the D10/d90 or D15/d85 criterion, can be used to assess the

penetrability of particulate grouts. In rock, the maximum particle size to fissure width is considered

(a ratio of three is commonly used).

Applicability

The type of grout applicable for different types of ground are shown in Table 3.

Table 3 – Indicative grouts for different types of ground

Grout placement

The injection process is governed by:

- the grout volume V per pass ;

- the injection pressure P;

- the flow or placement rate Q;

- the grout rheology.

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The design should indicate how to adapt Q, Vand Pfor a given mix design, or the rheology of the

mix design, to the anticipated ground response during grout placement.

For permeation, the flow (injection) rate Q should be controlled to ensure that the effective

pressure remains lower than the ground fracturing pressure.

Drilling pattern and borehole design

The number, position, spacing, depth, diameter, inclination and orientation of boreholes and

injection points shall be based on geological conditions, the type of structure to be grouted, the

results to be obtaineti, the grouting method and purpose, the type of grout to be used, injection

pressure and rate of grout take. The design shall make adequate provision for any variation in the

above parameters.

Grouting sequence

In its simplest form, a sequence constitutes a single grout type introduced through a single hole.

The grout placement sequence may progress to multiple stages, over many holes, with each

stage requiring a sequence of injection passes of differing grout types.

Grouting pressure

In general practice, the grouting pressure is measured at the grout delivery pump and/or at the

hole collar. However, variations in hydraulic head, and friction losses in the delivery system, will

result in this 'working pressure' being different from the 'effective pressure' acting in the ground.

During non-displacement grouting of soils, the effective (or limit) grouting pressure is dependent on

the confining pressure at the point of injection.

For non-displacement grouting, the permissible injection pressure is the maximum pressure at

which a grout is allowed to be introduced into the ground in order to avoid any undesirable

deformation of the ground.

In non-displacement grouting, a value for the permissible injection pressure shall be given in

the design.

Execution

The equipment required to perform a grouting operation includes:

- drilling and driving equipment ;

- mixing and proportioning equipment ;

- pumping equipment ;

- injection piping ;

- packers ;

- monitoring and testing equipment.

Drilling

The following drilling methods may be employed:

- rotational drilling ;

- percussion drilling using either an external or down-the-hole hammer ; cased percussion

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drilling ;

- grab-, chisel- and bailer borings ;

- driving of lances ;

- vibrating of casing or drill pipes.

In unstable ground full borehole penetration may require:

- the use of drilling muds, grouts or foams ;

- temporary casing ;

- direct insertion of sleeve pipes ;

- progressive stabilisation as the borehole advances.

Grout placement

The method of grout placement will be determined by the ground condition, the works requirement

and the type of grout used. The basic approaches are the following

a) injection in unsupported boreholes in stable ground ;

b) injection via sleeve pipes previously placed in a temporarily cased borehole, in unstable ground ;

c) injection through the drill string in unstable ground, generally considered as a pre-grouting

phase and to be followed by approaches a) or b) ;

d) compaction grouting is usually performed through a casing retrieved during upstage grouting.

Soil grouting can be achieved with casing, grout sheath, pierced casing, and sleeve pipes.

Sleeve pipes which are permanently seaied into the ground by use of a support mix (sleeve grout)

allow a repeated use of the injection points.

Large openings (voids, cavities, etc.) are generally filled under gravity, either directly, or via a

tremie pipe extending to the base of the opening.

Packers are used to isolate a grouting stage. Packers are either passive, mechanical or pneumatic,

and have to be long enough to minimise the risk of grout bypass through the medium being grouted.

Packers shall ensure tight sealing between the grout hole wall and the injection pipe at maximum

grouting pressure.

Grouting sequences

Descending or downstage grouting is commonly reserved for the treatment of unstable rock. If

several holes are grouted using downstage grouting, the uppermost stage in all holes is drilled and

grouted before drilling and grouting the next stage in all neighbouring holes.

Upstage grouting is only used in open holes in stable rock or if the aim is compaction grouting.

Multistage grouting, using sleeve pipes is generally used in soils and sometimes in unstable rock.

Combinations of these techniques are possible.

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13. JET GROUTING

The jet grouting method is covered by the EN 12716.

Definitions

jet grouting the jet grouting process consists of the disaggregation of the soil or weak rock and its mixing with,

and partial replacement by, a cementing agent; the disaggregation is achieved by means of a high

energy jet of a fluid which can be the cementing agent itself

jet grouted element volume of soil treated through a single borehole. The most common elements are:

- jet grouted column : a cylindrical jet grouted element (Fig.1 a) ;

- jet grouted panel : a planar jet grouted element (Fig.1 b).

jet grouted structure an assembly of jet grouted elements which are partially or fully interlocked. The most common

structures formed are:

- jet grouted diaphragm : a wall structure (Fig.2 a) ;

- jet grouted slab : a horizontal structure formed by essentially vertical jet grouting (Fig.2 b) ;

- jet grouted canopy : a structure formed by horizontal jet grouting - see 3.8 below (Fig.2 c) ;

- jet grouted block : a three-dimensional structure.

single system the jet grouting process in which the disaggregation and cementation of soil are achieved by a high

energy jet of a single fluid, usually a cement grout (Fig.3 a)

double (air) system the jet grouting process in which the disaggregation and the cementation of soil are achieved by

one high energy fluid (usually a cement grout) assisted by an air jet shroud as a second fluid (Fig.3 b)

double (water) system the jet grouting process in which the disaggregation of the soil is achieved by a high energy water jet

and its cementing is simultaneously obtained by a separate grout jet (Fig.3 c)

triple system the jet grouting process in which the disaggregation of the soil is achieved by a high energy water

jet assisted by an air jet shroud, and its cementing is simultaneously obtained by a separate grout jet

(Fig.3 d)

horizontal jet grouting treatment performed from a horizontal or sub-horizontal borehole (within ± 20° from the horizontal

plane)

jet grouting rig rotary rig able to automatically regulate the rotation and translation of the jet grouting string and tool

jet grouting string jointed rods, with simple, double or triple inner conduit, which convey the jet grouting fluid(s) to the

monitor

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monitor the tool mounted at the end of the jet grouting string, to enable jetting of the fluids into the ground

nozzle a specially manufactured device fitted into the monitor and designed to transform the high pressure

fluid flow in the string into the high speed jet directed at the soil

radius of influence effective distance of disaggregation of soil by the jet, measured from the axis of the monitor

spoil return the surplus mixture of soil particles and introduced fluids arising from the jet grouting process, and

normally flowing to the ground surface via the annulus of the jetting borehole

jet grouting parameters the jet grouting parameters are defined:

- pressure of the fluid(s) within the jet grouting string ;

- flow rate of the fluid(s) within the jet grouting string ;

- grout composition ;

- rotation speed of the jet grouting string;

- rate of withdrawal or insertion of the jet grouting string.

prejetting the method in which the jet grouting of an element is facilitated by a preliminary disaggregation

phase, with a jet of water and/or other fluids

Prejetting is also widely known as prewashing or precutting.

fresh-in-fresh sequence the sequence of work in which the jet grouted elements are constructed successively without waiting

for the grout to harden in the overlapping elements (Fig.4 a)

primary-secondary sequence the sequence of work

,in which the execution of an overlapping element cannot commence before

a specified hardening time or achievement of predetermined strength of the adjacent elements

previously constructed (Fig.4 b)

jet grouted material the material which constitutes the body of a jet grouted element

reinforced jet grouting jet grouted columns reinforced by steel or other high strength material

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Figure 1 a) – Jet grouted column Figure 1 b) – Jet grouted panel

Figure 1 – Examples of jet grouted elements

Figure 2 a) – Jet grouted diaphragms

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Figure 2 b) – Jet grouted slab Figure 2 c) – Jet grouted canopy

Figure 2 – Examples of jet grouted structures

Key 1 Monitor

Figure 3 a) – Single system

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Key 1 Monitor

Figure 3 b) – Double (air) system

Key 1 Monitor

Figure 3 c) – Double (water) system

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Key 1 Monitor

Figure 3 d) – Schemes of jet grouting systems

Figure 4 a) – Fresh in fresh sequence

Figure 4 b) – Primary – secondary sequence

Figure 4 – Work sequences

Materials

Mixes composed of water and cement are usually adopted.

Hydraulic binders other than cement can be used.

In water/cement mixes the water/cement ratio by weight should range between 0,5 and 1,5.

Water reducing, stabilizing, plasticising, waterproofing or antiwashing admixtures can be

added to the water/cement mix.

Other materials, such as bentonite, filler, fly-ash, can also be added to the mix.

When bentonite is to be used in the mix, a water/bentonite suspension should be prepared before

adding cement.

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Examples of applications

Jet grouting can be applied in either temporary or permanent works for different purposes.

For example:

providing foundations for structures to be erected (Fig.5 a) ;

underpinning existing foundations (Fig.5 b) ;

creating low permeability barriers ;

creating retaining or supporting structures ;

complementing other geotechnical works ;

reinforcing a soil mass.

Figure 5 a) – Foundation for structure to be erected

Figure 5 b) – Underpinning existing foundation

Figure 5 – Examples of applications

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Execution

The execution of jet grouting works requires knowledge and experience in this type of construction.

The high pressure employed in the jet grouting process is to generate a high speed jet to disaggregate the soil and is

not intended to be applied to the surrounding soil.

Jet grouted column execution method

The phases of execution usually consist of:

drilling a borehole of a predetermined length ;

- introducing to the end of the borehole a monitor connected to the jet grouting string. This

is unnecessary in some cases as the string and monitor are used for drilling ;

- jetting of the disaggregating and cementing fluid(s) through the monitor, simultaneously

withdrawing and rotating the rods, with pre-established withdrawal and rotational speed,

pump pressure and flow rate for each fluid.

Jet grouted panel execution method

The phases of execution are the same as defined for jet grouted columns, with the exception that

during jetting the rods are withdrawn and not rotated. Alternatively the rods can be rotated about

limited angles. The resulting panel is placed in a plane on the drilling axis, or is formed by two or

more sections on planes intersecting the drilling axis (Fig.1 b).

Alternative execution methods

If required by soil conditions, alternative execution methods may be adopted, both for column or

panel processes. Among alternatives the most usual is prejetting. An element can also be

executed in sequential treatment for a given length from the borehole collar is completed and

allowed to gain strength. Then, after redrilling the treated soil, the process is repeated at a deeper

stage, and so on, until the design length of the treatment is reached.

Equipment <

The jet grouting equipment usually comprises:

- the drilling rig ;

- the jet grouting rig (often is also the drilling rig) provided with the jet grouting string,

the monitor and the devices able to drive the jet grouting string at predetermined rotation

and translation speeds ;

- the mixing and pumping plant supplying the jet grouting fluid (or fluids) ;

- the high pressure lines connecting the jet grouting pump to the rig ;

- equipment to monitor pressures, fluids flow rates and volumes, rate of rotation and

withdrawal, depth.

The jet grouting string

- for the single system, one conduit conveying the high pressure the cement mix to the monitor;

- for the double system, two conduits separately conveying the two fluids (air and cement

mix, or water and cement mix respectively) to the monitor;

- for the triple system, three conduits to allow for the high pressure water, the compressed

air and the cement mix to the monitor.

The jet grouting mixing and grouting plant, for the different systems, mainly comprises

- for the single system : cement and other materials storage, colloidal mixing plant, agitator

tanks, high pressure grout pump ;

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- for the double (air) system: as for the single fluid system plus an air compressor ;

- for the double (water) system: as for the single fluid system plus a high pressure water

pump and a grout pump ;

- for the triple system: as for the double fluid (water) system plus an air compressor.

Drilling

Drilling can be performed with air or water or muds or grouts or foams as flushing media. If

required casing is used.

Jet grouting

Jet grouting shall be executed and supervised by trained and experienced personnel.

Jet grouting should be executed with a sufficient thickness between the upper nozzle and the

ground surface, to avoid possible local hydrofracturing.

The above thickness may vary from 0,5 m for vertical boreholes to 2,0 m for horizontal boreholes and

can be reduced in the presence of an adequate restraint to the surface, such as a slab or a wall.

Placing the reinforcement

Reinforcement can be installed in the fresh jet grouted material during or immediately after the

completion of the jet grouting operations. Alternatively it can be installed in a borehole drilled into

the element after hardening.

Ranges of jet grouting parameters

The jet grouting parameters usually adopted for the different systems fall within the following

ranges:

Jet grouting parameters Single

fluid

Double fluid

(air)

Double fluid

(water) Triple fluid

Grout pressure (MPa) 30 to 50 30 to 50 > 2 > 2

Grout flow rate (I/min) 50 to 450 50 to 450 50 to 200 50 to 200

Water pressure (MPa) N/A N/A 30 to 60 30 to 60

Water flow rate (I/min) N/A N/A 50 to 150 50 to 150

Air pressure (MPa) N/A 0,2 to 1,7 N/A 0,2 to 1,7

Air flow rate (m3/min) N/A 3 to 12 N/A 3 to 12

N/A Not applicable.

The disaggregating effect is obtained by the high velocity of the jet, mainly dependent on the

pressure of the fluid used for the disaggregation : grout in single and double (air) fluid systems,

water in double (water) and triple fluid systems.

For single and double (air) fluid systems, grout pressure usually ranges between 30 MPa and 50

MPa, as defined in the table above. Lower limits down to 10 MPa have also been adopted in

particular cases, such as small diameter jet grouted columns in very loose soils.

The most recent developments in pumping equipment enable the pressure of the disaggregating fluid to reach

up to 70 MPa or flow rates up to 650 I/min.