EMgt 9407 Topic-03 Construction Technology Foundation Systems Dr. Attaullah Shah.

EMgt 9407

Topic-03

Construction Technology

Foundation Systems

Dr. Attaullah Shah

FOUNDATION SYSTEMS• The foundation of a structure supports the weight of the

structure and its applied loads. – In a broad sense, the term foundation includes the soil

or rock upon which a structure rests, as well as the structural system designed to transmit building loads to the supporting soil or rock.

• Foundation failure usually refers to collapse or excessive settlement of a building's supporting structure resulting from soil movement or consolidation rather than from a failure of the foundation structure itself.

FOUNDATION SYSTEMS

FIGURE 10-1. Foundation systems.

SPREAD FOOTINGS• A spread footing is the simplest and probably the most common type

of building foundation. – It usually consists of a square or rectangular reinforced concrete

pad that serves to distribute building loads over an area large enough so that the resulting pressure on the supporting soil does not exceed the soil’s allowable bearing strength.

• The principal types of spread footings include individual footings, combined footings, and mat foundations.

• Individual footings include isolated (or single) footings, which support a single column and

• Wall footings supports a wall.

• Combined footings support a wall and one or more columns, or several columns

• Mat or raft foundations consist of a heavily reinforced concrete slab extending under the entire structure, in order to spread the structure's load over a large area.

SPREAD FOOTINGS

FIGURE 10-2. Types of spread footings.

SPREAD FOOTINGS

FIGURE 10-3. Soil densification under footing.

When the underlying soil can be strengthened, the allowable bearing pressure on the soil surface will be increased. As a result, it may be possible to use spread footings for foundation loads that normally would require piles or other deep foundation methods. The process of improving soils in place, called ground modification or soil stabilization,

PILES

• A pile is nothing more than a column driven into the soil to support a structure by transferring building loads to a deeper and stronger layer of soil or rock. – Piles may be classified as either end-bearing or

friction piles, according to the manner in which the pile loads are resisted.

– However, in actual practice, virtually all piles are supported by a combination of skin friction and end bearing.

PILES• Pile Types• Timber piles are inexpensive, easy to cut and splice, and require no

special handling. However, maximum pile length is limited to about 100 ft, load-carrying ability is limited, and pile ends may splinter under driving loads. Timber piles are also subject to insect attack and decay

• Precast concrete piles may be manufactured in almost any desired size or shape. Commonly used section shapes include round, square, and octagonal shapes.– Advantages of concrete piles include high strength and resistance

to decay. However, a precast concrete pile is usually the heaviest type of pile available for a given pile size.

– Because of their brittleness and lack of tensile strength, they require care in handling and driving to prevent pile damage.

– Since they have little strength in bending, they may be broken by improper lifting procedures. Cutting requires the use of pneumatic hammers and cutting torches or special saws.

– Pile-Driving Procedures• Determining Pile Lo. d Capacity

• Cast-in-place concrete piles (or shell piles) are constructed by driving a steel shell into the ground and then filling it with concrete. The principal types of shell pile include– uniform taper, step-taper, and - straight (or mono tube) piles.

• Steel piles are capable of supporting heavy loads, can be driven to great depth without damage, and are easily cut and spliced. Common types of steel piles include H-piles and pipe piles.The principal disadvantage of steel pile is its high cost.

• Composite piles are piles made up of two or more different materials. For example, the lower section of pile might be timber while the upper section might be a shell pile

• Bulb piles are also known as compacted concrete piles, Franki piles, and pressure injected footings. They are a special form of cast-in-place concrete pile in which an enlarged base (or bulb) is formed during driving.

• Minipiles or micro piles are small-diameter [2 to 8 in.(5 to 20 em)], high-capacity [to60 tons (54 t)] piles. They are most often employed in areas with restricted access or limited headroom to underpin

PILES

FIGURE 10-4. Bulb piles.

Pile Driving

FIGURE 10-5. Drop hammer pile driver.

Driving operations consist of lifting the pile, placing it into the leads,lowering the pile until it no longer penetrates the soil under its own weight, and then operating the drop hammer until the pile is driven to the required resistance. The remaining types of pile drivers are all powered hammers. That is, they use a working fluid rather than a cable to propel the ram (driving weight). Early powered hammers used steam as a working fluid.•Steam power has now been largely replaced by compressed air power. Hydraulic power is replacing compressed air in many newer units.-Single-acting hammers-Double Acting Hammer

PILES

FIGURE 10-6. Operation of a diesel pile hammer. (Courtesy of MKT Manufacturing, Inc.)

PILES-Driving

FIGURE 10-7. Hydraulically powered vibratory driver/extractor. (Courtesy of MKT Manufacturing, Inc.)

- For driving piles with an impact-type pile driver it is recommended that a hammer be selected that will yield the required driving resistance at a final penetration of 8 to 12blows/in. - For fluid-powered hammers, it is also recommended that the weight of the ram be at least one-half the pile weight.-For diesel hammers, ram weight should be at least one-fourth of the pile weight. When selecting a vibratory driver/extractor, a machine should be used that will yield a driving amplitude of 1/4 to 1/2-in. (0.6 to 1.2 cm).

PILES

FIGURE 10-8. Driving a shell pile.

PILES-Load CapacityThe geotechnical engineer who designs the foundation must provide a pile design that is adequate to withstand driving stresses as well as to support the design load of the structure without excessive settlement.The best measure of in-place pile capacity is obtained by performing pile load tests

The safe capacity of piles driven by powered hammers, has been incorporated in some U.S. building codes. Minimum hammer energy may also be specified by the building code.

Pile load test • Pile load test is governed by (ASTM D-1143) • It involves loading the pile to 200% of design load at

increments of 25% of the design load. • Each load increment is maintained until the rate of

settlement is not greater than 0.01 in./h (0.25 mm/h) or until 2 h have elapsed.

• The final load (200% of design load) is maintained for 24 h. • Quick load tests utilizing a constant rate of penetration test

or a maintained load test are also used.• Quick load tests can usually be performed in 3 h or less.• With all of the methods of load testing, pile settlement is

plotted against load to determine pile capacity• The tangent method, involves drawing tangents to the initial

and final segments of the curve

A procedure used by the U.S. Army Corps of Engineers determines ultimate pile capacity as the average of the following three values: 1. A settlement of 0.25 in. (6.35 mm) on the net settlement vs.load curve.2. The load determined by the tangent method previously described. 3. The load that corresponds to the point on the net settlement vs.load curve where the slope equals 0.01 in. per ton (0.28 mm/t).Factor of safety depending on the soil type is applied. However, a minimum factor of safety of 2.0 is usually employed.

Pile Capacity • Newer and better approach to predicting pile capacity is

provided by the use of wave equation analysis • It analyzes the force and velocity waves developed in a

pile as a result of driving. • For pile design, the analysis is based on a specific type

and length of pile, a specific driving system, and the expected soil conditions.

• Computer wave equation analysis programs, such as the WEAP (Wave Equation Analysis of Pile Driving) program, are available for analyzing wave data to predict pile behavior during driving and to confirm pile performance during construction.

PIERS AND CAISSONS• A pier is simply a column, usually of reinforced concrete,

constructed below the ground surface. – It performs much the same function as a pile. – That is, it transfers the load of a structure down to a

stronger rock or soil layer.• Piers may be constructed in an open excavation, a lined

excavation (caisson), or a drilled excavation• The terms pier foundation, caisson foundation, and drilled

pier foundation are often used interchangeably.

PIERS AND CAISSONS

• A caisson is a structure used to provide all-around lateral support to an excavation. – Caissons may be either open or pneumatic.

• Pneumatic caissons are air- and watertight structures open on the bottom to permit the excavation of soil beneath the caisson.

• The caisson is filled with air under pressure to prevent water and soil from flowing in as excavation proceeds.

STABILITY OF EXCAVATIONS• Slope Stability• The shear strength of a cohesion-less soil is thus due

solely to the friction developed between soil grains.• A normal force (or force perpendicular to the sliding

surface) is required to develop this strength. When an embankment composed of a cohesion-less soil fails , it fails.

• Material from the upper

Part of the slope breaks

away and falls to the toe

of the slope until the face

of the embankment reaches the natural angle of repose for

the soil.

STABILITY OF EXCAVATIONS

FIGURE 10-11. Slope failure of cohesive soil.

In cohesive soil s like clays and silts, a large mass of soil has moved along a surface, which we call a slip plane. The natural shape of this failure surface resembles the arc of an ellipse but is usually considered to be circular in soil stability analyses.

Theoretically, a vertical excavation in a cohesive soil can be safely made to a depth that is a function of the soil's cohesive strength and its angle of internal friction. This depth can range from under 5 ft (1.5 m) for a soft clay to 18ft (5.5 m) or so for a medium clay

In clayey soils, subsidence of the soil at the top of the cut usually results in the formation of tension cracks on the ground surface Such cracks usually occur at a distance from the face of the cut equal to ½ to 2/3 of the depth of the cut


FIGURE 10-12. Subsidence and bulging.

If lateral support is not provided, tension cracks will continue to deepen until failure of the embankment occurs. Failure may occur by sliding of the soil face into the cut

FIGURE 10-13. Formation of tension crack.

The stability of an embankment or excavation is also affected by external factors. These include weather conditions, ground water level, the presenceof loads such as material and equipment near the top of the embankment/excavation, and the presence of vibration from equipment or other sources


FIGURE 10-14. Modes of embankment failure.


FIGURE 10-15. Heaving of cut bottom.


FIGURE 10-16. Boiling and piping of cut bottom.

Embankment Failure • Side slopes may be stabilized by cutting them back to an

angle equal to or less than the angle of repose of the soil, or by providing lateral support for the excavation

• Both side and bottom stability may be increased by dewatering the soil surrounding the excavation.

• To protect more permanent slopes, such as highway cuts, retaining walls are often used.

• Slopes of cohesive soil may be strengthened by increasing the shearing resistance along the potential slip plane

• This may be done by driving piles or inserting stone columns into the soil across the potential slip plane

• Another technique for reinforcing slopes is called soil (or earth) reinforcement. One form of this process is known under the trademark name Reinforced Earth.


FIGURE 10-17. Soil reinforcement.

PROTECTING EXCAVATIONS AND WORKERS

• Excavation cave-ins are responsible for the greatest number of U.S. construction fatalities, accounting for over 300 deaths during a recent year. – Because of the frequency and severity of cave-in accidents,

OSHA has established a number of safety regulations affecting excavation operations.

– While it may be possible to avoid placing workers into an excavation through the use of remote-controlled equipment or robots in most cases workers must enter the excavation and OSHA regulations will apply.

• These regulations require, among other things, that workers in an excavation be protected from cave-ins by one of the following methods: – Sloping or benching of the sides of the excavation.– Supporting the sides of the excavation by shoring. – Placing a shield between workers and the sides of the

excavation


Table 10-1. OSHA soil and rock classification system

To comply with OSHA rules on sloping, shoring, and shielding, it is necessary to be familiar with the OSHA Soil and Rock Classification System shown in Table 10-1. In this system, soil and rock are classified as Stable Rock, Type A, Type B, or Type C.


• Sloping and Benching• Shoring and Shielding• Slurry Trenches

Table 10-2. OSHA maximum allowable slopes for excavation sides. (From Code of Federal Regulations, Part 1926, Title 29, Chapter XVII)


FIGURE 10-18. Timber shoring system.

Lateral support for the sides of an excavation is usually provided by shoring. A shoring system that completely encloses an excavation is essentially a cofferdam, which is a structure designed to keep water and/or soil out of an excavation area. A caisson is also a form of cofferdam, as we have seen.

timber shoring, aluminum hydraulic shoring, lagging, and sheet piling.


FIGURE 10-19. Aluminum hydraulic shoring system.


FIGURE 10-20. Trench shield.


FIGURE 10-21. Slurry trench construction.

A slurry (such as clay and water) isused to fill the excavation as soil is removed. The slurry serves to keep the sides of the trench from collapsing during excavation. No lowering of the water table is required with this: method. After completion of the trench, the slurry is displaced by concrete placement

The slurry trench technique eliminates the necessity for shoring and dewatering excavations.The soil between two rows of completed slurry trenches may be excavated to form a large opening such as a subway tunnel.

DEWATERING EXCAVATIONS

• Dewatering is the process of removing water from an excavation.

• Dewatering may be accomplished by lowering the groundwater table before the excavation is begun. – This method is often used for placing pipelines in

areas with high groundwater levels. – Alternatively, excavation may be accomplished

first and the water simply pumped out of the excavation as work proceeds.


Table 10-3. Appropriate dewatering methods

DEWATERING EXCAVATIONS• Wellpoint Systems• Technically, a wellpoint is the perforated assembly placed on the bottom of the inlet pipe for a well.• It derives its name from the point on its bottom used to facilitate driving the inlet pipe for a well• In practice, the term wellpoint is commonly used to identify each well in a dewatering system, consisting of a number of closely

spaced wells

– Vacuum Wells: Vacuum wells are wellpoints that are sealed at the surface by placing a ring of bentonite or clay around the well casing. A vacuum pump is then connected to the header pipe.

• The resulting differential pressure

between the well and the surrounding

groundwater will accelerate the flow

of water into the well. In fine-grained soils, it may also be necessary to place a sand filter around the wellpoint

and riser pipe.

FIGURE 10-22. Wellpoint dewatering system.

• Electroosmosis• Electroosmosis is the process of accelerating the flow of water

through a soil by the application of a direct current• The usual procedure for employing electroosmosis in

dewatering is to space wells at intervals of about 35 ft (1 0. 7 m) and drive grounding rods between each pair of wells. Each well is then connected to the negative terminal of a dc voltage source and each ground rod is connected to a positive terminal.

• voltage of 1.5 to 4 V/ft (4.9 to 13 V/m) of distance between the well and anode is then applied, resulting in an increased flow of water to the well (cathode).

• A measure of the effectiveness of electroosmosis can be gained by comparing the flow developed by an electrical voltage with the flow produced by conventional hydraulic forces.


FIGURE 10-23. Electrically powered submersible pump being placed into dewatering well. (Courtesy of Crane Pumps and Systems)

PRESSURE GROUTING

• Grouting or pressure grouting is the process of injecting a grouting agent into soil or rock to increase its strength or stability, protect foundations, or reduce groundwater flow.

• Grouting of rock is widely employed in dam construction and tunneling. – The need for such grouting is determined

by exploratory methods such as core drilling and visual observation in test holes.

PRESSURE GROUTING

• Grouting Methods• Injection Methods

FIGURE 10-24. Types of grouting. (Courtesy of Hayward Baker Inc., A Keller Company)

PRESSURE GROUTING

FIGURE 10-25. Grouting utilizing a sleeve port pipe. (Courtesy of Hayward Baker, Inc., A Keller Company)

Use of Grouting in Civil Engineering

• Its traceable record can be as early as in the beginning of 1800s. • In 1802, the idea of improving the bearing capacity under a sluice by the

injection of self-hardening cementitious slurry was first introduced• In 1864, Peter Barlow patented a cylindrical one-piece tunnel shield which could

fill the annular void left by the tail of the shield with grout. It is the first recorded use cementitious grout in underground construction.

• In 1893, the first systematic grouting of rock in the USA as performed at the New Croton Dam, in New York.

• In 1960s, jet grouting technique was developed. • In 1977, first application of compaction grouting for controlling ground movement

during construction of the Bolton Hill Tunnel. • In 1995, the first industrial application of the compensation grouting concept was

conducted at the construction site of the Jubilee Line Extension Project in London.

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Types of Grouts • Cement-based Grouts:

Cement-based grouts are the most frequently used in both water stopping and strengthening treatment. They are characterized by their water cement ratio and their Total Dry Matter / Water weight ratio. The properties and characteristics of these grouts vary according to the mix proportions used. However, they have the following properties and characteristics in common.

• Stability and fluidity according to the dosage of the various components and their quality

• Unconfined compressive strength linked to water cement ratio• Durability depending on the quantity and quality of the

components - Easy preparation and availability - Ease of use - Relatively low cost mixes

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• Pure cement grout • It is an unstable grout. However, bleeding can be

avoided with water cement ratio less than 0.67. • Usual mix proportions are from water cement ratio 0.4

to 1 for grouting. Very high mechanical strength can be attained with this type of grout.

• During grouting, cement grains deposit in inter-granular voids or fissures is analogous to a kind of hydraulic filling.

• The grout usually undergoes a significant filtration effect. The grain fineness is an important factor for fine fissures.

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Bentonite cement grout

It is a stable grout. When bentonite is added to a cement suspension, the effects are: - – Obtain a homogeneous colloidal mix with a wide range of

viscosity. – Avoid cement sedimentation during grouting. – Decrease the setting time index and separation filtering

processes.– Increase the cement binding time.

– Improve the penetration in compact type soils

– Obtain a wide range of mechanical strength values.

– In water stopping, grout will include a lot of bentonite and little cement. In consolidation works, grout will contain a lot of cement and little bentonite. Ideal mixes should be both stable and easy to pump.

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Grouts with fillers

• Fillers are added in order to modify the viscosity of a given grout so as to obtain a low cost product to substitute the cement. The most commonly used fillers are the natural sands and fly ash from thermal power stations.

• The term “mortar” is commonly used to specify grouts with fillers that have a high sand content. Adding fillers reduces the grout penetrability, as the fillers are of larger grain sizes.

• Grouts with fillers are used when water absorption and/or the size of voids are such that filling becomes essential and when the leaking of grout into adjoining areas should be limited.

• In addition, fillers in grout will produce low slump grout with high viscosity for certain grouting purposes.

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Silicate based grouts

• Slicates based grouts are sodium silicate in liquid form diluted and containing a reagent.

• Their viscosity changes with time to reach a solid state that is called the “gel”.

• They are used in soils with low permeability values such that all suspension grouts cannot penetrate. According to the type of grout used, the gel obtained will be water-

• Tightness and/or with strength that are temporary or permanent.

• When the temperature of a silicate decreases, its viscosity increases very rapidly. This temperature should not fall below 0 degree C in order to eliminate any risks of modification of its properties.

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Soft gels

• It is mainly for water stopping purpose. They are gels with a very low dosage in silicate in which the gelling process is most generally obtained by adding a mineral reagent

• Their very low degree of viscosity (close to water) ensures the injection of very fine sand to achieve the water stopping purpose.

• Reduction in permeability can be up to 1 x 10-6 m/s and, in some case even up to 1 x 10-7 m/s when more lines of grout holes are added. There is also a slight improvement in strength, about 0.2 MPa.

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Grout Injection Methods

• Different grout injection methods have been developed for different grouting techniques. There are four main injection methods to inject grout into the ground.

• Drill Hole Method – A hole is drilled through the pores/voids of the ground. Then grout is

pumped via the grouting line into the surrounding ground of a section with the use of single or double packers.

• Drill Tool Method– It is a one-stage grouting method by means of the drill casings or

rods. There are two injection methods.– A very permeable soil maybe injected during rotary drilling. During

the drilling of the grout hole, each time a re-determined distance has been reached the drill rod is withdrawn a certain length and the grout is injected through the drill rod into the section of soil drilled. During each injection the top of the grout hole, a collar is used to seal the gap between the hole and the drill rod. 53

• Grout Pipe Method • Grout pipes are installed in drilled hole for later on gout

injection operation. The gaps between the grout pipe and the drilled hole are normally sealed. When compared with above Drill Tool Method, it is more flexible as the drilling plant is not engaged in the grouting operation.

• For multiple-stage grouting, the sealed-in sleeve pipe injection method (the tube-à-manchettes method) is used. It allows several successive injections in the same zone.

• The method is to place a grout pipe with rubber sleeves into a grout hole, which is kept open by casing or by mud. This pipe is then permanently sealed in with a sleeve grout composed of a bentonite-cement grout.

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• Jetting Method • Finally, a different type of injection method, the jet grouting

method, is introduced in the 60s, which has a revolutionary change to the grouting concept so far.

• The grout, with the aid of high pressure cutting jets of water or cement grout having a nozzle exit velocity >= 100m /sec and with air-shrouded cut the soil around the predrilled hole.

• The cut soil is rearranged and mixed with the cement grout. The soil cement mix is partly flushed out to the top of the predrilled hole through the annular space between the jet grouting rods and the hole wall. Different shape of such soil cement mix can be produced to suit the geotechnical solution. The cutting distance of the jet varies according to the soil type to be treated, the configuration of the nozzle system, the combination of water, cement and shrouded-air, and can reach as far as 2.5m.

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Different Types of Grouting Mechanisms

• There are lots of names as far as grouting techniques are concerned. They can be categorized according to their functions, their grout materials used etc. Five major techniques are:

• the Rock Fissure Grouting, • TAM Grouting, • Compaction Grouting, • Compensation Grouting and • Jet Grouting.

The five selected grouting techniques should have covered the basic mechanisms of all existing grouting techniques.

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• Rock Fissure Grouting

• Rock fissure grouting is the use of a hole drilled through the fissures and joints of a rock mass to allow grout to be injected at close centers vertically and re-injecting, if necessary.- Grouting Mechanism

– There is only one grouting mechanism for rock grouting. The following schematic diagrams show how is the mechanism for grouting in rock. The grout is injected under pressure through the grout hole drilled into the rock mass to be treated.

• Rock fissure grouting technique has a long history of application in civil engineering.

• Its main applications are:

•

• 1. Sealing rock mass underneath and at ends of dams to prevent seepage or

• leaking of the reservoirs.

•

• 2. Sealing rock mass above and underneath a rock tunnel to prevent water

• seepage into the excavated tunnel.

•

• 3. Cementing fractured rock mass.

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Application

• Rock fissure grouting technique has a long history of application in civil engineering. Its main applications are:

• Sealing rock mass underneath and at ends of dams to prevent seepage or leaking of the reservoirs.

• Sealing rock mass above and underneath a rock tunnel to prevent water seepage into the excavated tunnel.

• Cementing fractured rock mass. Although Rock Fissure Grouting technique can be used to cemented sugar clubs rock formation, like in slope stability projects, its main application is in the field of water stopping, especially in tunnel excavation project.

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• Tube-à- Manchettes (TAM) Grouting • Tube-à-Manchette (TAM) grouting is the use of sleeved

perforated pipes in grout holes, soils or completely decomposed rock to allow grout to be injected at close centers vertically, and re-injected, if necessary

• Grouting Mechanism– It is a grouting technique for grouting in soil formation only, with

partial or complete displacement of in-filling ground water. The pores/voids in between the soil particles are filled with grout under pressure with partial or complete displacement of in-filling ground water.

– When the grout has set, the soil mass becomes a matrix of soil particles cemented by the grout. In addition to the sealing purpose, it also changes the property of the soil mass e.g. the strength of the soil mass The most obvious change in ground property by this treatment method is the reduction of permeability.

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• Ground consolidation is also attained, but the increase in strength is limited. For high strength improvement, it will be very expensive.

• Application of TAM

• Main applications of the TAM grouting technique are: -– Sealing soil mass above and underneath a tunnel

excavated in soil under compressed air condition.

– Sealing soil mass behind the soldier pile wall, pipe pile wall etc.

– Sealing “windows” in cofferdams

– Consolidation of loose soil mass (cohesion less granular sand)

– Sealing underlying soil of dams

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• Jet grouting • Jet grouting is a grout injection that cuts and mixes the soil

to be treated with cement or cementitious grout.• With regard to the CUT and MIX grouting mechanism, the

soil particles are cut by the grout jetting under high pressure and mixed with it to form a matrix. When the grout set, the matrix is not only impermeable, but also possesses some kind of strength.

• The strength of the matrix depends on the grout strength and the degree of soil replacement.

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• Application • The jet grouting technique is developed in the 1960s.

However, because of its unique properties, it is becoming quite popular in the civil engineering works. Its main applications are: -

• Grouting of clay / silt soils which is not suitable for TAM grouting technique.

• Jet grout wall and roof are used to reinforce tunnel portal excavation works.

• Sealing of windows of coffer dams • Used as jet grout raft to reinforce cofferdam to limit its

deflection and thus decrease the settlement caused by the excavation works.

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• Compaction Grouting • Compaction grouting is a single-stage grouting with high

strength mortar to the ground to create a grout-bulb at the end of drill pipe.

• Grouting Mechanism– A stiff grout with a very low slump is injected under relatively high

pressure through pipes or casings into soil. The grout exiting the bottom of the pipe forms a bulb-shaped mass that increases in volume.

– Displacement of the soil is produced by the weight of the overburden pushing back against the expanding grout bulb. Thus it densifies the soft, loose, or disturbed soil surrounding the mass.

– It can also be used to alleviate settlement problem during the excavation of tunnel or deep basement as the hardened bulb-shaped grout will induce an increase in the soil volume strain to the soil strata and cause heaving of ground at the ground surface.

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• Application

• Compaction grouting is a soil and foundation support improvement system that increases the bearing capacity of soils.

• A major advantage of using compaction grouting is that its maximum peak effect is realized in the weakest or softest strata of the infrastructure support.

• Its main applications are as follows: • a. Lateral static densification of soils. • b. Lifting and re-leveling roads, bridges, and other existing

structures • c. Blocking of flow-path of viscous liquids through stratum

layers and rock cracks, voids, and fractures • d. Construction of underpinning • e. The remediation of sinkholes 68

Compensation Grouting

• Compensation grouting is a grout injection that can ‘compensate’ for stress relief and associated ground settlement.

• Grout is injected through grout pipes, which are usually TAM grout pipes, under high pressure into the soil. Fractures in soil are created which are then filled with grout.

• The fractures filled with grout will follow the plane with the minor principle stress and formed in layers.

• The increase in volume will compact disturbed soil surrounding the mass, will compensate settlement caused by tunnel Excavation works and can be used to lift up settle structures.

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Grouting Equipment • Percussion Drilling. Percussion drills are operated by air-driven

hammers . The best known types are the jackhammer, drifter, and wagon drill. The drill proper consists of a hollow steel rod, fitted with a fixed or detachable bit on one end and a shank on the other.

• Operation. Percussion drills are used for drilling in rock. The percussion drill does not reciprocate. Its shank fits into and is held loosely in the chuck at the forward end of the machine, where it is struck by a hammer-like piston actuated by compressed air. During drilling the bit remains in close contact with the rock at the bottom of the hole at all times except during the slight rebound caused by impact of the hammer. Drills are provided with a mechanism that causes the drill steel rod to rotate between blows of the hammer.

• Cuttings or sludge are removed from the hole by air or water that passes through the machine, down the hollow drill steel rod to the bottom of the hole, and then rises up the hole to the surface. Removal of cuttings by water is preferred for grout-hole drilling but is not mandatory.

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• Jackhammer drills, due to their light weight, are usually held in position by hand. Drifter-type drills are designed for tripod or bar mounts.

• The wagon drill, as commercially available, is comprised of a drill head mounted in leads that are supported on a track-,wheel- , or skid-mounted chassis.

• Application. Percussion drilling produces acceptable grout holes

• and, generally, is the most economical method of drilling shallow holes. This advantage decreases with depth and disappears at depths from 75 to 125 ft depending on the type of rock. In operation, the edges or wings of the bit wear away so that a progressively smaller hole is drilled. Therefore, when pertinent, the specifications should state the minimum acceptable size of grout hole.

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• Rotary Drilling. Rotary drilling is the process of making a hole by advancing a drilling bit attached to a rotating column of hollow drill pipe.

• The drill pipe is turned by a motor at speeds ranging from a few hundred to 3,000 or more rpm. Pressure on the bit is applied hydraulically or mechanically. Water is forced through the drill pipe to wash cuttings out of the hole.

• Drill rigs vary in size from small lightweight machines capable of drilling a few feet holes to several miles in depth.

• Small rigs are suitable for grout holes.• A variety of rotary bits are used for various sizes of holes

for grouting. 73

Grout Mixer

• Grout Mixers. Many types of grout mixers have been used, including hand-turned dough mixers, concrete mixers of various sizes, and especially designed grout mixers. Any machine is suitable that has the desired capacity and that mixes the grout mechanically to a uniform consistency.

• Two mixers can be arranged to discharge into the same sump to satisfy high capacity requirements. Manual stirring of cement and clay grouts in a tub is not satisfactory except in emergencies. Hand-powered dough mixers are not recommended because of their limited capacity.

• (1) Central Valley-type grout mixer, 8-cu-ft capacity. – During the grouting at several dams of the Central Valley Project, a

small, air operated, lightweight grout mixer was needed that could be set up and operated in a 5- by 7-ft gallery.

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• Grand Coulee-type grout mixer, 21-cu-ft capacity. – In the grouting at Hoover Dam, considerable experimenting was

done with various equipment for mixing grout. Concrete mixers were first used but were later discarded for the type mixer.

• High-speed colloidal-type mixers. High-speed colloidal-type grout mixers are commercially available in

both the single - and double –drum types. These mixers are equipped with small centrifugal pumps, which cause the grout to circulate at high speed while being mixed. Particles of cement may be broken and rounded to a significant degree in high-speed mixers. This results in an increase in pumpability and penetrability for Portland-cement grout. In an emergency, grout can be pumped at low pressures into the foundation or other places with the centrifugal pumps of these mixers.

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Agitator sumps. – After mixing, grout should be agitated to prevent settlement while it is

being pumped. This can be done by pumping the grout into a sump equipped with a stirring blade.

– Agitator should have the same capacity as the mixer so that one batch of grout can be pumped while the next batch is being mixed. When emptying the grout from the mixer into the agitator, the grout should pass through a 1/8-in. -mesh screen to remove pieces of sacks, strings, wire, ties, or other foreign matter that may be dropped into the mixer.

• PUMPS.– Pumps for cement grouting should be sufficiently flexible to permit close

control of pressure and to provide for a variable rate of injection without clogging of valves and feed lines. With constant speed pumps, special arrangements of the supply piping systems and valves are needed to provide close control of the grouting operation. Constant speed pumps are powered by electric motors or internal-combustion engines. Variable speed pumps are hand operated, steam driven, or air driven.

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• Water meters.– A satisfactory water meter is the single-disk type, size

1-1/2 in., and threaded for pipe connection. This type has a 6 -in. vertical register with a long hand that makes one revolution per cubic foot of water and a short hand that indicates 10 cu ft per revolution. For use in grouting, the meter should have a reset knob to set the hands to zero and a direct-reading totalizer. A screen should be provided if sand or rock particles are present in the water supply

Grout Agitator 81

• GROUT LINES.• a. General. There are two primary arrangements of piping used to

supply grout from the pump to the hole. The simpler of the two is the single-line system. It consists of a pipe or a hose or a combination of both, extending from the pump to the header at the hole.

• The pump speed controls the rate of injection. The second arrangement is the double -line or circulating system. This system has a return line from the header to the grout sump in addition to the pump line of the single -line system. Thus, if the header connection to the hole is closed, grout can be continuously circulated from the grout sump to the pump, through the pump line, through the header, and back to the sump through the return line. While grouting, the amount of grout entering the hole through the header can be varied by opening or closing a valve on the return line without changing pump speed. The double-line system is generally preferred because it permits better control of grouting pressures and allows less material to settle out of the mix to plug the lines

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• Hose.

– Flexible hose is most commonly used for suction and discharge lines. If the length of the discharge line is such that pipe is necessary, a short length of hose should be provided at the pump discharge and at the connection to the grout header.

• Piping.

– Black steel pipe and fittings 1-1/2 in. in diameter are normally suitable for pressure lines ; but where large quantities of grout are to be injected and the supply line is long, it may be desirable to provide a larger size pipe and connection hoses.

• Grout Header.

– The grout header is usually assembled as a unit in order—that it may be moved from one grout hole to another. The assembly consists of the operating valves, a pressure gage, pipe, and the necessary fittings to attach the header to the hole and to attach the grout supply and return lines.

• Pressure Gages.

– Reliable pressure gages are essential in pressure grouting. They constitute the principal index to the behavior of the hole and the stresses that are being produced in treated material.

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Schematic Plan of Grout Plant

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EMgt 9407 Topic-03 Construction Technology Foundation Systems Dr. Attaullah Shah.

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