Ground Engineering Datasheets

Ground Engineering Datasheets Anchors

Grouting

Minipiles

Soil Nails

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Technical Data

ApplicationsTypical examples of where ground

anchors may be used include:

Supports to bored pile walls

Stabilising marine structures

Cofferdams

Anti-flotation for deep structures

Tie backs to river and canal walls

Dam upgrading

Rock face stabilization

Strengthening of dock structures

Advantages• Cost effective and

practical alternative to propping

• Provides openexcavation – removes obstacles

for bottom up construction

• Versatile form of earth retention

• High loads can be obtainedin relatively poor ground

• Can be used in a widevariety of soil conditions

• Used to install ‘active’forces into structures

factory conditions. Various types of anchor are available to suit a particular application. Permanent anchors incorporate full double corrosion protection via two concentric corrugated UPVC ducts. Depending on the design life, temporary anchors may incorporate a single duct, or no corrosion protection at all. Removable anchors can be used where there are wayleave issues beneath adjacent properties. Cementation Skanska have a comprehensive fleet of ground engineering drill rigs ranging in weight from 1.5 to 12.0 tonnes. Anchor holes can be bored using a variety of drilling techniques including rotary, top-drive rotary percussive, down-the-hole hammer, and augering. The type of drill rig used will depend on the access, working room and ground conditions. In difficult ground conditions simultaneous drilling and casing systems can be employed to temporarily support the boreholes prior to installation of the anchors.

Ground anchors can be used for many applications in civil engineering and building projects in a wide variety of ground conditions. Cementation Skanska has extensive experience in the use of ground anchor systems and can provide a full in-house service, from design and installation to testing. Anchor capacities generally range from 100kN to over 3,150kN, with lengths of up to 70m. The capacity achievable depends upon the quality of the anchored ground and the number of tendons used. A recent development has been the introduction of multistage anchors. These are used to improve efficiency and achieve high loads in poor ground through the use of multiple discrete unit bond lengths. Tendons can be made of steel bar, wire strand or GRP and are fabricated under

Ground Anchors

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Further information

Cementation SkanskaMaple Cross House

Denham WayMaple Cross

RickmansworthHertfordshire

WD3 9SWUnited Kingdom

Tel: +44 (0)1923 423100Fax: +44 (0)1923 423681

[email protected]

OfficesHead Office +44 (0)1923 423100

North +44 (0)1302 821100

South West, Midlands & Wales+44 (0)1454 453200

Scotland +44 (0)1698 735899

Northern Ireland +44 (0)28 9024 2746

Republic of Ireland +353 (0)1296 0790

When the borehole is complete, the anchor is either lowered into a pre-grouted hole or post-grouted after installation using an integral primary grout tube. When the grout has achieved a compressive strength of 30MPa the anchor is stressed using a portable hydraulic jack and locked off against a head plate in accordance with BS8081. Restressable head blocks with load cells can also be provided for long term monitoring and adjustment if required. †

Ground Anchors

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Technical Data

ClientMinistry of Defence

Main contractorCementation SkanskaSkanska Construction

EngineerSchal

However, due to the size and complexity of this project, Cementation, in ‘partnership’with Dywidag Systems International (DSI), set up a dedicated fabrication yard at Cementation’s plant depot in Bentley Works, Doncaster. This gave greater control over the programming and manufacture as well as significant cost savings for the client. All anchors incorporated full double corrosion protection in accordance with BS 8081. Holes up to 30m deep were bored using six Casagrande C6 rigs. The holes were constructed using down-the-hole hammer air flushed drilling techniques. Typical hole sizes were 200mm nominal diameter for the 2,250kN anchors and 130mm nominal diameter for the 450kN anchors. A vital component of the construction process were the temporary works platforms used to access the holes along the dock walls. These platforms consisted of portal towers supporting Bailey Bridgedecks, allowing up to five different levels to be utilised simultaneously.

Cementation Skanska together with Skanska Construction were involved in the design and installation of over 1,200 high capacity rock anchors to strengthen the entrance lock at the Royal Rosyth Dockyard. Associated civils works were carried out to replace the quayside subwayroofs and side walls. The aim of the project was to bring the lock structure up to the required seismic loading standards. Inclined anchors were installed at five different levels through the dock walls, along with vertical anchors either side of an existing subway at ground level. The working load was generally 2,250kN (15 no. strands), with a smaller number of450kN (3 no. strands anchors.) Ground anchor tendons would normally be made at an anchor manufacturer’s own facility and transported to site.

Groundanchors at

Rosyth RoyalDockyard

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The platforms were moved by the use of a wide range of mobile cranes. The programming involved in moving these supports whilst maintaining a high level of production was key to the success of the project. The vertical anchors were drilled prior to removal of the subway roof. After drilling, these were plugged to allow the roof to be removed in advance of the anchor installation. The anchors were lifted into the boreholes using mobile cranes. A neat O.P.C grout was batched on site using high shear colloidal mixer/pump units. The grout was injected into the base of the bore using an integral primary grout tube within the anchor body. In accordance with BS8081, the anchors were stressed after the grout strength had reached 30MPa. Access for stressing the dock wall anchorswas achieved using a purpose built stressing platform suspended from a dock running rail. Along with other operations on this project extensive craneage was used to move the jacking equipment into position. All stressing was carried out using DSI jacks which incorporated an innovative locking off stool within the jack itself. This enabled test cycles and locking off to be undertaken without jack removal thus allowing a much quicker stressing process. Project logistics were complex and required the interfacing of all operations on site and liaison with other facets of the dockyard activity. This continued throughout the contract, including the docking of a nuclear submarine during a testing programme.

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The project was completed within the agreed programme and budget, with successful installation and stressing of all of the anchors. This would not have been possible without the close co-operation of all parties on site.

Groundanchors at

Rosyth RoyalDockyard

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Bulk Infill/Ground Stabilisation Developers now seek to build new projects in areas once deemed uneconomic due to their poor ground conditions. In order to provide economic foundation solutions, ground stabilisation has become widely used for turning unsuitable soils into useful founding strata. The technique is often used in areas which have been heavily mined. Old workings are now in various states of distress and pose a potential risk of collapse – with or without any application of load from the surface. Expensive mass blanket treatments may be avoided by the effective use of detailed site investigation and knowledge of the workings. Cementation Skanska can provide a value-engineered solution to enable further development of the site. Permeation Grouting Basement construction, shaft sinking, dam cut-offs and tunnel excavations are all prime examples where the need for ground water control is necessary.

Application of Grouting Techniques Cementation Skanska’s grouting techniques can be used to provide a cost effective solution to both temporary and permanent geotechnical problems. Voids, soft ground, settlement and water inflow are just a few obstacles encountered where grouting solutions can be employed to mitigate their effects during construction. Since the Company was founded in 1920 Cementation Skanska has played a leading role in the development of grouting solutions to stem water flow, stabilise soils, improve ground bearing pressures and negate settlement. Effective grouting requires an understanding of theoretical principles, accurate interpretation of ground characteristics, skilled application and careful monitoring. Cementation Skanska can draw on a wealth of experience and resources to provide an effective grouting solution tailored to the client’s needs.

Grouting Grouting

Technical Data

TechniquesBulk Infill Grouting

Permeation GroutingCompaction Grouting

Compensation Grouting

ApplicationsBulk Infill

Old Coal WorkingsVoid Filling

Permeation GroutingShafts

TunnelsExcavations

Ground Stabilisation

Compaction GroutingUnderpinning

Ground Stabilisation

Compensation GroutingTunnelling

Settlement Prevention

AdvantagesBulk Infill

• Economic development of landpreviously considered unsafe.

Permeation Grouting• Ground improvement to ease

construction of basements.• Eliminates unwanted

ground water.

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[email protected]


North +44 (0)1302 821100


Scotland +44 (0)1698 735899



4

Awards Cementation Skanska’s proactive approach to safety, quality and production has received recognition from within the industry in recent years. Specifically, the Company has proven capability to design and carry out complex geotechnical projects and deliver them on time and within budget to their client’s satisfaction. †

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most appropriate grout and delivery system. Compensation Grouting The excavation of tunnels produces settlement which can propagate to the surface and cause structural damage to those structures which lie on or near their path. The philosophy of compensation grouting is to reduce, or even prevent settlement by injecting relatively small quantities of grout between the source of the settlement, (the tunnel) and the foundations of the structures that require protection. Typically, horizontal arrays of Tube a Manchettes are installed over the treatment area which allow repeat injections at any one location. This allows multiple injections to be made in areas where settlement is predicted or has occurred.

Permeation grouting relies upon the liquid grout flowing through the soil, displacing water and gases by forcing them out as the grout steadily advances. The grout must be pumped steadily, taking care not to disturb the soil structure. This is a critical operation and one which needs to be controlled and monitored appropriately. Cementation Skanska has custom made computer-controlled grouting units to monitor and control flow and pressure during specialist grouting operations. Specific instructions can be set to control each injection, and in turn each injection is recorded and downloaded immediately for the engineer to analyse. Grouting demands full application of the observational method, and electronic data management of the grouting data improves this iterative approach. Cost effective grouting requires comprehensive knowledge of the ground and ground water conditions in order to select the

Grouting

2 3

An essential component of compensation grouting is the monitoring of movements. Precise levelling and electrolevel monitoring of the ground and structures overlying the tunnel provide key data to designing the daily grouting instructions. The data is collated and analysed using our award winning software CemSMART (formerly known as Surpoint +). Close coordination and cooperation is essential to the success of the works. Plant and Resources The Company’s plant depot and workshops are centrally located in the UK to provide first class support to sites and projects throughout the UK. Bentley Works is the traditional home of Cementation Skanska and has grown into the premier plant depot within the industry. It houses and maintains the largest fleet of specialist plant in the UK. From the development of the Cementation pump during the early 1920’s to the latest computerised grouting units, Bentley Works.

Grouting

Coefficient of permeability (m/s) Choice of grout

10-1 10-2 10-3 10-4 10-5 10-6 10-7

Cement

Grout with filler (PFA/sand)

Bentonite (or clay)/cement

Grout with improved penetrability

Microfine cements

Silicate gel (high resistant gel)

Silicate gel (low resistant gel)

Resins

Ground conditions Coarse ground/scree/ coarse alluvial/highly fissured rock

Coarse pre-treated alluvial/fine alluvial (sand & gravel, sands, silty sands)/finely fissured rock

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Technical Data

Application

StructuralGround improvement

Basement slabsExcavation support

UnderpinningTunnelling

Groundwater controlDam cutoffs

Contaminated ground

Advantages• Vibration free

• Applicable to a wide rangeof ground conditions

• Slabs and supporting struts can be formed below the

water table and beforebulk excavation

• Single process allows programme advantages compared to

other techniques• Predictability of in-situ strength

and permeability

the ground and the placement and mixing of grout in the soil. This method produces the most homogeneous soil-cement element with the highest strength and the least amount of grout-spoil return, but can cause heave problems in certain ground conditions. Double system - A two-phase internal system is employed for the separate supply of grout and air down to different, concentric nozzles. Grout is used for eroding and mixing with the soil. The air shrouds the grout jet and increases erosion efficiency. The double system is more effective in cohesive soils than the single system. However, the presence of the air reduces the strength of the column as compared to the single system, and the air produces greater spoil returns. Triple system - Grout, air and water are pumped through three different lines to the tool. High velocity coaxial air and water form the erosion medium. Grout emerges at a lower velocity from separate nozzles below the erosion jet. This somewhat separates the erosion process from the grouting process and yields a higher quality inclusion. The triple system is the most effective system for cohesive soils, and because the grout replaces a substantial portion of the eroded soil, it is less likely to cause heaving of the ground. Applications Groundwater control - Often used for the control of groundwater around dams or areas of contaminated ground, the jet grouted columns are overlapped to form a continuous barrier of known thickness. Ground permeabilites can be reduced to the order of 10-9 m/s.

Jet grouting is a versatile and effective technique which can be used across a wide range of ground conditions. It involves the in-situ mixing of soils with cement grout to form a predetermined strength / permeability matrix. The inclusions formed by this process may be used for structural support, or for the control of groundwater. Process Cementation developed Jet Grouting in the 1960's for ground water control applications in the Middle East and Africa. The process involves the insertion of a special drilling tool to the required depth using a rotary drilling technique, followed by carefully controlled grout injection whilst rotating and withdrawing. The column is formed by the action of the high pressure grout eroding the in-situ ground perpendicular to the angle of insertion to a predetermined radius around the tool. The eroded material is mixed with the grout to form a soil-grout matrix. The strength and permeability of the columns can be controlled by the water / cement ratio and the addition of admixtures to the grout. The diameter of the columns is controlled by the rotation and lift speed of the drill tool. Jet grouting systems are traditionally divided into three categories, depending on the number of injection nozzles and the medium used to erode the soil: Single system - Grout is pumped down through the drilling rods and exits horizontal nozzles in the tool at high velocity. This causes erosion of

Jet Grouting

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Ground improvement - Columns are installed on a regular grid to improved the global stiffness and bearing capacity of the soil mass. Underpinning - The technique is extensively used for the improvement of existing shallow foundations. It is possible to drill through existing footings, forming a new jet grouted column underneath. The small size of the plant required means that it is ideally suited to congested city centre locations.

Excavation support - Jet grouting can be used to construct basement slabs and supporting struts for deep excavations. Overlapping columns can be formed below the water table and before bulk excavation minimising access constraints.

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[email protected]


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Tunnelling - Break out zones for tunnelling machines may be formed using overlapping columns adjacent to launching chambers. This locally stabilises the ground, enabling the tunnelling machine to complete the initial ring construction in conditions of controlled water ingress and ground movement. The technique is also used to stabilise tunnel crowns during open face tunnelling methods. Plant Cementation Foundations Skanska's plant depot and workshops are centrally located in the UK and provide first class support to sites and projects worldwide. Bentley Works is the traditional home of the Company and has grown into the premier plant depot within the industry. It houses and maintains the largest fleet of specialist plant in the UK. From the development of the Cementation pump during the early 1920's to the latest computerised grouting units, Bentley Works ensures that contracts are carried out with the best plant available.

Jet Grouting

A typical slab arrangement PrimarySecondary

Technical data

Client

Main Contractor

Engineer

Contract Value

Commencement Date

Construction Period

Site Address

Contact

Huntsman Petrochemicals Limited

Cementation Foundations Skanska Limited

ABB Eutech

£0.25m

August 2001

10 weeks

Huntsman PetrochemicalTeesport

Philip Ball

The tanks were constructed circa 1960 and

in July 2000 ground settlement was noticed

in the concrete floor and drainage channel

of the containment bund, just to the west of

tank Af8b. Precise-level monitoring carried

out revealed that further settlement was

continuing to occur reaching a maximum of

46mm by mid-February 2001.

Investigations conducted by Huntsman

and their consultants ABB Eutech revealed

that the settlement appeared to be the result

of movements within brick and concrete

rubbble used to infill a large hole in the

ground which existed some time prior to the

construction of the tanks. The hole was

present within the approximately 6m thick

layer of generally slag fill, derived from the

nearby steel works, which had been used to

reclaim the site in the early 20th century.

The hole itself was believed possibly to

have been created by a bomb dropped on

the area during the Second World War. The

hole was believed to have been back-filled

with materials arising from the demolition

of nearby buildings in 1948.

The settlements experienced appeared to

be limited to the concrete bund but put at

risk the integrity of containment. However

of greater concern was that the settlement

might develop to impair the stability of tank

Af8b. In view of the concerns expressed

Huntsman approached specialist contractors

including Cementation Foundations

Skanska to design and price ground

stabilisation schemes with the objective of

achieving long term stability of tank Af8b

and the containment bund by grouting voids

in the rubble fill. Included in the contract

would also be the repair/replacement of the

damaged concrete elements of the bund to

achieve integrity of containment.

It was not considered necessary or

economic to grout the rubble fill over the

whole of it’s plan area and the specialist

contractors were invited to propose means

of limiting the spread of grout within the

rubble fill while still attempting to

adequately fill the voids present within the

rubble. Further requirements were that the

spread of grout within the surrounding

general slag fill should also be limited and

that the cost of the project should be

minimised.

The successful design prepared by

Teesport TankAf8b Stabilisation

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Further information

Cementation Foundations SkanskaPO Box 293

Bentley WorksPipering Lane

DoncasterSouth Yorkshire

DN5 9RXTel: 01302 820888Fax: 01302 793203

[email protected]


North +44 (0)1302 821100


Scotland +44 (0)1698 735899



6

2

Cementation Foundations Skanska (see

inset picture) was based on the construction

of a grout curtain around the treatment area,

where it was practical to do so, in order to

minimise the spread of grout beyond the

designated treatment areas, followed by

bulk infill grouting to minimise the

subsequent grout takes during tube-a-

manchette (TaM) grouting conducted in

grout holes raked directly beneath the tank.

The drilling of the grout injection holes

and the installation of the TaMs were

carried out using a Casagrande C6 drilling

rig employing rotary and rotary percussive

water flush open hole and cased drilling

techniques. The grout curtain construction

and bulk grouting works were completed

using one of Cementation’s modular bulk

grouting stations and the TaM grouting

using one of the Company's containerised

TaM grouting units. Throughout the

grouting the injection pressures and

volumes were carefully controlled to

minimise unnecessary grout travel, grout

wastage and possible damage to the tank,

bund or other facilities structures.

Before, during and after the drilling and

grouting works a network of precise level

points and electrolevel beams installed in

conjunction with Cementation's Field Data

Acquisition Department (FDAD) were also

directly and remotely monitored to ensure

that distress was not caused to the

structures. Altogether over 1200 tonnes of

PFA, cement, sand and bentonite were

injected during a nine week site works

period in order to stabilise the designated

areas. As work proceeded the respective

grout takes of the primary, secondary and

tertiary holes and the phases of TaM

injections were monitored and compared to

assess the effectiveness of the grouting as

work proceeded. Test holes were also

successfully drilled and grouted.

The grouting works were completed in

November 2001 ahead of programme and

within the budgets set. This permitted the

removal of the previously distressed areas

of concrete slab and reconstruction, along

with additional works instructed during the

course of the contract, to be completed

within the 14 week tender programme.

In August 2001 Cementation

Foundations Skanska were awarded a

ground stabilisation contract by Huntsman

Petrochemicals Limited at their Teesport

Storage Site. This Storage Site is situated

within the extensive Teesport Docks

complex on the south bank of the River

Tees near Middlesborough, Cleveland.

Within the site are two large hydrocarbon

storage tanks used for storing cyclohexane.

Each tank is approximately 24.6m in

diameter and 14.4m high with a storage

capacity of approximately 6,00 m per tank.

Each of the tanks is surrounded by, and

contained within, a reinforced concrete

bund with the bund wall approximately

1.5m high.

3

Teesport TankAf8b Stabilisation

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Technical Data

ApplicationCan be used in most types of soil.

Ideal for underpinning or strengthening of existing

structures, internallyand externally.

Used to construct retaining walls, high capacity small diameter piles,

slope stabilization, high capacity small diameter tension piles.

Advantages• Can work within low headroom

in restricted working conditions• Virtually vibration free

• Ability to bore through masonry or concrete foundations

• Permanent liners can be incorporated as steel

reinforcement or throughvery soft strata

Cementation Skanska is one of the world leaders in piling and ground engineering. Since it was founded in 1920 the company has continually pioneered the research, development and implementation of numerous geotechnical solutions. One of these techniques is the grouted minipile which has been used successfully for over 25 years. Cementation Skanska offers a full in-house service, from advice through to detailed design and construction of complex foundation packages. Mini piling can also be used in conjunction with many of our other processes. Process A mini pile generally has a diameter of between 100 and 450mm and can extend to depths of over 50m. Either a reinforcing cage, circular hollow section or a centralised re-bar may be used. The Company can offer high capacity mini piles with SWLs of up to 1,200 kN. Some typical situations where mini piles may be used include:

Minipiles

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• Provision of high capacity small diameter piles.

• Underpinning or strengthening of existing structures both externally and/or internally.

• Slope stabilisation works. • Construction of propped or

unpropped retaining walls. • To resist hydrostatic uplift pressures.

Equipment Cementation Skanska has a fleet of mini pile drill rigs ranging in size from 1.5 to 12 tonnes. This plant is extremely versatile and the smaller rigs can travel through internal doorways. Piles may be vertical or raked and can also be pressure grouted for increased capacity if required. Drilling techniques include case and auger, rotary duplex and top or bottom driven rotary percussive. Some advantages of the grouted mini pile are: • Ability to bore through variable and

difficult ground conditions.

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[email protected]


North +44 (0)1302 821100


Scotland +44 (0)1698 735899



• Construction within restricted working areas and/or low headroom.

• Working within existing premises with minimal disruption to other operations.

• Low vibration. • Remote power packs can be used to

further reduce noise and fumes within enclosed areas.

• Permanent liners can be incorporated through very soft ground conditions. †

Minipiles

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Technical Data

ApplicationCan be used in a wide

range of strata.

Where non-cohesive or water bearing soils exist temporary

casings and/or bentonite or polymer suspension can be used

to progress the bores.

Diameters range from 600mmto 3000mm with pile depths

up to 70 metres and maximum working loads of 20,000kN

for straight-shafted pilesor 30,000kN for

under-reamed piles.

Advantages• High load capacity

• Can be used with CEMLOC® to plunge structural steel columns

• In stiff clays under-reamedbases can be formed

to increase pile capacity• Depending on ground

conditions, pile concrete canbe terminated below piling

platform level.

PatentsUK Serial No. 2138033 Class 7, 37

UK Patent No. 2373801US Patent No. 6739412UK Patent No. 2362665

Trade MarkCEMLOC®

can impart a vertical load on to the kelly bar to improve production in difficult strata. In addition to installing vertical piles, rigs can install raking piles, up to 1:4 rake, without modification. Depths Kelly bars can be of single or telescopic construction. Standard triple telescopic kelly bars allow for depths of up to 55m. Exceptionally, when required, extended triple telescopic kelly bars can reach to 70m below ground. Boring Tools Boring tools are available to cope with different strata. The range includes general purpose augers, rock augers, boring bucket and coring barrels amongst others.

Cementation Skanska has a wide range of piling rigs within the plant fleet, including crane-based units, and all-hydraulic purpose-built mast machines. Both are suitable for the construction of large diameter cast-in-situ piles. Mast machines are self-erecting. Establishment time on site is shorter than for crane-mounts and for contracts with small sites and/or few piles, this can be an advantage. The crane-mounts are more suitable for the larger diameter and deeper pile range. All of the rigs are fitted with a rotary boring unit which operates a kelly bar. The boring tools are fitted to the kelly bar. This equipment has been used to construct large diameter piles in a wide range of strata, including very soft silty clays, non-cohesive soils and weak rocks. The rigs

Large Diameter

Bored Piles

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Standard sizes of boring tools range from 600mm to 1800mm in increments of 150mm, and thereafter in increments of 300mm up to 3000mm. In suitable strata it is possible to construct a dry bore; in water-bearing strata it is often necessary to progress the bore under flooded conditions, i.e water, bentonite or polymer. Concrete Concrete grades up to 40N/mm2 are common, and higher grades can be used where necessary. Where the pile bore is dry, a hopper with a short tube is used to direct the concrete down the centre of the reinforcement. Under flooded conditions a full-length tremmie pipe is used.

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[email protected]


North +44 (0)1302 821100


Scotland +44 (0)1698 735899


Republic of Ireland +353 (0)1296 0790 In both situations it is often practical to terminate the concrete at a low level. This is typically used for top-down construction of deep basements. In this situation it is possible for a steel column to be plunged into the head of the concrete. Our unique CEMLOC® equipment can be used to position the columns to structural steel tolerances. Pile Load Bearing Capacity Depending on ground conditions pile loads of 20,000kN or greater can be safely carried on straight-shafted piles. Special tools are available to form enlarged bases or "under-reamed" piles in suitable strata, typically stiff clays. Under-ream diameters are usually specified in increments of 150mm, and diameters of 5400mm or greater can be provided. Piles of 30,000kN capacity have been formed in London clays using under-reamers. †

Large Diameter

Bored Piles

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Technical Data

With a wide range of experience, expertise and foundation techniques at its disposal, Cementation Skanska is able to offer a solution to nearly all slope stabilisation problems. The term "slope stabilisation" is relevant to the stabilisation of both existing slopes and new excavations, in either natural or man-made ground conditions. Examples of situations requiring stabilisation include:

• infrastructure embankments and cuttings

• excavations • existing retaining walls • tunnel portals • natural slopes • cliff faces.

The range of techniques that can be applied is as necessarily diverse as the range of problems and includes ground anchors, soil nails, minipiles, bored piles, lime stabilisation, drainage, earthworks and vegetation.

SlopeStabilisation

Infrastructure Embankments and Cuttings The constantly increasing demands upon railway and highway infrastructure are necessitating renewal and remediation works to both cuttings and embankments. Remediation processes implemented by Cementation Skanska have comprised both hard (or mechanical) stabilisation solutions, such as bored and mini-pile walls and ground anchors, and soft solutions such as lime stabilisation, gabions, drainage, mix-in-place grout logs, reinforced soil and regrading of slopes in combination with revegetation.

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Further information





Tel: +44 (0)1923 423100Fax: +44 (0)1923 423681

[email protected]


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Scotland +44 (0)1698 735899



Slope Stabilisation

Excavations Excavations for new developments often require support in the temporary condition, before a permanent retaining structure is constructed. Where appropriate the temporary support can be incorporated within the permanent works leading to cost savings. Cementation Skanska can offer a range of methods to support excavations. These include soil nailing, anchoring, mini-piling and guniting. Such methods often produce not only cost effective solutions but clear and open excavations. Existing Retaining Walls Existing retaining walls, which are in an unstable condition can be stabilised by the use of ground anchors or soil nails, where ground conditions are appropriate. These methods of renovation are generally less disruptive than demolition and subsequently more cost effective. Cementation Foundations Skanska has carried out the remediation of several existing reatining walls ranging in height from 3m to 6m. Tunnel Portals Access for tunnel headings often require excavation into an existing slope. Where a portal is being constructed in soil it is usually necessary to stabilise the surrounding soil either by soil nailing and/or some form of retaining wall and anchoring. Anchored or reticulated mini pile walls have successfully been used in this situation by Cementation Foundations Skanska for retained heights of up to 15m. Natural Slopes Natural slopes can often creep due to changes in ground water conditions, the existence of residual shear surfaces, or a combination of both.

In-situ retaining walls (e.g. reticulated minipiles & contiguous bored piles), soil nails and ground anchors can be used to stabilise slopes in this situation. Drainage measures assist with the stabilisation process by reducing the disturbing forces. Cliff Faces There is a significant number of cliff faces in the UK that border on an unstable condition and their failure could be detrimental or dangerous to adjacent properties. The stabilisation of cliff faces can be effected by a variety of methods; however, access is usually the prime consideration in proposing the most appropriate method. Cementation Skanska With an extensive range of foundation techniques and technical support at its disposal, Cementation Skanska is equally able to tackle minor stabilisation works, or major design and construct packages, with the degree of quality, safety and reliability expected of the UK’s leading foundation and ground engineering contractor.

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Technical Data

ApplicationsSlope stabilisation

Vertical or battered cuttings

Embankments

Support to existingor new gravity walls

Can be used forboth permanent and

temporary applications

Advantages• Cost effective

• Quicker than alternativeretention methods

• Small rigs can achieve access todifficult and tight locations

• Working space requirementsare less than for normal piling rigs

• Excavation and construction ofwall progresses concurrently

• Provides open excavation• Can be used in a variety

of soil conditions

The nails are installed using a variety of processes, including driving or drilling and grouting. Access requirements often dictate the method and plant used. The most frequently used method is that of drilling and grouting, as it copes with a large variety of ground conditions. It also has the advantage of mobilising high bond stresses between the soil and nail, and facilitates the installation of corrosion protection measures. For shallower slopes, vegetation is often adequate to stabilise the face. As the angle becomes progressively steeper, the use of a geogrid in combination with seeded mats or ultimately reinforced sprayed concrete is used. The facing is held in place by plates bolted onto the threaded ends of nails. Drainage measures are also provided if deemed necessary to maintain long term stability and to reduce the potential for sloughing of the surfaces.

Soil nailing forms part of the comprehensive range of ground engineering processes designed and constructed by Cementation Skanska. Developed in the late 1960’s, nailing has since been widely used throughout the world. It is a slope stabilisation process that utilises arrays of fully bonded passive ties installed in the ground. These are usually grouted bars, made from steel, stainless steel or glass fibre. The technique can be cost effectively employed to create both temporary and permanent cuttings. It can also be used to support slopes or to repair slipping embankments and gravity walls. Soil nails tend to work best when installed in granular materials, but are also commonly employed in soft rocks and stiff clays.

Soil Nails

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The process is designed to improve the strength and deformation characteristics of the existing ground. It is similar to reinforced fill techniques in that the soil nails generate tensile forces in response to slope deformation. This is in contrast to ground anchors that are intentionally stressed to minimise ground deformations. Soil nails are normally designed to operate with working loads in the range 25kN to 100kN. Long term monitoring of full-scale structures has increased Cementation Skanska’s fundamental understanding of soil nail design. Load testing of soil nails is often a design requirement and the Company has the capability to carry out both manual and fully automated soil nail pullout tests. †

Further information





Tel: +44 (0)1923 423100Fax: +44 (0)1923 423681

[email protected]


North +44 (0)1302 821100


Scotland +44 (0)1698 735899



Soil Nails

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Technical Data

ClientUnion Rail

Main Contractor

Hochtief/Norwest Holst JV

EngineerRail Link Engineering





Tel: +44 (0)1923 423100Fax: +44 (0)1923 423681

[email protected]


North +44 (0)1302 821100


Scotland +44 (0)1698 735899



The second location where soil nails were used was at the Pepper Hill junction of the A2 where improvement works were carried out for the Highways Agency. Permanent corrosion protected nails of 3-6m in length were installed through embankment fill and chalk. The face of the cutting was at 50° to the vertical and was stabilised using a flexible facing (comprising double twist galvanised wire mesh). For both sites comprehensive testing was carried out. †

Soil nailing was used at two locations on the Ebbsfleet project. The first application was to allow construction of a wing wall to bridge 3590. This involved installation of 11m long fully corrosion protected nails through rock fill, made ground and chalk to form a near vertical triangular shaped cut. Sprayed concrete was used to provide temporary face stability, followed later by permanent cast-in-situ concrete wing wall to provide a compatible architectural appearance to other wing walls for the bridge.

Soil Nails atEbbsfleet

Further information

Cementation Skanska

Maple Cross House Denham Way Maple Cross Rickmansworth Hertfordshire WD3 9SW Tel: 01923 423100 www.skanska.co.uk

Ground Engineering Datasheets

Documents

Transcript of Ground Engineering Datasheets