Bored cast-in-placeconcrete piles

The Task

High structuralloads

Difficultgroundconditions

Excavationclose toexistingbuildings

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In the past the position of a buildingwas generally chosen according to thesuitability of the ground. Nowadaysdifficult ground or the presence of ex-isting buildings close to the siteboundaries are no longer consideredas obstacles. Whether it is a questionof making the most economic use of asite, the need for new traffic routesthrough difficult terrain, the need forthe maximum use of expensive land,design engineers are increasingly con-fronted with one or more of the follow-ing circumstances: - Shallow foundations are ruled out

because settlements will be too great or the subsoil cannot take highloads without lateral yielding.

- Large point loads have to be trans-ferred into the subsoil.

- The subsoil is contaminated from past industrial pollution.

- Deep basements have to be exca-vated close to the existing buildingswhich must be protected against damage.

- The excavation extends below thegroundwater table.

Front cover:Tunnel project in Lugano, Switzerland

Back cover:Top left: Construction of a pile wall for the BMW-Welt,Munich, Germany

Top right: EUROVEA International Trade Centre in Bratislava, Slovakia

Bottom left: Bored pile foundation for the Tampa Museumof Art, USA

Bottom right: Construction of bored piles in rock for a newbuilding of SWR in Stuttgart, Germany Pasing Arcaden, Munich, Germany

The Solution

Deep foun-dations to supportstructures

Bored pile retainingwalls fordeep excavations

Deep foundationsThese are several ways of transferringstructural loads into the subsoil onsites where ground conditions are unfavourable.The bearing capacity of the subsoilcan be increased by ground improve-ment techniques such as:- Replacement of non-load bearing

layers of soil close to the surface- Soil consolidation using pre-loading

or vertical drains- Soil compaction using grout injec-

tion, deep vibration or stone columns.

Alternatively, structural loads can betransferred to stronger competentstrata at depth by the use of- Bored piles- Diaphragm wall elements- Mixed in place (MIP) piles- Piles reinforced by steel bars- Vibrated concrete columns.Technical literature on all these specialalternative construction techniques isavailable on request from BauerSpezialtiefbau.

Retaining wallsThe problem of providing stable re-taining structures close to existingbuildings or of constructing watertightexcavation pits can be solved in anumber of ways. However, the mostappropriate solution is almost alwaysthe installation of a bored pile retainingwall.

Bored pilesIn general bored piles offer the mosteconomical foundation as they can beconstructed in a wide choice of diam-eters, typically ranging from 300 to1,800 mm, and to depths of up to 70 m at rakes of up to 1:4. They canthus be tailored precisely to the partic-ular requirements of the building or ex-cavation. This flexibility means thatbored piles can provide solid founda-tion elements suitable for almost allsite conditions.Bored piles can be classified into twomain groups, according to their loadbearing behaviour: friction piles, whichtransfer load mainly by frictional resist-ance along the shaft; and endbearingpiles in which load is primarily trans-ferred to the surrounding soil ofthrough the pile base. Depending onthe structural requirements, boredpiles may be constructed singly, ingroups or as walls using secant, con-tiguous or king piles, with or withoutinfill.

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"Friction pile"

Single piles Pile groups

Vertical and raked piles Piled wall

"End bearing pile"

Techniques

Cast-in-place concretepiles

Piling systems differ in respect of thetechniques used (e. g. grab, rotary drill,direct circulation drill); the methodused to support the borehole (with orwithout drill casing, dry, hydrostaticpressure, slurry stabilisation), andmethod of concreting (poured or in-jected). Pile construction comprises

three main steps, drilling, placing rein-forcement and concreting. Some ofthese stages may be carried out si-multaneously. Selection of the mostappropriate piling technique dependson the prevailing soil conditions, thetechnical specifications relating to thesite and the overall cost.

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Reichenbachbrücke, Munich, Germany

Airport Wien, Austria

Wedding Towers, Moskau, Russia

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Main applications:

All types of soilWhere site conditions are restricted

Standard cast-in-place pile

Install casing tubesby rotating andcrowding using rotary drive

Remove spoil withdrilling tools attachedto kelly bar with bore-hole stabilisation bytemporary casing

Insert reinforcingcage into borehole

Place concrete bytremie and with-draw casing usingrotary drive

Completed pile

Rotary dril-ling with kellya) Cased

Special features:

Vibration free drillingHigh output with casings installed byrotary driveCasing oscillator can be used for larger pile diameters and greater depthsPile diameter generally 600 - 1,800 mmDepths generally up to 40 m but grea-ter depths are possible

Concrete

b) Borehole supported by hydrostatic pressure

Main applications:

In all kinds of soil, for large pile diameters and pile depths

Standard cast-in-place pile

Rotate starter casing to depth

Remove drilling spoilwith bucket attachedto kelly bar with bore-hole supported byslurry

Recycle slurry toremove soil and ins-ert reinforcing cage

Place concretesimultaneously displacing slurry

Completed pile

Special features:

Vibration free drilling No casing requiredStarter casing used for top section only Wall of borehole supported by ben-tonite or polymer slurryBorehole dia. generally 400 - 2,400 mmDepth generally up to 40 m, but greater depths possibleVertical piles only

Concrete

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Main applications:

All types of soilRestricted sites

Auger cast-in-situ pile (SOB-pile)

Rotate continuousflight auger to required depth

Inject concretethrough hollow stem,simultaneously withdrawing augerwithout rotation

Vibrate into place orpush reinforcementcage fitted withspacers into freshconcrete

Completed pile

Special features:

Vibration freeReinforcement can be pushed or vibrated into the fresh concretePile bore diameters from 400 - 1,000 mmDepths generally up to 18 m,bigger drilling depths are possible

Main applications:

All types of soilOn restricted sites

Drilling with double rotary head

Install casing and continu-ous flight auger to requireddepth using counter-rotat-ing drives

Inject concretethrough hollow stemauger, simultaneouslywithdrawing augerand casing

Insert reinforce-ment cage intoconcreted borehole

Completed pile

Special features

Vibration freeContinuous flight auger and casing installed simultaneously by counter rotating twin rotary drivesCan be installed against existing wallsDepth generally up to 15 mDrilling diameter 620 - 880 mm (DKS)

Rotary drillingusing twin rotary head

Vibrator

Vibrator

Auger cast-in-situ pile

Concrete Pump

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Main applications:

Contaminated soils to avoid dispo-sal of drill spoil Limited space, e. g. track con-structionSoft soils

Displacement pile

Set up at drilling point

Turning in and pressing of drilling tools

Following up kellyextension. Drillingup to final depth

Continued pullingand turning duringthe concreting process

Subsequent installation of reinforcement cagewith additional crane

Special features:

High bearing capacity throughhighly compacted skin areaAvoiding drill spoilHigh performanceDrilling diameter 420, 510, 610 mmDrilling without tremorsDrilling depth up to 34 mReduced concrete consumptioncompared to auger cast-in-situ piles

Displace-ment pile

Pump

Grab constructionCased

Main applications:

Soil such as sand and gravels withhigh demands on casing technologyWhere it is economically viable to use chisels to break up bedrock andboulders

Special features:

Minimum distance to existing buil-dings is requiredPile diameters generally ranging from620 - 2,000 mmDepths generally up to 50 m

Using crawler crane and casing oscillator

Install casing usingcasing oscillator

Simultaneouslyremove drill spoilwith grab

Insert reinforce-ment cage intocased borehole

Place concrete bytremie and with-draw casing usingoscillator

Completedpile

Concrete

Planning considera-tions

SubsoilBefore starting piling operations thesubsoil must be fully investigated inaccordance with the appropriate stan-dards such as DIN 1054. The stratifi-cation of the subsoil and groundwaterconditions should be determined byexploratory boreholes and soundings.It is recommended that site investiga-tions are taken to about 6 m below theproposed foundation levels in deepfoundations. Based on the results ofthe site investigations the most suit-able type of pile can be selected andthe detailed design carried out.

Pile designThe pile design is based on two ele-ments: internal and external bearingcapacity. The minimum diameter re-sults from the proof of the inner bear-ing capacity as stated in the standardDIN 1045. The inner bearing capacitydepends on the concrete cross sec-tion and the reinforcement content. On the basis of the standard EN 1536(previously: DIN 4014) the proof of theexternal bearing capacity results fromthe minimum embedment length in thebearing soil, taking the loads, the pilediameter and the soil specific bearingparameters (skin friction, pressurepeak).

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Underground car park StrasbourgPassages de l'Etoile, France

Project Mixed-Use-Development in Abu Dhabi, UAE

Increasingthe bearingcapacity ofpiles

Shaft groutingPressure grouting along the shaft ofthe pile compresses the soil aroundthe shaft, producing stronger adhesionbetween the concrete of the pile andthe soil. Depending on the type of soil this can result in a considerableincrease in shaft friction which en-hances the bearing capacity and thusthe performance of the pile.

Base groutingThe end-bearing resistance of the pilecan also be increased by injecting cement grout under pressure into thecontact zone between the toe of thepile and the underlying soil. Basegrouting not only offsets the almost inevitable softening of the material atthe borehole toe but also reducessome of the early settlement.

Preparatory works for pilingPiled foundations and piled walls re-quire planning approval. The clearedsite should be made available in rea-sonable time before piling starts. Typical preparations would involvesearching for underground channels,services, cable ducts and other sub-surface installations, remains of exist-ing foundations, archaeologicalartifacts, and unexploded bombs orother war material. Authorization foraccess can be given by utilities,clients, national institutions for theprotection of ancient monuments orbomb disposal services. In additionstable and leveled work platformsmust be provided where piling rigs willbe operating.

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Injection hoses for skin grouting Bauer Lift-Cell to pre-stress the pile bottom

100 % end-bearing resistance maximum endbe-aring resistance of an ungrouted pile in sand with a settlement s = d/10 where (d = pile diameter)

100 % skin friction resistance maximum skinfriction resistance of an ungrouted pile in sand

End bearing resisteance (%)

Pressure grouted pile

Pile without pressure grouting

Set

tlem

ent

(mm

)

Skin friction resistance (%)

Pressure grouted pile

Pile without Pressure grouting

Set

tlem

ent

(mm

)

Pile load testsThe most cost-effective bored pile de-signs are those based on load tests onsite. They are generally only economicfor large construction projects. As aresult of the large number of pile loadtests we have carried out over manyyears we are able to design boredpiles for all types of ground conditionsso as to achieve the greatest possibleeconomy. The diagrams below illus-trate typical pile test results.

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Pile test below tent at Daun upon Eifel

Pile test in Rotterdam-Maasvlakte, Netherlands for E.ON power station

Distribution of force and skin friction versus settlement chart of a pile diameter 1,180 mm in stiff marine clay, 5 m socketed in moraine

Axial load distribution over depth Skin friction-settlement graphs

Pile shaftpressure grouted

Pile basepressure grouted

Load cell

Set

tlem

ent

Marine clay

Skin friction

Moraine shaft pressure grouted

Quality-assurance

Pile installation is carried out by quali-fied personnel whose technical experi-ence is constantly monitored andimproved by in-house seminars andquality audits. To ensure both sitesafety and optimum production levels,all drilling rigs and tools are regularlytested. All construction materials areselected on the basis of the specifiedstructural and process criteria to main-tain quality to the standards required.The pile production is documented ac-cording to EN 1536 (previously: DIN 4014). During construction of cast

in place continuous flight auger (CFA),Front of wall (FOW) or mixed in place(MIP) piles, all the parameters relatingto construction are displayed for therig operator on a monitor and arestored in a data logger developed byBauer Spezialtiefbau. The stored dataare computer processed, evaluated fortechnical content and plotted out in a standardised format. All other pro-cesses are recorded by the piling su-pervisor in accordance with standardprocedures.

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BAUER Spezialtiefbau GmbHBAUER-Straße 186529 Schrobenhausen, GermanyTelephone: +49 8252 97-0Telefax: +49 8252 97-1496BST@bauer.dewww.bauer.de