Overview of Construction

8/11/2019 Overview of Construction

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OVERVIEW OF CONSTRUCTIONAND DESIGN OF AUGER CAST-IN-PLACE ANDDRILLED DISPLACEMENT PILES

Monica Prezzi, Assistant Professor, and Prasenjit Basu, Doctoral Student, Purdue University, USA

Auger cast-in-place (ACIP) piles and drilled displacement piles are being increasingly used

as foundation elements for structures, particularly in projects requiring acceleratedconstruction or involving the rehabilitation of foundations of existing, overstressed structures.

Auger cast-in-place piles (also referred to as continuous-flight-auger piles) are widely usedto construct the foundations of all types of structures. There are many different types ofdrilled displacement piles, with the installation methods varying according to the equipmentused. Depending on the specific rotary piling technology used, responses ranging fromthose associated with non-displacement to those associated with full-displacement piles areobtained. Conventional pile design methods do not account for how the variousconstruction techniques involved in auger piling change the soil state around the pile duringinstallation and, hence, cannot accurately estimate the pile resistance in a consistent way.Research on this subject, identifying the different variables that must be accounted for indesign and linking these variables to installation methods, is lacking. This paper describesthe different piling methods available for auger cast-in-place and drilled displacement piles,

the equipment used to install them and the quality control processes typically used. It alsoreviews some of the design methods currently used.

Introduction

Deep foundations are extensively used ingeotechnical engineering practice. The widespectrum of piling methods results in a variety of piletypes. Each type behaves differently, depending onthe installation or construction methods. On oneend of the spectrum are non-displacement piles, theclassical examples of which are bored piles or drilled

shafts. These piles are constructed by removing acylinder of soil from the ground and replacing it withconcrete and reinforcement. On the other end arefull-displacement piles, such as closed-ended pipepiles or precast reinforced concrete piles, which aretypically driven into the ground. Driven piles preloadthe materials below the toe of the pile and displacethe soil surrounding the pile shaft laterally during theinstallation process. Therefore, displacement pilesare, in general, more likely to have a stiffer responsethan non-displacement piles. This is true particularlyin the case of sandy soils where displacementcauses densification.

Other pile types show behavior that is intermediatebetween non-displacement and full-displacementpiles, e.g., open-ended pipe piles (Basu et al., 2005).In general, displacement piles are preferable from adesign point of view because they are capable ofcarrying larger loads than non-displacement piles.However, the driving procedures may cause

excessive vibration to neighboring structures ornoise that may be unacceptable under certainconditions. Additionally, in some soil profiles (e.g.quick clays), the use of driven piles may not beadvisable.

A large number of pile types can be referred to asauger piles if the similarities in the installationmethods are considered. A continuous- or partial-flight auger or a helical tool is drilled into the ground

to install these piles. A variety of auger pileequipment is available in the market; each isassociated with a certain degree of soildisplacement during installation. The morecommonly used terminology for auger piles ispresented in Fig.1. For example, under auger cast-in-place (ACIP), we have augercast piles, which arecalled continuous-flight-auger (CFA) piles in Europe.

CFA piles are installed by drilling with a hollow-stem,plugged, continuous-flight auger until a competentlayer is reached. After the auger tip reaches thedesired depth, concrete or grout is pumped throughthe hollow stem while, at the same time, the auger iswithdrawn from the ground. The plug is released bythe weight of the concrete as soon as the auger islifted. The installation of CFA piles causes, at most,small horizontal displacement of the soil around thepile shaft as most of the soil within the pile volume istransported to the ground surface through the augerflights. As augercast or auger pressure-grouted(APG) piles are the USA-equivalent of CFA piles,


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they are installed following the same stepsdescribed above. In the case of APG piles, high-

strength grout, instead of concrete, is injected underpressure as the auger is withdrawn from the ground(Brettmann, 2003; Brown, 2005; Brettmann andNeSmith, 2005).

As result of the advances in piling technology,another class of auger piles was created; these areknown as screw piles in Europe and drilleddisplacement or augered displacement (Brown andDrew, 2000) piles in the USA. Drilled displacementpiles are rotary displacement piles installed byinserting a helical, partial-flight auger into the groundwith both a vertical force and a torque. The soil is

displaced laterally and the void thus created is filledwith grout or concrete. The significant advantagesof these piles are (i) the ease of construction withminimal vibration or noise and almost no spoil(important for contaminated sites), (ii) the higherload carrying capacity due to partial or fulldisplacement of the soil surrounding the pile, and (iii)the associated savings that result when they areinstalled in the right soil conditions.

This paper presents a review of the different augerpiles available, their installation methods, and thequality control procedures typically used. Some of

the design methods available in Europe and theUSA for ACIP and drilled displacement piles arepresented and discussed.

ACIP Piles

The progress in auger piling technology wasmotivated in part by the development of ACIP piles.

These piles have been in use for more than fivedecades (Brettmann and Nesmith, 2005; Van Impe

2004). Typically, the diameter of ACIP piles rangesfrom 0.3 to 1.0 m (Brown, 2005) and the lengthsreach up to 30-35 m (Brettmann and NeSmith, 2005;Mandolini et al., 2002).

To install an ACIP pile, a plugged hollow-stem,continuous-flight auger is drilled into the ground at acertain rate (Fig. 2). The plug prevents soil fromentering the hollow stem of the auger during drilling.The rate of auger penetration during the pileinstallation is very important as it has an impact onthe pile performance. During auger penetration,some soil is removed by the auger flights, and

bulking of the soil adjacent to the auger occurs.Ideally, the rate of auger penetration should be suchthat there is minimal release of lateral stress due tosoil removal. In reality, there is always some lateraldisplacement (Van Impe, 2004). Problems may beencountered during ACIP pile installation when thereis the need to penetrate a comparatively hardstratum underneath a soft clayey or loose sandy soillayer. If the penetration rate decreases when theauger tip enters the hard stratum, then the supply ofsoil into the auger flight from the auger tip drops. Atthe same time, there is more lateral feed of soil intothe auger flights from the relatively soft / loose

overlying layers. This may cause considerable lossof lateral confinement to adjacent piles andstructures. Ground subsidence may also occur(Brown, 2005).

Auger Piles

European Nomenclature North-American Nomenclature

Continuous-

Flight-Auger

(CFA)

Screw Piles

Auger Cast-In-Place(ACIP)

Auger

Pressure-

Grouted

(APG)

Auger Pressure-

Grouted Displacement

(APGD)

Drilled Displacement/ Auger Displacement

Partial

APGD

Augercast /

Continuous-

Flight-Auger

(CFA)

Screw

Piles

Full

APGD

Auger Piles

European Nomenclature North-American Nomenclature

Continuous-

Flight-Auger

(CFA)

Screw Piles

Auger Cast-In-Place(ACIP)

Auger

Pressure-

Grouted

(APG)

Auger Pressure-

Grouted Displacement

(APGD)

Drilled Displacement/ Auger Displacement

Partial

APGD

Augercast /

Continuous-

Flight-Auger

(CFA)

Screw

Piles

Full

APGD

Figure 1 Nomenclature used for Auger Piles in Europe and the USA.


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According to Viggiani (1989), the critical penetration

rate vcris given by

2

0

21cr

dv nl

d

=

where n is the rate of auger rotation, d is thediameter of the auger, d0is the outer diameter of thehollow stem of the auger and l is the pitch of theauger. If, for a given penetration rate v, the rate ofauger rotation n is comparatively high, then v< vcr.Consequently, the horizontal stresses are reduced,and more soil is removed from the region around theauger than from the region below the auger tip.

After the desired depth is reached, concrete or groutis pumped into the hollow stem, and the auger israised a small distance (about 0.3 m) to release thehollow-stem plug and then lowered back to theoriginal position. A certain amount of concrete orgrout is then pumped to form a concrete or grouthead on the auger flights. Subsequently, the augeris withdrawn, while concrete or grout (high-strengthgrout is used in the case of Berkel's APG piles) iscontinuously pumped under pressure throughout theauger withdrawal process. Auger withdrawal isaccomplished by initially rotating the auger

clockwise to fill out with concrete or grout the lowerflights of the auger and then by lifting it withoutrotation (CFA piles); alternatively, the auger isrotated clockwise at low speeds (Berkel's APG piles)at the same time it is lifted (Brettmann and NeSmith,2005). After concrete or grout placement iscompleted, the reinforcement cage is inserted or

vibrated down into the fresh concrete or groutmixture and tied off at the surface.

The rate of withdrawal of the auger is important aswell; it needs to be synchronized with the concreteor grout pumping rate. The average cross-sectionalarea of the pile is equal to the ratio of the concretepumping rate to the auger withdrawal rate. Thisratio should be selected based on the pile diameterassumed in design. An erroneous selection of thisratio may lead to a different pile diameter. If thewithdrawal rate is too fast compared to the concretepumping rate, the integrity of the pile iscompromised. A smaller diameter will result inlesser capacity, while a larger one will lead to

excessive consumption of concrete (Mandolini et al.,2002).

Computer monitoring of the rate of auger penetration,the concrete or grout pumping rate and the rate ofauger withdrawal from the ground providesadditional confidence on the integrity andperformance of these piles. With the currentlyavailable equipment, CFA and APG piles can beinstalled with diameters ranging from 0.3 to 0.9 mand lengths reaching approximately 40 m(Brettmann and NeSmith, 2005).

Another type of ACIP pile is the Starsol piledeveloped by Soletanche SA. The basic differencein the installation of CFA or APG piles and Starsolpiles is that in the case of Starsol piles, the rotationhead drives a hollow-stem auger and a tremie pipesimultaneously into the ground. The auger and thetremie pipe are fitted with earth-cutting tools at thebase and rotate and drill together. After drilling is

Figure 2 Installation of auger cast-in-place piles a) drilling to the desired depth and b) concreteplacement (Geyer Estaqueamento Ltda.).


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completed, the tremie pipe is clamped in positionwhile the auger is raised slightly to open two holeson the sides of the tip of the tremie pipe. Concreteis then pumped through these holes under pressureas the auger is raised slowly. Typical diameters ofthe Starsol pile are between 0.4 and 1.0 m, and themaximum length is about 20 m.

Drilled Displacement Piles

Modifications in the installation of ACIP piles haveled to the development of displacement piles thatproduce larger lateral soil displacements than ACIPpiles. These piles are classified under a broadcategory as drilled displacement piles. Drilleddisplacement piles not only include those that arevariations of the ACIP piles but also a variety ofother piles that have different installation tools.Drilled displacement piles include, for example,those developed by Bauer Maschinen GmbH

(Brunner, 2004) and Berkel and Company, Inc.(Brettmann and Nesmith, 2005).

The soil displacement produced during theinstallation of these piles can vary from that of apartial- to a full-displacement pile. The soildisplacement is enhanced by using modified drillingtools that laterally displace the soil and also byproviding additional vertical thrust during theaugering process. This technology is available dueto a remarkable development in piling rig hydraulicsin recent years that has produced rigs with torquecapacity ranging from 150 to 500 kNm (Van Impe,2004). Several companies fabricate drilled

displacement pile rigs. Accordingly, many drilleddisplacement pile types - Atlas, Bauer, AugerPressure-Grouted Displacement (APGD), De Waal,Franki VB, Fundex, Olivier, Omega, Pressodrill, SVB,SVP and Tubex - are available throughout the world.

During the drilling process, the downward thrust isgenerated not only by the rotation action but also bya vertical force (the crowd) typically applied byhydraulic rams. Different drilling tools are used byeach of the different pile types. In general, thedrilling tool contains one or more of the followingcomponents: a) a soil displacement body, b) a

helical, partial-flight auger segment and c) aspecially designed sacrificial tip, which is attached tothe bottom of the drilling tool. The shape of thedisplacement body varies significantly from one piletype to another. Broadly, it consists of a cylindricalbody that in some cases also contains single ormultiple helices that help in the lateral displacementof the soil. A casing (or mandrel) of diameter

smaller than or equal to the diameter of the pile isconnected to the drilling tool. Once the drilling toolreaches the desired depth, the sacrificial tip (if used)is released from the casing or displacement body.Concrete or grout is then placed through the casingas the drilling tool and casing are extracted from theground. Reinforcement is inserted either before or

after concrete placement. The drilling tool andcasing can be withdrawn from the ground without orwith rotation (which may be clockwise or counter-clockwise). A nearly smooth pile shaft is obtained if

the casing is withdrawn with alternating 180clockwise and counter-clockwise rotations (Fundex).

A nearly smooth shaft results as well if the drillingtool is rotated clockwise as it is withdrawn from theground (APGD, De Waal, and Omega). However, ifthe displacement body is rotated counter-clockwise(Atlas, Olivier) during withdrawal, then a screw-shaped shaft is obtained.

Proper knowledge of the subsurface profile isneeded in the selection of the most efficient pile typefor a given site. Although drilled displacement pileshave been successfully used for various soilconditions, these piles are not recommended incertain situations. According to Bustamante andGianeselli (1998), in the case of very loose sandysoils or very soft clayey soils (N < 5, qc< 1 MPa), theperformance of drilled displacement piles may becompromised because of difficulties that may beencountered during their installation in theseconditions. In the case of very dense sandy soils orthick alluvium layers, a drastic drop in thepenetration rate may be observed and premature

wear of the screw head (drilling tool) may result if itis often used in these soils.

A distinction should be made betweenconcrete/grout cast drilled displacement pilesdescribed in this section and those where a single-or multiple-helix steel auger is screwed into theground to form the pile. These piles are similar tohelical ground anchors but installed vertically tofunction as piles. Their design and installation differgreatly from those of the concrete drilleddisplacement piles covered in this paper.

Despite the existence of many types of drilleddisplacement piles, the literature contains limitedinformation on the design and installation of thesepiles. The installation procedures of the mostcommon drilled displacement piles are describednext.


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Figure 3 Installation of Atlas pile.

Atlas Pile

The Atlas screw pile is a drilled, dual-displacement,cast-in-place concrete pile (De Cock and Imbo,1994). Lateral displacement of soil occurs bothduring drilling and extraction of the auger (this is thereason why it is called a dual-displacement pile).

The drilling rig has two hydraulic rams that can workindependently (one taking over from the other afterits full stroke is achieved) to allow a continuousdrilling operation. In the case of hard soils, the twohydraulic rams can work simultaneously. The rigcan be operated at dual rotational speeds. Thishelps to control the drilling tool penetration rate indifferent soil types.

In the Atlas pile installation, a sacrificial tip (a lostpile shoe) is attached to a displacement body, which,in turn, is attached to a steel casing or mandrel (Fig.3). The displacement body consists of a cast-iron

dismountable helical head with an enlarged helical

flange. The joint between the displacement bodyand the sacrificial tip is made watertight. Thecombined action of the torque and the vertical thrustforces the casing down into the ground with acontinuous, clockwise, helical penetrating movement.

After the desired depth is reached, the steel shoe isdetached from the casing. A steel reinforcing cageis inserted into the casing. High-slump concrete is

then poured through a hopper placed on top of thecasing to cast the pile shaft. As the casing and thedisplacement body are extracted by a vertical pullingforce and counter-clockwise rotation, concretecompletely fills the helical bore formed by theupward-moving displacement screw. This way, ascrew-shaped shaft is formed. After concrete

placement, it is possible to push into the pile asupplementary reinforcing cage. Typically, thediameter of the displacement body (minimumdiameter of the pile shaft) ranges from 0.31 to 0.56m, and that of the enlarged helical flange, from 0.45to 0.81 m (Bustamante and Gianeselli, 1998; DeCock and Imbo, 1994). The Atlas pile length canreach up to 22-25 m.

A modified Atlas pile with a thin-walled casingattached to the screw head is used in highlycompressible soils, or in soils with large cavities orvoids. The casing is left in the ground with the

sacrificial tip. This type of pile is characterized by

the thick flange of the helical head.

APGD Pile

The APGD pile technology, which is patented by theBerkel & Company Contractors, Inc., is amodification of the original APG piling system(Brettmann and NeSmith, 2005). Compared with


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Fi ure 4 Installation of the Berkels APGD ile.

APG piles, there is minimal spoil of soil at the groundsurface during the installation of APGD piles. This isespecially crucial for a contaminated site. Duringthe installation (Fig. 4) of an APGD pile, thesurrounding soil is displaced laterally as the drillingtool is advanced into the ground. There are twotypes of APGD piles: 1) auger pressure-grouted with

partial soil displacement and 2) auger pressure-grouted with full soil displacement. The partial-displacement pile installation causes less lateral soildisplacement around the pile shaft than the full-

displacement one. In contrast to APG pile rigs, theAPGD pile rigs are capable of producing both atorque and a downward crowd force, whichfacilitates the drilling operations. Once the desireddepth is reached, high-strength grout is pumpedunder pressure through the drill stem and the drillingtool is withdrawn as it rotates clockwise. Thereinforcement cage is inserted into the grout columnto complete the pile installation process. Full-displacement piles can be 0.3 to 0.45 m in diameterand up to 24 m in length. These piles are used inloose to medium dense sands (NSPT < 25). Thepartial-displacement APGD piles can be 0.3 to 0.5m

in diameter and up to 17 m long. These are used inloose to dense sand with NSPT< 50 (Brettmann andNeSmith 2005).

Bauer Pile

Bauer Maschinen GmbH fabricates equipment forconstruction of partial- or full-displacement auger

piles (Brunner, 2004). The tool for the partial-displacement pile consists of a lower auger with asmall hollow stem with large flights and an upperauger with a large hollow stem with small flights.During drilling, the soil is transported by the bottomauger upwards; as the soil moves up, it displacesthe surrounding soil laterally because there is less

room available in the helical space of the upperauger which has a larger diameter. This pileinstallation method is effective when a loose stratumis underlain by a dense layer. After the design

depth is reached, concrete is pumped through thehollow stem, and the auger is withdrawn. Thereinforcing cage is either pushed in or inserted withthe help of top vibrator. The Bauer pile can be up toabout 30 m in length. Piles with a diameter of up to0.6 m are possible with this technology.

The tool for the installation of the full displacementpile consists of a lower tip, a middle displacementpart and an upper auger section with counter-rotating flights. The installation method is identicalto that of the partial-displacement pile. However, theuse of a Kelly extension may increase the drilling

depth by 6 to 8 m.

De Waal Pile

The drilling tool used to install the De Waal pileconsists of a sacrificial tip, a partial-flight auger anda displacement body (Fig. 5). The drilling tool isattached to a casing that has additional helices


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Figure 5 Installation of the De Waal pile.

welded near the top. The partial-flight auger isclosed at the bottom with the sacrificial tip. To installthe De Waal pile, the drilling tool is rotated clockwiseto the required depth with a torque and a verticalforce, the sacrificial tip is released and thereinforcement cage is installed. Concrete is injectedinto the casing as the casing is extracted withclockwise rotation and a vertical force. Unlike the

Atlas piles, installation of the De Wall pile creates anearly smooth shaft. The helices near the top of the

casing produce an enlarged shaft near the pile head.

Franki VB Pile

The Franki VB (Verdrngungsbohr) pile is a termused in Germany for "displacement auger" pile. Toinstall this pile, a large-stem auger is rotated andpushed into the ground. A sacrificial bottom plate isattached to the auger. Once the desired depth isreached, reinforcement, which can be anchored tothe bottom plate, is installed. The casing is thenfilled with concrete. As the casing is withdrawn,more concrete is pumped into the casing to

guarantee the quality of the shaft.

Fundex Pile

In the Fundex pile installation, a casing with aconical tip attached to its end is rotated clockwiseand pushed down into the soil (Fig. 6). The jointbetween the casing and the conical tip is made

watertight. As the casing is drilled into the ground,soil is displaced laterally. In dense or hard layers,drilling can be combined with grout injection or water

jetting through the conical tip. After the desireddepth is reached, the sacrificial conical tip, whichforms an enlarged pile base, is released. Thereinforcement cage is then inserted into the casingand concrete is placed. As the concrete is placed,the casing is extracted in an oscillating upward and

downward motion with alternate 180clockwise and

counter-clockwise rotations. The withdrawal of thecasing with both clockwise and counter-clockwiserotations produces a nearly smooth shaft. Thediameter of the conical tip ranges from 0.45 to 0.67m, and that of the casing ranges from 0.38 to 0.52 m(American Piledriving, Inc.). The length of theFundex pile can reach up to 25 to 35 m, dependingon the piling rig used.

Olivier Pile

The installation of the Olivier pile is similar to that ofthe Atlas pile (Fig. 7). A lost tip is attached to a

partial-flight auger which, in turn, is attached to acasing. The casing, which is rotated clockwisecontinuously, penetrates into the ground by action ofa torque and a vertical force. At the desiredinstallation depth, the lost tip is released, and thereinforcing cage is inserted into the casing.Concrete is then placed inside the casing through afunnel. The casing and the partial-flight auger are


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Figure 6 Installation of the Fundex pile.

Figure 7 Installation of the Olivier pile

extracted by counter-clockwise rotation. Similarly tothe Atlas pile, the shaft of the Olivier pile is also in

the shape of a screw.

Omega Pile

In the case of the Omega pile, drilling is done by adisplacement auger which is closed at the bottomwith a sacrificial tip (Fig. 8). A casing is attached tothe upper end of the displacement auger. Unlike the

other drilled displacement piles, concrete is injectedunder pressure into the casing even before the

desired depth is reached. After reaching therequired depth, the sacrificial tip is released, and theauger is slowly rotated clockwise and pulled up. Thewithdrawal of the auger with a clockwise rotationproduces a nearly smooth shaft. The reinforcementcage is then vibrated down into the fresh concrete.


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Figure 8 Installation of the Omega pile

Pressodrill Pile

The installation equipment consists of a crane thatsupports a leader on which a rotary head slides. Alarge hollow-stem auger, sealed at the base with aplate, is inserted into the ground by rotation and by avertical force provided by the weight of the rotaryhead and the weight of the casing. After the

installation depth is reached, reinforcement islowered into the casing and locked to the bottomplate of the auger. The lower ends of the bars arebent towards the pile center. A hollow-steel mandrel,provided with side holes, is then lowered downthrough the auger to rest on the auger bottom plate.The mandrel and the auger are then filled with high-slump concrete. The top of the auger is equippedwith a device that forces the mandrel to movedownward and the auger to move upward. Thisupward force extracts the auger in successivestages, while the downward movement of themandrel exerts a reaction force on the bottom plate,preloading the soil under the pile base. Afterwithdrawal of the auger, the mandrel is removedfrom the ground.

SVB Pile

The SVB pile (Schnecken-Verdrngungsbohrpfahl),which was developed by Jebens GmbH, is a drilled,

partial-displacement pile. The drilling is done by alarge-stem auger which also acts as a casing. Botha torque and a pull down force are used duringdrilling. The bottom of the casing is sealed off with adisposable plate (Fig. 9). When installing the casing,some of the soil is transported along the helices tothe surface, while a certain amount of soil isdisplaced laterally. When the desired depth isreached, reinforcement is installed and concrete is

pumped into the casing. The casing is extracted bya pull-out force and a torque, leaving the bottomplate in the ground. Since the casing is rotatedclockwise during extraction, a nearly smooth shaft isformed. The SVB-pile can have diameters rangingfrom 0.40 to 0.67 m with a maximum length of 24 m(Geoforum).

SVV Pile

The SVV pile (STRABAGVollverdrngungsbohrpfahl), which was alsodeveloped by Jebens GmbH, is a drilled large-

displacement pile (Fig. 10). The pile is installedusing a patented casing that has a segment with anenlarged diameter and a drill head. The installationprocedure of the SVV pile is similar to that of theSVB pile. The SVV pile typically has a diameter of0.44 m and a length of up to 20 m (Geoforum).


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Figure 10 Installation of the SVV pile

Figure 9 Installation of the SVB pile

Tubex Pile

The Tubex pile, developed by Fundex VerstraetenB.V, is a drilled displacement pile with a permanentcasing that is left in the ground. The pile casing isfabricated from a tube by welding a special drill pointto its base and helical flanges to its shaft. In order to

install this pile, the casing is drilled into the grounduntil the desired depth is reached. The casing isthen cut off at ground level, reinforcement is insertedinto the casing and concrete is placed. This type ofpile can be used in very unstable ground and is wellsuited for temporary foundations because it can bedrilled out and removed from the ground. This type


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of pile can also be installed under limited headroom;in this case it is known as Tirex pile.

Installation Monitoring

Depending on the equipment available, some or allof the following quantities can be measured or

calculated during the installation of ACIP piles: therate of auger rotation, the rate of auger penetration,the torque, the concrete pumping rate, and theauger extraction rate (Mandolini et al., 2002). In thepast, quality control (QC) of these piles wasperformed by field inspectors, based mainly on theindustry standards published by the DFI in the1990s (Brettmann, 2003). Currently, automatedsystems are attached to many pile rigs throughoutthe world. Even though these monitoring systemscan provide valuable information on the quality ofthe piles, they are not meant to replace qualifiedfield inspections. Automated QC monitoring

techniques are based on measurements of eithervolume or pressure of the grout/concrete. Typicalautomated systems measure: i) time, depth andhydraulic pressure during drilling and ii) time, depth,grout/concrete volume or grout/concrete pressureduring casting. Continuous, real time graphs ofrelevant data are available to the operator during theinstallation (this facilitates any impromptuadjustments that may be needed). These files canalso be stored electronically for future reference.

Similar automated monitoring systems are availablefor the drilled displacement pile rigs as well. Thesecan be used to continuously monitor the depth of

penetration, the vertical force, the torque, and therate of auger/casing penetration and rotation. Aspecific energy term can be calculated whichinvolves the variables mentioned above and othermachine-specific installation parameters. Thespecific energy profile along the depth of the pile canbe correlated with in-situ test results and used tovisualize the effects of pile installation and to helppredict pile load capacity (De Cock and Imbo, 1994).

Design Methods

ACIP and drilled displacement piles are designed

based on in-situ test results. The design methodsavailable for these piles follow the same designphilosophy of any other pile. The unit base and shaftresistances of the piles can be related to the conepenetration test (CPT) tip resistance qc, the standardpenetration test (SPT) blow count N or thepressuremeter test (PMT) limit pressure pl. Theultimate pile capacity Rucan be expressed as

Ru= Rb+ Rs

where Rb and Rs are the ultimate base and shaftcapacities calculated as

Rb= rbAb

Rs= rsAs

where rband rsare unit base and shaft resistances,

and Ab2

4

sD =

and As ( )sD= are the

representative pile base and shaft areas, with Dsbeing the representative pile diameter. For ACIPpiles Ds is equal to the shaft diameter. For drilleddisplacement piles that have a smooth shaft, suchas the De Waal and Omega piles, Dsis taken equalto the maximum diameter of the screw head(displacement body) Df. In general, for the Atlaspiles, Ds = 0.9 Df, but, in the case of thick-flanged

Atlas piles with thin-walled casing, Ds = Df

(Bustamante and Gianeselli; 1993, 1998).

ACIP piles

According to Moss and Stephenson (2004), severalof the design methods available for ACIP piles weredeveloped either for drilled shafts or fordisplacement piles. Two of the available designmethods for ACIP piles are presented in Table 1.

The design methodology of ACIP piles described inthe German standard uses CPT tip resistance qc tocalculate the unit base and shaft resistances (seeTable 1). In the case of clay, the undrained shearstrength su can be derived from qc (Table 1) or,alternatively, from unconfined compression tests(ONeill, 1994). According to Rizkallah (1988), theGerman standard does not account for thedifference between a bored pile and an ACIP pile (orpiles that are installed using a continuous-flightauger).

Bustamante and Gianeselli (1982) proposed adesign method based on the results of 197 full-scale,static-load tests on different types of piles. It is to benoted that Bustamante and Gianeselli (1982) usedthe term cast-screwed piles to describe ACIP piles.

In this method, the equivalent CPT resistance qcatobe used in design is determined from the original qcprofile obtained in the field as follows: 1) the originalqcprofile is smoothened out by eliminating peaks, 2)the arithmetic mean qca* is calculated over a depth d(d=1.5 times the pile diameter) above and below thepile base, 3) the qc profile is modified again byeliminating values higher than 1.3 qca* and lower


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Table 1 Design unit shaft and unit base resistance values for ACIP piles

Source Soil Type rb(MPa) rs(MPa) Remarks

Sand0.12 0.1cq + (qc25 MPa)

0.008qcGerman Standards

(Moss andStephenson, 2004;

based on 5%relative settlementcriterion)

Clay 6su

0.02 0.2us

+

(0.025 su0.2MPa),

c vbu

c

qs

N

=

Nc= 16 22vb= total vertical stress at the pile base

Bustamante andGianeselli (1982)

kcqcacq

qca= equivalent cone resistance at the pilebase (in kPa)

and kc= coefficients that depend on soiltype (Table 2)

than 0.7 qca*, and 4) the arithmetic mean qca (to beused in design) is calculated from the modified qcprofile (obtained in step 3) over a depth dabove andbelow the pile base. Unlike the German standard,this method takes into account different soil types

through the coefficients kcand (Table 2).

Table 2 Values of kcand to calculate rb and rsfor ACIP piles (Bustamante and Gianeselli, 1982)

Nature of soilqc

(MPa)kc

Soft clay and mud 5 0.55 60

Soft chalk 5 0.3 100

Moderately compact sand

and gravel

5 12 0.5 100

Weathered to fragmentedchalk

> 5 0.4 60

Compact to very compactsand and gravel

> 12 0.4 150

Drilled Displacement Piles

Bustamante and Gianeselli (1993; 1998) developeda design method for drilled displacement piles basedon the results of 24 load tests on Atlas piles. Theultimate load for these tests was selected based ona 10% relative settlement criterion. The ultimateload was reached only for 14 of the load tests

performed. For the other 10 load tests, the ultimateload was determined by extrapolating the load testdata (Bustamante and Gianeselli, 1993). Accordingto this method, the unit base resistance is calculatedas

rb= K

where represents an equivalent average of the in-situ test results spanning over a length 2a(aaboveand below the pile base) (Table 3). Table 4 providesvalues of the coefficient K, which depends on soiltype. Based on the guidelines given in Table 5, adesign curve is selected (Q

1, Q

2, Q

3, Q

4, or Q

5).

These design curves depend on pile and soil type.Fig. 11 is then used to estimate the unit shaftresistance rs for the design curve selected. Thismethod was proposed based on correlationsdeveloped for the Menard pressuremeter, the SPT,and the mechanical CPT. When using an electriccone, the unit cone resistance qc needs to bemodified according to:

qc,m=qc,e

where qc,mand qc,eare the unit cone resistance for amechanical and an electrical cone, respectively.

The coefficient can be taken equal to 1.4 - 1.7 forclayey soils and 1.3 for saturated sands(Bustamante and Gianeselli, 1993).

Table 3 Values of and a for drilleddisplacement pile design (Bustamante andGianeselli, 1998)

N1, N2, N3 and pl1, pl2, pl3, are calculated at and 0.5 mabove and below pile base level.

In situ Tests Description of (MPa) a

SPT 31 2 3

1000 N N N 0.5 m

CPT

Arithmetic Mean over

a length = 2a 1.5 Ds

PMT 31 2 3l l lp p p 0.5 m


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Q5Q4

Q3

Q5

Q1

0 1 2 3

0 3 6 9CLAY or CLAYEY SILT

0 15 30 45

0 8 16 24

0 15 36 45SAND or GRAVEL

0 20 40 60

0 3.5 7 10.5

0 4 8 12

MARLS0 20 40 60

0 6-12 12-24 18-36CHALK

rs (MPa)

pl (MPa)

Q5

0

0.1

0.2

qc(MPa)

NSPT

Q2

qc(MPa)

NSPT

qc(MPa)

NSPT

qc(MPa)

NSPT

Figure 11 Values of unit shaft resistance rsas a function of pl, qc, or NSPT.

Table 4 Values of K for drilled displacementpiles (Bustamante and Gianeselli, 1998)

Table 5 Criteria for selection of a design curveto estimate rs from Fig. 11 (Bustamante andGianeselli, 1998)

NeSmith (2002) developed a design method forAPGD piles. It is based on 28 load tests on APGDpiles. In this method, rbis calculated as

rb= 0.4 qcm+ wb, for qc19 MPa, or

rb= 0.19 Nm+ wb, for Nm50 (rbin MPa)

where qcm and Nm are representative values of the

cone resistance and blow count number in thevicinity of the pile toe, and wb is a constant thatdepends on soil gradation and angularity. Forrounded materials with up to 40% fines, wbis equalto zero and the rb upper limit is 7.2 MPa. For well-graded, angular materials with less than 10% fines,wbis equal to 1.34 MPa and the rbupper limit is 8.62MPa. To determine qcm and Nm, NeSmith (2002)suggests the method described by Fleming andThorburn (1983), but recommends that the influencezone be extended to four times the diameter of thepile above and below the pile base.

The unit shaft resistance is calculated from

rs= 0.01 qc+ ws, for qc< 19 MPa, or

rs= 0.005 N+ ws, for N< 50 (rsin MPa)

where ws is a constant similar to wb. For uniform,rounded materials with up to 40 % fines, wsis equalto zero and the limiting value of rsis 0.16 MPa. Forwell-graded, angular materials with less than 10 %fines, wsis equal to 0.05 MPa and the limiting valueof rs is 0.21 MPa. Interpolation is suggested forintermediate materials. This relationship isrecommended only for sandy soils, where

Soil Type For PMT For CPT For SPT

Clay 1.6 1.8 0.55 0.65 0.9 1.2

Sand 3.6 4.2 0.50 0.75 1.8 2.1

Gravel 3.6 0.5 --

Chalk 2.6 0.6 2.6Marl 2.0 2.6 0.7 1.2

CurvesSoilType

Limitpressurefrom PMT

(MPa)

ConeResistance

(MPa)C M

Clay

/ClayeySilt/SandyClay

< 0.3> 0.5

1.0

< 1.0> 1.5

3.0

Q1Q3Q4

Q1Q2Q2

Sand /Gravel

< 0.3> 0.5

1.2

< 1.0> 3.5> 8.0

Q1Q4Q5

Q1Q2Q2

Chalk> 0.5

1.2> 1.5> 4.5

Q4Q5

Q2Q2

Marl< 1.2

1.5< 4.0

5.0Q4Q5

Q2Q2

C = Cast-in-place screw piles,M = Screw pile with casing


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displacement of the surrounding soil due to pileinstallation results in soil densification.

NeSmith (2003) correlated the installation torqueand the drilling tool penetration rate with the capacityof drilled displacement piles. In his approach, themeasured fluid pressure of the motor driving tool tfp

and the tool penetration rate PR are normalized withrespect to some base values to obtain a torqueindex TI and a penetration rate index PRI. Theproduct of TI and PRI is defined as the installationeffort IE, which can be used to predict the capacityof APGD piles. Although IE could not be correlatedwell with the base and shaft resistance, areasonable correlation was reported between IE andthe ultimate capacity of the APGD piles tested.

Discussion on the Design Methods for DrilledDisplacement Piles

A design method should capture as closely aspossible the essence of the relationship betweenpile resistance and both the state and intrinsiccharacteristics of the soil. As different equipmentand procedures are used to install piles, the degreeof soil displacement induced on the surrounding soilcan differ significantly. There is a pressing need tobetter understand how the installation of pileschanges the state of the soil around them, as thesechanges reflect directly on the load-carrying capacityof the piles. The effect of pile installation on pilecapacity is particularly important for drilleddisplacement piles because there are many differenttypes of these piles. Vertical and lateral soil

displacement and densification occur as the drillingtool (with or without a sacrificial tip) advances intosandy soil, and these changes are a function of thedesign of the drilling tool and drilling operations.Different drilling tools and different installationprocedures also create piles with different shapes.Drilled displacement piles can have eithercorrugated screw-shaped (Atlas, Olivier) or smooth(Berkel, De Waal, Omega, etc.) shafts. For the sameouter pile diameter, a screw-shaped shaft maydevelop a slightly larger shaft capacity than asmooth shaft on account of passive pressures thatmight be mobilized in sub-vertical directions, but that

has not been quantified or even demonstrated as yet.Empirical methods are directly related to the specificdrilling tool employed to install the piles. Forexample, the method presented by Bustamante andGianeselli (1993) (Fig.11) is based on load testresults for Atlas piles. However, the shaft and basecapacities of other drilled displacement piles will notbe the same as those of the Atlas piles, as these

quantities depend on the degree of soildisplacement and disturbance around the pilescaused by installation.

Presently available design methods were all derivedfrom pile load test results performed in a particulararea, which means they are only valid for the site

conditions for which they were developed. For sometypes of geologic conditions, the methods are notavailable. For example, Bustamante and Gianeselli(1998) pointed out that there is a lack of experiencewith drilled displacement piling technologies in soilslike marls, gravels and chalk. There is also a needfor design methods to be more discriminating, goingbeyond just textbook soils (sand and clay). There isrealization of this need in practice. For example,NeSmith (2002) proposed a method in which finescontent, particle shape and gradation are factors.

Understanding of the fundamental behavior of non-

textbook soils (silty sands, clayey sands, and othermixtures of silt, clay and sand between the twoextremes of clean sand and pure clay) has beenincreasing (Carraro et. al., 2003). This knowledgewill gradually be incorporated into pile designmethods. As an illustration of the benefits to piledesign of understanding how the clay content of thesoil affects its behavior, consider pile shaftresistance. It is directly related to the large-strainshear strength of soil, which in turn depends on theclay content of the soil. The clay content of the soildetermines whether the shaft resistance is related tothe residual or critical-state shear strength of the soil.If the clay content of a soil exceeds approximately

50%, the residual strength (the strength at which theclay particles are aligned with the direction ofshearing) of the soil is the same as that of pure clay.So shaft resistance depends on the same residualfriction angle in both cases. If the clay content isless than approximately 25%, shaft resistance isclosely related to the critical-state shear strength(the shear strength at constant effective stressesand constant volume) of the clay-silt-sand soil. Thisis so because clay particle realignment does nothappen for low clay contents. Finally, for claycontents increasing from 25 to 52%, the residualstrength of the soil drops towards that of the pure

clay (Salgado, 2005).

Another important capability of a pile design methodis whether or not it establishes the link between pilecapacity, relative settlement, and the pertinent limitstates. Ultimately, a pile foundation supports astructure, which must remain serviceable and safe.

A design method should allow prediction of ultimate


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BUSTAMANTE, M. and GIANESELLI, L., 1993.Design of auger displacement piles from in-situ tests.Deep Foundations on Bored and Auger Piles, BAP II,Balkema, Rotterdam, pp. 21-34.

BUSTAMANTE, M. and GIANESELLI, L., 1998.Installation parameters and capacity of screwed

piles. Deep Foundations on Bored and Auger Piles,BAP III, Balkema, Rotterdam, pp. 95-108.

CARRARO, J. A. H., BANDINI, P. and SALGADO,R., 2003. Liquefaction resistance of clean and non-plastic silty sands based on cone penetrationresistance. J. Geotech. and Geoenviron. Eng.,

ASCE, 129(11), 965-976.

DE COCK, F. and IMBO, R., 1994. Atlas screw pile:a vibration-free, full displacement, cast-in-place pile.Transportation Research Record, n 1447, Oct, 1994,pp 49-62.

FLEMING, W. G. K. and THORBURN, S., 1983.Recent piling advances, state of the art report,Proceedings of the Conference on Advances inPiling and Ground Treatment for Foundations, ICE,London.

GEOFORUM

MANDOLINI, A., RAMONDINI, M., RUSSO, G. andVIGGIANI, C., 2002. Full scale loading tests oninstrumented CFA piles. Proceedings of theInternational Deep Foundations Congress 2002,Geotechnical Special Publication No. 116, Vol. 2,

ASCE, pp. 1088-1097.

MOSS, J. and STEPHENSON, R. W., 2004. A studyof design procedures for augered cast-in-place-pilesin clay. Recent experiences and advancements inthe U.S. and abroad on the use of auger cast-in-

place piles. Proceedings from the Michael WayneONeill Auger Cast-in-Place Pile Sessions, FHWA,pp. 89-95.

NeSMITH, W. M., 2002. Static capacity analysis ofaugered, pressure-injected displacement piles.Proceedings of the International Deep Foundations

Congress 2002, Geotechnical Special PublicationNo. 116, Vol. 2, ASCE, pp. 1174-1186.

NeSMITH, W. M., 2003. Installation effort as anindicator of displacement screw pile capacity. DeepFoundations on Bored and Auger Piles, BAP IV,Balkema, Rotterdam, pp. 177-181.

ONEILL, M. W., 1994. Review of augered pilepractice outside the United States. TransportationResearch Record, n 1447, Oct, 1994, pp 3-9.

RIZKALLAH, V., 1988. Comparison of predicted andmeasured bearing capacity of auger piles. DeepFoundations on Bored and Auger Piles, BAP I,

Balkema, Rotterdam, pp. 471-475.

SALGADO, R., 2005. The role of analysis in non-displacement pile design. To appear in theProceedings of the Modern Trends inGeomechanics Conferenceheld in Vienna.

VAN IMPE, W. F. (2004). Two decades of full scaleresearch on screw piles.

VIGGIANI, C. (1989). Influenza dei fattori tecnologicisul comportamento dei pali. Atti, XVII ConvegnoNazionale di Geotecnica, Taormina, Vol. 2, pp. 83-

91.

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