new Piles Installation Systems

8/9/2019 new Piles Installation Systems

1/38

Recent evolutions in deep foundation technologies ir Maurice Bottiau, Franki Geotechnics B

It is a quite challenging objective to aim at covering in one paper the mostrecent evolution in piling and deep foundations technologies. This report hasto be understood within the limits of the session 2b. It will thereforeconcentrate on the technological evolution of deep foundation techniques,addressing design issues only when directly related to execution aspects.For the same reason, it will not address the related codes, as a separatesession of this conference is specifically dedicated to this topic. Monitoringand deep excavations being covered in other sessions, they will only beaddressed when clearly relevant. We will try to show, from a practicalviewpoint what are the main changes and the most exciting or critical issuesover the last years, as they appear from the topics addressed in the literatureor in the papers published in this session of the conference. As the papermostly intends to explain trends and critical topics, it cannot be exhaustive,neither can it give the full description of the case studies. The author invitesthe reader to read the full papers, for a more complete description.

We have divided our report in three main topics: Piling, soil improvement andtreatment and retaining walls. Anchors and tie-backs will not be treated,neither tunneling.

INTRODUCTION

Before addressing the technical issues, it isworthy to look at the current trends in today’sDeep Foundations market. We have beenquestioning hundreds of practitioners abouttheir interpretation of their respectivefoundations market. The results of our inquirywill be the red line throughout our Report.Pile foundations remain by far the most useddeep foundations system worldwide (~50 %).Ground improvement technique keepprogressing, though differently in the differentcontinents (Fig.1)

Deep Foundations Worldwide

36%

48%

10%6

0%

10%

20%

30%

40%

50%

60%

Shallowfoundations

Deep found. w.Piles

Groundimprovement

Piles f. reduc.settlement

Fig.1 Deep foundations market worldwide

The interaction between technology anddesign plays a determinant role in the

evolution of our profession. Theintroduction of hydraulics and theexponential increase in available power onone hand, the miniaturisation and theintroduction of electronic components onthe other hand exerted a major influenceon new foundation systems. The recenttechnological evolution has sometimesbeen so quick that our understanding ofthe phenomena hasn’t been following atthe same tempo.

PILING Very few general reports or papers onpiling intend to present a classification ofthe different pile systems. Referring to therecent advances made in the Belgian NADworking group, we propose the followingclassification, mainly based on the stressstate resulting from the pile installationprocedure.


2/38

CATEGORY I : HIGH SOIL DISPLACEMENTDRIVEN PILES- precast concrete without enlarged base- cast in situ, without enlarged bottom plate - with lost driving tube

- shaft in plastic concrete- cast in situ, with enlarged bottom plate (Db > 1,1 Ds) - with lost driving tube - shaft in plastic concrete-cast in situ, with shaft in dry concrete, in situ formed enlarged base- steel pile - close ended - open ended with pluggingSCREW PILES- without lost driving tube- with lost driving tube

CATEGORY II : LOW SOIL DISPLACEMENT OR LOW SOIL RELAXATIONDRIVEN PILES- open end steel pipe without plug- H-profiles and sheet pile wall elementsCFA piles with special provisions to limit soil relaxation- with overpressure- with casing- with large diameter of the hollow stam and small flangesCATEGORY III : SOIL EXCAVATIONCFA PILES without special provisionsBORED PILES- executed with temporary casing or under thixotropic liquid

Table 1. Pile classification

The piling market worldwide, as it appearsout of our survey is shown on fig.2.The use of one or another pilingtechnique is related to several factors:

Geological issues and soilconditions

Local historical factors Local construction habitudes

Looking closer to the figures, we can cometo a few conclusions:1. Driven piles are still extensively used,

even considering the stricterregulations with respect to noise andvibrations in still more urban areas.The technological developments ofeconomical alternative vibration-freesystems (displacement auger piles-screw piles or jacked piles) offer acompetitive answer withoutsucceeding to put the driven piles outof the market. This is particularly the

case in the “soft soils” regions, like thedelta areas: Netherlands, Sweden,North America (partially). We will

report on recent development andresearch and on a few paperspresented in this session.

2. Alternatively, vibratory driven piles arenon-equally used, though anincreasing interest is expressed by theresearch community. Although nopapers have been presented on thistopic, we will analyse the recentadvances in the understanding ofthese systems.

3. Displacement auger piles (ADCIP orscrew piles) continue theirdevelopment, but their application stillvaries geographically. This canpartially be explained by soilconditions, but not completely. Howcan we explain, for example, thatdisplacement screw piles represent 60% of the small diameter piling marketin Belgium, but are still marginallyused in the soft alluvial areas in Italy,

or in the London clay. We will comeback on this topic.


3/38

Pile foundations worlwide

10%

21%

8%

1%2%

25%

23%

7%2%

1%

Driven cast in placeDriven precast pilesDriven H-pilesVibrated cast-in-placeVibrated precast pilesLarge diam. bored pilesCont. flight auger pilesDispl. screw pilesDriven Pipe pilesDrilled-in micro piles

Fig.2 Piling market worldwide

4. Bored piles are still widely used, especiallywhere more difficult or heterogeneous soilconditions are encountered: France,Germany, North-America. A still largerpart of this group is constituted by CFA(ACIP) piles, and cased augercast piles.We will try to see how the reliability ofthese systems has been evolving.

We will begin this report by quickly stressingwhich progresses have been made in theunderstanding of the global behaviour of piles

and the influence this had on the evolution ofthe piling market. We will then concentrate onthe technological evolution in piling techniques(new processes, machines,..) together withspecific lessons learned by the practice foreach of these techniques. Specific casehistories or particular references will be givenwhen appropriate.

UNDERSTANDING OF THE PILEBEHAVIOUR AND RECENT EVOLUTION INDESIGN

The authors believe the one of the mostcritical evolution in the understanding of thebearing behaviour of piles is due to the

analysis of instrumented full-scale loadtests with a particular emphasis on the

works by W. Van Impe and M.Bustamante. Instrumented load tests haveenabled to assess separately the endbearing and the shaft bearing capacity ofpiles.


4/38

Fig. 3. Example of an instrumented load teston a full displacement Atlas auger pile.The understanding that many piles bear themost of their loads by friction, certainly in therange of settlements, which are usuallyauthorized, exerted a capital influence on the

evolution of codes and design methods, whichno longer put the accent on base resistanceonly. This evolution was particularly beneficialto piles installed by other means than drivingand contributed indirectly to the increase ofuse of piles installed by lateral displacement ofthe surrounding soil.

The second largest evolution, partially linkedto the first one, is the better understanding ofthe deformational aspect of pile design (VanImpe, 199?, Poulos, 2003, Mandolini, 2005).The fact that piles cannot be considered asno-settlement elements and hence theincrease in use of piles as settlement reducersinstead of rigid supports for concentratedloads. The developments of combinedfoundations, piled rafts and the works byPoulos, Mandolini or Katzenbach haveprovided for a new era of unusual pilefoundation concept.

Last but not least the introduction of theEurocode 7 and the partial safety factorsapproach, coupled to the better use of statisticapproach to soil investigation enables for amore accurate design when properly applied.In this frame, new technological developmentscame to the market, trying to fully benefit ofthe evolution in design trends.

The evolution in piling techniques wasoriented by the lessons learned out of theresearch as explained here above and madepossible by the tremendous evolution of thetechnology over the last decades.

Driven piles Key issues- Environmental aspects (noise, vibrations)- Monitoring (PDA, ...)- Capacity prediction, set-up

For the first half of the 20th century, most pileswere driven piles and their control was mostlybased on the measurement of the set. Drivenpiles are still widely used worldwide (nearly 50% worldwide), in no urban centres. Lookingback to the answers to our questionnaire, wededuce that the market of driven piles isdivided between cast-in-place (10%), precast(21%) and H or pipe piles (10%). The choicebetween these different systems again varies

in function of soil, applied loads, or localfactors.Diesel hammers have been the referencefor many years, but recent concern fornoise impact and recent technologicalimprovements have lead to the larger

development and use of hydraulichammers and more recently of vibratorydriving. Hydraulic hammers have gainedmore and more popularity over the lastyears. Their Energy Transfer Ratio ishigher than the one of diesel hammers(see table 2), but the advantages of thediesel hammers:- relatively light weight,- sturdy construction,- no external power supply needed,- lower costoften lets the balance weight in the favourof diesel, at least for on-shore driving. Inorder to answer the environmentalconcerns, noise-reducing systems havebeen developed for application of dieselhammers in noise sensitive environment.

Fig. 4 Driving silencer: special soundenclosure

Technical details of impact hammers Table 2 gives the technical details of mosthammers in use (after Rausche, 2000).


5/38

Type ofhammer

Ramweight

Ratedenergy

Efficiencytransfer Ratio(ETR)

KN KJDiesel


6/38

gives set-up factors in function of soil type.Recommended set-up factor varies from 2.0for clay to 1.0 for sand and gravels, thoughobserved values may reach 5.5 for clay and2.0 for sand. Although it appears that set-up will usually be

beneficial, the large scatter observed makesthe non-calibrated use of a single value eitherconservative or dangerous.EOD formulae should therefore be used withmuch caution, as they can lead tomisinterpretation. The only objectiveapproach is the calibration of the driving curvewith respect to the previous soil investigationand calculation of bearing capacity. Blow onRestrike (which is the testing of the pile after acertain waiting time) is now recommended, butit puts scheduling and time burden on theconstruction process. Rausche (2000)suggests that, for an economical and reliablecapacity test, a 24 h restrike seems to bebetter than any other EOD based method orformula. We would like to add, unless a goodcorrelation can be found with a sufficient andreliable soil investigation.In this context, automatic monitoring anddynamic analysis have been introduced (e.g.Rausche et al, 2004). Practitioners from North America even identify the generalised use ofPile Driving Analysis as one of the majoradvances in the field of deep foundations.Noteworthy, systems like PDA are much morewidely used in the US than in Europe. Another session being dedicated tomonitoring, we will not address this issue morein detail.

Vibratory driving Key issues- Vibrodriveability- Bearing capacity

The use of vibrators in the field of deepfoundations is known for several years nowand has been widely applied, and reported bymany authors. Viking (2002) reports that thefirst production units were built in Russiaduring and after the Second World War. Infavourable soil conditions, the vibratory drivingof H-profiles or tubes offers an economicalalternative to impact driving. The techniqueuses a harmonic, vertical excitation forcegenerated by a vibrator fixed on the top of theelement to be driven. The recentdevelopments of high frequency vibrators (upto 100 Hz) and variable frequency havehelped vibratory driving to gain in popularity.Our survey identifies a little 10% of the market.The uncertainties of the method and the lack

of reliability probably play a role in thelimited propagation of these systems.

Holeyman (2002) provides a lot of usefulinformation for a better understanding ofthe soil under vibratory loading. He

summarizes the key engineering issuesrelated to vibratory driving (fig. 6)

Fig. 6 Major issues in vibratory driving

Table 3a and 3b out of Holeyman (2002)provide a good summary of vibrator’s dataand recommendations for different types

of soil and piles. Vibrator choice,however, remains mostly based onexperience and field observations.

As stated by Rausche (2002), the methodis still fraught with uncertainties. Amongthese, we can list:

Vibro-driveabilityThe vibratory driving of piles is based onthe reduction of the static resistance of thesoil due to the degradation of soil strengthand the build-up of excess pore pressures

(Holeyman, 2002). Although sophisticated models wereproposed by many authors, the reliabilityof vibratory pile driving remains elusive.The models usually should allowpredicting the required penetration timeand enable the choice of the adequatehammer. Raussche (2002), though,recognises that the question of whichhammer could drive the pile to therequired depth often cannot be answeredwith sufficient certainty. Premature refusalcan often be encountered.

In an interesting report from a researchproject at the BBRI, Huybrechts etal(2002) propose a simplified model for


7/38

prediction of driveability. The authors alsoprovide a list of different reasons forpremature refusal attributed to the soil, thevibratory hammer or the piles:

Attributable to the vibratory hammer

- Insufficient weight of the non vibratingpart of the hammer.- Insufficient eccentric moment of the

vibratory hammer leading to a deficientvibration amplitude

- Deficient power of the vibratingpower-pack leads to a decrease ofthe vibration amplitude or of thevibration frequency of the hammer

- Deficient serviced hammer will notbe able to run at their nominal

amplitude or frequency Attributable to the pile

- Although the weight of the pile playsa favourable role, a too heavy pilereduces the vibration amplitude.

Type Frequency range(rpm)

Eccentric moment(kg.m)

Maximumcentrifugalforce (kN)

Free hangingdoubleamplitude (mm)

"Standard frequency" 1300-1800 up to 230 up to 4,600 up to 30High frequency 2000-2500 6 to 45 400 to 2,700 13 to 22Variable eccentricity 1800-2300 10 to 54 600 to 3300 14 to 17Excavator mounted 1800 to 3000 1-13 70 to 500 6 to 20Resonant driver 6000 50 20,000 (in theory) Self destructingTable 3a. Vibrator typesCohesive soils Dense cohesionless soils Loose cohesionless soils

All cases Low pointresistance

High pointresistance

Heavy piles Light piles

High acceleration

Low displacementamplitude

Predominant shaftresistance

Requires highacceleration for eithershearing of thixotropictransformation

High acceleration


Requires highacceleration forfluidization

Low frequency, Large displacementamplitude

Predominant end resistance

Requires high displacement amplitudeand low frequency for maximum impactto permit elastoplastic penetration

High acceleration


Requires highacceleration forfluidization

Recommended parametersv > 40 Hz v : 10-40 Hz v : 4-16 Hz v : 10-40 Hz

a: 6-20 g a: 5-15 g a: 3-14 g a: 5-15 g

s : 1-10 mm s : 1-10 mm s : 9-20 mm s : 1-10 mm

Table 3b. Vibrators classifications (Holeyman, 2002 – after Rodger and Littlejohn)

- When the pile is too elastic (e.g. toosmall pile), the vibration amplitude canbe insufficient at the pile base, too muchtransverse vibration can occurpreventing the pile from penetrating.

- Clutch friction of poor quality sheet piles

Attributable to the soil- Bouncing caused by a too large base

resistance- Increase in soil resistance caused by

compaction (e.g. sands)

- Dynamic soil resistance (e.g. hardclays) can be insufficientlydegraded.

- Soil sticking (e.g. stiff clays)- Too elastic soil-strain behaviour

(clays)-

As can be seen out of the last section, thedriveability in cohesive soils pose morequestions than in cohesionless soils;interestingly, it has been less studied. Arecent case study (Tavernaro, 2006)


8/38

reports the vibro-driving of large caissons, 3 min diameter, at a depth of 45.7 m depth in 30m alluvium and fine sands and clays, andfinally into weathered rock. The vibatory-driving proved to be challenging, according tothe authors themselves, and the skin friction

could in some cases not be overcome by thelargest vibratory hammers available today.However, and mainly due to economicreasons, systems based on vibratory drivinghave been gaining in popularity like the VCCsystem (Vibrated Concrete Columns - Keller),or similar systems by Liebherr or Bauer.

Fig.7 Vibratory driving of Moebius type sandpiles – Hamburg – Germany - 2002

Large scale applications have recently beenreported for the vibratory driving of largeconcrete tubes diameter 12 m to a depth of 25m for the foundations of a bridge on the Yang-Tse river in China. The driving operationsemployed four APE 4B hammers with 683kgm eccentric moment and 750 kW each withfrequencies between 19.4 and 20.8 Hz. Mostof the penetration occurred prior to driving dueto the static weight of the hammers andtransfer beams. One of the issues here wascaisson thickness: the caisson wasdiaphragming to an oval shape and then backto a round shape at a rate consistent to thespeed of the vibratory hammer.

Fig.8 Large diameter pile driving at theYang Tse river - China

Bearing capacityThere are relatively few publicationsproviding guidelines for calculating thebearing capacity of vibrated piles.Raussche (2002) explains that manyattempts have been made to deduce thepile capacity on the basis of the drivingresistance but that, to date, it is usually stillrequired to re-drive the pile with an impacthammer for acceptance. Viking (2002)correctly states that too few case studiesprovide enough detailed information toincrease the knowledge in this field. Borel& Guillaume (2002) showed that, forpermanent structures, no example couldbe found of accepted vibratory driven pileswithout field load tests.

Some recent analysis and comparativetests in Europe and in the US (e.g. Borel,S. et al, 2002) have shown that thebearing capacity obtained by vibrated(sheet) piles can be significantly lowerthan the one obtained by driven piles inthe same soil conditions. Further analysisis needed, but the extrapolation ofinstallation factors corresponding toimpact-driven piles should be used withcaution.


9/38

Fig. 9 Soil information at the site of Cachan

Fig. 10 Compared bearing Capacity of impact

driven and vibro-driven sheet piles installed atthe site of Cachan – Borel (2002)

Jacked piles Key issues- Equipment capacities- Relaxation

Jacked piles are becoming a more populardisplacement pile option for urbandevelopment (Lehane, 2005). For manyyears, jacking systems have been presented

as alternative to driving or vibratory driving ofsheet piles or tubes in urban areas. Thelimited penetration capabilities of the systems

and the relative high cost of the installationremained a limitation for a larger use.Both the need of vibration-free systemsand the increase in equipment capabilitieshave been enhancing the possibilitiesoffered by this technology. This new

equipment, however, as stated by Poulos(2003) can be affected by significant sideeffects due to its weight. This aspectshould be analysed by the promoters ofthese systems in future publications. Twopapers presented at this conference dealwith new developments of jackingtechniques. The first one (Filip, 2006) isdealing with pile elements ; the secondone (Gogh et al, 2006) covers more theaspects of retaining walls and will betreated later in this report. Both authorsstress the “sustainable” character of thesystems.

Filip describes the design and constructionof high capacity steel elements installedwith the use of purpose built quiet andvibration-less equipment. The steelbearing piles were prolonged out of theground and used as bridge columns andabutments, and then cast directly into thesoffit of the bridge deck. The piles wereinstalled into a glacial boulder clay, stiffbecoming very stiff, and containing sandylenses. The piles were installed at a depthof 12 m for the abutments and 16 m for thepiers. They were formed out of 4 HoeschLarssen 43 sheet piles, clutched togetherto form a 750 mm square box.The piles were considered to plug duringinstallation, but it is not clear if this wasobserved during execution. Installationoccurred by a four-cylinder “push-pull”system, assembled and mounted on aLiebherr LRB255 leader rig, with a 30 mhigh fixed lead. (fig. 11).

Once the pre-assembled box piles lifted upinto location, each of the sheet piles arepushed down in sequence, relying on theskin friction generated by the other threesheets and self-weight of the equipment.Two maintained load tests were carriedout to 1,5 times the safe working load(1440 kN), two weeks after driving andprior to partial filling with concrete. Alateral load test on a pile-abutment wasalso carried out.


10/38

Fig 11 Push-Pull system configured for box-pilesOne of the often cited advantages of jackedpiles is that the installation load is measuredand can be considered in sand to beequivalent to (or less than) the pile’s capacity.However, compiling the data from differentauthors, Lehane (2005) discusses the possible“relaxation” affecting jacked piles in sands.Ratios of installation loads to static capacitiesare plotted on fig 12 against the so-calledequalisation period.These data appear to suggest that the staticultimate base capacity will be less than thatmobilised during installation.

Fig. 12 Ratio of static capacity to installationcapacity of jacked piles in sand

2. Bored piles

Cased bored piles (drilled shafts) Key issues- Curing of borehole- Post-grouting- Drilling fluid: polymers

Conventional bored piles or drilled shaftsremain popular (>25 % worldwide). Themain reason for this is their ability ofcarrying out high concentrated loads evenin difficult ground conditions. There existsa large variation of cranes, rigs andattachments, … to install large diameterbored piles in the most variable siteconditions. In the same time, there exist alot of variations of execution, with respectwith the temporary support of theexcavation : casing, bentonite, and morerecently polymers. Typical case studiesillustrating this variety are submitted by afew authors. Davie et al (2006) give acase history on drilled piers of diam. 1,93m installed in Tenesse, USA for thefoundations of a massive gantry crane.The piles, installed under partial temporarycasing were installed with a truck-mountedrig. Farouz and Failmezger(2006) explainhow the design of drilled shafts installed ina cobble formation, were optimized on thebasis of pressuremeter tests.

In Europe, the most recent developmentsare directly linked with the increase inmachine power and capacity and theimprovement of the excavation tools,which enable the easier installation ofbored piles in very resistant rock. The lastgeneration rigs are characterized by highinstalled powers resulting in high availabletorques and crowd.

When addressing the issue of constructionrelated concerns, bored piles certainlyconcentrate most of the questions. Anumber of key factors influence the axialcapacity of piles (O’Neill (2001), Poulos(2003), Maertens (2003))

Borehole roughness in soft rocks Presence (or absence) of highly

degraded smeared rock at theinterface

Effects of seams or discontinuitiesin the rock.

Cleaning of the pile basis


11/38

Influence of the drilling fluid on thebearing capacity.

This type of questions has led to the increasedcontrol of the bored piles execution.

Execution control and monitoring As far as the quality control of the piles isconcerned, recent experiences have beenleading to the generalized sonic coring of thepiles together with bottom core drilling in orderto check he integrity and the soil-concretecontact at the bottom of the piles and theintegrity of the shaft (e.g. Maertens et al-2003).Sonic coring (Cross-hole sonic logging) is alow strain integrity testing method commonlyused in Europe and the US to evaluate thecondition of concrete within cast-in-place pilesand more specifically bored piles. Theintegrity of the concrete can be evaluated bydetermining the propagation time and relativeenergy of an ultrasonic pulse as it travelsbetween two ultrasonic probes or transducers.Fig. 13 shows typical results of a sonic coringtest performed on bored piles diameter 800mm installed down to rock at a depth of 19.00m. The panel 2-3 shows a slight irregularity atthe bottom of the pile, enlarged on the detailshown on fig.26 c

Fig. 13 a and b : Results of Sonic coring inbored piles – two panels of measures.

Fig. 13 c Enlargement of slight defaultzone on panel 2-3

This testing method is usually completedby a core drilling of the base of the pilethrough a reservation tube placed on thereinforcement before concreting (fig. 14)

Fig. 14 : Core drilling through base ofbored pilesThese controls have been questioning thecorrect curing of the pile base in manycases.

Post-grouting Alternatively, post-grouting of both theshaft and the base of the piles has beendeveloped in order to minimize thesettlements and to increase the reliabilityof the piles.Both Dapp et al and Klosinsky and Szymankiewicz present a paper dealingwith base grouted bored piles, respectivelyin Poland and in the US.The construction of normal bored piles issubject to some physical and constructionlimitations, as repealed by Dapp et al(2006):


12/38

- Strain incompatibility between side sheardevelopment (required movement 0.5 to1% of pile diameter) and base resistancemobilisation (10 to 15 % of pile diameter).

- Soil stress relaxation due to the process,especially in cohesionless soils. Correct

cleaning and curing of the pile base asexplained here above.The post-grouted bored pile is normallyconstructed, but a grout delivery system isforeseen which enables the injection of groutunder high pressure once the concrete hasgained sufficient strength (Bruce, 1986). Thepost-grouting can concern both the shaft andthe base of the pile. Base grouting can berealised by tow main mechanisms (Dapp et al (2006)): - the flat-jack : grout delivery tube to a steel

plate with a rubber membrane wrappedunderneath- the tube-a-manchette (sleeve-port) : U-tubes covered by a tight fitting rubbersleeve and arranged in variousconfigurations at the bottom of the pile.

Dapp et al report on the results of post-grouted piles on 10 projects since 2003.These projects include 17 full-scale load testsand nearly 600 bored piles (drilled shafts).The authors explain the normal qualityassurance program practiced in theSoutheastern US:- pilot grouting- load testing programon the initial piles. The main purpose of thisprogral is to: 1) corroborate the design; 2)evaluate the construction process; 3) establish

grouting criteria.These criteria consist of three maincomponents:- grout pressure- upward displacement- minimum grout volume

Evaluation of the skin friction (taking intoaccount the direction of the loading) will benecessary in order to determine the targetmaximum upward displacement criterion.This value, according to Dapp et al, istypically around 6 mm, but higher values(up to 15 mm) can be allowed in veryclean sands. The authors review variouscase histories, showing how the measuredupward displacement can be linked withsome forms of construction difficulties,waiting times, caving of the shaft, concreteoverrun, etc.. They introduce the VerifiedLoad Ratio (VLR):

Load Design ForceGrout Applied

VLR

The Applied Grout Force is the total of theupward and downward grouting force, andthus equal to two times the grout pressuretimes the nominal shaft diameter. Theapplied grout force can be considered as averification of load capacity, given thatdownward directed side shear is as leastas great as the mobilized side shear fromthe upward portion of the grout force. Theupward displacement and VLR for variousbored piles is shown on fig. 15.

0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28Shaft Number

U p w a r d

S h a

f t D i s p

l a c e m e n

t ( i n c h e s )

0.0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

4.0

V e r i

f i e d L o a

d R a

t i o ( V L R )

Displacement

VLR

Verified Load Ratio

Upward Displacement

Test Shaft

36 Hr BentoniteExposure

Soil StrataChange


13/38

Klosinski and Szymankiewicz report on thePolish experience of post-grouted bored piles,mostly 1.0 m to 1.5 m in diameter, founded ingranular and cohesive material. The soilinvestigation results are not enough detailed toget the full benefit of the load tests results.

Depending on the soil conditions and the pileconstruction, the authors report a reduction ofsettlement of 30 to 50 % under working load(see for example fig.16)

Both Dapp et al and Klosinsky emphasize theenhancement of the reliability and thepossibility to mitigate construction problems,as bottom hole cleanout.

Fig. 16 Full-scale load test on post-groutedand no post-grouted piles – Klosinski (2006)

Polymers

Another aspect of the execution of bored piles,which regularly comes back in recent papers,

is the interaction between the drilling fluid andthe bearing capacity, and the increase ofinterest for polymer-based slurries.Theoretical and laboratory testing as well ascase studies have recently been reported byseveral authors (Majano and O’Neill (1993);O’Neill and Reese (1999),Thasnanipan(2003); Bustamante (2005)).

Bentonite and polymer slurry do reactdifferently when in contact with soil:- Bentonite maintains the soil particles in

suspension and stabilises the borehole

wall by its density and the formation ofcake.

- Polymers do not suspend sand. Sandparticles will therefore sediment at thebase of the borehole. Thissedimentation is stable with the timedue to progressive agglomeration ofthe slurry and migration into what

O’Neill and Reese (1999) call“oatmeal” material.Sometimes, as reported by Thasnanipan(2003), a small percentage of bentonite isadded to the polymer slurry, in order toreduce the high filtration in the sandlayers.

Fig. 17 Generalised behaviour of slurriesin borehole (a) bentonite slurry (b)polymer-bases slurry – Thanasnanipan

(2003) Although the use of polymer-based slurryis getting more accepted, information onthe desirable properties remains limited.Table 4, out of Thasnanipan (2003) showsthe range of the properties specified by the ADSC (1999), O’Neill and Reese, andthose commonly applied in Bangkok soils.


14/38

Table 4. Properties of polymer slurriesspecified by ADSC and polymer-based slurryused in Bangkok - Thanasnanipan (2003)

Most of the studies we refer to are based on

the use of partially hydrolysed polyacrylamide(PHPA) polymers. In a paper reported at thisconference, Lennon et al (2006) report the useof a new polymeric technology specificallydesigned for use in piles and diaphragm walls.This new polymer system comprises severaldifferent polymers that work together to helpprovide the required criteria. They mostlycombine the use of CDP and MPA baseproducts. The authors report the successfuluse of this vinyl polymer support fluid onseveral jobsites in Glasgow, Scotland. Thecase studies include limited geotechnicalinformation, and no detailed technicalinformation (density, viscosity, pH,..) about thepolymer used. The results of full-scale loadtests show limited settlements at working load.It is interesting to note that Bustamante (2005)reports on three case studies using polymerslurries for the execution of very long piles oflarge diameter, which the only successful oneis reported to be the one using CDP-basedpolymer slurry.

Hybrid systems and new applicationsConsidering the extremely strict requirementsin terms of settlement for the foundations of anew viaduct for the high-speed railway train inBattice (Belgium), a new hybrid bored pilesystem was used, in order to overcome someof the risks connected with conventional boredpiles (too large displacements). The structureis conceived in inclined supports as shown onfig 18. Each pier was founded on 30 piles,both vertical and inclined.

Fig. 18 Typical cross-section – Batticeviaduct - 2003

The piles diameter 620 mm were drilledunder casing like conventional bored piles.Once the required depth reached (top ofthe rock: varying between 8.00 and 32.00m), a steel H-profile was inserted. Thisprofile was provided with a steel plateunderneath and reinforcement rings werewelded on the profile (see fig.19). Theprofile was then top-driven for a few blows,ensuring the plate with the knife to be

anchored within the weathered rock layer.The pile was then concreted using highslump concrete.

Fig. 19 Steel bottom plate and knife – Postdriven bored piles – Battice 2003.

The piles were instrumented and load-tested by the LCPC and showed verygood results, combining a very good shaftfriction with an enhanced end-bearingcapacity.


15/38

Fig. 20 Soil profile at Battice – Belgium

Fig. 21 Results of full-scale load-test on hybridbored-driven piles-Battice-Belgium

Continuous Flight Auger piles(Augercast piles)

Key issues- Loosening of the surrounding soil- Influence of the equipment- Proprietary systemsThe most spectacular penetration of thepiling market worldwide over the three lastdecades is certainly this one of CFA piles(22 %, worldwide according to our survey,reach 50 % in some areas). Despite itsapparent simplicity, or even because of it,the system has been the topic for largecontroversial debates among the pilingspecialists. The main risk is associatedwith the sensitivity of the system to the rigoperator and to the capacity of theequipment itself, which, in case ofinsufficient installed power and hence ofinsufficient penetration rate can lead to“over-excavation” of the soil. Van Weele,very early, described the effect of a badlyinstalled CFA pile on the surrounding soil. A lot of recent papers have beenproducing data on this topic. The mostrecent information can be found inHannink & Van Tol (2005), Evers et al(2003). Most of these case studies,however, report too few information aboutthe equipment used, which is ofoutstanding importance on the final result. A lot of authors have covered the systemsspecificities as well as the mechanics ofsoil decompression in connection with aninsufficient penetration rate (Bottiau &Massarsch, 1988 ; Viggiani, 1988) and theimportance of the concreting phase (VanImpe, 1997).

Fig. 22 Mechanics of augering – Viggiani(1993)


16/38

Based on these considerations, a secondgeneration of CFA piles has been growingthrough the development of proprietarysystems as the Starsol pile (Soletanche) or thePCS pile (Socofonda). The main advantagesof these more recent systems, are the

following:- High capacity Rotary drive units combiningmaximum torque > 20 Tm with rotationalspeeds > 8 to 10 rpm.

- Crowd (pull-down) forces exceeding 10 T.- High capacity concrete pumps (50 to 70

m3/h).- Auxiliary retractable concreting tube- Full monitoring of the installation

measuring in real time.1. The vertical thrust Nd on the auger

while drilling in (kN);2. The vertical penetration speed

during drilling vi (m/s)3. The torque Mi while drilling in(kNm).

4. The rotational speed ni duringdrilling in (m/s).

And during concreting:5. The total volume of concrete (or

grout) injected and the over-consumption ;

6. Ideally, the detailed andcontinuously monitored volume ofconcrete injected

7. The vertical upward speed whiledrilling out.

Fig 23 Typical out-print of the monitoringsystem for PCS piles

The second generation of CFA systems alsoallows for the installation of larger diameters,(till 1200 mm) and longer maximal length

(about 30 m). By selecting an adequateconcrete mix and by using proper tools, aswell as appropriate reinforcement cagesconstruction, large and long cages can beinstalled on the full length of the pile. Alternatively, steel fibres reinforcement

systems have been developed.The monitoring system allows the operatorto follow and react in real time; it allowsalso for an adequate documentation of thepile installation by providing out-prints ofthe recorded data (see fig 39)The correct use of this abundantinformation is questionable. Bustamante(2003) published an interesting paper withrespect to the potential limitations ofmonitoring if not properly used. Inparticular, he showed that the integrationof the recorded parameters in the model ofViggiani, could lead to false conclusion.The piles installed in the sandy soils of LeHavre, didn’t satisfy the theoreticalequation of Viggiani : V > n.pwithV = rate of penetration of the auger(m/min)n= revolution rate of the auger (r/m)p = pitch of the auger (m/r)Both the pile load tests and the CPT testsperformed after the pile installation,showed however that no soil loosening didoccur.Bustamante finally states that engineering judgement should never be forgotten whenanalysing the lot of information comingfrom monitoring systems.We moreover fully support his statementthat monitoring remains a relativelyeffective and reliable tool provided thepresented records- Come above all from rough data which

were not subjected to prior correctionsor smoothing

- The sensor selected to measure eachrespective parameter has thecapability to do it

- Is examined in its entirety by takinginto account the real soil conditions,the rig characteristics, but also themany possible incidents, which are socommon on site.

Finally, considering the importance of theequipment parameters and the installationfactors, the final monitoring using controlsoil investigation (e.g. CPT executed afterpile installation) or the certification ofproprietary systems remain the best wayto evaluate the real installation influence.


17/38

Auger piles with larger stems have also beendeveloped, also called partial displacementlike the PCS-lambda pile. This pile was usedextensively for many foundations for theconstruction of bridges or piled embankmentsfor the Highspeed Railway line in Belgium.

The main advantages are the following:- Applicable in nearly all soil conditions,even in dense sands and gravels, wheredisplacement piles will be difficult to install.

- Rigid auger allowing for tight verticalitytolerances.

- Large stem enabling the placement of areinforcement cage before concreting.

- Partial displacement provided the installedpower of the piling equipment is correctlydimensioned with respect to the soilconditions.

Fig. 24 shows the first application in Belgiumof PCS-lambda piles diameter 60 cm at a siteof Brussels-South, presenting a resistant sandlayer with variable resistances and thickness.The piles had therefore to be installed to level+3.00.

Fig. 24 PCS lambda pile at Brussels South –F. Theys - 2003

Full-scale load tests were performed onseveral piles showing a very good behaviour.They can be consulted in F.Theys, 2003.

Cased CFA piles or front-of-the-wallsystems Key issues- Soil loosening- Pile walls

Between the conventional bored piles and theauger-cast piles, new systems have been

introduced called Twin Rotary Drive DrillingSystem or Front-of-the-wall system. Theprinciple is based on the simultaneous drilling

of casing and auger by two rotary-drivesrotating in opposite directions. The soil,which is loosened at the auger tip istransported to the surface (gate at the topof the tube underneath the rotary drive) onthe auger flights.

Fig. 25 Cased CFA pile

This system has been specially developedfor the execution of secant pile walls just infront of existing buildings for small tomedium excavation pits in urban centresas we will explain in our section onretaining walls. The system also evolvedto the drilling of larger diameters, forbearing piles. The speed of execution andthe compactness of the equipment offer aneconomical alternative to moreconventional systems. Here again, thetechnological evolution was more rapidthan its analysis. Few correctlydocumented load tests have beenpublished on this topic (e.g. Theys, 2003).Bustamante (2001) identified a series ofadvantages with regard to CFA piles:- Less disturbance (loosening) of the

surrounding soil, especially in sandysoils

- Limitation of the over-volume ofconcrete.

We believe that this point-of-view needs tobe nuanced. Particularly, the influence ofthe equipment should not beunderestimated. It should be observedthat most twin rotary drive units arecharacterised by low installation torques.Within these limits, the beneficial influenceof high capacity CFA piling rigs as well asthe injection of the concrete underpressure will eventually result in higherbearing capacities. The (limited) availableload tests show that the system clearly


18/38

should be considered as a bored pile with areduced base bearing capacity. We give theexample of a control CPT after the executionof cased CFA on a jobsite for the High-speedRailway Line (Loenhout-Belgium, F. Theys,2003). Fig.26 clearly shows the reduction in

cone resistance at the level of the pile base.The shaft friction, in the same time, will notbenefit of the stress improvement linked to theconcreting phase of a CFA pile.

Fig. 26 Reduction of the cone resistance forcased CFA pile – Loenhout - Belgium

Full-scale load tests showed that installationfactors were clearly those of bored piles.

Displacement auger piles (Screw piles)

Key issues- Equipment and systems specifics- Dependence on soil variations- Installation control

Displacement auger piles know an importantdevelopment worldwide (currently 6 % of thetotal piling market, the screw piles aredifferently represented in the different regions:up to 30 % in Belgium, 20 % in Japan). In hisgeneral report at the Conference of Osaka,Lehane (2005) stated that it is only a matter oftime before they will dominate the market of

medium scale bored piles.

Conceptually classified in the category of“auger” piles, the displacement auger pilesare characterized by some majordifferences.Starting from the beginning, it is desirableto (re)define :

1. auger piles allowing soil de-compaction ;2. auger piles with lateral soil

displacement.

Fig. 27 Difference between drilling with orwithout soil excavation.

In the first category, typically representedby CFA piles, the soil is excavated duringdrilling. In the second category, the soil isnot excavated but laterally displacedduring the drilling operation. This ispossible by the special shape of the auger.It is important however to realize that theshape of the different systems existing onthe market can present large differences inthe actual displacement as well as in thefinal result.

Without intending to classify the systems,it is interesting to show which are the maindifferences in term of shape, andexecution process.

Many authors have been publishing aboutthis topic. One can refer in particular toVan Impe (1988, 1989, 1994), Bustamante(1988, 1993), Huybrechts (2001).

Most of the first generation ofdisplacement auger piles arecharacterized by a short auger headintending to displace the soil very rapidly.The Atlas auger head for example (fig.28 Atlas auger head ) results in a very stiffdisplacement and in a helical shaped pile.

This pile has been, in its category, themost extensively used and studied overthe last three decades. Its particular


19/38

shape, realising a perfect pile-soil contact andhence a very high shaft friction and itscapability to achieve very high bearingcapacities even in mediocre soil conditionshelped to make it one of the best-seller of itscategory. It is installed by means of a

purpose built machine, with a base rotarydrive.

Fig.28 Atlas auger head.

Fig.29 Atlas pile

Recent purpose-built Atlas rigs (BT 60) offeran installed power of more than 40 T.m andenable to install up to 180 m of daily pileproduction even in difficult soil conditions.

Other more recent systems allow for some soilexcavation at the base, transporting the soil

from the tip, and displacing it upwards.This of course is favourable in terms ofpenetration into dense soil layers, but theinfluence on the achieved bearing capacityshould not been underestimated. Fig. 30shows the displacement process of more

recent systems.

Omega auger head Berkel auger head

Fig. 30 Second generation displacementscrew piles

Finally, the concrete casting procedureexerts a major influence, which is notalways considered with the importance itshould request. Some systems just cast

the concrete under gravity, others injectunder overpressure as CFA piles. Theinfluence of the concreting phase isimportant and has been described amongothers by Van Impe (1988).

The execution process as describedabove obviously influences the final result.Main systems used in Belgium were partof two comprehensive load-testcampaigns– one can in this respect referto the proceedings of the two Symposia onScrew piles, Brussels, (A. Holeyman,

2001) and J.Maertens &N.Huybrechts(2003)). These campaignsresult in global conclusions and installationcoefficients, but some particularitiesassociated with each system were alsonoticed. We want to present here somegeneral points of attention, which are validfor all displacement auger systems.

In a paper presented to this conference,Gwizdala et al describe recent experiencein Poland with the Atlas pile and showstwo case studies with well-described soil

investigation including CPT tests andStatic Load Tests in mostly clayey andsandy soils. He clearly introduces the


20/38

particularity of the screw pile system and itsdependence towards local soil resistancevariation. We try to explain hereunder whyscrew piles should be considered as acompletely specific piling system.

The combination, which governs thesuccessful installation of displacement augerpiles is:

- Intensive and reliable soil investigation.

- Specific design method.

- Adequate and reliable control of the pileasset during execution.

Displacement auger piles are more sensitivethan other pile systems to the interplaybetween soil type and equipment capacity.Furthermore, the final bearing capacity highlydepends on the precautions taken during theexecution. This pile type is geotechnicallyspeaking at the confluent between bored pilesand (driven) displacement piles so that itshould not be treated by one or anotherdesign approach, but well specifically.

Displacement auger piles, if treated byanalogy with bored or CFA piles, will berequested to penetrate into dense layers muchmore then needed for achieving a comparablebearing capacity as well as impossible toachieve technologically. On the other hand, iftreated by analogy with driven piles, becauseof the soil compaction, the problem of thecorrect choice and reliable control of their

asset is of outstanding importance.

For this reason, this category of piles hasto be specifically approached. Although amore reliable form of control becomesavailable (energy measurements, see

below), the importance of an extensive soilinvestigation is more crucial than withother systems.

As displacement auger piles, by theirconception, “feel” quicker then othersimilar systems any change in soilcondition, their depth (or asset) will varymore according to the surrounding soilconditions. The essence of system is tobenefit as much as possible of locallybetter resistances, but of course thisshould be related to previous soilinvestigation. Insufficient available soilinformation can have more dramaticimportance with this pile type then others.Especially in changing soil conditions, thedensity of CPT, boreholes or SPT datashould be increased. This is commonpractice in Belgium, but less evident inother countries. Though, Petersen et al(2002) have presented an interestingpaper in this respect showing theimportance of an adequate “guidance” ofdisplacement auger piles by additionalCPT execution on a project in Florida. Fig.31 shows, as a matter of example, alongitudinal soil profile with typical depthsof displacement auger piles, which clearlyindicates a large variation following the soilresistance.

Fig. 31 Typical variable soil profile and asset of displacement auger piles (Petersen, 2002)


21/38

Control of the execution

As previously explained, the choice of anadequate asset level should be directlyrelated to the in-situ soil investigation. Thelarger variation of depths should be

accepted as an intrinsic component of thesystem. It should not be tried to achieveimpossible anchorages into resistantlayers but instead to benefit of anyincrease of the soil resistance.

The logical question that arises is: howcan we control the correct execution andthe respect of the asset. Van Impe(Ghent, 1988) or more recently Bottiau etal (Stresa, 1989; Vienna, 1999) have beenemphasizing the importance of themonitoring of a number of parametersduring the pile performance. The waythese parameters are controlled can varybetween the careful annotation by theforeman to the most sophisticatedmonitoring systems as explained before.

These parameters can be used forcomparison between the available soilinformation and the calibration of theexecution. The common use should bethe following. Based on the preliminarysoil investigation campaign, the site isdivided in different areas of (slightly)different asset levels.The first installation of the piles should be“calibrated”, in order to characterize theencountered layers of soil and todetermine the adequate torque and/orpenetration speed to be used as areference. The first piles should beinstalled in the close vicinity of reliable soildata. The layers of soil are then definedand the installation parameters aremeasured.For each pile installed far apart from soilinformation and, it is then possible tocompare the installation parameters and tosubsequently proceed to the control of itsbearing capacity on site.Fig. 32 shows the installation torque inparallel with the soil profile (CPT) for an Atlas pile.

Fig. 32 Soil profile and installation torque – Atlas

The method can be refined by thecalculation of the installation energy. If allthe above-mentioned measurements areavailable, a specific installation energy Escan be derived,

Es = Nd.vi + ni. Mi / . vi in kN/m2.

withNd = Thrust force (pull-down) in kNvi= downward speed in m/secni = rotational speed in m/secMi : Torque in kN.m

pile section in m²

This installation energy can be related tothe soil investigation. The author haspreviously explained (Vienna, 1998) howthe installation energy, correctly calibrated,can be used to control on site the bearingcapacity of installed piles.

Fig.33 Measured bearing capacity derivedfrom the energy formulae vs this onecalculated on the basis of CPT tests.


22/38

Micropiles and small diameter groutedpiles To fulfil the picture of recent piledevelopments, this category would needanother paper. Many recent technological

developments have been made, especiallywith the construction of equipmentcombining higher capacities on compacterrigs. The introduction of electronicrecording of the drilling parameters andinjection volumes have provided for abetter installation monitoring.

We will not cover this topic in detail.

SOIL IMPROVEMENT Soil improvement techniques are gainingin popularity and understanding, especiallyfor large infrastructure projects or logisticalplatforms. Here again, the technologicaldevelopments have driven new practicalapplications.Terashi and Juran (2000) have providedan excellent, though limited, State-of-the- Art report in Melbourne and we will usesome of their tables to introduce theclassification needed between all theexisting Ground Improvement methods.They classify the wide variety of methodsin the following way:

- Replacement: the simple replacementof soft inappropriate soils by a goodquality foreign material.

- Densification: the densification ofloose granular soils, waste orliquefiable soils by one of the followingmethods: Vibro-compaction (vibro-flotation,

vibro-rod) Heavy tamping (Dynamic

Compaction, dynamicconsolidation)

Sand Compaction Pile- Consolidation/Dewatering: preloading

associated with vertical drainage,vacuum consolidation, are typicalapplications of consolidation

- Grouting: placement of a pumpablematerial which will subsequently set orgel in pre-existing natural or artificialopenings (permeation grouting) oropenings created by the groutingprocess (displacement or replacementgrouting), (ASCE, 1995)

- Admixture stabilization: mixingchemical additives with soil to improvethe consistency, strength, deformation

characteristics, and permeability of thesoil. The most frequently usedadditives in the current applicationsare lime and cement. These are thewell-known Deep-Mixing methods.

- Thermal stabilization: heating and

freezing.- Reinforcement: creating a compositereinforced system by insertinginclusions in predetermined directionsto improve the shear strengthcharacteristics and bearing capacity ofthe soil. This includes severaltechniques as: deep-mixing elements,fiber reinforcement and geo-synthetics, ground anchors and soilnailing, lime-cement columns,micropiles, vibro concrete columns,stone columns,..

- MiscellaneousIt is obvious that we will not aim atdiscussing the whole range of thesetechniques in detail. A few recentresearch works or new developmentsseem to emerge, which we would like todiscuss, assisted by the papers presentedat this session.

Deep Mixing Methods

Key issues- Reproductability- Strength scatter

The Deep mixing methods originate in the70’s, together in Japan and in the Nordiccountries, first using lime as the binder.The techniques evolved in Wet Mixingusing a cement slurry in Japan, whereas adry lime/cement mixture was used in theNordic countries. According to Massarsch(2005), deep mixing can today beclassified with regard to the method ofmixing (wet/dry, rotary/jet-based, auger-based or blade based) or the type ofbinder used. Bruce and Bruce (2004)provided a classification of 24 types ofDeep-Mixing systems clearly showing theexplosion of the systems.

Dry deep mixing is mostly used in theNordic countries (3 to 4 millions linearmeters yearly), with the following typicalfigures (Massarsch, 2005):Mixture 50%lime/50%cementTargeted strength 100 kPa to 200 kPa Amount of binder 80 to 200 kg/m3 of

stabilised soil


23/38

Wet Deep Mixing uses a cement slurry,mixed in the soil by means of severaldifferent tools (see table xx), in order tocreate a relatively rigid column or wallelement (Massarsch, 2005)Mixture cement

Targeted strength > 1 MPa Amount of binder 80 to 450 kg/m3of stabilised soil

More details of the compared Nordic andJapanese methods are given in table 6,from Massarsch, 2005.

Comparison of European and Japanese dry mixingtechniques

Equipment Details Nordictechnique

Japanesetechnique

Mixingmachine

Number ofshafts

1-3 1-4

Diameter ofmixing tool

0,4 m to1,0 m

0,8 m to 1,3 m

Maximumdepth oftreatment

25 m 33 m

Position ofbinder outlet

the upperpair ofmixingblades

Bottom of shaftand/ormixing blades(single ormultiple)

Injection Variable Maximum 300

Pressure 400 kPato 800kPa

Kpa

Batchingplant

Supplyingcapacity

50 kg/minto 300kg/min.

50 kg/min to200 kg/min.

Comparison of European and Japanese wet mixingtechniques

Equipment Details On land,Europe

On land,Japan

Mixingmachine

Number ofmixing rods

1-3 1-4

Diameter ofmixing tool

0,4 m to 0,9m

1,0 m to 1,6m

Maximumdepth oftreatment

25 m 48 m

Position ofbinder outlet

Rod Rod andblade

Injection 500 kPa to1000 kPa

300 kPa to600 kPa

Batching plant Amount ofslurrystorage

3 m3 to 6m3

3 m3

Supplyingcapacity

0,08 m3/minto 0,25m3/min.

0,25 m3/minto1 m3/min.

Binder

storage tank

Maximum

capacity

30 t

Mixing machine

Onland,

Europe

On land,Japan

Marine,Japan

Penetrationspeed ofmixing shaft

0,5m/minto 1,5m/min

1,0m/min.

1,0 m/min

Retrievalspeed ofmixing shaft

3,0m/minto 5,0m/min

0,7m/min to1,0m/min

1,0 m/min

Rotationspeed ofmixingblades

25rev/minto 50rev.min

20rev/minto 40rev/min

20 rev/minto 60rev/min

Bladerotationnumber

mostlycontinuousflightauger

350 permeter

350 permeter

Amount ofbinderinjected

40kg/m3to 450kg/m3

70kg/m3 to300kg/m3

70 kg/m3 to300 kg/m3

Injectionphase

Penetrationand/orretrieval



Table 6 Comparison between Nordic andJapanese mixing techniques – Massarsch

2005Without intending to explain all differentsystems, we think we can currently identifythree main systems:

1. Systems using multiple (usually three)mixing tools (augers, mixing rods), asshown on fig. 34 & 35. Thesesystems will be mainly used to formcolumns walls for retaining function.

Fig. 34 Triple rod mixing system (Bauer)


24/38

Fig. 35 Triple rod mixing system (Bauer)2. Nordic mixing system, used to form

lime-cement columns and mainly usedfor soil reinforcement purposes.

Fig. 37 Swedish Limix system

3. Cased systems where the mixing toolacts under protection of an outer tube,again mainly used for formingretaining walls. Primary soilmix pilescan be used in conjunction withsecondary concrete piles.

Terashi, 1997, 2000 summarizes thepotential factors affecting the strengthincrease (table 7).

I Characteristics of hardening agent1. Type of hardening agent2. Quality3. Mixing water and additives

II Characteristics and conditions of soil1. Physical, chemical and mineralogical

properties of soil

2. Organic content,3. pH of pore water4. Water content

III Mixing conditions1. Degree of mixing2. Timing of mixing/re-mixing3. Quantity of hardening agent

IV Curing conditions1. Temperature2. Curing time3. Humidity4. Wetting and drying/freezing and

thawing, ..

Table 7. Potential factors affecting thestrength of Deep Mixing – Terashi (2000)

He also identified, in 2000, tasks for thecoming decade, which we believe are notall solved yet. We list hereunder those,which seem critical in the dailyapplications- Precision of the strength prediction,

taking into account the soil variability- Clearly understand the failure mode,

especially for bending (as the use ofdeep mixing for retaining walls isincreasing)

- Identify, group and understand theinfluence of the differentmanufacturing processes.

Other issues, directly influenced by theexecution process are regularly discussed:- Homogeneity of the columns,

especially in stiffer cohesive soils- Reproductability of the mixing process- Execution tolerances, especially for

columns walls- Overlapping of columns in columnswalls


25/38

One of the critical issues here is the one ofquality and reliability of the treated soil.Quality control is therefore essential. Asstated by Kitazume, 2005, the qualitycontrol and quality assurance is required,before, during and after construction. For

this reason, quality control of Deep Mixingshould consist of- Laboratory mixing tests- Quality control during construction- Post construction quality verification

through check boring and fieldinvestigation

Here again, our profession would benefitof well-documented full-scale tests,enabling to validate both the functionaland the process design.

Three papers are presented in this sessionof the conference, that deal with DeepMixing:The first one, by Breitsprecher and Stihl show comparative tests between dry deepmixing columns and concrete columnsused as soil reinforcement. We willdiscuss the result of this paper in thesection on soil reinforcement.

Both Stötzer et al (2006) and Mathieu et al(2006) introduce a recent developed Deep

Mixing Cutter (CSM). The CSM Systemdiffers essentially from traditionaltechniques, by using a mixing tool thatrotates about a horizontal axis. This newtechnique is derived from the cutter(Hydrofraise) technology. The tool is

mounted on a kelly-bar, which allows agood accuracy of position and verticality ofthe soil-mixed pannels (Fig. 38). The soilis mixed with self-hardening slurry, whichis simultaneously introduced into the soilmass, to produce a Deep Mixing Wall.

Stötzer et al report a number of jobs withvarious applications: retaining walls, orfoundation elements. In particular, theygive an overview of a test site in xxx,where values of strength between 6 MPaand 10 MPa are reported. Unfortunately,very little information concerning theuntreated soil is provided, so that it isdifficult to correlate the obtained resultswith other similar experiences.Nevertheless, the system seemspromising particularly in terms ofhomogeneity of the treated soil andrespect of execution tolerances.

Fig. 38 Cutter Soil Mix System (Bauer)

Mathieu et al report a better documentedtrial site in Le Havre, where thirty trialpanels, including numerous 20m depthpanels have been constructed in a soilconsisting of variable hydraulic fill withvery soft clayey lenses overlying naturalsand. An extensive control program wasrealized, including Compressive strengthcontrol (fig. 39)


26/38

0

2

4

6

8

10

12

14

16

18

20

0 2 4 6 8 10 12 14 16 18

UCS (MPa)

D e p

t h ( m )

Fig. 39 UCS control tests in CSM panelsat Le Havre – Mathieu et al (2006)

It can be observed that there is a relativelybig scatter in the values of UCS obtained:2 to 10 MPa, differing from the dataprovided by Stötzer et al . This scatterremains one of the main problems ofeverybody wants to routinely use DeepMixing, as explained here above.

Jet GroutingKey issues- Reliability of the achieved diameter- Strength scatter

According to our survey, jet-groutingrepresents nearly 10 % of the groundimprovement technologies. Jet grouting isa ground improvement process wherebythe ground is eroded using a high velocityfluid jet (eventually air-shrouded) andgrout is simultaneously injected to mix orreplace the soil. The obtained resultdepends on:- The process used (simple, double or

triple jet)- The process parameters (speed of

rotation, speed of uplift, flow pressure,grout,..)

- The type of soil.

Morey (1992) reported by Schlosser(1997) or more recently Bustamante(2001) show the relationship between thediameter of the formed column and thetype of soil, and the process used (Fig.40)

Fig. 40 Diameter of Jet-grouting columnsvs Soil type – Schlosser(1997) after Morey(1992)

A few papers are presented with regard toJet-grouting projects at this conference, inthe session dedicated to North-South line.They illustrate interesting case studies,and commonly addressed concerns, asalso stated by Chu (2006) .- The achievable and achieved column

diameter for a given set of operationalparameters

- The strength of the grout column.One usually specifies for the latter thecement content or the water-cement ratio.Trial laboratory tests are needed toconfirm the design value. Table 8 givesthe indicative values proposed byBustamante (2001).

Type of soil Average StrengthUCS

Clay 3 MPaClayey silt 5 MPaSilty sand 8 MpaSand 15 Mpa

Gravel 25 MPaChalk 12 MPa

Table 8. Average UCS for Jet-Grouting(after Bustamante, 2001)

The question of the control of the diameterin the field remains one of the big issue.Either trial columns, or electrical methodsor mechanical devices are used, no onedefinitively answering the question. In-situcontrol tests or coring are also performed.In the papers presented in the Session onNorth-South line, a new device is


27/38


28/38

question the real improvement obtained bythe stone columns with respect to theuntreated embankment, in terms ofreduction of the settlements. Alternatively and increasingly, soilreinforcement using rigid inclusions has

been applied. The principle of the solutionis illustrated in fig. 43

Fig 43 Rigid inclusionsThe main advantages of the method arethe following:

- Applicability in all soil conditions (evenin very soft soils, where stone columnsproved to be inefficient).

- Settlement reduction accurate andefficient, provided that a appropriatetransfer layer is realised.

- Some system enable installinginclusions without vibrations.

Several systems can be used to install theso-called rigid inclusions (Vibratedconcrete columns, Compaction groutingOmega, Controlled Modulus Columns,Deep Mixing, etc…). Theoretical andpractical studies have been proposed byseveral authors (Combarieu,1988).

A state-of-the-Art was recently proposedby Briançon et al. (2004). The FrenchResearch body IREX just launched aresearch project on this topic. The mainissues in the system are linked to therepartition between soil and inclusions.

The inclusions, being more rigid points“attract” the load. The transfer layer playstherefore an essential role in the globalconcept of the solution. Our own studieshave lead to the following conclusions- Transfer layer with cohesion should be

preferred (cement or lime/cementmixing) of the first 30 to 50 cm. Alternatively, granular material withgeogrid(s) is used.

- Approximately 80 % of the load will becarried by the columns

- Settlement reduction is highlydependent on the ratio height of thetransfer layer/distance betweeninclusions (as for stone columns)

The mostly used computation methods arethe ones of Combarieu, Plaxis, or theGerman recommendations Ebgeo. Fig. 44gives the theoretical comparison betweenthe different approaches (Combarieu,Plaxis, Ebgeo), for one research example:Friction angle 30°

Applied load 54,25 kN/m²Transfer layer no cohesion, no geogrid,

thickness HrInclusions diameter 44 cm

distance sm betweeninclusions 2,2 m (1,5 minsquare pattern)

Compressible layer :silt (c = 2kN/m²)thickness : 10.0 m

Fig.44 Rigid inclusions: load reduction factor in function of Hr/sm - Leclercq (2005)


29/38

Documented and instrumented casestudies are needed in order to correlatethe theoretical results.

Three papers proposed at this sessiondeal with rigid inclusions. The first one isthe previous mentioned paper byBreitsprecher et al (2006) on the use ofso-called wet stabilizing columns (actuallyconcrete columns) compared with drylime/cement columns. The 5600 columns,or rigid inclusions, were designed for aservice load of 80 kN. The columns had adiameter of 121 mm and a varying lengthbetween 2.00 (!) and 7.00 m, aiming at asmooth transition between treated anduntreated soil. The project included a loadtest program on both dry deep mixingcolumns and concrete columns, the resultof which are presented.

Two other papers in this section describea new and recently patented system ofunreinforced piles used as settlementreducer named PCC pile (Liu et al (2006)and Zithao et al (2006)). The PCC pile isa cast-in-place concrete thin-wall pipe pile,installed by vibrating a double casing intothe ground and pouring concrete in thespace between the two casings, and finallyextracting the casings. The final result isan un-reinforced concrete pipe pile.

(a) (b)

Fig.45 PCC pile (a) steel pipe casing, (b)movable tapered pile shoe

Fig.46 The construction process of a PCCpile

The authors report on tests performed onthe PCC pile for the improvement ofembankment on soft ground for the Yan-

Tong Expressway. Both vertical load tests(Liu et al(2006)) as horizontal load tests(Zithao et al (2006)) , have beenperformed.

The characteristics of the piles are thefollowing:Diameters: 1000 mm or 1240 mmThickness: 100 mm or 120 mmSpacing: 2.80 m ; 3.00 m ; 3.30 mLength: 16.00 m or 18.00 m

A cap cushion is placed to ensure the pileand the surrounding soil to share thebearing of the applied loads. Followingfigures give the principle of the application.

PCC pile

GeotextileEmbankmentCushion

Locate

Drive

Pour Extract Complete


30/38

Geotextile layer

25 cm thick gravel

Geotextile layer

25 cm thick gravel

Ground surface

50 cm C15 plain concrete

C15 plain concrete

Fig 47 Principle of Ground reinforcementusing the PCC pile – Liu (2006)

As part of the testing program, a series of14 piles were excavated and visuallyinspected. An important aspect is therelative fragility of the piles to themovement of the equipment. Load-settlement curves are shown. A maximalbearing capacity of 1650 kN is obtained,which is 9% higher, according to theauthors, than the design values.Unfortunately, no design calculation isprovided, but we can deduce that thecontribution of the inner soil to the bearing

capacity is minor. An interesting, and not so commonlyavailable information is the analysis of theload mechanism in the composite body:soil + inclusions. A load test of thecomposite foundation is provided. Fig. 48shows the stress in the surrounding soil atvarious distances from the piles and abovethe piles, for different loading steps.

Topof the inside soilPile wallPile wallSurrounding soil of 1mSurrounding soil of 1.5mSurroundingsoil of 2m

Load on the pile top / KN

S t r e s s

/ M P a

Fig. 48 Stress in the foundations elementsvs applied load – Liu (2006)

The question arises if these piles arecapable to take any horizontal loads.

Zhitao et al. (2006) analysed this problemand provide load-deflection curvesshowing that a limited lateral load can beborn by the PCC piles (around 120 kN),but that strengthening of the upper part ofthe piles is preferable as well as surface

soil improvement. All these case studies show that soilreinforcement with rigid inclusions ofdifferent kinds is increasing. Well-instrumented and documented casestudies are needed in order to betterunderstand the load transfer mechanismand to improve the design.

RETAINING WALLS In the area of retaining walls, the technicalsolutions again vary quite a lot fromcountry to country, and according to thetype of problem. We can distinguish:- Soldier piles and lagging usually used

for small to medium excavations in nowater environment.

- Sheet piles or combined walls (H-pilesand sheet piles) mainly used for quaywalls

- Slurry walls, cut-off walls, used forlarge excavations

- Bored Pile walls, used in difficult soilconditions or for smaller excavationswith difficult contours.

- Deep mixing walls become morepopular- Nailing remains a case to case

approach

Fig. 49 gives the repartition between thedifferent techniques worldwide.

Retaining walls worldwide

19%

48%

10%8%

1%

8%5%

0%

10%

20%

30%

40%

50%

60%

Series1 19% 48% 10% 8% 1% 8% 5%

Slurry walls Pile walls Soil mixing Jet groutingSoil nailedwallsSoldier pile& lagging

Sheet pilewall

Fig.49 Worldwide repartition of retainingwalls.


31/38

As another session of this conference isdedicated to deep excavations, we willlimit the extent of this section totechnological developments, in connectionwith papers submitted to the conference.

Sheet pilesKey issues- Jacking- Sealing

Sheet piles are traditionally installed bydriving or vibratory driving. Our previouscomments on the technological evolutionin this field remain valid, and particularlythe revival of the press-in technologies,certainly in Japan.

Dubbeling et al (2006) explain the recentdevelopment in press-in (jacking)technological equipment enabling to installsheet piles and H-profiles in more difficultconditions. They introduce newconstruction concepts using more compactand lightweight “press-in” equipment alsocalled Silent Piler. (Fig. 50)

Fig. 50 Press-in system – Dubbeling(2006)

Combining innovations in material,auxiliary equipment like water jetting oraugering, the new generation of Silentpiler is reported to be able to penetrateinto dense and hard soil layers.

Water-jetting:

High pressure water jetting reduces thepressure bulb formed during pressing-inby loosening granular soils and softening

cohesive soils. Simultaneously thereturning water lubricates the pile surfaceand reduces the tendency of the pile toplug (fig 51 and 52).

Fig 51 Water jetting for press-in system –Goh (2006)

Fig. 52 Typical soil profile where Water-jet jacked sheet pile are installed – Dubbeling(2006)

Crushing system (augering)The Silent Piler can also be equipped withan integral Pile Auger to enable the Press-in Method to be used in hard groundwhere water jetting would not be effective.The authors report that hard ground layerswith an UCS up to 200 MPa can bepenetrated.


32/38

Fig. 53 Crushing or augering system forpress-in piles – Dubbeling (2006)

The compactness of the equipmentenables to install piles in tight workingspaces, or limited headroom. Eveninclined piles or sheet piles can beinstalled. Systemized equipments havebeen developed to bring the piles on a so-called “pile runner” on the top of the justinstalled pile wall, to the clamp crane.This system allows piling over water orsloped embankments.

Sealing of sheet pilesLehtonen and Laaksonen (2006) introducea new innovative system of watertightsealing using continuous cement groutingduring driving. (fig 54)

Fig. 54 Continuous cement grouting forsheet piles watertightness – Lehtonen(2006)

The method was tested on a field test sitewhere the main installation parametersand permeability figures have beenobserved and analyzed. After two weeksof monitoring, no leak could be observed

and the authors report the obtainedpermeability of the system to be less than5x10-9.

Slurry walls and cut-off wallsIt is surprising how similar techniques cantake such different directions in differentcountries. Slurry walls don’t escape thisreality. Slurry walls are common practicein some countries, and nearly completelyignored in others.In some countries, most excavations areexecuted with cut-off walls, realized withself-hardening bentonite-cement slurry,with structural elements (H-profiles, sheet-piles,..) installed into the fresh slurry.In France, Belgium, and more recently theNetherlands, the techniques of slurry wallsin concrete with watertight joints iscommon practice. A full section will bededicated to the project North-South line,including the slurry walls for the MetroStations at Vijzelgracht and Rokin, andanother to deep excavations, we willtherefore not cover this topic in detail. We just want to summarise the most recenttechnological evolution or trends that wehave been noticing in this field- The use of hydraulic grabs- The use of hydromills or cutters for

excavating in difficult soil conditions,including limited headroom, or in tightworking spaces.

- The monitoring of the execution, werekey parameters are registered, asdepth, inclination, deviation of the grabin the two directions.

- The use of improved systems forwatertight joints

These technological improvements enableto guarantee the respect of tightertolerances in the execution of the walls,and hence a higher quality of the finishedproduct.

Raffaela and Crippa (2006) report a casehistory where two contaminated sites in apetrochemical plant, were encapsulatedusing a self-hardening slurry with a HDPmembrane. Few detailed soil data areprovided. Due to the necessary continuityof the membrane, a rather complicatedexecution process was chosen combining


33/38

a pre-excavation with a hydromill or pre-boring with bored piles equipment in hardsoil layers. The pre-excavation was filledby plastic concrete, which was re-excavated with a clamshell working underself-hardening slurry. The slurry was

tested in function of the pollutedenvironment.

Secant pilingKey issues- Cased augercast- Tolerances and quality control

Pile walls represent nearly 50 % of theretaining wall market. A lot of differenttechniques co-exist in this segment :- Tangent pile walls with CFA piles- Secant pile walls using CFA piles- Secant pile walls using conventionalbored piles- Secant pile walls using cased CFA

piles. As already mentioned, the maindevelopment in this field is the cased CFA(also called Front-of-Wall), which hasliterally exploded in some markets, and isreported by many practitioners as a majordevelopment in this field. In Belgium, notless than 14 rigs work with this system,typically used for one or two levelsunderground in urban areas. The usualdiameters range from 42 to 62 cm, and thelength typically reaches 16.00 m.

Main advantages of the system:- Tight tolerances on both position (


34/38

by arching to structural elements placed inthe fresh “slurry” (fig. 55)

Fig 55 Arching mechanism for soil-mixwalls.

In this case, overlapping columns are usedin order to create interlocking walls (Fig.56). Simple or double H or U profiles areinserted in the fresh slurry to form thestructural stability of the retaining wall, thesoil mix transmitting the ground and/orwater pressures via arching.

Fig. 56 Overlapping soil-mix columns forretaining walls.

The critical issues are then:- As in all applications of deep mixing:

homogeneity of the treated soil. In thecase of retaining walls under watertable, this issue can be a veryimportant one.

- Tolerances of execution. As the wallis formed by overlapping columns ofsoilmix, tight tolerances are needed inorder to guarantee that the columnsare effectively overlapping. In thecase of the use of the three augers orrods systems, the rigidity of the rods isquite low and can subsequently leadto problems in this respect. No realguide beam can be constructed, as forsecant pile walls.

CONCLUSIONS

We have been trying to give acomprehensive overview of the mostrecent evolution in the deep foundationtechnologies over the last years, what isobviously an impossible task. We retain:1. The better understanding of energy

transfer and set-up phenomenon fordriven piles.

2. The use of vibratory driving and jackedpiles in replacement of driven piles.

3. The increasing part of displacementauger piles enabling to fully benefit ofthe soil capacity.

4. The development of post-grouting inorder to increase the range ofapplication of bored piles.

5. The better understanding of thenegative effect of soil looseningrelated to CFA pile installation andhence the development of proprietarysystems or more recently of the casedCFA piles.


35/38

6. The use of rigid inclusions or pilesused as settlement reducers for soilreinforcement

7. The increased use of of Deep Mixingtools for various deep foundationproblems.

Although the technological advances havebeen enormous, in terms of systems orinstalled power, the back analysis of manycase studies for deducing installationeffects is fraught by the lack of well

documented cases with correctlydescribed soil investigations and above all,equipment related data. As already pointed out by O’Neill andFinno (2001), there is a need to improvethe understanding of the installation

effects of deep foundations techniques onthe surrounding soil and hence, the levelof the information contained in our papersto provide exploitable data.

PAPERS PRESENTED in THIS SESSION

BREITSPRECHER Georg, STIHL Dirk.Ground improvement by means ofstabilising columns.

BZÓWKA Joanna, PIECZYRAK Jacek. Application of CFA piles for foundation of ashopping centre on long-standing dumpingground.

DAPP Steven D., MUCHARD Mike,BROWN Dan A. Experiences with basegrouted drilled shafts in the SoutheasternUnited States.

DAVIE John R., CLEMENTE Jose L.M., ANDERSON Myron R., HEADLANDLouise C. Drilled piers support massivegantry crane.

DUBBELING Philip, VRIEND Ad, NOZAKITsnunenobu. Press-in piling technologyfor sustainable construction.

FILIP Ray K. Recent advances in quiet &vibration-less steel pile installation andextraction.

GRANATA Rafaella, CRIPPA Carlo..Confinement of two contaminated sites ina petrochemical plant; case history.

GWIZDA A Kazimierz, KRASI SKI Adam,BRZOZOWSKI< Tadeusz,. Experiencegained at the application of Atlas piles inPoland.

Ho Chu E., Prediction of jet grout columndiameter in cohesive soil.

KHARE Makarand G., GANDHI ShaileshR., Performance of bituminous coats in

reducing negative skin friction.

K OSI SKI BOLES AW A.,SZYMANKIEWICZ Czes aw. Bored pileswith base preloading by grouting – ThePolish experience.

LAMBERT John W.M., WHIFFIN VictoriaS., WOLFS Patrick A. Bacteria help civilengineers; report of a pilot project.

LEHTONEN Jouko L., LAAKSONEN JariP. Continuous grouting in embedding ofsheet piles.

LENNON Derek J., RITCHIE David,PARRY Geraint O., SUCKLING Tony P.Piling Projects constructed with vinylpolymer support fluid in Glasgow,Scotland.LIU Hanlong , GAO Yufeng, ZHANG Ting. Application of PCC piles on soft groundimprovement of expressways.

Ma Zhitao, LIU Hanlong. Behaviour ofPCC pile under lateral load.

MATHIEU Fabrice, BOREL Serge,LEFEBVRE Laurent. CSM : An innovativesolution for mixed-in-situ retaining walls,cut-off walls and soil improvement.

SNELL T.J., SINGLETON M. Bearingcapacity and slope instability solved bynovel ground engineering solutions.

STOETZER E., BRUNNER W.G.,FIOROTTO R. GERRESSEN F.W.,SCHOEPF M. CSM Cutter soil mixing – Anew technique for the construction ofsubterranean walls. Initial experiencesgained on completed projects.


36/38

REFERENCES

BOREL S., BUSTAMANTE, M., &GIANESELLI, L., 2002. Two comparativefield studies of the bearing capacity of

vibratory and impact driven sheet piles,Vibratory pile driving and Deep soilcompaction TRANSVIB 2002 Holeyman,Vandenberghe & Charrue (eds), pp167-174

BOREL S., GIANESELLI L., DUROT D.,VAILLANT P., BARBOT L., MARSSET B.& LIJOUR P., 2002. Full-scale behaviourof vibratory driven piles in Montoir ,Vibratory pile driving and Deep soilcompaction TRANSVIB 2002 Holeyman,Vandenberghe & Charrue (eds), pp179-192BOTTIAU, M & MASSARSCH, K.R., 1991Quality aspects of reinforced augercastpiles, Proceedings of the 4 th InternationalConference on Piling and DeepFoundations, Stresa, pp 41-50

BOTTIAU, M. & CORTVRINDT, G. ,1994. Recent experience with theOmega-Pile, Proceedings of the FifthInternational Conference on Piling andDeep Foundations, 13-15 June, Bruges.

pp 3.11.0-P3.11.7.

BOTTIAU, M., 2003 Fundamental issuesof displacement auger piling : theEuropean perspective. Auger cast-in-placePiles Committee Specialty Seminar, DFI,

Atlanta.

BRIANCON, L., 2004. Etat desconnaissances : amélioration des sols parinclusions rigides. ASEP-GEI 2004, Paris,Dhouib, Magnan, Mestat Eds, pp 15-43.

BRUCE, D.A., 1986. Enhancing theperformance of large diameter piles bygrouting, Ground Engineering, May/July1986.

BUSTAMANTE M. & GIANESELLI, L.1993. Design of auger displacement pilesfrom in-situ tests. Proceedings of the 2ndInternational Geotechnical Seminar onDeep Foundations on Bored and Auger

piles, Ghent. pp 193-218.

BUSTAMANTE, M., and GOUVENOT,D.,2001. Dimensionnement des colonnesde Jet Grouting comme élément porteur et

d’ancrage, XVth International Conferenceon Soil Mechnics and GeotechnicalEngineering, Istanbul, pp 2777-2782

BUSTAMANTE, M. 2003. Auger andbored pile monitoring and testing.DeepFoundations on Bored and Auger Piles,Van Impe (ed.). Ghent.

COMBARIEU, O., 1988. Améliorationsdes sols par inclusions rigides verticales,Revue française de Géotechnique, N°53,PP33-44.

DE COCK F.A., 2001. A databaseapproach to overview pile loading tests ondisplacement screw piling in WesternEurope – 1970-2000, Proceedings of thesymposium on Screw piles – Installationand Design in stiff clay, Holeyman (ed.),15 March, Brussels. pp89-125.

DE COCK, F. & IMBO, R., 1994. The Atlas screw pile – A vibration free fulldisplacement cast-in-place pile. 73dannual meeting of the USA transportationResearch Board, Washington D.C.

EVERS, G., HASS, G., FROSSARD, A.,BUSTAMANTE, M., BOREL, S. &SKINNER, H., 2003. ComparativePerformances of Continuous Flight Augerand Driven Cast in Place piles in sands.Deep Foundations on Bored and AugerPiles, Van Impe (ed.). Ghent, 2003.

FASCICULE 62 – TITRE V, 1993. Règlestechniques de conception des fondationsdes ou

Documents

new Piles Installation Systems