field axial cyclic loading experiments on piles driven in sand

ri

, J b

rial

mpe

ised

11

Abstract

(1992) tests with the 102 mm diameter Imperial College

and apply downward tractions during down-strokes andvice versa. This mechanism promotes top-down progressivecyclic degradation. Stable conditions can be reached if local

The Japanese Geotechn

www.sciencedirejournal homepage: www.elsev

Soils and Foun

nCorresponding author.

Soils and Foundations 2012;52(4):723736shaft capacity losses over the upper region can be balancedby load transfer to the toe, or by shaft capacity enhance-ment at depth (denitions of stable and other states aregiven later in the paper).

0038-0806 & 2012 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved.

http://dx.doi.org/10.1016/j.sandf.2012.07.012

Peer review under responsibility of The Japanese Geotechnical Society.their overview of recent developments is not repeated here,we note their comments on the scarcity of eld cyclic tests

two-way local failure over the upper section of the shaft.The top section of the pile will move more than the soilE-mail address: [email protected] (R. Jardine).While axial load cycling can impact signicantly onpiles, the potential effects are often neglected in design.This paper describes a eld investigation into how cyclicloading might affect piles driven in sands. Tsuha et al.(2012) report a related recent laboratory investigation,remarking that inuential factors include the number ofcycles (N); their frequency (f); the mean load and cyclicamplitude (Qmean and Qcyclic) relative to static capacityQstatic; loading history; and the sand characteristics. While

Instrumented Pile (ICP) in Labenne dune sand and (ii)Chows (1997) ICP experiments and static tests on largerinstrumented tubular piles in Dunkerque marine sand.The limited available data appear to support the cyclic

mechanisms proposed by Jardine (1991, 1994).

While one-way load cycling involves applying cyclic loadsof only one sign (tension or compression) to the head of thepile, it is likely, especially at higher load levels, to generateMultiple axial cyclic and static loading tests have been performed on industrial steel pipe-piles driven at Dunkerque, northern France.

This paper describes the sites geotechnical characteristics and experimental arrangements before dening and describing the stable,

unstable or meta-stable responses observed under various combinations of cyclic loading. The interpretation draws on numerical

analyses and a parallel model study by Tsuha et al. (2012), relating the eld response to the probable shaft shear stress distributions and

local effective stress conditions. It is argued that cyclic degradation is controlled by: (i) contraction in the highly constrained interface

shear zone and (ii) kinematic yielding within the surrounding soil mass. Finally, interaction diagrams linking shaft response to cyclic

loading parameters are proposed based on the eld test data and a simplied cyclic capacity predictive approach.

& 2012 The Japanese Geotechnical Society. Production and hosting by Elsevier B.V. All rights reserved.

Keywords: Driven piles; Sands; Time; Cyclic loading; Field monitoring

1. Introduction on piles driven in sands and their reference to (i) LehanesField axial cyclic loading expe

R J Jardinea,n

aProfessor of Geomechanics, ImpebSenior Lecturer in Soil Mechanics, I

Received 27 November 2011; received in rev

Available onlineR Standing

College London, SW7 2BU, UK

rial College London, SW7 2BU, UK

form 20 April 2012; accepted 20 June 2012

September 2012ments on piles driven in sand

ical Society

ct.comier.com/locate/sandf

dations

dr

the CLAROM2 group (Brucy et al., 1991; Chow, 1997).Capacity variations with different applied cycling levelswere tracked carefully, using conventional instrumentationfor eld pile testing (details are given by Jardine et al.,2006), to allow load normalisation. The programme of 21static and 14 cyclic experiments is set out in Table 1. Mosttesting was performed in tension to simplify the shaft-to-base load split. Numerical modelling was undertaken toevaluate the shaft shear stress distributions and the resultsare summarised in reports issued to the project sponsors(e.g. Jardine and Standing, 2000). We present here asummary and interpretation of those measurements.

1.2. Ground conditions

The site prole consists of 3 m of hydraulic marine sandll over marine sand. Jardine et al. (2006) describe the

Fig. 2. Location of the test site relative to the Port of Dunkerque (Jardine

and Standing, 2000).

RJ Jardine, JR Standing / Soils and Foundations 52 (2012) 723736724witear1ll thicknesses and the precise depths to which they wereiven are given in Table 1. The cyclic tests shared facilitiesh the GOPAL project and were conducted near to thelier experiments performed on driven steel pipe-piles byhawa Two-way cyclic pile loading that involves both com-pression and tension head loads has the potential to bemore damaging than one-way load cycling.

Local capacity losses result from radial effective stressesreducing in the soil adjacent to the shaft under kinema-tically controlled conditions, where vertical and circum-ferential straining is prevented and radial contractionunder cyclic shearing is constrained by the (non-linear)stiffness of the soil mass.

Tsuha et al. (2012) report laboratory model tests designedto model these eld pile conditions and conclude that shaftcapacity can benet from low-level stable cycling as well asdegrade markedly under high-level cycling. In this paper theterms low-level and high-level cycling are used broadly torelate to cyclic load levels that result in an increase ordegradation of load capacity compared with the static loadcapacity. Tsuha et al.s study also indicates that theinuence of prior testing history on cyclic shaft responsecan be largely accounted for by tracking the changingtension capacities, which they use to normalise the appliedcyclic shaft loads.

1.1. Aim and scope of the present study

Full-scale eld testing is essential to test the aboveconjectures. A fully comprehensive study would include alarge number of fresh installations to avoid ambiguitiesrelating to any prior testing, but this has yet to be done.The present study employed just seven industrial-scaleun-instrumented piles but covered a broad range of Qmeanand Qcyclic combinations, as dened in Fig. 1.The steel pipe-piles (all with 457 mm outer diameter)

were driven at a at part of the Dunkerque Port OuestIndustrial Zone (see Fig. 2); sited about 100 m south of theInstitut Pasteur and about 40 m east of the road leading toan oil tank farm. They were installed as part of theGOPAL1 research project to investigate the potential offorming an enlarged jet-grouted bulb at the base of adriven steel pipe-pile to increase base capacity (see Parkeret al., 1999). Two primary piles were installed of the samedimensions: C1, a reference or control pile, and JP1. Thelatter was a driven steel pile under which a 2.8 m diametercylindrical jet-grouted base had been formed, but this testis not discussed here. Six additional piles, all approxi-mately 19 m long, were installed to provide reaction forloading the two primary piles, as shown in Fig. 3. Resultsfrom the reaction pile predictions and load test measure-ments indicate that the construction of the jet-grout based negligible effect on their capacities. Details of the pileGOPAL is an acronym for Grouted Offshore Piles Alternating Loading.Qmax

Qmin

OTime

Q

Qcyclic

Qmean

Cyclic period T

Qcyclic=(Qmax-Qmin)/2Qmean=(Qmax+Qmin)/2

Fig. 1. Schematic illustrating denitions of Qmean and Qcyclic (Tsuha et al.,

2012).2CLAROM is a French acronym for CLub for Research Activities on

Offshore Structures.

Jarplucam

1.

2.

3.

and FouFig. 3. Plan showing layout of test and reaction piles and CPTs from

GOPAL project, Dunkerque (Sections A-A and B-B relate to the CPT

RJ Jardine, JR Standing / Soilsgeology and summarise the site characterisation whichincluded multiple CPT tests, a 26 m sampled borehole,seismic CPT and Marchetti dilatometer proling, Rayleighwave testing and laboratory testing. Mineralogical, index,direct and interface shear tests, triaxial stress path, benderelement, hollow cylinder torsional shear and resonantcolumn experiments were performed at Imperial College.The typical site prole is shown in Fig. 4 while Fig. 5

illustrates the local CPT variations and Fig. 6 the particlesize distributions. The sub-rounded to rounded grainscomprise quartz (84%), albite and microcline (8%) andCaCO3 shell (8%). CPT qc traces uctuate with depth andlocation, typically ranging between 10 and 35MPa. Relativedensity averages around 75%, but approaches 100% atshallow depth and falls to low values in thin organic layers.Direct shear and triaxial compression tests indicate peakj0 values of 35401 and critical state values of about 321,while interface shear tests against steel show design d valuesof about 271. Information is also available regarding elasticanisotropy, non-linear stiffness characteristics and creepbehaviour; see Jardine and Standing (2000), Jardine et al.(2005a), (2006), Kuwano (1999) for further details.

1.3. Testing programme

The GOPAL tests applied compression loading to pilesC1 and JP1 (see Table 1), bearing against the six reactionpiles (R1R6) as shown in Fig. 3. The minimum pile

2.

0 0

proles shown in Fig. 5).tf srcDsr tandf in compression andtf 0:9 0:8s0rcDs

0r

tandf in tension

3. Where the dilatant component of sr change isThe local maximum shaft shear stresses tf expected at anygiven depth on the shaft, and height h above the pile tip are R* RouterRinnerh height above pile tip and h=R*Z8performed up to and including that experiment. The reac-tion loading for the GOPAL tests was considered to havenot affected the reaction piles signicantly as none wasloaded beyond 60% of its (then current) shaft capacity.

1.4. Effects of local variations in soil conditions

on pile capacity

ICP capacity calculations were undertaken to provide anobjective assessment of how local geotechnical variationsinuenced individual pile capacities. These procedures arerecognised as providing far better predictive reliability thanconventional methods for piles driven in sands and arenow applied routinely in offshore geotechnical engineering.Independent database studies by Jardine et al. (2005b) andLehane et al. (2005) each involving more than 70 highquality pile load tests (typically conducted some days afterdriving) gave mean ratios of prediction to measurement of0.950.99 and standard deviations around 0.28. As set outby Jardine et al. (2005b), the main steps are as follows.

1. Evaluate the pre-loading shaft radial effective stressdistributions from the local CPT tip resistances qc, thefree-eld vertical effective stresses sv0, Pa the atmo-spheric pressure and Rn the equivalent radius

s0rc 0:029qcs

0v0=Pa0:13h=R*0:38 where

2 2 1=2(1TOctober to November 1998Static testing on C1 andJP1 and both cyclic and static testing on R1, R3, R4, R5and R6.April 1999Final static and cyclic testing on all reac-tion piles; static re-tests on the CLAROM piles.

Table 1 gives pile test codes comprising the: campaign3), pile (e.g. R1), type of test (Cstatic compression,static tension, CYcyclic) and the number of testsdine et al. (2006) report on the driving noting that soilgs rose to around 60% of the embedded lengths. Threepaigns of load testing took place.

August to September 1998Pile installation and anearly static test on R1.spacing (s) to diameter (D) ratio was approximately 15.

ndations 52 (2012) 723736 725Ds0r 2GDr=Router

ting

sion

sion

ctio

sion

ctio

sion

lic

ick

ctio

sion

sets cyclic tension tests 14 to 15/11/98 2.R3.CY2

andTable 1

Summary of pile histories and test codes.

Pile Pile make up Tes

R1 20 mm wall thickness Ten

Tip at Over top 2.5 m, Ten

19.32 m 13.5 mm to base Rea

Driven 24/08/98 Ten

R2 As above Rea

Tip at Driven 21/08/98 Ten

18.85m Cyc

Qu

R3 As above Rea

Tip at Driven 20/08/98 Ten

19.24 m Two

RJ Jardine, JR Standing / Soils726where Dr is the pile peak-to-trough shaft surface rough-ness, and G is the operational secant shear stiffness.Jardine et al. (2005b) provide simple rules to estimate G,and the base resistance qb from CPT tests. Variationsbetween the predicted individual capacities and the overallmean predicted capacity of the reaction piles of up to17.1% are indicated in Table 2, falling within the standarddeviation expected from the database studies. The resultsfrom the static tests also correlate with the hierarchy ofdriving resistances reported by Jardine et al. (2006).Fig. 7 reproduces the latter authors summary of tension

shaft capacities, normalised by the respective ICP designcapacity predictions, and corrected for the pile and soil plugweights. It is shown that the capacities of piles C1, R1 and

Quick

Tension

R4 As above Reactio

Tip at Driven 24/08/98 Tension

19.37 m Cyclic

Quick

Cyclic

Tension

Extend

23/04/9

Quick

R5 As above Reactio


19.05m Two se

Quick

Tension

R6 As above Reactio


18.90 m Cyclic

Tension

Cyclic

Quick

Cyclic

Quick

C1 As above GOPAL


10.02 m Three s

Tensionhistory Test Code

failure 02/09/98 1.R1.T1

failure 28/10/98 2.R1.T2

n for GOPAL pile tests 02/11 to 06/11/98

failure 26/04/99 3.R1.T3


failure 18/04/99 3.R2.T1

tension test 18/04/99 3.R2.CY2

static tension failure 18/04/99 3.R2.T3


to 2MNno failure 13/11/98 2.R3.T1

Foundations 52 (2012) 723736R2 varied with age after driving. Undisturbed piles showedmarked and steady gains with time (dened by the IntactAgeing Characteristic, IAC), while pre-failed piles followeddiscontinuous trends. Testing to failure generally reducedcapacity. Some recovery took place afterwards, but this couldnot match the gains developed by undisturbed piles. Statictesting to failure before any particular cyclic experimentcould degrade capacity, and piles tested after high-level cyclictesting generally could not achieve their pre-cycling capa-cities. A mixed series of rst-time tests and re-tests was stagedto allow best estimates to be made of the static tensioncapacities applying before each cyclic loading test, accountingfor local variations, possible brittleness and ageing. Theseestimates are listed in Table 3.

2.R3.CY3

static tension test 15/11/98 2.R3.T4

failure 20/04/99 3.R3.T5


to 2MNno failure 16/11/98 2.R4.T1


tension to failure 17/04/99 2.R4.T3


failure 18/11/98 2.R4.T5

ed 1000 cycle tension testno failure 3.R4.CY6

9

tension to failure 24/04/99 3.R4.T7


to 2.0MN no failure 19/11/98 2.R5.T1

ts cyclic tension tests 20 to 21/11/98 2.R5.CY2

2.R5.CY3

tension test 21/11/98 2.R5.T4

failure 15/04/99 3.R5.T5


failure 9/11/98 2.R6.T1


failure 11/11/98 2.R6.T3


tension failure 12/11/98 2.R6.T5

tension failure 22/04/99 3.R6.CY6

tension failure 22/04/99 3.R6.T7

compression failure 01/11/98 2.C1.C1

failure 02/11/98 2.C1.T2

ets two-way cyclic tests 02 to 05/11/98 2.C1.CY3

2.C1.CY4

2.C1.CY5

failure 06/11/98 2.C1.T6

2. Cyclic test results and interpretation

RO

and1.5. Pile testing procedures

Precision monitoring and control (PMC) of Teeside(UK) provided specialist pile testing equipment and sitepersonnel. Loads were controlled by an automatedhydraulic system and the beam arrangements describedby Jardine et al. (2006). A high quality load cell was

Fig. 4. Typical geotechnical proles for CLA

RJ Jardine, JR Standing / Soilsemployed and four independent displacement transducerswere attached to reference beams supported at least 2 maway from the piles and reaction pads. Screens erectedover the installations reduced thermal and environmentaleffects. Loading was controlled by a regulator that couldcycle (with periods between 1 and 2 min, depending on pileresponse), between maxima and minima that could gen-erally be maintained to 75 kN over extended durations.Figs. 8 and 9 illustrate a typical one-way test, 2.R3.CY3,that failed after around 15 cycles. The waveforms wereintended to be sinusoidal, but compliance effects led totime histories that were less rounded and symmetrical thansine waves.Slow and quick static tests were staged to track shaft

capacity; Jardine et al., (2006). Slow tests were governedby creep rate criteria and involved incremental loadingstages separated by pauses and could take many hours,while quick tests led to failure within tens of minutes.Check tests indicated that capacity did not vary signi-cantly with loading rate, although quick tests developedsmaller displacements. Some brittle tension failures werenoted while others exhibited stick-slip modes. Jardine andStanding (2000) reported load-displacement curves for alltests, noting that all tension failures required displacementsless than 7% of the pile diameter while the compressiontest on C1 developed no distinct peak. Static tests wereThis studys main focus is on cyclic failure character-istics and Table 3 summarises the loads applied (note thatgenerally unloaded as soon as failure was clear, so limitingthe damage to capacity.

M/Imperial College test site (Chow, 1997).loaideme

incmelat(45plaFoundations 52 (2012) 723736 727d values are expressed to nearest 5 kN). One aim was tontify piles that were subjected to stable, unstable orta-stable cycles as dened below.

Stable (S): pile head displacements accumulate slowlyover hundreds of cycles, under one-way loading (witheither tension or compressions loads applied) or two-way loading (involving tension followed by compressionloads applied, or vice versa, passing through zero loadduring each cycle).Unstable (US): displacements develop rapidly underone-way or two-way conditions leading to failure atNo100 and marked shaft capacity losses.Metastable (MS): pile head displacements accumulate atmoderate rates over tens to hundreds of cycles withoutstabilising and cyclic failure develops within the100oNo1000 range.

Stable cycles lead to shaft capacity gains, while eitherreases or decreases in shaft capacity are possible withtastable cycles. Cyclic failure was identied as: (i) accumu-ed displacements reaching 10% of the pile diameter.7 mm), or (ii) a sudden acceleration in permanent dis-cement rates. Rates were considered slow ifo1 mm/103

andRJ Jardine, JR Standing / Soils728cycles (10 times the limit applied by Tsuha et al. to their36 mm Mini-ICP pile tests).Table 4 lists the cyclic test outcomes. Applying the

above denitions, the cycles applied led to just oneexample of a stable test, while nine were unstable andfour metastable. We describe and discuss examples of eachbelow. Jardine and Standing (2000) reported equivalentplots for all 14 cyclic tests.

2.1. Stable cyclic loading

Figs. 10 and 11 illustrate results from the stable cycletest: 3.R4.CY6. A slender and immobile load-displacementloop was set up after the rst cycle. The permanent

Fig. 5. CPT proles with depth and interpreted soil proFoundations 52 (2012) 723736displacements grew by just 0.4 mm over the rst 500 cyclesof one-way tension cycling (from 0 to 800 kN) but thenstabilised, or even reduced, as N increased to 1000. Cyclicamplitudes also tended to reduce slightly once N4500.The subsequent quick static loading test (3.R4.T7) showedan 18% (albeit brittle) gain over the estimated pre-cyclingtension capacity.

2.2. Metastable cyclic loading

Metastable cyclic behaviour is illustrated in Figs. 12 and13 using results from test 3.R6.CY6, where the pileeventually failed under metastable cycling (similar to2.R5.CY2). Permanent displacement rates grew steadily

le (see Fig. 3 for locations of Sections A-A and B-B).

andRJ Jardine, JR Standing / Soilsby an order of magnitude from about 0.013mm/cycle(up to N=50) up to about the 190th cycle, after whichrates accelerated more sharply. The pile pulled out by 8 mmover its last cycle, with stick-slip uctuations between 1200

Fig. 6. Range of particle size distribution curve

Table 2

ICP design assessment of pile capacity at nominal 10-day age.

Pile CPT prole applied

R1 R1R2

R2 Mean of R1R2 and R2R3

R3 R2R3

R4 R4R5

R5 Mean of R4R5 and R5R6

R6 R5R6

C1 C1

1 10 100 1000 10000Time after driving (days)

0

0.5

1

1.5

2

2.5

3

Qs

(t) / Q

sICP

Dunkirk IAC

Jardine and Chow(1996) trendline

R1

R2

C1

Line representing capacity at end of driving

?

Fig. 7. Normalised pile capacities versus time for rst-time and pre-failed

tension tests for control pile C1 and reaction piles R1 and R2 (Jardine

et al., 2006).s from CLAROM borehole (Chow, 1997).

Foundations 52 (2012) 723736 729and 1400 kN. Tension loads varied between 1150 and1600 kN (about a similar mean) in a quick test, 3.R6.T7.Overall, the cyclic and static capacities fell 14 to 21% belowthe estimated pre-cycling tension capacity. Cyclic failureloads generally matched the tension capacities seen insubsequent tension tests, indicating that rate effects andcapacity losses due to unloading after cyclic failure areeither negligible or self cancelling. All four metastable cycletests involved signicant tension capacity reductions; seeTable 3.

2.3. Unstable cyclic loading

The behaviour of an exemplar unstable one-way high-level cyclic test, 2.R3.CY3, was illustrated earlier in Figs. 8and 9. The load-displacement data are added in Fig. 14.While almost constant displacement amplitudes (73.1 mm)developed over the rst N13 cycles, the permanentdisplacements were initially relatively high (around 0.5 mmper cycle) and accelerated progressively after reaching N7.The test was terminated after displacing 10% of the pilediameter (i.e. 46 mm). The pile was unable to re-achieve itstarget of 1900 kN tension on re-loading from the 13th cycle

Calculated ICP design capacity (kN)

1500 tension (3.3% above mean for reaction piles)

1390 tension (4.3% below mean for reaction piles)


1700 tension (17.1% above mean for reaction piles)



910 (shaft: compression), 673 (shaft: tension), 753 (base)

Table 3

Key features of static and cyclic tension tests.

Test code Key observations

1.R1.T1 Ductile failure: 1450 kN (24 mm displacement)

2.R1.T2 Marginally brittle failure: 1500 kN (8 mm displacement)

3.R1.T3 Marginally brittle failure: 1645 kN (8 mm displacement)

3.R2.T1 Ductile failure: 3210 kN (34 mm displacement)

3.R2.CY2 Qcyclic1000 kN, Qmean1000 kN; estimated initial Qmax2500 kN3.R2.T3 Stick-slip failure: 1655 kN

2.R3.T1 No failure on loading to 2000 kN (10.3 mm displacement)

2.R3.CY2 Qcyclic700 kN, Qmean700 kN; estimated initial Qmax2315 kN2.R3.CY3 Qcyclic950 kN, Qmean950 kN; estimated initial Qmax2050 kN2.R3.T4 Stick-slip failure: 1650 kN in quick test

3.R3.T5 Brittle stick-slip failure: 1990 kN (10 mm displacement)

2.R4.T1 No failure on loading to 2000 kN (8.7 mm displacement)

2.R4.CY2 Qcyclic1000 kN, Qmean1000 kN; estimated initial Qmax2960 kN2.R4.T3 Failure: 2000 kN in quick test

2.R4.CY3 Qcyclic750 kN, Qmean1250 kN; estimated initial Qmax2100 kN2.R4.T5 Brittle stick-slip failure: 2000 kN, reducing to 1450 kN

3.R4.CY6 Qcyclic400 kN, Qmean405 kN; estimated initial Qmax2110 kN3.R4.T7 Brittle stick-slip failure: 2490 kN (reducing to 1900 kN) in quick test

2.R5.T1 Loaded to 2000 kN with 8.9 mm displacement; estimated Capacity2450 kN2.R5.CY2 Qcyclic750 kN, Qmean1250 kN; estimated Qmax2465 kN2.R5.CY3 Qcyclic700 kN, Qmean700 kN; estimated Qmax2000 kN2.R5.T4 Stick-slip failure: average 1300 kN in quick test

3.R5.T5 Brittle failure: 1795 kN (reducing to 1636 kN)

2.R6.T1 Loaded to 2400 kN with 30 mm displacement, estimated Capacity2450 kN2.R6.CY2 Qcyclic750 kN, Qmean1250 kN; estimated Qmax2000 kN (test aborted after rst cycle)2.R6.T3 Ductile failure: 1585 kN (7 mm displacement)

2.R6.CY4 Qcyclic700 kN, Qmean700 kN; estimated Qmax1585 kN2.R6.T5 Stick-slip failure: average 1325 kN in quick test

3.R6.CY6 Qcyclic700 kN, Qmean700 kN; estimated Qmax1650 kN3.R6.T7 Stick-slip failure: 1425 kN

2.C1.C1 Compression load to 2820 kN after 34 mm, load at 46 mm estimated2850 kN2.C1.T2 Stick-slip tension: 820 kN (33 mm displacement)

2.C1.CY3 Qcyclic600 kN, Qmean40 kN (compression); amplitudes increase suddenly at N21 after correct loading applied at N17 with equaltension and compression loads of 600 kN and pile reverses to pull out 45 mm in next 20 cycles, estimated initial Qmax840 kN

2.C1.CY4 Qcyclic445 kN, Qmean165 kN (tension); large permanent displacement with each cycle; pile pulls out 45 mm in 3 cycles, estimated initialQmax620 kN

2.C1.CY5 Qcyclic410 kN, Qmean10 kN (tension); amplitudes increase suddenly at N2 and pile reverses to pull out 45 mm in next 10 cycles,estimated initial Qmax620 kN

2.C1.T6 Stick-slip failure, maximum load of 500 kN at 46 mm

0 5 10 15 20 25 30 35Time (minutes)

0

500

1000

1500

2000

Load

(kN

)

Fig. 8. Tension loads applied in typical unstable tension cycle test:

2.R3.CY3.

0 5 10 15 20 25 30 35Time (minutes)

0

5

10

15

20

25

30

35

40

45

50

Dis

plac

emen

t (m

m)

Fig. 9. Upward pile head displacements developed over 14 cycles in

typical unstable tension cycle test: 2.R3.CY3.

RJ Jardine, JR Standing / Soils and Foundations 52 (2012) 723736730

l pe

s. P

cles

s. A

ov

andTable 4

Outcomes of all cyclic loading tests.

Test Key factors

3.R2.CY2 Qcyclic/Qmax0.40, Qmean/Qmax0.40. Failed in 9 cycles. Initia2.R3.CY2 Qcyclic/Qmax0.30, Qmean/Qmax0.30. Unfailed after 200 cycle2.R3.CY3 Qcyclic/Qmax0.46, Qmean/Qmax0.46. Brittle failure after 12 cy

cycle

2.R4.CY2 Qcyclic/Qmax0.34, Qmean/Qmax0.34. Unfailed after 221 cyclesharply over last 30 cycles

2.R4.CY4 Qcyclic/Qmax0.36, Qmean/Qmax0.59. Failed in 3 cycles. 6 mm

RJ Jardine, JR Standing / Soilsand lost about 10% of its capacity in its nal brittle failure.An overall capacity loss of 24% is interpreted.The two-way high-level cyclic experiment 2.C1.CY3

was the rst cyclic test and one of the most difcult toperform. As illustrated in Figs. 15 to 17, the rst 16 cyclesinadvertently applied 100 kN less tension than intended;the loading system also halted unintentionally at N=20for 25 min and the loading system had to be re-adjusted.Despite these imperfections, 2.C1.CY3 is the mostinteresting two-way test. Its early tendency to settle(at an initial rate of 0.50 mm/cycles) corresponds to themaximum compressive loads applied being greater than

3.R4.CY6 Qcyclic/Qmax0.19, Qmean/Qmax0.19. Unfailed after 1000 cycles.2.R5.CY2 Qcyclic/Qmax0.30, Qmean/Qmax0.51. Failed after 345 cycles. Aver

and increasing signicantly after N275; 6 mm over last cycle2.R5.CY3 Qcyclic/Qmax0.35, Qmean/Qmax0.35. Failed after 27 cycles. Initial

sharply after N21; 8 mm over last cycle2.R6.CY2 Qcyclic/Qmax0.38, Qmean/Qmax0.63. Failed in 1 cycle2.R6.CY4 Qcyclic/Qmax0.44, Qmean/Qmax0.44. Failed after 24 cycles. Initial

sharply at N17; 9 mm over last cycle3.R6.CY6 Qcyclic/Qmax0.42, Qmean/Qmax0.42. Failed after 206 cycles. Ave

markedly after N190; 8 mm over last cycle2.C1.CY3 Qcyclic/Qmax0.71, Qmean/Qmax -0.05. Failed after 40 cycles. Initia

at N21, nally pulling out; 5 mm over last cycle2.C1.CY4 Qcyclic/Qmax0.72, Qmean/Qmax0.27. Failed in two cycles. Pulling2.C1.CY5 Qcyclic/Qmax0.68, Qmean/Qmax0.02. Failed after 8 cycles. Rapidl

stages; pulling out 8 mm over last (13th) cycle

0 2 4 6 8 10 12 14 16Time (hours)

0

0.5

1

1.5

2

2.5

3

3.5

Dis

plac

emen

t (m

m)

Fig. 10. Displacement-times trace over 1000 cycles for stable tension cycle

test: 3.R4.CY6. (roughly only every tenth cycle shown).Class

rmanent displacement rate 0.3 mm/cycle; 9 mm over last cycle US

ermanent displacement rate constant at 3.5 mm/102 cycles MS

. Initial permanent displacement rate 0.5 mm/cycle; 21 mm over last US

verage permanent displacement rate: 8.5 mm/102 cycles, increasing MS

er last cycle US3

Foundations 52 (2012) 723736 731the tensile maximum (600 kN compression versus500 kN tension). This trend continued up to the timewhen the loads were adjusted to give equal increments oftension and compression load maxima from N=17. Fromthis point the displacement amplitudes increased sharply.The resumed balanced cycling imposed after N=21 led toprogressively increasing upward pile head displacements.Failure occurred after 20 further cycles of growingamplitudes and uplift drift. The post-cycling tensioncapacity (620 kN) was close to the maximum cyclictension. The overall tension capacity loss is estimated as2629%.

After rst cycle, permanent displacement rate o1 mm/10 cycles Sage permanent displacement rate: 7.7 mm/102 cycles, higher at start MS

permanent displacement rate around 4.0 mm/102 cycles, increasing US

US

permanent displacement rate around 3.5 mm/102 cycles, increasing US

rage permanent displacement rate: 4.6 mm/102 cycles, increasing US

lly tending to settle, changing sign of permanent displacement rate US

out 83 mm overall in 5 cycles US

y increasing permanent displacement rate and amplitudes over nal US

0 0.5 1 1.5 2 2.5 3 3.5Displacement (mm)

0

200

400

600

800

1000

Load

(kN

)

Fig. 11. Load-displacement curves over 1000 cycles for stable tension

cycle test: 3.R4.CY6.

0 1 2 3 4 5 6Time (hours)

0

5

10

15

20

25

30

35

40

45

Dis

plac

emen

t (m

m)

N=50N=100

N=150N=200

Fig. 12. Displacement-time trace over 208 cycles for typical metastable

tension cycle test 3.R6.CY6.

0 5 10 15 20 25 30 35 40 45Displacement (mm)

0

200

400

600

800

1000

1200

1400

1600

Load

(kN

)

Fig. 13. Load-displacement curves over 208 cycles for typical metastable


0 5 10 15 20 25 30 35 40 45 50Displacement (mm)

0

500

1000

1500

2000

Load

(kN

)

Fig. 14. Load-displacement curves over 41 cycles for typical unstable


0 0.5 1 1.5 2 2.5 3Time (hours)

-800

-600

-400

-200

0

200

400

600

800

Load

(kN

)

Stage IStage I Stage II

Fig. 15. Load-time trace over 41 cycles for two-way unstable cycle test

2.C1.CY3.

0 0.5 1 1.5 2 2.5 3Time (hours)

-20

-15

-10

-5

0

5

10

15

20

25

30D

ispl

acem

ent (

mm

)

N=17 N=21

N=40

Fig. 16. Displacement-time trace over 40 cycles for two-way unstable

cycle test 2.C1.CY3.

-20 -15 -10 -5 0 5 10 15 20 25 30Displacement (mm)

-800

-600

-400

-200

0

200

400

600

800

Load

(kN

)

Stage I Stage II

Fig. 17. Load-displacement curves over 40 cycles for two-way unstable

cycle test 2.C1.CY3.

RJ Jardine, JR Standing / Soils and Foundations 52 (2012) 723736732

laboratory (simple shear, triaxial or hollow cylinder)experiments. The Dunkerque model was derived fromlaboratory constant volume simple shear tests on a com-parable North Sea dense sand. Atkins (2000) reports howthe approach outlined in Appendix A was extendedsuccessfully into more complex numerical post-predictions(Class C after Lambe, 1973) of the Dunkerque cyclic tests.The predicted numbers of cycles to failure, Nf, are broadlyconsistent with the Dunkerque eld tests, although indivi-

-0.2 0 0.2 0.4 0.6 0.8 1Qmean / Qmax static

0.2

Q 1000

Fig. 18. Interaction diagram based on simplied methodology given in

Appendix A and eld test interpretation for predicting number of cycles

to failure Nf in terms of normalised loading parameters Qcyclic/Qmax and

Qmean/Qmax.

-0.2 0 0.2 0.4 0.6 0.8 1Qmean / Qmax static

0.2

0.4

0.6

0.8

1Q

cycl

ic /

Qm

ax s

tatic

No cyclic failureFirst failureCyclic failure after previous cyclic or static failure

13

3 1

345

24

27>221>200

1241

1

>1000

9206

S

MS

US

S = stable cycle zoneMS = metastable cycle zoneUS = unstable cycle zone

Fig. 19. Interaction diagram indicating inuence of number of cycles N

and normalised loading parameters Qcyclic/Qmax and Qmean/Qmax on cyclic

response along with tentative stable, metastable and unstable cycle zones.

and2.4. Cyclic displacement trends and predictions

Many of the tests showed cyclic displacement ampli-tudes that remained relatively steady until failure wasapproached. As described by Jardine et al. (2005a), multi-ple numerical analyses were made of the Dunkerque piletests with the Imperial College Finite Element Program,ICFEP (Potts and Zdravkovic, 1999, 2001) that utilised thedetailed site characterisation data referred to in theintroduction. While no attempt was made to match theeld rates of permanent displacement or capacity reduc-tions, the ICFEP analyses provided a generally goodmatch for the eld static load test capacities and theload-displacement responses; see Jardine et al. (2005a).They also reproduced the initial eld stiffness responses toload cycling, conrming that the rst loops tted thepatterns expected for the non-linear, anisotropic, pressuredependent, Dunkerque sand. The ICFEP analyses pro-vided further insights into the local distributions of shearstresses acting over the shafts. For example, applying apurely tension cycle applied at the pile head induced two-way cycling failure (i.e. alternating between upward anddownward shaft shear stresses and relative slip) at the topof the shaft that extended down to a depth that dependedon the applied loading level. Similar observations havebeen reported by Jardine (1991, 1994). The analyses alsoestablished the conditions that would promote progressivetop-down degradation, with the two-way cycling zone(and the full mobilisation of tension shaft resistance) migratingdownwards with each cycle under unstable cyclic loading.While the loading patterns that led rapidly to cyclic

failure also tend to show relatively high initial rates ofcyclic displacement, the eld tests did not indicate a simplelink between rates of permanent displacement and thenumber of cycles to failure; see Table 4. Further analysis ofthese data is in hand; Tsuha et al. (2012) argue that thepermanent displacement and capacity reduction trendsdepend on the complexities of relatively small-strain kine-matic yielding, dilatancy in the soil mass and local graincrushing under interface shear.

2.5. Combined interactive cyclic failure criteria

Interaction diagrams express how the number of cyclesN and the normalised loading parameters Qcyclic/Qmax staticand Qmean/Qmax static act together to determine theresponse to uniform load cycling. Figs. 18 and 19 sum-marise these interactions for the Dunkerque tests. The rstplot reproduces the linear interpretation made by Jardineand Standing (2000) of the combinations of cyclic andmean shaft loads required to bring about cyclic shaftfailure in specied numbers (Nf) of regular cycles. Withthis are shown the positions of Nf lines obtained byapplying the Jardine et al. (2005b) predictive approachset out in Appendix A as calibrated for conditions at

RJ Jardine, JR Standing / SoilsDunkerque. The latter model involves tting the empiricalparameters A, B and C to either pile load tests or cyclic0.4

0.6

0.8

1

cycl

ic /

Qm

ax s

tatic

Nf = 1

4

10

2040

100200400

n.b. full lines derived from Equation A2(Appendix A) with A = -0.126, B = -0.10and C = 0.45; broken lines represent interpretation of Dunkerque field tests.

Foundations 52 (2012) 723736 733dual tests could deviate from interpreted lines signicantly.Precise predictions are hard to obtain (see Figs. 18 and 19).

radsimtorycycl

denintecha

1.

2.

3.

4.

5.

6.

andFig. 19 extends the interpretation by proposing boundariesfor the stable, metastable and unstable cyclic zones ofbehaviour. The individual tests are also plotted and allbut two tests conform to the proposed stable (S), unstable(US) and metastable (MS) cycle response zones. Theboundaries do not appear to be sensitive to whetherthe piles had experienced prior cyclic or static failure, butmore comprehensive testing might identify a more signi-cant inuence.

2.6. Insights offered into fundamental processes affecting

cyclic stability and degradation

Tsuha et al.s (2012) model pile experiments withmedium dense ne silica sand led to broadly similar resultsto the eld tests, including closely comparable interactiondiagrams. The highly instrumented Mini-ICP experimentsoffer further insights into the local effective stressesapplying on pile surfaces and within the sand mass duringcycling.Stable cycle loading conditions were shown to (i) avoid,

over most of the shaft, local interface slip and (ii) generateeffective stress paths to the adjacent soil mass that remainprincipally within the Y2 threshold kinematic yield sur-face, as dened by Jardine et al. (2001), or Kuwano andJardine (2007). Behaviour could be locally inelastic at theinterface, but there was no large-scale tendency for radialcontraction. Modest top-down progressive degradationmight develop, but this was balanced by capacity growthelsewhere. Overall, shaft capacity increased by up to 20%as an optimised soil fabric developed.Unstable cycle loading conditions invoked markedly

inelastic behaviour. The soil mass contracted and lostmean effective stress, and local slip developed progressivelyas s0r reductions took place at the interface where acompacted and fractured shear zone grew in thickness.Shaft failure took place in less than 100 cycles, governedby a Coulomb failure law that was well-predicted byinterface ring shear tests. Hysteretic buttery-wingeffective stress paths were observed on the shaft alongwith progressive top-down failure. Displacements couldgradually accelerate (as in 2.R3.CY2) or reverse undertwo-way loading, as in 2.C1.CY2. Shaft capacitiesdegraded markedly and failure took place with No100.Metastable cycle loading led to an intermediate pattern.

Interface slip, hysteretic stress paths, mean stress statemigration and shaft capacity reductions could all develop,depending on the cyclic loading levels imposed. However,hundreds of cycles could be sustained before failure, andmarkedly plastic (post Y2) behaviour was concentratedclose to the shaft. It is interesting that the metastablemodel tests could develop either modest capacity losses orgains, depending on the severity of cycling.Any advanced numerical modelling performed to match

the above features would require constitutive models

RJ Jardine, JR Standing / Soils734capable of capturing the cyclic soil element response,including the growth of permanent displacements, localcapacity.7. Low-level cycling can have benecial effects on pile

capacity, and piles can self-heal with time after modestlosses of cyclic capacity. Tension capacity gains of upto 20% have been developed after applying stablecyclic loading to piles in eld and model tests.

8. High-level cyclic loading can impact very signicantlyon shaft capacity.

9. Associated numerical studies and instrumented modelpile tests show that stable cyclic loading conditionsavoid interface slip over most of the shaft length, andkeep the soil stress paths primarily within the Y2threshold kinematic yield surface. Any modest degra-dation developed over the upper shaft is balanced bycapacity growth elsewhere.10.reported by Tsuha et al. (2012).The simplied procedures outlined by Jardine et al.(2005b) provide a good quantication scheme formodelling and predicting the effects of cycling on shaftaffect cyclic response. The diagram interpreted forDunkerque captured key aspects of the 14 testsperformed and has a similar pattern to the model testsled to less symmetric and a more progressive style ofdegradation.Interaction diagrams express how the cyclic loadingparameters N, Qcyclic/Qmax static, and Qmean/Qmax staticby the current tension capacities: Qcyclic/Qmax static, andQmean/Qmax static.High-level cycling under one-way and two-way condi-tions invoked quite different responses. The latter gavescope for higher normalised cyclic loading levels thatpromoted more severe cyclic losses, while the formercapacity on unloading after brittle rst time failures.Capacity recovered partially with time after cyclic orstatic failure, but at relatively modest rates, leading todiscontinuous time-capacity traces.Cyclic loading led to stable, metastable or unstableresponses, depending on the loading levels normalisederiments. Twelve main conclusions follow.

The piles developed substantial increases in tensionresistance with time. However, aged piles lost shaftprocexpormed on large open-ended steel pipe piles driven inse silica Dunkerque marine sand. The results have beenrpreted with reference to: the comprehensive siteracterisation; numerical analyses; simplied designedures and related highly instrumented model pileMperfultiple static and cyclic loading experiments have been3. Sial effective stress and shaft capacity changes. Theplied procedures set out in Appendix A apply labora-based constant normal stiffness or constant volume

ic shear test data to predict the effects on capacity.

ummary and conclusionsFoundations 52 (2012) 723736The same studies show that unstable cyclic loadingconditions invoke markedly inelastic behaviour in the

environmental loading.

of Dunkerque, France.

APcycof D

Tet aradload

Ds0r

somducT

que

1

2.

3.

5.

7.

8.

9.

and FoundN in place of the N term may be more applicable ine cases. Cyclic soil element, model or eld tests can be con-ted to choose the most appropriate variant and parameters.he key assumptions and steps applied for the Dunker-piles are as follows.

. The entire applied cyclic load is taken in shaftresistance, with base cyclic loading being negligible.Jaloghe analysis ows from Eq. (A1) as given by Jardinel. (2005b) that expresses the changes expected in localial effective stress acting on the pile shaft due to cyclicing.

=s0rc A Btcyclic=tmax static

NC A1

rdine et al. (2005b) note that a variant of adoptingCPENDIX A. Simplied procedure for predictinglic interaction diagram for shaft capacity degradationunkerque piles under cyclic loadingAcknowledgements

The Authors acknowledge funding from the UK Healthand Safety Executive (HSE) and the EU and thank thePort Autonome de Dunkerque for providing the site. Theyalso acknowledge the contributions of Mr Eric Parker ofDAppolonia (Italy); Precision Monitoring and Control(UK); Dr Nebojsa Kovacevic of GCG (UK); formercolleagues at Imperial College, Dr Fiona Chow, Dr ReikoKuwano and Mr Tim Connolly; the UK BuildingResearch Establishments in-situ testing team and Simecsolfrom the rst cycle. Top-down progressive failuredevelops; displacements can accelerate monotonicallyin one-way tests or reverse under two-way loading.Failure occurs within 100 cycles and shaft capacitydegrades strongly.

11. Metastable cyclic loading leads to an intermediatemechanical response at the pile-soil interface. Interfaceslip, hysteretic stress paths, mean stress state migrationand shaft capacity reductions could all develop, depend-ing on the cyclic loading levels imposed. While pilescould sustain hundreds of metastable cycles withoutfailing, signicant capacity losses were noted in all fourof the metastable cyclic loading Dunkerque eld tests.

12. Cyclic loading can degrade pile capacity and stiffnessmarkedly and its effects should both be researchedfurther and addressed more routinely when designingfoundations that carry a high proportion of variabless

and and at the shaft-sand interface, leading to locallip (governed by a Coulomb law) and soil contraction

RJ Jardine, JR Standing / SoilsThis assumption is marginally conservative in caseswhere some of the loading is compressive.10.shape of the curves that separate stable and meta-stable states.

The effects of non-uniform batches of cycles thatexceed the stable zone limits can be consideredthrough a moving equivalent cycle approach inwhich the cycles are grouped into batches of cycleswith constant amplitudes.

Consider the case where a rst series of Ni cycles isapplied at cyclic load level (Qcyclic/Qmax static)i beforestant Nf well, as shown on Fig. 18.

A further limit is assumed to apply to the levels ofQcyclic/Qmax static below which cycling improves ratherthan degrades capacity. The single stable one-way test atDunkerque showed that this applied for cycling with

Qcyclic=Qmax static Qaverage=Qmax static 0:25

Lower limits will apply at higher values of Qaverage/Qmax static and possibly higher limits at lower averageload ratios. A suggestion is given on Fig. 19 as to the6.DQmax static=Qmax static A BQcyclic=Qmax static NCA2

Direct calibration with the Dunkerque test resultsgives the following values:

A0:126; B0:10; C 0:45

These values reproduce the Dunkerque lines of con-degradation of shaft resistance, and hence overallshaft capacity. The expression for DQstatic shaft resistan-ceDQmax static the loss of static shaft resistancecompared with its original pre-cycling value is then

4.

Nf is the number of cycles to failure).We assume for the Dunkerque tests that the local Eq.(A1) can be applied globally to cover the averages0r given by Eq. (A1) as linear functions of tcyclic/tmaxstatic. Noting that at failure tftcyclictmean thecombinations of tcyclic/tmax static and tmean/tmax staticrequired to reach failure under cycling can beexpressed in an interaction diagram as a familystraight lines, each representing a constant Nf (whereanalysis can be extended to cover interface dilation incases where this is important.Neglecting interface dilation leads to local shaft pilecapacity being given by tfs0rf tan d and the changein tension capacity can be calculated from the changesthat pile loading will engender such a component ofradial effective stress change that is inversely relatedto pile radius. While this contribution can be signi-cant for small piles, it is relatively minor (o15%) forthe industrial-scale Dunkerque piles. Naturally, theWe can neglect the effect of constrained interfacedilation on shaft capacity. The ICP approach predicts

ations 52 (2012) 723736 735moving to the next (i1)th batch involving Ni1cycles applied at load level (Qcyclic/Qmax static)i1.

11. The equivalent number of cycles NEquivalent that wouldneed to have been applied at the i1 level to producethe same degree of degradation as that developed inthe preceding (ith) set is calculated as

DQmax static=Qmax static A B Qcyclic=Qmax static

i

NCi

A B Qcyclic=Qmax static

i1

NCEquivalent

so that

B Qcyclic=Qmax static

i

NCi

B Qcyclic=Qmax static

i1

NCEquivalent

giving

Refe

Atkin

Brucy

sa

O

Chow

O

C

Jardine, R.J., 1991. The Cyclic Behaviour of Offshore Piles. Chapter.

In: Brown, OReilly (Eds.), The Cyclic Loading of Soils. Blackie and

Son, Glasgow.

Jardine, R.J., 1994. Offshore Pile Design For Cyclic Loading: North Sea

clays. HSE Offshore Technology Report, OTN 94 157.85.

Jardine, R.J., Standing, J.R., 2000. Pile Load Testing Performed for HSE

Cyclic Loading Study at Dunkirk, France. Offshore Technology

Report OTO 2000 007, Health and Safety Executive, London, two

volumes 60p, 200p.

Jardine, R.J., Kuwano, R., Zdravkovic, L., Thornton, C., 2001. Some

fundamental aspects of the pre-failure behaviour of granular soils.

In: Proceedings of the 2nd International Symposium on pre-failure.

RJ Jardine, JR Standing / Soils and Foundations 52 (2012) 723736736, F., Meunier, J., Nauroy, J.F., 1991. Behaviour of pile plug in

ndy soils during and after driving. In: Proceedings of the 23rd

ffshore Technology Conference, OTC 6514, Houston, pp. 145154.

, F.C., 1997. Investigations Into Displacement Pile Behaviour for

ffshore Foundations. Ph.D. Thesis. University of London, Imperial

ollege.Of

Exrences

s Consultants Ltd., 2000. Cyclic degradation of offshore piles. HSE

fshore Technology Report OTO 2000 013. Health and Safety

ecutive, London.the full set of cyclic batches.NEquivalent Ni B Qcyclic=Qmax static

i

h

= B Qcyclic=Qmax static

i1

i1=CA3

12. The value of NEquivalent is updated by adding Ni1,the number of cycles in batch i1, to nd theequivalent number of cycles at the end of batchi1. The total degradation of capacity at this pointis found by substituting NEquivalent into Eq. (A2).

13. Eq. (A3) is updated again on moving to the next(i2)th batch of cycles, and the process repeated forDeformation Characteristics of Geomaterials, IS-Torino, vol. 2, Swets

and Zeitlinger, Lisse, pp. 1077113.

Jardine, R.J., Standing, J.R., Kovacevic, N., 2005a. Lessons learned from

full-scale observations and the practical application of advanced

testing and modelling. Keynote paper. Proceedings of International

Symposium on Deformation Characteristics of Geomaterials, vol. 2,

Lyon, pub Balkema, Lisse, pp. 210245.

Jardine, R.J., Chow, F.C., Overy, R., Standing, J.R., 2005b. ICP Design

Methods for Driven Piles in Sands and Clays. Thomas Telford Ltd.,

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effects of time on the capacity of piles driven in sand. Geotechnique 56

(4), 227244.

Kuwano, R., 1999. The Stiffness and Yielding Anisotropy of Sand. Ph.D.

Thesis. University of London, Imperial College.

Kuwano, R., Jardine, R.J., 2007. A triaxial investigation of kinematic

yielding in sand. Geotechnique 57 (7), 563579.

Lambe, T.W., 1973. Predictions in geotechnical engineering. Geotechnique

23 (2), 149202.

Lehane, B.M., 1992. Experimental Investigations of Pile Behaviour Using

Instrumented Field Piles. Ph.D. Thesis. University of London,

Imperial College.

Lehane, B.M., Schneider, J.A., Xu, X., 2005. A Review of Design

Methods for Offshore Driven Piles in Siliceous Sand. Geomechanics

Group Report GEO 05358. University of Western Australia.

Parker, E. J., Jardine, R.J., Standing, J.R., Xavier, J., 1999. Jet grouting

to improve offshore pile capacity. Offshore Technology Conference,

Houston, OTC 10828, Vol. 1, pp. 415420.

Potts, D.M., Zdravkovic, L., 1999. Finite Element Analysis in Geotech-

nical Engineering: Theory. Pub Thomas Telford, London 440p.

Potts, D.M., Zdravkovic, L., 2001. Finite Element Analysis in Geotech-

nical Engineering: Application. Pub Thomas Telford, London 427p.

Tsuha, C.H.C., Foray, P.Y., Jardine, R.J., Yang, Z.X, Silva, M., Rimoy, S.,

2012. Behaviour of displacement piles in sand under cyclic axial loading.

Soils and Foundations 52 (3), 393410.

Field axial cyclic loading experiments on piles driven in sandIntroductionAim and scope of the present studyGround conditionsTesting programmeEffects of local variations in soil conditions on pile capacityPile testing procedures

Cyclic test results and interpretationStable cyclic loadingMetastable cyclic loadingUnstable cyclic loadingCyclic displacement trends and predictionsCombined interactive cyclic failure criteriaInsights offered into fundamental processes affecting cyclic stability and degradation

Summary and conclusionsAcknowledgementsSimplified procedure for predicting cyclic interaction diagram for shaft capacity degradation of Dunkerque piles under...References

field axial cyclic loading experiments on piles driven in sand

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