Niazi Mayne Woeller 2010 Pakistan Conference

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Review of CPT-based methods for responseevaluation of driven piles in dense sands.

Conference Paper December 2010

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3 authors, including:

Fawad Niazi

Georgia Institute of Technology

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Paul W. Mayne

Georgia Institute of Technology

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International Conference onGeotechnical Engineering

November 5-6, 2010Lahore, Pakistan

International Conference on

Geotechnical Engineering

November 5 6 2010

Lahore Pakistan

Proceedings of theroceedings of the

Editors:

Sohail KibriaHamid Masood QureshiArooj Mahmood Rana

Editors

Sohail Kibria

Hamid Masood Qureshi

rooj Mahmood Rana

National Engineering ServicesPakistan (Pvt.) Ltd.

Universityof Engineering & TechnologyLahore, Pakistan

Associated Consulting Engineers (Pvt.)Ltd. Lahore, Pakistan

Pakistan Geotechnical Engineering Society (PGES)

In Association With


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INTRODUCTIONPile response to axial loading consists of evaluat-

ing the ultimate capacity for design (Qult = Qt),transfer of Qt to the pile shaft (Qs) and the base

(Qb), and pile settlements for different loads, tradi-tionally termed as the load-settlement response.Load-settlement response for pile compressibilitycan be accounted for by evaluating the total settle-

ments corresponding to total, shaft and base loads(wtvs. Qt, wtvs. Qs, and wtvs. Qb), and base set-

tlements corresponding to base loads (wb vs. Qb).Pile load tests are conducted on instrumented piles,

involving colossal effort, time, and money, besidesensuring redundancy of costly instrumentation tocompensate for expected damage during driving orcasting. Nevertheless, the readings are not perfect-

ly reliable, more so, in case of damage to the in-

struments, which is commonplace during thesetests. Subsurface soil strata affecting the perfor-mance of these foundations are characterized usingthe conventional boring and sampling methods,which are time consuming and tedious, besides thelimitations of sample disturbance. Site investiga-tions for the driven piles in the offshore environ-ment are much more affected by the aforemen-

tioned specifics.

Seismic piezocone tests (SCPTu) provide an alter-nate, yet quick and reliable means of obtaining

geotechnical parameters via well established corre-lations from 4 separate readings: [total tip resis-

tance (qt), sleeve friction (fs), tip (u1) or shoulder(u2) porewater pressure, and shear wave velocity(Vs)]. Pile foundations analysis can be performedusing multiple-readings-based methodologies. The

penetrometer readings (qt,fs, u1or u2) allow for theevaluation of Qult. At the opposite end of the stress-

strain-strength response, the initial soil deforma-

tions (for shear strains s< 10-6%), and the small

strain stiffness (Gmaxor Emax) can be obtained fromthe Vs. Applied within the elastic continuum

framework, these results enable evaluation of thecomplete load-displacement-capacity response forthe axial loading performance of deep foundations

(Randolph & Wroth 1978, 1979).

SITE CHARACTERIZATIONSCPTu data can be used to evaluate the soil strataat a site in terms of soil classification and engineer-ing parameters to estimate the pile capacity. Asummary of the selected established correlations isgiven in Table 1.

Review of CPT-based Methods for Response Evaluation of Driven Piles

in Dense Sands

F.S. NiaziGeorgia Institute of Technology, Atlanta, Georgia, USA ([email protected])

P.W. MayneGeorgia Institute of Technology, Atlanta, Georgia, USA ([email protected])

D.J. Woeller

ConeTec Investigations Ltd., Richmond, British Columbia, Canada: ([email protected])

ABSTRACT: The response of deep foundations to axial loading can be evaluated from the profiles of 4 inde-pendent readings provided by the Seismic Piezocone Tests (SCPTu): qt,fs, u1or u2, and Vs. Established corre-lations are used to assess geotechnical parameters at the site for pile capacity evaluations. Alternatively, CPTreadings are used for direct capacity evaluations. Vsreadings enable estimation of the soil stiffness (Gmax), al-

lowing derivation of the load-settlement response by integrating elastic solutions with the Gmax softeningschemes. A review of selected methods is presented relevant to the EURIPIDES case study illustrating the

application of SCPTu results for the response evaluation of driven pipe piles in dense sands.

259
https://www.researchgate.net/publication/279903835_Analysis_of_Deformation_of_Vertically_Loaded_Piles?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/293341486_SIMPLE_APPROACH_TO_PILE_DESIGN_AND_THE_EVALUATION_OF_PILE_TESTS?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/279903835_Analysis_of_Deformation_of_Vertically_Loaded_Piles?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/293341486_SIMPLE_APPROACH_TO_PILE_DESIGN_AND_THE_EVALUATION_OF_PILE_TESTS?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==


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TABLE 1 Summary of CPT-based Correlations for Site Characterization.

Relationship Soil type Reference

Soil Classification

a3 1 1 1.5 1.3 All Jefferies & Been 2006Total Unit Weight

t= 1.95w(vo'/atm)0.06(fs/ atm)

0.06 All Mayne et al. 2010

t(kN/m3)=11.46+0.33log[z(m)]+3.1log[fs(kPa)]+0.7log[qt(kPa)] All Mayne et al. 2010

t(kN/m3) = 8.32log[Vs(m/s)] + 1.61log[z(m)] All Mayne 2007

Effective Stress Friction Angle, c'(deg.) = 17.6o+11.0log(qt1); where qt1= (qt/atm)/(vo'/atm)

0.5 Sands Kulhawy & Mayne 1990a, d' (deg.) = 29.5 Bq

0.121[0.256 + 0.336 Bq+ logQ] Clays Senneset et al. 1989

Shear Wave Velocity

Vs(m/s) = {10.1log[qt(kPa)] 11.4}1.67[fs(kPa)/qt(kPa) 100]

0.3 All Hegazy & Mayne 1995Vs(m/s) = 118.8log[fs(kPa)] + 18.5 All Mayne 2006

Soil Stiffness (Modulus)

Gmax= T Vs2; where, tis the total mass density = t/ga; and gais the

gravitational acceleration constant = 9.8 m/s2

All Timoshenko & Goodier1951

Emax= 2 Gmax (1 + )eDrained: d0.2, Undrained: u0.5

AllLehane & Cosgrove 2000

G/Gmax= 1f(/max)g1 f(Qop/Qult)

g1f(1/FS)g All Fahey & Carter 1993

Geostatic Lateral Stress Coefficient

Ko= ho'/vo' = (1 sin') OCRsin', where ho' is the horizontal

effective stress; OCRis the overconsolidation ratio = p'/vo'

All Kulhawy & Mayne 1990

Stress History

p'=0.33(qtvo)

m

(atm/100)

1-m

, where m=0.65+1/(80010

-Ic

+2.5)All Mayne et al. 2010

p' = 0.101 atm0.102 Gmax

0.478 vo'0.420 All Mayne 2007

OCR= {[0.192(qt/atm)0.22]/[(1 sin')(vo'/atm)]}

{1/(sin' 0.27)} Sands Mayne 2005

Relative Density

DR= 100{qt1/(300OCR0.2)}0.5 Sands Kulhawy & Mayne 1990

DR= 100{0.268ln(qt1) 0.675} Sands Jamiolkowski et al. 2001

Normalized Undrained Shear Strength

Ladd & Degroot 2003g(su/vo')OC= (su/vo')NCOCR= sin' OCR Clays

aQ=(qtvo)/vo', Bq=(u2uo)/(qtvo), F=fs100/(qtvo), and vo' (effective vertical stress) = vouo; vo (total overburden

stress) = tizi, uo(hydrostatic porewater pressure) = whw; hwis the height of water, tiandziare the total unit weight and

depth of ithsoil layer, respectively, and w(unit weight of water) = 9.8 kN/m

3.IC: clays: 2.82


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PILE CAPACITY EVALUATION FROM CPTThe total axial compression capacity (Qt) of a cir-cular pile foundation is calculated from:

Qt= Qs+ Qb= (fpiDLi) + qbD2/4 (1)

wherefpiis the unit side resistance

DLiis the shaft area of the ithsoil layer

Dis the pile diameter.fp and qbvalues can be calculated using the engi-neering parameters obtained from the aforemen-

tioned, using the so called indirect methods: -method and limit plasticity solutions.

Certain methods, derived to scale the data fromcone penetration tests up to fp and qb, also allowuse of the CPTu measured readings for the directcapacity evaluations. Selected methods applicableto driven piles, used for the case study presented in

this paper are summarized in Table 2.

The axial capacity of piles in tension is primarilyderived from side shear. DeNicola & Randolph(1993)showed that the tensile side capacity, QsTis

less than that in axial compression (QsC) via:

QsT/QsC={10.2log[100/(L/D)]}(18+252) (2)

where

=ptan(L/D)(Gavg/Ep),

tan=CMtan',

is the soil-pile interface friction,

pis the Poissons ratio of the pile,Gavg=average shear modulus along the pile length,

LEp=pile modulus

LOAD-SETTLEMENT RESPONSE

The pile response in terms of settlement and axialload transfer (Qsand Qb) can be evaluated from the

closed-form elastic pile solution given by Ran-dolph & Wroth (1978, 1979) (see Fig. 1). Themodulus reduction corresponding to operationalload can be conveniently applied in this solution. It

accounts for homogeneous as well as Gibson typesof soils. It also encompasses the floating- and end-

bearing type piles. Fig. 1 also shows a model pro-posed for layered soils in which the capacity of

each pile segment embedded in ith layer can be

evaluated. The load-displacement response foreach segment of the pile embedded in i

thlayer cor-

responding to the load transferred through thatlayer can be conveniently obtained and integratedto evaluate the overall pile response.

CASE STUDY

OverviewAn extensive axial pile load tests program, the Eu-ropean initiative on piles in dense sands (EURI-

PIDES), was conducted on a highly-instrumented0.76m diameter pipe pile driven open-ended in

dense sands at Eemshaven, the Netherlands. Itcomprised a series of static compression (C) andtension (T) tests conducted at two locations, 18 mapart [driven and tested at location 1 at threedepths (30.5m, 38.7m and 47m), extracted and re-driven and tested at location 2 at 46.7m depth]. De-tails on the load test program, equipment, instru-

mentation and results have already been published(e.g., Fugro 2004, Kolk et al. 2005a, Zuidberg &Vergobbi 1996). Later researchers have also at-tempted to evaluate the capacities of these piles us-

ing several design methods.

Soil profile at the site was characterized based onthe site investigations from three boreholes (BH),seven CPTu, two SCPTu, and laboratory investiga-tions (Zuidberg & Vergobbi 1996). Most of theCPTu soundings portrayed comparable qc, fs, u1

and Vs profiles. Selected results of CPTu andSCPTu are shown in Fig. 2, being closest to thepile load test conducted at location 2, which isthe focus of this study [separate study for location1 has already been done by the authors (Niazi &Mayne 2010)]. Soil at this site consists of a se-

quence of Holocene and Pleistocene fine to me-dium, dense to very dense sands extending from

the water table [~1.0m below ground level (bgl)] toin excess of 60m. Very dense over consolidatedsands occur from about 25m bgl to at least 68mdepth. Holocene sands extend to about 22 m depth

with an average qcof 5.8 MPa. Below that, the qcvalues vary between 20 and 90 MPa (Zuidberg &Vergobbi 1996). Soil conditions evaluated from

the bore holes are also presented in Fig. 2.

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https://www.researchgate.net/publication/240504654_Tensile_and_Compressive_Shaft_Capacity_of_Piles_in_Sand?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/240504654_Tensile_and_Compressive_Shaft_Capacity_of_Piles_in_Sand?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/279903835_Analysis_of_Deformation_of_Vertically_Loaded_Piles?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/279903835_Analysis_of_Deformation_of_Vertically_Loaded_Piles?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/293341486_SIMPLE_APPROACH_TO_PILE_DESIGN_AND_THE_EVALUATION_OF_PILE_TESTS?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/290727768_Results_from_axial_load_tests_on_pipe_piles_in_very_dense_sands?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/254538883_EURIPIDES_Load_Tests_on_Large_Driven_Piles_in_Dense_Silica_Sands?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/254538883_EURIPIDES_Load_Tests_on_Large_Driven_Piles_in_Dense_Silica_Sands?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/254538883_EURIPIDES_Load_Tests_on_Large_Driven_Piles_in_Dense_Silica_Sands?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/263773174_Evaluation_of_EURIPIDES_pile_load_tests_response_from_CPT_data?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/263773174_Evaluation_of_EURIPIDES_pile_load_tests_response_from_CPT_data?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/254538883_EURIPIDES_Load_Tests_on_Large_Driven_Piles_in_Dense_Silica_Sands?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/254538883_EURIPIDES_Load_Tests_on_Large_Driven_Piles_in_Dense_Silica_Sands?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/279903835_Analysis_of_Deformation_of_Vertically_Loaded_Piles?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/279903835_Analysis_of_Deformation_of_Vertically_Loaded_Piles?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/293341486_SIMPLE_APPROACH_TO_PILE_DESIGN_AND_THE_EVALUATION_OF_PILE_TESTS?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/263773174_Evaluation_of_EURIPIDES_pile_load_tests_response_from_CPT_data?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/263773174_Evaluation_of_EURIPIDES_pile_load_tests_response_from_CPT_data?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/240504654_Tensile_and_Compressive_Shaft_Capacity_of_Piles_in_Sand?el=1_x_8&enrichId=rgreq-ad553cafb27d5f34e9abdd171f162b4a-XXX&enrichSource=Y292ZXJQYWdlOzI2Mzc3MzQ3NztBUzozNzEwOTQ0NjU4NTk2MTZAMTQ2NTQ4NzIyMzc5OA==https://www.researchgate.net/publication/240504654_Tensile_and_Compressive_Shaft_Capacity_of_Piles_in_Sand?el=1_x_8&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TABLE 2 Some CPT-Based Design Methods for Unit Side and Base Resistances applicable to Driven Pipe Piles

Methods Design Equations Reference

Pile unit side resistance (fp) Pile unit end bearing (qb)

Indirect Methodsa-Method fp= CMCKKovo' tan ' Kulhawy et al.

1983

Limit plasticity Drained: qb= 0.1*Nqvo' Lee et al. 2003;Vesic 1977Undrained: qb= *Ncsu

cNGI ForNCclays with < 0.25:

fp= NC

NC

vo' = 0.32(Ip10)0.3

NC

vo'

For OC clays with > 1:

fp= suUU

Ftip= 0.570.3su

DSSFtip

For clays with 0.25 12 MPa: = 200 (fpmax= 0.12 MPa), soft clay with qc< 1 MPa: = 30 (fpmax= 0.015 MPa); kcis thepenetrometer bearing capacity factor with values for different material corresponding to steel pipe pile: silt & loose sand with

qc12 MPa: kc= 0.4. For open ended pipe piles, full values of kcshould only be adopted once it is established that plug occurs

under the pile tip capable of taking up the load equivalent to close ended pile. qcfor qbis the average value betweenL+ 1.5D.eqEis the effective cone resistance = qt u2(in MPa); qtis the cone resistance corrected for shoulder pore water pressure (u2)

= qc+ u2(1an); an= ratio between shoulder area (cone base) unaffected by the pore water pressure to total shoulder area; Cse

is the side correlation coefficient found from the zones in the UniCone soil classification chart using qE(in MPa) andfs(in

kPa): zone 2 (soft clay and silt, Cse= 0.05), zone 4 (silty sandy mixtures Cse= 0.01), and zone 5 (sands Cse= 0.004); Cte= toe

correlation coefficient, generally taken as 1. For pile diameterD> 0.4 m, Cte= 1/(3D), whereDis in m.fhis the height above pile tip; R* is the equivalent pile radius = (R

2Ri

2)0.5

whereRiis the internal pile radius = Di/2; atm=100 kPa; qc,avgis the average value of measured tip resistance betweenL+ 1.5D;Aris the area ratio = 1(Di/D)

2.

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Fig.1 Elastic pile solution for load-displacement response.

The pile load test program was designed to providepile-soil interaction data below 22m bgl. The pilecomprised 27m long instrumented section. Load

tests were performed for head displacement of 0.1D(tension) and 0.25D (compression). Load testsmeasured load-displacement at the pile head and at adepth of 22 m bgl, friction along pile shaft and end

bearing. Axial force at the pile base was computedfrom strain gauges 0.38m above the pile tip.

The measured u1readings were converted to u2via

the relationships: u20.742u1for clay and silt lay-ers (Chen & Mayne 1994), and u2u1for sand lay-ers (Bruzzi & Battaglio 1987). The site consisted,essentially, of sand, the overall effect was consi-dered minimal. qcvalues were also taken as compa-rable to qt, since correction is not considered

paramount for granular soils (Mayne 2007).

Site Characterization from CPT ResultsSoil engineering parameters were evaluated using

the correlations from Table 1. Fig. 3 presents the re-sults obtained by the post processing of mean values

from CPTu.

Capacity Evaluation from CPT-based Methods

Qb and Qswere calculated using different CPT based

methods given in Table 2. Soil strata at the site were

divided into seven layers keeping in view the soil

profile and pile embedment depth, L = 46.7m. Qs

was calculated from summation of the individual

side capacities through each layer (i.e. Qsi), which

in turn were found as shown in Fig. 1. The mean

values of Gmax, calculated for each layer (see Fig. 4),

were then used to find settlements corresponding todifferent load levels for those layers.

Fig.2 CPTu and SCPTu Soundings at Location 2 of EURIPIDES Project (after Fugro 2004).

Compressible pile solution:

Ro = Do/2 = pile radiusRb = Db/2 = pile base radius= rb/ro = eta factor (bell-shaped pier)Ep = pile modulusG

sL

=soil shear modulus at z=LGso = soil shear modulus at the pile topGsb = soil stiffness below the pile baseGsM = soil shear modulus at mid-shaftE = GsM/GsL = Gibson parameter

= Ep/GsL = pile-soil stiffness ratio = GsL/Gsb = xi factor = ln(rm/ro) = zeta factorrm = L{0.25 + [2.5E(1)0.25]}L = 2(2/)0.5(L/D) = mu factorwti = settlement at top of pile segmentwi = settlement of individual pile segmentwb = pile base settlementEb = soil Youngs modulus below pile base

Pile

Pile Length L

GsL

z = Depth

Pile diameter D

Qt

Gso1

Loadtransferto base:

Gsb

GsM

Qb

Qs

Shaft load distribution:Qs = QtQb

Layered soil load andsettlement distribution:

L1

L2

L3

Layer 1

Layer 2

Layer 3

Qt1 = Qs1 = fp1D1L1wt1 = wt2 + w1

Qt2 = Qs2 = fp2D2L2wt2 = wt3 + w2

Qt3 = Qs3 + QbQt3 = fp3D3L3 + Qbwt3 = w3 + wb

GsL1

GsL2

Gso2 = Gsb1

Gso3 = Gsb2

GsL3Gsb

Pile basedisplacement:

Gso

G =Gmax[1 f(Q/Qt)g]

Operational soil modulus:

0 0.4 0.8 1.2 1.6

Sleeve Friction, fs (MPa)

CPTu 40

CPTu 41

SCPTu 42

0 0.3 0.6 0.9 1.2

Porewater, u1 (MPa)

CPTu 40

CPTu 41

SCPTu 42

uo

Soil Profile

FINE SAND, medium to verydense(0to 5.3 m)

FINE SAND, sil ty, mediumdense (5.3 to16.0 m)

Alternating layers of softC LAY, loose sandy S ILT &FINESAND (16 to21.8 m)

FINE to MEDIUM SAND,local ly s il ty, medium dense(21.8to 25.0 m)

FINE to MEDIUMSAND, silty,medium to dense (25 to 27.5m)

FINE to MEDIUM SAND,sligh tly to very s ilty, verydense (27.5to 41.5 m)

SILT (41.5TO 42.8 m)

FINE to MEDIUM SAND, siltyto very sil ty,very dense (42.8m to max. depth of investigation)

0

10

20

30

40

50

60

0 20 40 60 80

D

epth(m)

Tip Resistance, qc (MPa)

CPTu 40

CPTu 41

SCPTu 42

0 100 200 300 400 500

Shearwave, Vs (m/s)

SCPTu 42

SCPTu 36

263


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algorithm. 'f' and 'g' parameters were adjusted start-

ing with reference values of 1 and 0.3, respectively,and varying within the ranges given in Table 1 to fitthe measured results. Cumulative load-displacementcurves for the compressiontensioncompression(C1TC2) tests, shown in Figure 6, were obtainedby integrating individual responses of seven layers

and the base, yielding comparable results to themeasured values.

Fig.5 fpand qb profiles from different CPT-based me-thods for EURIPIDES pile load tests.

TABLE 3 Pile Base and Shaft Capacities from differentCPT-based Methods

MethodBase Capacity, * Shaft Capacity,

Qb(MN) Qs(MN)

LCPC 10.02 7.82

UniCone 12.83 14.45

Limit Plasticity 6.85 -

Beta - 13.07

NGI 5.10 14.76

Fugro 6.57 11.10

* Qs= fpiDiLi

CONCLUSIONSPile load tests conducted at the EURIPIDES projectsite in dense sands have been reviewed. A metho-dology of applying SCPTu readings to evaluate theaxial pile performance including the load-displacement-capacity behavior and axial load trans-fer with depth is presented. A considerable scatter in

the estimates of fpand qbwas observed from differ-ent capacity design methods. Drof sand in addition

to soil layering and pile type/geometry appears to

affect the applicability of these methods. In this

case, averaging of fpvalues yielded results compa-rable to the measured values. NGI method affordedbest results for qb. The load-displacement responsethrough the layered soil profile was assessed fromthe elastic solution along with the modulus reduc-tion scheme to account for the soil nonlinearity. In-

dividual responses of pile segments embedded indifferent soil layers were found and the overall re-sults were obtained by integrating them all together.

Fig.6 Load-displacement response for EURIPIDES pile

load tests (measured and evaluated).

ACKNOWLEDGEMENTS

The authors gratefully acknowledge the assistanceof Philippe Jeanjean of BP America Inc. and Harry

J. Kolk of Fugro Engineers B.V. who provided thefield test data.

REFERENCEBruzzi, D. & Battaglio, M. (1987). Pore pressure mea-

surements during cone penetration tests. Report No.229, I quaderni dellISMES, Experimental Institute for

Models and Structures, Milan, 125p.Bustamante, M. & Gianeselli, L. (1982). Pile bearing ca-

pacity predictions by means of static penetrometer CPT.Proc. 2nd European Symp. on Penetration Testing,

ESOPT-II, Vol. 2, Amsterdam: 493500.Clausen, C.J.F., Aas, P.M. & Karlsrud, K. (2005). Bearing

capacity of driven piles in sand, NGI approach. Proc.Int. Symp. on Frontiers in Offshore Geotechnics,IS-

FOG,Taylor&Francis, London:677681.

Chen, B.S.Y. & Mayne, P.W. (1994). Profiling the over-consolidation ratio of clays by piezocone tests. ReportGIT-CEEGEO-94-1 , Civil Engineering, Georgia Insti-tute of Technology, Atlanta, 280 p.

-15

-10

-5

0

5

10

15

20

25

30

0 50 100 150 200 250 300 350

Force(MN)

Pile Head Displacement (mm)

Qt Measured

Qt Elastic Solution (C1)

Qs Elastic Solution (C1)

Qb Elastic Solution (C1)

Qt=Qs Elastic Solution (T)

Qt Elastic Solution (C2)

C1

C2

T

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Documents

Niazi Mayne Woeller 2010 Pakistan Conference