2001 - nlc-bnc.ca · At-rest Iateral earth pressure coefficient Initial in- situ vertical effective stress Upper Iirnit of the lateral stress coefficient Lirniting incremental unit

Shalt Resistance of a Single Vertical or Batter Pile in Sand Subjected to Axial

Compression or Uplift Loading

Mohab Sabry

A Thesis

in

The Department

of

Building. Civil and Environmental Engineering

Presented in Partial FuIfillment of the Requirernents for the Degree of Master of Applied Science at

Concordia University Montreal, Quebec, CANADA

May 200 1

O Mohab Sabry, 2001

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Shaft Resistance of a Single Vertical or Batter Pile in Sand Subjected to Axial

Compression or Uplift Loading

Mohab Sabry

The cases of shaft resistance of a single vertical or batter pile in sand subjected to

compression or uplift loading have been investigated. Several theories and design

procedures can be found in Iiterature for vertical piles however little information can be

found for batter piles.

Numeiical model has been deveIoped using finite element technique to analyze

the problem stated. The result of this numerical model together with the experimental

d m produced at Concordia university as well as other field and experimentd data

available in literature have been used to examine the shaft resistance of these piles.

it is of interest to note that beside the goveminp parameten listed in literature,

the pile diameter play a paramount role in detennining the shaft resistance of these piIes.

Design procedures have been presented to predict the Shaft Resistance of a Single

Vertical or Batter Pile in Sand Subjected to Axial Compression or Uplift Loading.

ACKNOWLEDGEMENTS

I would like to express my sincere gratitude to my supervisor. Professor A. M. Hanna,

for his valuable guidance, constant support and encouragement that he provided me

throughout the course of this work, which made it possible to complete this research. I

am honored to c w out the present investigation under his supervision.

1 would like to express my deep thanks to my parents. for their full support and

encouragement, without their support this work could not corne to life.

My deep gratitude is due to my wife, for her patience and support during preparation of

this thesis, and to my daughter Bassant.

TABLE OF CONTENTS

LIST OF SYMBOLS LIST OF TABLES LIST OF FIGURES

CHAPTER 1

INTRODUCTION

1. I Pre face

1.2 Research Objectives

CHAPTER 2

LITERATURE REVIEW

2.1 General

2.2 Review of Previous Work

2.3 Discussion and Scope of Preseneted Research

CHAPTER 3

ANALYSIS

3.2 ShaB Resistance for a Single Vertrocal Driven Püe in stand Subjected to Axial Compression l u d 29

3.2.1 Numerical Anrilysis 29 3.2.2 Experimental Investigation 39

3.2.3 Parameters Governing the Shaft Resistance of a Single Verticai Pile in Sand Subjected to axial Compression Load. 42

3.2.3.1 Effect of Pile Length 42 3.2.3.2 Effect of Angle of Friction between Pile and Sand. "8' 47 3.2.3.3 Effect of angle of soi1 Shearing Resistance, "*@ " 51 3.2.3.4 Effect of Pile Dimeter on the Shafi Resistance 51

3.3 Shafl Resistunce For Buîter Piles 58 3.3.1 Effect of Angle of Inclination on the Laterd Exth Pressure 5 8 3 -32 Theoretical Mode1 for Unit Shaft Resistance for Venical and Batter Piles in Sand 63 3.3.3 Design Procedure 70

3.4 Llplifl Capacity of Dn'ven Piles in Sand 3.4.1 Genenl 3.4.2 Paramemc Study 3.4.3 Cornparison Between Axial Compression and Tension Single Piles 3.4.1 Effect of ioading on Radial Stresses 3.4.5 Results 3.3.6 Venfication of Approximate methoci

CONCLUSION AND RECOMMENDATIONS

4.1 Conclusion

4.2 Recornmendations for Furfier Research

REFERENCES

LIST OF SYMBOLS

Symbols Represents

Vertical effective stress

Totai horizontai stress

Pore water pressure

Average shear stress

Shaft resistance Ratio

Laterai Emh- pressure coefficient

Angle of friction between the pile and the soil

At-rest Iateral earth pressure coefficient

Initial insitu vertical effective stress

Upper Iirnit of the lateral stress coefficient

Lirniting incremental unit shaft friction

Incremental reconsolidation lateral stress ratio

Uplift capacity

S haft resistance

Weight of shaft

Pile length

Pile diameter

The soil-shaft effective-stress interface friction angle

Operative coefficient of horizontal soil stress

Shaft resistance parameter

Total passive earth pressure acting on the pile shaft

Ansle of inclination of pile with the vertical

Unit weight of sand

üplif i coefficient for batter piles

Void ratio

Pile circumference

Bearing capacity factors for the pile in tension

Vertical component of the shear stresses

Weight of soi1 wedge bounded by the slip iines

Net ultimate uplift capacity

Poisson ratio

Ideal shaft capacity of pile

Compressibility paruneter

Pnnciple stress rotation

Interface slip Dilation

Coefficient of ewth pressure

Net uplift cripacity factor

mobilized mgle of friction

mobilized angle of shear strength

modulus of elasticity

Coefficient of earth pressure as a function of D and z

Average unit shaft resistance

The Coefficient of earth pressure at a = O

The Coefficient of euth pressure at a = +a

The Coefiïcient of earth pressure at cc = -a

Distance between the pile and the faiiure surface

Distance from the pile base to a certain point o n the pile shïft

Average shear modulus of soi1 over embedded depth of pile

LIST OF TABLES

Table

3.1

3.2

Description

Typical load tests from the numerical model.

Sumrnery of pile load test results for 38mm Diameter pile-

After Hanna & Nguyen (1956)

Summery of pile load test results for 76mrn Diameter pile.

After Hama & Nguyen (1986)

Summery of test results, after Hanna & Afram (1986)

Comparison between the obsemed critical depth and the

theoretical values.

Experimental Test data on 0.76m-mode1 pile test

diameter. After Das (1989)

Experimental data perfomed by Vesic (1967) and

Tavenas (197 1)

Trial and error procedure for the presented model.

Cornparison between experimental data and the present

theory for vertical pile subjected to compression lorici.

Cornparison between experimentd data and the present

theory for batter pile subjected to compression load.

Comparison between experirnental &ta and results from

equation 3.6

Page

38

40

LIST OF FIGURES

Figure Description Page

Assumed distribution of the unit shaft resistance around the pile, after

Hanna and Nguyen (1986) 24

Pile and Failure Surface. after Chattopadhyay and Pise (1986) 26

Sketch of Pile Interface System and View of Boundary Conditions 33

Sketch of the Finite Element Mesh. 34

Shows the Failure Pattern for a pile Under Compression Load. 36

Shaft resistance korn Compression Test (2) in dense sand. After

Mansour & Kaufman (1956)

Shaft resistance from Compression Test in very dense sand. After

Benngen et al (1979)

Shaft resistance from Compression Test in very dense sand. After

Hanna & Nguyen (1986)

Numencal Test Results: The Effect of the pile interface angle of

fnction on the coefficient of eanh pressure from the numericd data.

Numericai Test Results: The Effect of the pile interface angle of

friction on the coefficient of emh pressure from the numencal data 49

Numencai Test Results: The effect of the pile friction ratio 6/4 on the

coefficient of earth pressure, K,. 50

Numericai Test Results: Ks versus Pile Length/Diameter "UD" with

respect to Angle of Sheving Resistmce "@". 53

Experimental Data Shows the Pile Length/Diameter (UD) versus The

Coefficient-of Earth Pressure K,, after, Das (1989) 53

The Relation Between the Average Unit Shaft Resistance, f, and the

Pile Diameter D, after 55

The Relation Between the Average Unit Shaft Resistance and the Pile

Diameter, after Ismail(1986) 56

Average Unit S hafi Resistance, f, versus the ratio of Pile Length /

Diameter, UD, after Das (1 989) 57

(a) Battered pile subjected to axial compression load. (b) Stress

distribution on the pile cross - section.

The Relation between the shaft resistance Qs and the angle of

inclination a for different shearing resistance angles @. eq. (3.4)

The Relation between the shaft resistance Qs and the ande of

inclination a for different shearing resistance angles @. eq. (3 -4) 62

Flow chrirt for the presented method to end with a relation between

(6JQm)avc versus "D" 66

A Chart gives the relation between Pile Diameter and (6J@,),,, with

respect to Pile length /Pile Diameter (UD). 69

The Relation between the Coefficient of Earth Pressure Ks and Pile

Inclination angle a in respect to @. After Caquat & Kensel, (1949). 75

The Relation between the Coefficient of Earth Pressure Ks and Pile

Inclination angle a in respect to $. After Caquat & Kerisel, (1949). 76

A chart to obtain the reduction factor. RI for given $ and S/+. After

Caquat & Kensel, (1949).

A chan to obtain the reduction factor, R2 for given 6 and a/$. After

Caquat & Kerisel, (1949).

The Failure Pattern for Pile under Tension.

The Variation of "x" wit the depth "2'' according to &@ with fixed

"6", from eq (3.5).

The variation of the value of "x" with depth "2" with respect to %/@"

for fixed "@", from eq (3.5)

Skin Friction Profile from Compression and Tension Test in Very

Dense Sand. After Beringen et al, (1979).

Figure 3.34, Skin Friction Profile from Compression and Tension

Test (7 and 6) in Dense Sand. After Mmsour & Kaufman, (1956).

Radial Variation of Radid Suess at Shaft FaiIure (After De Nicola,

1993)

Profiles of Radial Stress at Shaft Failure in Tension and Compression

After De Nicola, (1993)

The ratio between tension and compression shaft resistance with

respect to, IID and for different "8' values

CHAPTER 1

INTRODUCTION

1.1 PREFACE

Pile foundations are recornmended to support high-rise buildings. This type of

foundation is universally accepted for poor subsoil or difficult loading condition. Piles

are also industnally needed especially for offshore structure and communication towers

where the piles may be subjected to compression o r uplift loading. The common factor in

the compression and the tensile capacities for long pile foundations is that they both rely

on the shdt resistance between the pile and the soil.

The estimation of the axial capacity of piles driven into sand involves

considerable uncertainty, and the design rules are generally not consistant with the

physicd processes involved. The methods generaly used to evaluate the shaft resistance

capacity takes into account the effect of pile length, angle of shearing resistance between

the soi1 particles and the angle of friction between the pile's shaft and the soil.

Batter piles are commonly used to support offshore structures and towers since these kind

of structures are subjected to over turning moments due to wind, waves and ship impact.

In the literature a very limited information and experimentd data c m be found.

1.2 RESEARCH OBJECTIVES

The objective of this research program is:

To conduct a literature survey on the subject of shaft resistance o f shaft friction for

verticai and batter single piles driven in sand and subjected to compression or upliti

loriding.

To evaluate the factors governing the shaft resistance of these piles using the results

of the present numerical mode1 and the available field and experimental data.

To recommend design procedures for these piles.

To recommend future research on the subject.

CHAPTER 2

LITERATURE REVIEW

2.1 GENERAL

Several reports can be found in literature dealing with shaft resistance of vertical

piles or batter piles in sand. Tnese reports have presented design theories, based on some

assumptions, w hich are rather empirical.

in case of piles under tension, the design procedure has taken the same value as

the shaft resistance capacity for piles under compression; this overestimates the pile

capacity under tension. Researchers did not agree on a certain reason that makes the pile

capacity under tension less than the shaft resistance for piles under compression. and

severai failure patterns were proposed.

In case of battered piles, a few research reports c m be found in literature in these

reports, the cdculation of the battered pile capacity was not accurately evdusited and noc

well understood. Experimentd data showed different interpretation that ended with

conflict conclusions.

2.2 REVIEW OF PREVIOUS WORK

Azzuz, Baligh and Whittle (1990), produced a method to predict the axial

capacity of friction piles placed in rnoderately over consolidated clay (ISOCRS) within

a systematic and rationai framework. Their rnethod was applied on single, vertical. rigid

ruid cylindrical piles driven in deep soil.

in this paper a piezo-lateral stress ce11 wlis used as an instrumented mode1 pile

37.8 mm in diameter that was developed at iCIlassachusetts Institute of Technology (MIT)

in order to provide simultaneous rneasurements of the total horizontal stress oh. the pore

pressure, U, and the average shear suess,.r:

The authors used the B rnethod for its simplicity and its high degree of reIitibiIity.

Fs=P O,, 2.1

where

c,,,: vertical effective stress

p is affected by the two cornponents p& K,

W here:

p : is the shuft resistance ratio

K, : coefticient of laterd earth- pressure

The factors affecting K, (laterai emh pressure) prediction are:

1 ) Pile -Installation

3) Soi1 mode1

3) Overconsolidation r ~ t i o

4) Clay type

The friction ratio p was easily estimrited since it is not sensitive to the in situ OCR

(over consolidation ratio) by the normalized peak strength ratio cd&,, measured in

undrained direct simple shear of the clay at an OCR=1.2 (60.1).

Miller, and Luteneggier. (1997). performed experirnental anaiysis to investisate

the effect of the method of pile installation (dnving versus jacking) and the mode of

penetmtion ( plugged versur unplu,oged) on the shaft resistance developed around piles

subjected to first time axiai compressive loading. In addition to that. a method \vas

developed to andyze pile shaft resistance taking into account the installation and

penetration sffiects. taboratory and in situ soil test data were obtained to clarify the

proposed method.

The required parameters obtrùned for design include the interface friction ringle

between pile and soil, and the iikely range of laterai effective stresses K,, o ,.,, to K.,,,,,

o ' v o

Where:

&: coefficient of lateral earth pressure at-rest

O',, : Initial insitu verticai effective stress.

K.,,,,: Upper limit of the laterril stress coefficient

Open ended and close ended piles were tested in this investigation. ft was observed

dunng installation that pile plugging depends on several factors including :

1 ) Method of installation (driving versus Jackins)

2 ) The pile cross - section geometry

3) The soil stress history

The specific recovery ratio (SRR) and the plug length ratio (PLR) were measured durine

the field test.

From the field test and laboratory test the unit s h d t resistance was determinate based on

two formulas.

fs = o,,~, tan 6 -.- 7 7

Where

f,= iirniting incrementd unit s h d t friction

Ki= incrementd reconsolidation laterd stress ratio

6 = interface effective stress friction angle.

And

(kt,, - K'. ,, Kci = 1 O0

+ K,,, ,

Where

Li and K, ,, i represent average values of K, and

From the analysis it was found that for nsürly nomrilly consolidatrd soils K, ,,, is

approximateiy equd to K,,. The ratio between K, ,, to K,, increnses with increrising

OCR. It was also found that driven piles are plugged mucli lcss than jacked piles and for

both driven and jacked piles shüft resistmce was greater for piugged piles.

Lutenegger, and Miller (1994), performsd experimentril work to determine if

accurate prediction of the ultimate uplift capaciry could be predected using the resrilts of

relatively simple in situ tests.

They modle uplift capacity as

Q upiift = Q s ~ t + W

The shaft resistance Q is given by:

where:

W= the weight of shafi

L= the shaft length

D= the shaft diameter

S.= The soil-shaft effective-stress interface friction angle

K= the coefficient of horizontai soil stress

a',, =the initial in situ vertical effective stress

p is a shaft resistance parameter and is given by :

p = K tan 6' 2.6

for layered soil profile it's characters will change from one Iriyer to another. acourdingly

the andysis will be pedormed for each individual soil Iliyers. In this case shaft resist;mce

will be evaluated as:

Q shafr = xDEL, tan 8 iKi~ 'vo i 2.7

where the subscript i denote the irh lqer in the soi1 profile. The soil variable are 6' and K

were evaiuated in the tield,

In this paper it was suggested that the appropriate friction mgle for use in design

is the effective-stress friction angle of the soil, @'. in which case (2.7) becomes:

Q shaft = ~ D z L t m @' Li o v o i 2.8

The authors performed soil testing to evduate the sheu strength by getting the Borehole

Shear Test (BST) results and the coefficient of horizontal soil stress by getting the results

of a series of prebored pressuremeter tests (PMTs).

The author performed uplift tests on 6 different size piles placed in the same kind of soi1

profile. A c o m p ~ s o n was made between the rnerisured capücity and the predictsd

capacity that has a max and min value. It was found that the minimum value is rnuch

closer to the measured capacity.

The authors found that an effective stress approach to the design of smdl-dimeter drilled

shtifts c m be made using the results of the insitu tests. in stiff soils. a conservritive

approach to design may be triken by using @' deterrnined with the BST and (KJ,,, values

interpreted from the PMT.

Shlash, Malkawi and Al-Deeky (1999), describe he different factors that effect

the net ultimate uplift resistance of piies placec! in sand. The results obtained in their

paper rue based on laboratory test resufts.

The author studied experimentall y the different variables affecting the ultimrits

uplift capacity and they are:

I ) Pile placement rnethod (dnving. jricking)

2) Pile end type (open-and closed-ended piles)

3) Pile surface roughness (smooth and rough)

4) Pile size (4 1 and 6 1 mm out-side diameter pile)

5) initial sand density (medium dense and dense sand)

Each variable was studied separately in order to evali late its effects on shi

resistance cornpared to the other variables. The author highlighted the major and the

minor effects. The rating of these factors are the initial sand density, pile placement

method . pile surface finish . and pile end type. According to this study. the driving

method yields higher shaft resistance than the jacking method. The rough model piles

tested in this study experienced 12-55922 greater capacity than the smooth model. The

closed - ended model piles exhibited npproximately 23% increase in shrift resistance at

ultimate uplift. Piles placed in dense sand yields higher shrift resistance than the medium

dense smd.

The riuthor however did not study the effect of pile diameter on the average unit

shaft resistance.

Mochtar and Edil. (1988), studied the load uanskr dong the shaft of a mode1 pile

placed in a cylindrïcal specimen of clay. A laboratory apparatus was used to measure the

pile shaft resistance taking into account the following factors:

1) Independently controlled vertical and horizontal effective stresses and

overconsolidation ratios.

2 ) Diameter.

3) Length of pile-soi1 contact on the pile shaft.

4) Pile surface roughness.

The mesurements included the axial load-displricement response of the model pile rit

different time after the application of stresses with different rates of loading and

monitoring of pore-water out-flow and clay specimen deformtion with time.

It was reponed thüt load-displacement response. the maximum axial load increascs

with increasing horizontal consolidation pressure applied on the lateral surface of the

clay specimen.

The angle of pile-soi1 friction 6 is effected significantly by the surface roughness of

the mode1 pile, It wris also found that shaft resistance decreascs for lrirger diameter

piiss.

Hanna and Afram (1986), conducted expenmentd investigation to evaluate the

pullout capacity for single vertical and batter piles. Two piles frorn difkrent sizes were

used in this experiment. The authors based their analysis according to MayerhoTs theory

(1973).

Pu= P,sin 6 R D + Wp

W here:

P, = Total passive emh pressure acting on the pile shaft.

D = Pile diameter.

Wp = Own weizht of the pile

d = the mobilized angle of wall friction at soi1 -pile interface.

This investigation showed good agreement with the Mayerhof theory. It was fo~ind thrit

pull-out capacity of batter piles decreases slightIy when the pile inclination is incrased.

The authors ended their investigation with an empirical formula to predict the up-lift

capacity of batter piles in sand and a design chart was established.

CI Pua = Pu cos - (OS& 30°) 2

u = angle of inclination of pile with vertical.

P.,[email protected]'. Gu+ Wp COS a

Where:

y = Unit weight of sand

Ku,= uplift coefficient for bütter piles

L= length of pile

In this investigation it was found that the shaft resistance was not highly affected by the

inclination of the pile and the empirical formula was based on the experimrntal tests rhüt

showed this behavior was not accurate and could not be generdized on any batter pilr.

Tejchman (1976) attempted to prove that the stresses existing around the pilr in

compression and in tension are different. The author based his proposal o n mode1 tests.

andysis of status of earth pressure around the pile subjected to compression and tension

forces and some proposais on calculation of bearing cüpacity of tension pile driven in

cohesionless soi1 media.

The üuthor applied compression force on the pile then üpplied tension force then

compression then tension again. It was found from the expenment that diffsrent states of

stresses occur around the skin of a pile drpcnding on the type of force applicd. The

foLlowing equation was postulated to determine the magnitude of the coefficienr of e m h

pressure dong the pile skin in compression and tension condition as a function of the

void rate 'e.' or mgle o f internai friction "$".

K' = 8.09 - 9.66e or KC =9.06 t an@-4 .19

Kt = 1 -96 - 1.85e or Kt = 1.85 tm - 0.47

A formula was presented to determine the ulumate tension force as follows.

Qur =oh S p + s/h =oh2-/NIN'

Where:

y = bulk density of soil

h = pile penetration depth in soi1

O = Pile circumference

Nt = bearing capacity factors for the pile in tension

p = vertical component of the shear stresses

s = Weight of soil wedge bounded by the slip lines.

in this paper the author proved that uplift cüpacity is less than the compression friction

capacity. The author also proposed a method to cdculate the pile tension capacity. The

author didn't take into account the effect of the soil - pile friction angle 6 and the effefrct

of the pile diameter on the lateral e m h pressure.

Feda (1976). The author attempted to find ri different method to evaluace the shah

resistmce for piles other than the standard formulas, he also attempted to develop a

method thut satisfies piles imbedded in cohesion and non cohesion soil.

He interprets Cu. as the sheruing strength of a foundation soi1 under constant volume

condition since undrained test of water satursited specimens is basically ri constant

volume test.

The author studied the effect of residential pile stress on its premechmical behavior.

Residud is the stress of an unloadrd pile head and it is created by the previous loading

history of the pile.

He proposed his theory that shearing stresses at the pile-soi1 contact occur due to

the load transier. He modeled this phenornenon by a shear box test. The author rilso

showed the effect of residual shaft resistance and exphined why shaft resistünce in

tension and compression piles is sometimes are identical and some other times are

different.

Das (1989), perfonned a laboratory mode1 test where the ultimate uplift capacity is

predicted from its results. Rouph rigid single and group piles embeded in sand have been

tested. The author conducted the single piles in loose. medium. and dense sand.

The author presented the unit shaft resistance ($) at the depth Z as:

f =y ZK, tans

W here

p Unit Weight of sand

Ku = uplift coefficient

6 = Angle of friction betwveen the soi1 and the pile surface.

From the analysis of the results of single piles the averrtge unit s h d t resistance

contributes to the resistance against uplift force between depths Z=L, to Z=Lz W;~S

given as:

(2.1 1)

where:

P, = net ultimate uplift cripacity

D= Pile dirimeter

L= Length of pile

in this proposal the critical depth wris identifieci and it was found that it increrised by the

increrise of the average relative density of compaction for sand (Dr). An expression for

the critical depth was conservatively presenced as

(UD),, = 0. LS6 Dr + 3.58 I 14.5

Assuming that eq. (2 . L ) c m be used for UD 5 (UD),,.

From the proposal it was found that the author presented a procedure for uplift crtpacity

prediction for piles in sand without showing a clear procedure for evriluriting the ~iplift

coeftïcient, Ku.

Kulhawy. Kozera and Withiam(l979), perforrned ri long-scale uplift tests on straight-

sided cast-in-place mode1 drilled shafts in stinci. These tests were made to make the

results meaningful. and to stimulate field construction and lotlding condition as much as

possible. The test was perforrned in loose and dense sand. The preceding approach

represents the field constmction in a reasonsible mmner because:

1) The smd deposit is essentially undisturbed.

2) This small distortion around the opening in the field caused by ausuring or jacking

casing in and out. or both, is simulated when the casing is pulled for the mode1 shaft.

3) The shaft is cast in situ.

The author made a cornparison between the results obtained tiom the test and different

rnethods proposed in literature to predict the uplift capacity of a bored pile. He concluded

the following:

The sheru surface dong which the shaft t'ailed was found to be a cylindrical on the

order of % in.-out from the soil -concrete interface with the soil.

The strain in the shafts showed a general parabolic distribution from 0% at the tip to

100% at the top.

The soil displacement and shaft strain data showed that a cylindrical shear mode1 wris

appropriate.

The load- top deflection response is a non-linear and cumulative net compression

occurs during the cyclic loading.

For the test conducted. the cornputed laterril stress coefficient at the ultimate uplift

faiiure agreed welf with K, in the loose and dense smd.

Residual capricities of the shaft ranges from approx. 70% of the ultimate load for the

loose silnds to approx. 30% for the dense sand.

Ismael and Al-Sanad (1987), studied the uplift capacity of bored piles in

calcareous soils. In-situ expriment were developed in 3 locations in Kuwait. three pires

were tested in each location.

The authon that uplift capacity bored piles is hieher than that the predicted values using

Mayerhof ernpirical relations, Le. the uplift capacity of bored piles in cdcareous soils is

higher than driven piles in the sarne soils.

The authors ended their study with these conciusions:

1) The shaft resistance increased with dspth for the shüliow depth. which mnged up to

14.5 m (47.5 ft)

2) The coefficient of lateral earth pressure in uplift (Ku) ranges between 1 and 1.2 for the

piles where failure was reached.

3) Failure of bored tension piles is usually reached at an upward displricement of 5- 10%

of the pile diameter. The higher values are associated with relatively deeper piles.

The author pointed out is that the carbonate content effects the shaft resistance and the

point resistance.

It is cleür in this paper that shaft resistance depends not only on the type of soil but also

on the method of pile placement, as it wris found that the uplift capacity for driven piles

can be less thm bored piles in some kinds of soil. The study was lirnited to the type of

soil and was not taking into account other factors.

De Nicola and Randolph (1993), in this theory they consider that:

1) Poisson's ratio expansion and contraction of the pile shrift.

2) Difference in totai stresses field, with compressive loading tends to increue and

tende loading tends to decrease the mean stress level in the soil.

3) Changes in rnean effective stresses due to rotation of the pnncipd stress directions

depending on the detaited residuai stress field dong the pile shaft.

In the anaiysis the author used n simple elastic-perfectly soil mode1 with n Mohr-

Coulomb failure criterion in the soil m m and at the pile-soi1 interface. The theory was

based on numericd analysis, from the resuh of these analyses the ratio between tensile

and compressive shaft capacity was evaluared as follows:

Where v, is Poisson ratio which was assumed to be zero in this case.

The theoretical ratio of tensile to compressive shaft capacity was cdculated as.

where:

Q,= ideal shaft capacity of pile

This relritionship for the capricit y ratio Lveri- derived. brised on the Iollowing:

1) The foregoing theoretical solution. which quantifies the Poisson's ratio's. effecécrs on

the shaft capacity.

2) The numerical results for the assumsd case of zero Poisson's ratio captured the effect

of changes in mean stress on the shaft capacity. This led to a final expression for the

capacity ratio as:

where:

q: Compressibility parameter.

The final formula \vas compxed to the field data obtained by other researchers and was

found that the formula is a reasonable one. From this analysis, it was found d so that

usually the tensile shafc capacity is lower than the compression shaft friction. This priper

explained the difference between the tensile and compression shaft capacity. It provides a

guide to evaluate the ratio between thern.

Lehane, Jardine, Bond and Frank (1993). Cornprehensive measurements of the

effective stresses were developed during the instrtllation. equalization. and load testin_o of

displacement piles in a Loose to medium dense quartz sand was presented.

From the authors' work they observed that radial effective stresses on the shah cit f i ' l ; 1 ure

differ from the equilibrium values (O',) by an amount AG',

CS'^ = + Aar*

It was found also chat the local radid effective stress changes during pile loriding couid

be split into two factors due to the principle stress rotation (Ac',) in the sand and the

dilation due to slippage at the interface AC',^)

It was suggested that the principle stress rotations associated with pile loading criused the

reduction in (o',). The reductions were small for compression loading, but were more

significant in tension tests.

Concerning the Interface slip Dilation (Aatrd), an initial reduction occurred followed by a

marked increase in (a',) was obsewed as eüch section of the pile approached the local

failure. The author explained his observation that an increase in (o',) is due to such rridiril

displxements.

The interface friction (6) controls the shnft capacity which appears to br independent of

relative density. The data presented in the paper showed that high stresses are mobilized

near the pile tip and that stabilization of the average ultimate local shear stress (G,) with

pile depth is resulting frorn the tendency of (G',) to decrease at al1 levels ris relative pile-

tip depth (MR) increases.

Tsien (1986). The author illustrated the factors affecting the shnft resis tance

without giving a formula for evaiuüting each of them. These factors are:

1) Pile length:

It was reported that the coefficient of lateriil eanh pressure on the pile shüft (K,) is a

variablé decreasing progressively with depth. Furthermore the pile penetratrs bryond

certain depth called "critical depth", where no further increased occurs to the shrift

resistance and the tip resistance its tip resistance

2 ) Structure and Relative density of sand:

It was reported that the smd passes through dilation compression at Fiilure. Cyclic

loading generaily produces volumetric decreasing in s u d deposit.

3) Pile - Soil Load Transfer characteristics.

The distribution of the shaft fnction load transfer depends on the size of the pile. the

method of driving the pile and the strain compatiblity among soil layers within the

pile's depth.

4) Soi1 plugging of open-ended pipe piles.

The criteria of plugging during driving should be considered. The inside wall friction

should be considered and evaluated to estimate the shaft resistance.

5 ) Techniques used for driving and loading the pile.

The hamrnering driving method reduces f, and tip resistance.

This paper opened the door for more research in evaiuating the pile shaft resistance

taking into account the several factors mentioned previously.

Randolph, Dolwin and Beck (1994), proposed a framework for prelirninÿs pile

design approach for axial capacity of pile driven into sand. They based their theory on

previous experimental data. The authors gave a new ti-amework for calculating the end-

bearing capacity, peak shaft friction, shrift friction distribution dong the pile shaft and

compressive and tensile shrift capacities.

For end-beriring cripacity it was assumed that the soil immediately bensath the

pile tip has been sheared to its uItimate state. the effective friction angle of soi1 0'. is

assigned the critical state friction angle. &. For the peak shaft friction the author didn't

present how to calculate or evaluate the vertical effective stress K, instead he used

another term called ratio of shaft friction to in-situe vertical effective stress. P. The

interface friction angle, S was evaluated by using previous rnethod proposed by

(Beringen, Windle & Van Hooydonk. 1979). The shah fnction distribution dong the pile

shaft was presented by an exponential formula. Some hctors were taken in account for

cdculiiting the shaft friction distribution. there are:

1 - Compressibility and /or crushability of the surrounding soil.

3- - Roughness of the pile surfrice.

3- lncremental dnvinp ener=y needed to advance the pile.

4- Effective displacement ratio at the pile tip.

Concerning the compressive and tensile shaft capacities the author showed thrit there

is a differenc between them. An empericai formula was presented.

Robinsky and iMorrison (1964). They study the effect of shaft resiscance on the

ultimate pile capacity. The paper deds with two major points. First. the study of sand

displacement and compaction patterns arround driven mode1 pile. Second. the study of

load distribution at the point and dong the surface of the sarne piles.

The author performed laboratory experiments on straight and tapered piles. The

shripe of the displacement envelope was expsrimrintdly identified. The tiuthor concluded

that the pile capacity increasrs with the increase of the envelope diameters. It wris dso

observed that there is a vertical expansion at various eievations adjacent to the pile shaft.

This expansion is believed to be caused by the drag down effect of the pile walls within

the surrounding sand as the pile moves downward. It was also found that tapered pile

appears to be much more efficient than suaight-sided pile.

This paper didn't present m y method for evaluating the shaft capacity; it however

presented some observations from the laboratory experirnents.

Randolph and Murphy (1985), proposed an anaio_oytical fornulri based on

previous experimentai work to evaiuate the shaft capacity based on the local effective

stress rather thm CO the shear strength of the intact soil.

The work done concenuated on long driven piles for that the efkct of pile length

was taken into account. The proposed method for calculating pile shaft capacity \vas

assessed in terms of average pressure expériences and added some assumptions to

calculate the length factor and the factor or wkch is related to the suength of the soil.

It was found that this method has several limitations and assumptions.

Joshi (1989), performed laboratory experiments on mode1 piles with different

U D ratio. The author presented several graphicd representation showing the relation

brtween the top losld versus the pile top movement with several U D ratios, the point lond

and shaft resistance were also piotted versus the same previous parameters. From these

results the u i a l load distribution dong the pile drpth was determined.

The Author didn't present any method for predictinf the pile shrift resistmce. he

presented his observations on the expenmental results.

Hanna and Nguyen( 1986 ). This paper presents an experimentai investigation

on the ultimate shaft resistmce of batter piles. The mode1 piles were pushed in medium

dense sand deposits at different inclination up to 30" with respect to the vertical. and

tested under axial compression loads. From the experimentai results it was found that the

total shaft resistance decreases with increrising pile inclination. The author related the

rerison of this reduction to the reduction of the average mobilized angle of friction

between the pile shrift and sand taking inco account the vertical e m h pressure

distribution.

To evaiuate the shaft resistance capacity the authors attempted two-sirnplif?crition

assumptions:

1- The rnobilized angle of friction between the pile and sand remains constant around

the pile shdt for a given distance 'z'.

2- The local coefficient of earth pressure Kze is a function of the angle 0 and the depth z.

see figure (2.1 ).

In this paper. a method to calculate (&,,J$,) taking d l the factors into account where &,, is

the rnobilized angle of friction between che sand ruid the pile. Q, is the mobilized angle of

sheru strength.

Chattopadhyay and Pise (1986). An analytical method was proposed to predict the

ultimate uplift capacity of piles embedded in sand. The method talces into consideration

the Iength. dimeter, and surface chwacteristics of piles and soil ptopertit-S. The proposzd

analytical mode1 of a verticai pile of diameter. D. and Length, L. is assumed ro be

embedded in a soil having an angle of sherinng resistance "$" and effective unit weight y.

The suis system and configuration of the pile is shown in Figure (2.2).

The authors assumed that an axisymmetric volume of soil is initiated to move up dong

the pile surface as shown in Figure (2.2). The movement is resisted by the mobilized

shearing strength of the soil dong the failure surface and the weight of the soil and the

pile.

Figure 2.1, Assumed distribution of the unit shaft rmistance around the pile, after

Hanna and Nguyen (1986)

By conducting 'limit equilibrium analyses', the ultimate uplift capacity of the pile was

predicted The following assumptions have been made:

1- The shape and extent of the failure surface depend on the slendemess ratio A, the

angle of sheînng resistance t$ of the soil. and the pile friction angle 6.

2- For pile friction angle 6 = O, under ultimate upiift force, P., the resulting Mure

surface initiates tangentially to the pile surface at the tip of the pile and moves

through the surrounding soil.

3- For 6 > 0, the inclination of the failure with the horizontal at the ground surface

approaches (15 - $12) and for 6 = O, it is 90'.

The authon presented a non dimensional complicated formula calculating the uplift

capacity of the pile:

Al = (1-sin 0) tan 6/2 Taking: Ks = ZAi/tan 6

W here:

XI = net uplift cripricity factor

K, = coefficient of earth pressure

The resulting formula is not practicdly used for design engineen. And the other

thing is that the diarneter is not a factor considered in evaluating the coefficent of eanh

pressure "K,".

Figure 2.2, Pile and Failure Surface, after Chattopadhyay and Pise (1986).

2.3 DISCUSSION AND SCOPE OF PRESENETED RESEARCH

Based on the above it can be concluded that besides some experirnental data, no

acceptable solutions can be found for determining shaft resistance for compression and

uplift. Conflicting theories of Lutenegger (1994) and Chattopadhyay (1986) was noted.

Shlash (1999) & Lehane (1993) did not present design theories. Most of the researchers

neglected the effect of the pile diarneter in their results.

The purpose of the present research program is to take advantage of the

experirnental data available and to study al1 the effects that should be taken into account

to evaluate the shaft resistance and to determine the pile capacity under compression or

uplift for vertical or batter piles.

CHAPTER 3

ANALY SIS

3.1 GENERAL

The shaft resistance shares the tip resistance in cxrying the load transtèrred to the

pile from the super structure. The importance of the shaft resistance kept researchers

investigating its mechanism and trying to formulate the most accurate method to evaluate

its capacity. In this present investigation the shaft resistance of a single verticai driven

pile in sand subjected to axial compression load will be extensively examined, and

practical methods that takes into consideration the panmeters affecting it's capacity.

Based on the presented study, it will be demonstrated that there is difference

between compression and tension shaft resistance.

In literature shaft resistance for batter piles are not well understood. In this

chapter an attempt is made to present a reliable method to predict the shaft resistance of

batter piles.

3.2 SHAFT RESISTANCE FOR A SINGLE VERTICAL DRIVEN

PILE IN SAND SZTBJECTED TO AXIAL COMPRESSION LOAD

3.2.1 Numerical Analysis Numerical analyses using finite element techniques have been particularly

popular these days in the field of geotechnical engineering in recent years for solving

many engineering problems.

Since the behaviour of soil can be approximated by the use of an appropriate stress-strain

law applied to discrete elements, the finite element method provides a valuable anaiytical

tool for the interpretation of cases where unusual geometry or three dimensional effects

are sigificant, and where realistic simplified rnodels c m be specified. It is particularly

relevant when it is possible to compare or back anaiyses the performance of a well

instrumented prototype. either full scaie in the field or at mode1 scale in the centrifuge. In

calibrating these tests, design procedures may be developed and proven.

For anaiyses using criticai state soil mechanics rnodels, Kusakabe (1982) and

Philips (1986) have shown that good results can be achieved by providing a finite

element rnesh, which is fine enough in the areas of high strain gradient. and where the

loading increments were relatively small. The choice of element and the rnesh design has

to reflect a compromise between an acceptable degree of accuracy and computing costs.

As we found out in the previous section that L, D, @ and 8 are the main factors

that affect the unit shaft resistance for a single pile in sand. In this section, these factors

will be studied to verify their effect. Two size piles were used. and an increment of load

was applied upto failure point to study the behavior of the pile under certain condition.

Program "CRISP" used in this investigation was written and developed by The

Geotechnical Group in Cambridge University. It was initiated by Zytynski and developed

further twice Dy Bntto & Gunn (1987) and (1995). It includes the following features:

(1) Undrained, drained and coupled consolidation analysis cm be handled by the

program either for two dimensional plane strain or axisyrnmetric loading conditions,

or three dimensional plain strain soIid bodies.

(2) The following soi1 models are available: Anisotropic linear elastic; inhomogeneous

linear elastic (properties vary IinearIy with depth); elastic-perfectly plastic with Von

Mises, Tresca, Dmcker-Prager, or Mohr-Coulomb yield criteria. For elastic-perfectly

plastic modeIs, the Stress State is corrected back to the yield surface at each loading

increment. Therefore, a limited increment size is required in order to achieve a

reasonable convergence. It is worth rnentioning that the program uses a tangent

stiffness solution scheme in which the global stiffness matrix is updated at each

increment.

The mesh used in the present investigation was determined according to the size of

the pile and the amount of deformation expected dunng the analysis. Since the region of

interest is limited to a few diameters around the pile, an axisymrnetric analysis for a mesh

with &ris coincides with the axis of the pile foundation is considered the most efficient

solution.

The following boundq conditions are imposed on the mesh.: the nodes belonging to

the periphery of the cylindrical mesh are fixed against displacement in both horizontal

directions, yet remain free to move verticdly; and the nodes constituting the bottom of

the mesh are fixed against displacement in both horizontal and vertical directions.

Additiond boundary conditions, which satisfy static loading, may have to be irnposed in

each case due to symrnetry conditions, Le., nodes lying on an a i s of symmetry cannot be

displaced perpendicularly to that axis. However, the boundary should be placed far

enough from the region of interest in order not to affect the deformations within that

region. The mesh is designed to be denser in the vicinity of the pile shaft, where the

deformations and stresses are expected to have a major variation.

Randolph (1977) recommended boundary conditions for the finite element mesh to be 50

times the piie radius in the lateral direction, and to be 1.5 times the pile length below the

tip in the vertical direction. Since the need is to study the failure pattern around the pile

shaft, the boundary conditions used in this study will be as follows:

-The horizontal boundary was placed at least 50 times the pile ndii measured from pile

a i s , see (Figure 3.1)

-The vertical boundary was placed at 1.5 times the pile length below the pile tip. These

conditions will Vary depending on pile geometry and the obsemed zone of failure around

the shaft. (Figures 3.2) show schematic views of the adopted finite element meshes and

the distribution of elements. These boundary conditions were irnposed to minimize the

boundary effect on the zone of interest (around the shaft), and to provide sufficient

accuracy for the analyses.

For a realistic model, a rough (or adhesive) interface is required between the pile

shaft and the soil. A relative slippage should be pemitted when the shear stress

mobilized on the shaft exceeds the limiting values. The slip element used in the andysis

was treated as a one-dimensional element with six distinct nodes; three of each is on one

side of the longitudinal direction of the element. The soil is assumed to behave as a linear

elastic - perfectly plastic (Mohr - Coulomb material) which is govemed by the following

parame ters:

- Soi1 cohesion, c

- Interface angle, 6

- Stiffness in the normal direction, Kn = E(1-v)/(L+v)(Mv), Where E & v are the

modulus of elasticity and the poisson's ration respectively

- Shear modulus, Ks = E/(2(l+v))

- Thickness of the element. t (usually: O.lbi>O.OlL, where L = the element lene@.

The slip element behaves elastically upto the shear stress reaches the limiting shear stress

as defined by the Mohr - Coloumb equation:

.c = c + a tan(@

Failure Pattern

In the following analysis two methods were used to detennine the failure pattern

around the pile shaft as deduced from the finint element results. The f in t rnethod was by

producing contour lines at the ultimate point. The second method is by dictating the

friiled soi1 element around the shaft.

Chin of slip 50 ro (at Ieast)

Figure 3.1 Sketch of Pile Interface System a d View of Boundary Conditions

6 Divisions

4 8 Divisions Divisions

i v GROUND

Figure 3.2 Sketch of the finite element mesh.

Method 1:

From the results of finite element andyses, the contour lines of stress ratio (ds) which is

equal to sin $, are plotted.

Where:

T = the radius of Mohr's circle (effective stress) = (al - a3)/2

s = the coordinate of the center of Mohr's circle dong the direct stress a i s (al+aj)/s

@m = mobiiized angle of shearing resistance.

Since d s = [(n - 03)/2]/[(oi + -)/SI = (61 - o3)/(oi+c3) = sine &,

The failure or slippage takes place at the point where (sine &&in @) = 1.0, ie when @,, =

@ where factor of safety against shear failure is equd to unity.

Merlrod 2

The Stress State for each element was deterrnined after each increment. The deduced

stress was then compared with the allowable stress computed from the soi1 strength

parameters. If the ratio is less than unity, this means that this eiement did not reach the

failure state yet if it became equal or higher than one then the element is in a state of

failure.

In this investigation both methods were utilized to deterrnine the failure pattern

around the pile. By using these data (pile depth = 12m, pile width = 0.25m, 6 = $ = 30°,

Ki = E) The results are presented in Figure (3.3). After loading the pile, contour lines

showin:: the factor of safety against shear failure were generated. From the analysis of

Figure (3.3):

1- It was observed that the mobilization of skin resistance started first before the

mobilization of tip resistance and this occurred at senlement of - 0.989cm, which is

equal to about 33% of the total settlement at uitimate load. This reveals how small a

movement is needed for the skin resistance to be mobilized before the tip resistance.

2- The Mure mechanism start around the pile tip then p d u d l y extended upwards.

3- The failed volume due to mobilized skin resistance is shape approximately as an

inverted cone with the base located at ground surface.

4- The failed zone due to mobilization of shaft resistance at a certain increment is

extended horizontiilly to a distance of R = 2D from pile a i s , where D = pile

diameter, and extended vertically from ground surface to a vertical distance Hl = 5D.

G.L. v

Figure 3.3, Shows the Failure Pattern for a pile Under Compression Load.

Numerical Results

The results for load tests are introduced in table 3.1. The load test was carried out for the

pile diameter o f (D = 0.7Sm Br 0.4m) and length (L = 144m & 36m). The propeny of

sand used in this investigation has a unit weight 17KN/m3 and angle of sand shearing

Table 3.1, Typical load tests from the numerical model. Test No. 1 L (m) 1 D (ml 1 @ 1 1 a (W 1 f, (ma) 1

3.23 Experimental Investigation

For the purpose of evaiuating the factors effecting the shaft resistance, well-

documented expenmentai results were used in this thesis extensively in this thesis. The

main source of experimentd data was taken from the experimentd investigation

conducted by Hanna & Nguyen (1986) and by Hanna and Afram (1986). These tests were

produced at Concordia University laboratory.

The experimentai set-up comprises a 1.22m x 2.13m x 2.13m steel frame testing

tank, designed for load tests on mode1 piles up to 1.7m long and 76mm in diameter. The

placement of sand in the testing tank is carried out by depositing sand through a

distributing hopper installed on carrïage travelling back and forth over the test tank.

Provisions are made to permit replating the fiow rate of sand, the speed of camage

travel and dropping distance of the sand. Once the tank is filled, the model pile can be

pushed into the sand deposit at a predetermined inclination angle by a strain-controlled

screw jack attached to the loading column.

Piles were tested vertically and inclined, under tension (Hanna & Afrarn, 1986) and under

compression (Hanna & Nguyen, 1986). The piles used in this investigation were 0.076m

and 0.038m in outside diameter. The model piles were made of steel. Their surface was

made rough by gluing sandpaper on the pile, in order to simulate the condition of

concrete piles. The angle of shearing resistance (Q) was 3g0. The unit weight (y) was

1 5 . 6 ~ ~ / m ' .

Surnmary of test results is presented in TabIe (3.2 & 3.3) for compression and tests in

Table (3.4) for pull out test.

After Hanna & Table 3.2, Summery of pile load test results for 38mm Diameter pile. Nguyen (1984)

Table 3.3, Summery of pile load test results for 76mrn Diameter pile. After Hanna &

WD

Nguyen (1986)

Average Unit Shaft Resistance,

Angle of inclination a mg.)

LfD

Total Shaft Rais tance,

(N)

Average Unit Shaft

Resistance, fa

Angle of Inclination cx

(deg.1

Total Shaft Resistance

(KN)

Table 3.4, Summery of test results, after Hama & Afrarn (1986) Average Unit

Shaft Resistance, fa (Pa) 8300

Weight of Pile (N) 69

Pile Length L, (ml

1 -549

WD

40

Piie Diameter

D (d 0.038

Angle of inchation

a(deg.) O

Mauimurn axial pull-

outtoad(N) 1535

323 Parameters Governing the Shaft Resistance of a Single Vertical

Pile in Sand Subjected to axial Compression Load. In this section, the pile shaft resistance for driven piles will be critically examined

using numencal results of the present investigation and the available data. By defining

the goveming factors affecting the shaft resistance, it will be possible to evaluate the

design theories. These goveming factors are:

1 - The pile length, L

2- The pile diameter, D.

3- The pile - soi1 friction angle, 6

4- The soi1 angle of shearing resistance of sand, @

If the effect of each of these parameters is well undeatood and evaiuated, then the pile

shaft resistance can be easily determined.

3.2.3.1 Effect of Pile Length

From experimental and numerical data it is found that the shaft resistance

increases with the increase of pile length. This increase is due to the increase of the

overburden pressure with the embedment in depth that generate the honzontrtl earth

pressure that acts as a normal force on the pile shaft. It was found that at a certain depth

which is defined as the critical depth, the rate of increase in shaft resistance start to

decrease with depth. Randolph et al (1993) related this phenornenon to the relative

density, pile embedment depth and pile diameter. From the published reports in literature

the critical depth was established at UD = 10 - 20 depending on the sand condition

whether loose or very dense. This values where proved experimentally by several

resemhes, shown in Table (3.5). Figure (3.4, 3.5 & 3.6) shows experimental chta

reported by Mansour and Kaufrnan (1956), Bringen et al (1979) and Hanna & Nguyen

(1986). In table 3.5 the cornparison between the observed critical depth and the

theoretical values are presented. From this table (3.5) it cm be noted that there is a good

agreement between the observed critical depth and the theory values. Researchers have

provided di fferent explmation to the cri ticd depth.

Table 3.5, cornparison between the observed critical depth and the theoretical

Theory 1 Observed

values.

Mansour & Kaufrnan (1956) pile 2 1 Dense Sand ( 18 1 l8

Data 1 Soü State

Mansour & Kaufman (1956) pile 6 1 Dense Sand 1 18 1 l6

WD (Critical)

Benngen (1979) pile 2 1 Very dense smd 1 20 1 16.3

Benngen (1979) pile 1 (Fig. 3.5) 1

Very dense sand

Hmna & Nguyen (1986) 1 Q = 41.2

Present Numerical iModel

20 1 18

20

45

13

20 33

Shaft Residance, fs (KPa)

O 20 40 60 80 100 120 140

Figure 3.4, Shaft resistance from compression Test (2) in dense sand. After Mansour

& Kaufman (1956)

Shaft Resistance, fs (ma) 100 150 200 250

I

Figure 3.5, Shaft tesistance from compression test in very dense sand. After

Beringen et al (1979)

Unit Shaft Resistance, fa(Kpa) 5 10 15 10

Figure 3.6, Shaft resistance from compression test in very dense sand. After Hanna

& Nguyen (1986)

3.232 Effect of Angle of Friction between Pile and Sand, L'a"

From Table (3.1) it can be noted that angle 5 bas an effect on the coefficient of earth

pressure Ks. Typicd test results for two piles are illustrated in figure (3.7 & 3.8). Ks

increases due to an increase of angle "8'. It was clear from the results that "@'* has a kind

of control on the amount of effect that "6' can produce on the coeFFicient of earth

pressure so as shown in the Figure (3.7) when "ô" is much smdler than "4I" slight

increase to Ks is observed but when "6/@" become bigger than 0.6 the amount of increase

become much higher. This observation support for rough shafts were "8' close or equal

to "4I" the Ks ~ i ~ ~ f i c a n t l y increases. The data presented in Figure (3.7 & 3.8) c m be

plotted in a more general form as presented in Figure (3.9). Angle 6 used in the

calculation of the shaft resistance should be less than angle @, because if 6 > @ then no

slipping will occur between the pile and the soil and it will be easier for the soil to slip

intemdly between its particles. If such situation occurs then 6 = @ or in other words @ is

taken insteûd of 8 in the calculations. Angle 6 is obtained frorn the shear box test, for the

soil and the pile materid.

Figure 3~7~~uner iwLTes t Results: Effect-of4hepile HiterfaceangleoFfrictien on

the coefficient of earth pressure.

Figure 3.8, Numerical Test Results: Effect of the pile interface angle of friction on

the coefficient of earth pressure.

Figure 3.9, Numerical Test Results: Effect of the ratio S/+ on the coefficient of earth

pressure, K.

3.2.3.3 Ef'fect of angle of soi1 Shearing Resistance, 66@ "

The angle 9 is one of the key factors that determine the value of shaft resistance

of piles depends on the level of mobilization of the ansle of shearing resistance, Q.

It was found that K, exhibit greater increase after the pile installation and during

loading than the instu values IK, = 1- sin @). This increase reflects the stress state in soil

mass occurred due to pile installation & loading. It is also observed that K, has a

maximum value at shallow depths then starts to decrease with the increase of depth.

Figure (3.10) shows the relationship between the coefficient of earth pressure Ks and

angle of soil friction @ versus the ratio "UD". The experimental data presented by Das

(1989) in Table (3.6) and plotted in Figure (3.1 1) and agrees with the numerical results in

Figure (3.10) such that it is dear that the coefficient of earth pressure decreases dong the

depth of the pile such that it reaches a value approximûtely equals to the value of &.

Since the over burden pressure starts to build up gradually with the increase of depth the

soil particles will be prevented from king displaced laterally so it starts to move

downward with the piles base building up the tip resistance. This can give an explmation

that the shaft resistnnce stops to increase after the critical depth. It is also noted that in

dense sand the increase in the earth pressure due to the installation of the pile is much

higher than in loose sand. This is because the voids in dense sand are much smaller than

in loose sands.

3.2.3.1 Effect of Pile Diarneter on the Shaft Resistance

Analyzing the experimental test data available it was found that the pile diameter

"D" has an effect on "Ks" although it is not added as a factor in the most common

formulas calculating the unit shaft resistance. The experirnental data represented in

(Figure 3.12& 3.13) is reported by ( Hanna 1986) and @mail et ai 1987) show that the

unit shaft resistance increases due to an increase of "D" this increase corne from the

increase of the lateral earth pressure that is developed from the pile during driving and

accordingty by the movement of the soi1 around the pile. The effect of the pile diarneter

on the lateral earth pressure will be much sensible in dense sand than that in loose sand as

demonstrrited in the Experimental data presented by Das (1989) and Figure (3.13). It is

clear that in dense sand the average unit shaft resistance increases in a higher rate thm

that in Ioose sand.

Table 3.6, Experimental Test data on 0.76m-mode1 pile test diarneter. After Das (1989)

Test No.

1

(@ = 43O)

I 2

L (ml

0.228

0.34

0.76

O. 1 14

0.228 h

a (KN) 0.24

0.69

4.132

0.00575

0.03 1 1

- -

WD

3

4.5

10

i -5

3

fa (Kpa)

4.4

8.5

22.6

0.2 1

0.56

Coeffkent of Earth Pressure, Ks

Average Unit Skin Friction, fa (M'a)

Average Cnit Skin Friction, Fa (Kpa)

Average Unit Skin Friction, fa (Kpa)

3.3 SHAFT RESISTANCE FOR BATTER PILES

Batter piles are commonly used to support offshore structures and towers since

these kind of structures are subjected to over tuming moments due to wind, waves and

ship impact. In order to trmsfer the overturning moment to rt compression and tension

forces a combination of batter and vertical piles foundatim are used.

In the literature a very limited information and experimentd data can be found. In

this section shaft resistance for batter piles wiIl be analyzed in light of the available data

from the literature. It was found from the expenmentd data done by Hanna & Npyen

(1986) showed that the shaft resistance decreases by the increase of angle of inclination

for both compression and tension. On the other hand it was found from the full scde

results reported by Mayerhof (1973) that the shaft resistance capacity for the pile

increases due to an increase of the inclination angle, CL While Hanna and Afrarn (1986)

showed that there is no significant change in shaft resistance with the increase of

inclination. In this section it will be proved that al1 of these trends are correct and it may

take place under different soil conditions.

3.3.1 Effect of Angle of Inclination on the Lateral Earth Pressure

Due to the inclination of the pile the radial stresses around the pile's shaft is not uniform.

Figure (3.15) present the earth pressure distribution on a cross-section of a bîtter pile.

This trend increases the problem complicity that derived researches to take the average

radial stress dong the pile. The mobilized angle of soil shearing resistance and 6, the

mobilized angle of pile friction was taken as (6m/@&,, average.

(a)

Figure 3.15, (a) Battered pile subjected to axial compression load. (b) Stress

distribution on the pile cross - section.

In this investigation the pile cross section was divided into four zones as shown on

figure (3.24b). Each zone was subjected to passive esirth pressure according to its position

with respect to the soil.

Zone 4 & 2, are assumed not to be effected by the pile inclination and accordingly they

are considered as a vertical surface.

Zone 1, its surface is inclined at -a, the euth pressure increases in this zone with the

increase of the angle of inclination.

Zone 3, Its surface is inclined at +a, where the earth pressure decreases in this zone with

the increase of the inclination angle.

The sumrnation of the shah resistance in the four zones wiII resuh in the totai pile shafi

resistance. Zone 3 and Zone 1 are the two zones that governs whether the shaft resistance

increases with pile inclination or decrectses this depends on the net value of the earth

pressure. From Figure (3.16 and 3-17), it c m be noted that shaft resistance decreases

slightly due to an increase of pile inclination a when angle @, is less than 30'. Further

more when angle @m becomes higher than 30" then the shaft resistance increases

sigificantly due to the increase of the angle u. It can be concluded that when O, equals

30" there is no change in the shaft resistance. i.e. the net earth pressure remain

unchmged.

Shaft Resistance, (KN)

Shaft Resistance, Qs (KN)

3.3.2 Theoretical Mode1 for Unit Shaft Resistance for Vertical and

Batter Pies in Sand

Based on the above pararnetric study it can be noted that K, are effected by the ratio

(6d&), the pile diameter, D, pile inclination cc and the pile length, L. A method is

presented to evaluate Ks taking in account al1 the above mentioned factors. A solution

was possible if the following simplified assumptions are made:

1- The mobilized angle of friction between the pile shaft and sand, (&& remains

constant around the pile shaft for a given distance z. i.e. (6&3 becomes (6,),. (&),

will be usually expressed as a ratio (&/@& where &,, is the rnobilized angle of

sheaing resistance for sand. Once (6JQm), is evaiuated and ern is known then 6, will

be evduated.

2- The local coefficient of earth pressure KzD is a function of the pile diameter and the

depth.

i .e Ka = F(D). R(z) (3.1)

Where F(D) is the function representing the variation of K z ~ at any given cross

section of the pile.

R(z) is set equal to reduction factor which, in tum is a function of ratio (&&$&

(Caquot and Keriset, 1949). From these two assumptions the formula used to evaluate the

average unit shaft resistance will be as follows:

fa = '/2 Ly Ka sin 6,

Where:

Ka = is the coefficient of earth pressure

L = Pile length

y = Unit weight of sand

6, = Mobilized interface angle of friction

Since the variation of (&), and (S,.&,), are unknown, the analysis wilI be based

on the average value of (Sm), and (6dqm), i.e. (Sm), and (6d@& are replaced by 6, and

(&J+m)ave respectiveiy.

The analysis proceeded as follows:

First to find the variation of (6,41&, with pile diameter based on Visics & Tavenas

(1967, 1971) experimental data on 0.45m and 0.33m pile diameter respectively the field

data is represented in tabIe (3.7). From this data a trial and error procedure as presented in

the flow chat in (Figure 3.18) sirnilar to Hanna's (198 1) was followed:

Assume a value for (&/&),,,

Evaluate 6 , by assuming the angle of shearing resistance of sand such that it is fully

mobilized (Le. set Q, = @)

Estimate R(z) from Caquat and Kerisal's tabulated table (Caquat & Kerisel, 1949)

Calculate f, using equation (3.2)

Compare the theoretical value produced from step-4 with the experimental value fa.

The procedure is repeated until a close agreement occurs between both sides of

equation (3.3). A typical trial is presented in Table (3.8). The variation of (6Jk) with

the dimeter is represented in Figure (3.19) as a straight line determined by two points

one is for the 0.32m and the other is for 0.45m pile diameter, and selected for L/D = 5 to

40 it was found that (6,J@&,e decrease with the increase of UD for a fixed diameter

which proofs that Ks decreases with the increase of pile length.

Table 3.7, Experimental data performed by Vesic (1967) and Tavenas (1971) L

F - = 2

- 6 - w U *-

- rl b e - - " er: r O * g

Type of

Pile

O , œ

c E o m eT - II 8 Q 6 -

Q) œ .a

P. a - , - E 2 Pl 0 -

5 0 . u II

2 Q 0 - ' 2 e

Pile Test No.

H - I l

H-12

H-13

' H-14

H - 15

J - I

5 - 2

J - 3

J - 4

J - 5

5 - 6

Pile Embodirnent

Depth, L

3.017

6.126

8.86

1 1.978

15.026

5.79

8.839

11.88

14.93

17.98

21.031

Effetive Stress, a',

23.84

39.78

53 -96

69.95

85.6

25.75

40.36

54.96

69.56

84.17

98.77

@ (deg) -

31

33.8

35

38.9

36.3

23.7

24.5

24.9

25.1

25.3

25.4

UnitShaft resistance, f, (Kpa)

30.808

59.6795

59.4472

68.803 1

67.2 138

13.0174

25.5778

30.660 1

34.94 19

35.7348

37.074 1

Shaft resistance, a (KN)

133.446

534.89

756.19

1 183.2

1450

76.5

229.47

369.7

529.5

652.14

79 1.39

Assume @, = @

(Caquat & Kerisel, 1949)

1 Evaluate fa (eq 3.2) l

Figure 3.18, Flow chart for the presented method to end with a relation between

($JQm)ave versus 'W"'

N 'Si

The previous analysis can serve as a guide to detemine (&&&vc by knowing the

pile diameter, D and JfD.

The second stage is to obtain the value of K, from the charts in Figure (3.10 to 3-29),

which shows the variation of Ks with (6J@&ve and u for a certain $. Where CY is the pile

inclination angle.

The third stage is to evaluate the shah resistance for batter piles. As presented in the

above the pile wu divided into four zones due to the ununiformity of the stresses around

the pile. Earth pressure acting on the pile "P(9)" cm be expressed as:

P(0) =1/2 &(O) y h

Where:

K,(9) = Coefficient of eaxth pressure around the pile, as obtained from Caquat and

Kensel's tables (1948)

y = Unit weight of soi1

h = The vertical depth of the pile, where h = L cos a.

L = LRngth of the pile

= Angle of pile inclination

From equation (3.4) the shaft resistance can be calculated as follows

Q, = DI ~ ( e , z)z sin ~dûdz

Since there is four zones (1,2,3,4) then

Qs = 1 ~ ~ ' ~ r c y cos u[0.5KS2,~ + 0.25& + 0.25& J sin (a),

Figure 3.19, Pile dianieter verses ((G Jl),,Jyva willi respect tu pile lenglli /pile diumeler (LID).

Where:

KS2.a = The Coefficient of earth pressure at a = O

Ks3 = The Coefficient of earth pressure at u = +U

Ksi = The Coefficient of earth pressure at u = -a

Ks for the four zones cm be obtained from the chart in Figure (3.20 & 3.21) together with

the reduction factors if (S&#I&, < 1.

3.3.3 Design Procedure

The procedure for predicting the shaft resistance for a single vertical pile subjected to

axial compression load and driven in sand can be calculated according to these steps:

1- The value of (6d@m)ave is obtained from the chart in figure (3.19), given the pile

Iength and diameter.

2- From the value obtained from (6Jom)a,e knowing the angle of shearing resistance @

of the soil, the value of the coefficient of e m h pressure "Ks" is obtained from Figure

(3.21) multipiied by the reduction factor Rr obtained from Figure (3.23).

3- The unit shaft resistance will be evaluated from eq. (3.2).

Example:

By taking the given experimentd data presented by (manna & Nguyen 1986) such that:

@ = 39O L = 0.76111 D = 0.0761-11 y = 16KNfrn3

Solution:

Since D = 0.076 and UD = 10

From Figure (3.19) (6J@,) = 0.4

By interpolation between the values in both charts presented in Figure (3.37 & 3.28)

K, = 8.04

The unit shaft resistance will be evaluated according to equation (3.2)

fa = 0.76*0.5*8.û4*16*sin 15.6 = l3.lSKpa

The result from experimental test gave a value for f, = 13.93Kpa

The presented theory will be verified with experimentd data avaiIabIe for severai

researches, Table (3.9). Big difference was observed between the theory and some

experimentd data, this cm be due to error in the experimental setup. The soil condition

could be incorrectly tested that gave misleading results. Generally errors cm happen

mainly due to the inaccuracy in evaluating the angle of soil shearing resistance "0''

experimentall y.

The procedure for the shah resistance for battered piles c m be performed as follows:

1- Determine the value of the ratio of (6J&JaVe is obtained from the chart given Figure

(3.19), knowing the pile Iength and diameter.

2- Knowing the ntio (6J@,),,, the angle of soil shearing resistance of soil. @ and the

angle of pile inclination, the values of KSI & Ksj are obtained from Figure (3.20)

and Figure (3.2 1) respectively. If (6JQm),, c 1 then the reduction factors R L for Kj

and R2 for Ks3 will be obtained from Figure (3.12 & 3.23) respectively

3- KS2 and Ks4 are obtained from the chart mentioned above for an angle of inclination =

0.

4- From equation (3.4) the battered pile shaft resistance is obtained.

Example:

By taking the given experimental data presented by (Hanna & Afrrim 1986) such that:

@ = 3 9 L = 1.52m D = 0.076m y = 15.6KN/m3

u= 10

Solution:

Since D = 0.0761~1 and UD = 40

from Figure (3.15) (&J@,)., = 0.33

From 6/@ = 1/3 charts at angle of inclination 10'.

KS3 = 5.2 & KSI = 9

KS2,& is evaluated by the sarne previous procedure but at angle 0'.

KSt*j = 7.2

By using equation (3.4)

Qs = 1/2 L ~ D ~ COS a[0.5Knl + 0.25K,; + 0.25Ks1] sin (6),

Qr = ?h * 1-52I * 0.076 * x * 15.6 COS 101 0.5 * 7.2 + 0.25*5.2 + 0.25*9]* sin 12.9

Qs = 6.7KN

The Experimental result was Qs = 5.86KN

The theory was verified by six experimental test results reported by Hanna &

Nguyen (1986). These tests were perforrned on two pile diameters 0.038m and 0.076m.

The soil has an angle of shearing resistance. @ = 39 and soil density. y = 16.6KNrn3. The

verification is presented in Table 3.10.

per i i i ~e~ ih l duta uiid the present tlieury l iw verlicd pile subj,jectcd tu

--

Data (Sm/$ ni) ave

Average Unit S l i d 1 l<esistaiice, fa (wDal

tlunnii & Nguyen ( 1986)

1 Vcsiç (1967)

Grcgcrscti cl al. ? ( 1 073) Brucy et al. (1991) t-- Munsour & 1 Kuuli~ian (1956)

Table 3.10, Cornparison befween experimentd data and the present thmry for batter pile subjected tto compression load.

QS (Io (eq 3.4)

0.8

a (Degrees)

10

Data i

Qs (KN) Experimentai

1.4

Pile Diameter L/D

i ! CoeCtecicnt of Lateral Eauth Pressure. K,, I - -

Vi r u

'a N

C Cn c 'A '4

c '4 CI

C C C C C C C C

C

Figure (3.23), Heductiur factor, Kr for given $ and S/$ for pussitive value of a After Cuquat & Kerisel, (1949)

3.4 UPLIFT CAPACITY OF DRIVEN PILES IN SAND

3.4.1 General Generally, quit often it is assumed that the shaft capacity of a pile for uplift is

identical to the compressive loading. However, there is wide spread expenmentd

evidence that in sand the shaft capacity is sigificantly lower for uplift? than for

compressive loading (De Nicola et a1 1993). Potential mechmism for such a difference

include the following:

1- Poisson's ratio during the expansion and the contraction of the pile shaft are not the

same and accordingly the radial effective stress field in the soil around the pile is dso

not the same.

2- Differences in the total stress field, with compressive loading tending to increase and

tensile loading tending to decrease the mean stress level in the soil.

3- Changing in mean effective stress due to rotation of the principle stress direction

depending on the detailed residual stress field dong the pile shaft, the degree of

principle - stress rotation will Vary with direction of loading.

3.4.2 Parametric Study

Since the uplift capacity of piles was not widely investigated the available

expenmental data was not enough to make a well parametric study. In the experimental

study the failure mechanism in investigated from the experimental data provided by

Kulhawy (1979). It was found that the soil movement decreases with depth. Surface

heaving was observed. This behavior is attributed to dilation that occurs when dense sand

is subjected to shear stresses. The same mode of failure was presented by Chattopadhyay

& Pise (1986) Figure (3.30). Never the less researchers did not agree on the value of the

angle ''O" however they agree that it is a function of "8' and "@". The most comenly used

value for "8" at the ground surface is:

0 = 35+2

Further more, it is found that the distance "x" which is the distance between the pile and

the failure surface increases with the increase of the angles "@" and "S.' the following

formula was presented by Chattopadhyay & Pise (1986).

Where:

= uD (50 - @)/26

Two types of analysis were perfonned, by assuming a 1Om pile length and a 0.5m

dîmeter. The First was to find out the effect of the angle of shearing resistmce "@" as

shown in Figure (3.31). The second, was to find the effect of the pile - soi1 angle of

friction "6" on the failure surface of the pile as shown in Figure (3.32). It was found that

the maximum value for "x" was at the ground surface and it decreases until it reaches a

constant value near the base. The value of "x" was found to be more sensitive to the

increase of "6" as compared to the increase of bb$". When "8' increases from 20 to 40

Figure 3.24, The failure pattern for pile under uplift.

Z = (m) 0 00

De+gees, the value of "x" was increased by 12m, on the other hand when "Q1' was

increased from 20 to 40 degrees, the value of "x" increaed about 0.5m only. The most

increase was done at the increase from 35 to 40 degrees and small changes occurred

before that. The previous analysis can give an explanation that the pile during uplift tends

to carry a certain volume of soi1 upwards which give it it's capacity the bigger the volume

the bitter is the pile capacity for tension. This volume has a force preventing it from

moving with the pile which is the soil shearing force that is governed by the angle "@".

From the above analysis it c m be concluded that increasing the pile roughness will give

better results than placing a smooth pile in a dense sand soil.

3.43 Cornparison Between Axial Compression and Tension Single Piles

Experimental data from Benngen et al (1979) and Mansour et al (1956) were used to

investigate the ratio between compression and tension capacity. Figure (3.33 8; 3.34)

support that tensile capacity for piles is lower than that for compression.

It was found that the ratio is small near the ground surface and the tip and it increases

between the two boundaries.

Due to the shortage in experimental data numericd modeling was a substitution to

understand the pile behavior under tension more clearly. De Nicola et ai (1993)

performed numerical mode1 for pile under tension, from the results he came to a

panmetric study will be done as a cornparison between compression and tension.

Shaft Friction, f, (KPs)

O 100 200 300 400

I t Compression i 4 Tension

Figure 3.17, Sliin friction profile from compression and uplift test in very dense

sand. After Beringen et al, (1979).

Skin Friction. f, t KPa j

- + - Compression

Figure 3.2& Skin friction profile from compression and uplift test (2 and 6) in dense

sand. After Mansour & Kaufman, (1956).

3.44 Effect of loading on Radial Stresses

Under tensile loading there is a tendency for the growth of radial stress to level

out as failure is approached This is because the total force applied reaches a fixed value

at failure. On the other hand, under compression, the pile load continues to increase once

failure occurs dong the shaft, due to additional load being carried by the base. This

accounts for the steeper rise in radial stress close to the point of failure.

In Figure (3.35) shows the changes in radial stress induced from loading at three

different depths. It can be noted that the final radial stress to initial stress is always

geater than unity in compression, and less than unity in tension. Figure (3.36) present a

profile of compression/ tension radial stresses around the pile shaft together with the ideal

case of normalized interface shear stress. The ideal Iine is for normalized shaft friction

had K = &. It is observed that shear stress mobilized in compression is greater than that

mobilized in tension. However, close to the pile tip the curves are reversed such that

compression friction becomes smaller than tensile friction due to the additional effects of

the stress field around the base of the pile.

This emply that a kind of relaxation t&es place in to the soil when the pile is under an

uplift force this can be explained by:

1- During uplift, the soil moves upwards with the pile, accordingly the eanh pressure

reduces from a high value to a lower one at failure such that the earth pressure

reaches to limit less thm the insitu earth pressure.

2- When the pile starts to move slightly upward a vacuum space will be formed beneath

the pile that gives a space for the soi1 around the pile to be dngged downwards to fiIl

this space this will result in a pressure relaxation around the pile.

Figure 3.29, Radial variation of radial stress at shaft failure (After De Nicola. 1993)

Fipre 3-34), Profiles of radial stress at shaft failure in tension and compression

After De Nicola, (1993)

3.4.5 Results

Based on the analysis on the pile tension capacity des ip chart was established to

evaluate the tension capacity by knowing the compression friction capacity. This is based

on the fact that the compression resistance c m be evaluated by following the procedure

developed in the previous section. The uplift capacity cm be then calculated as a ratio of

the compresion value. The chart represented gïves good agreement with the experimental

results. The represented chart in Figure 3.23 is established by using the formula presented

by De Nicola (1993).

Where:

9 = v, tan 6 (UD)(G,"&)

G,, = average shear modulus of soi1 over embedded depth of pile

Ep = Young's modulus of pile

v, = Poisson's ratio of pile

In the represented chart these values were considered:

&=?O* 103MPa

GW=5*LMpPa

v, = 0.3

3.4.6 Verification of Approxîmate method To assess the merit of the proposed approximate method, a total of 7 experimentai tests

were andyzed.

Table 3.11. Cornparison between experimental data and results from equation 3.6

Beringen et al. (1979) Brucy et al (1991) Mansure and Kaufman ( 1959)

Foray et ai (1998) 9

L

*After Randolph et al. (l!

0.8 0.8 1 Very dense sand 0.85 0.82 0.54 0.8 Pile driven

1 through a silt 1 strata into dense

sand 0.58 0.8 1 Very loose sand 0.69 0.8 0.83 0.78 6 = 3 0

CHAPTER 4

CONCLUSION AND RECOMMENDATIONS

4.1 CONCLUSION

A numerical mode1 was developed and used to examine the mechanism of the

shaft resistance of a vertical single pile under axial compression load driven in sand. A

parametnc study was perforrned on single verticd or batter pile subjected to compression

or uplift loading. The following can be concluded:

1- The diameter of the pile has an effect on the average unit shaft resistance, which was

not taken in account in previous studies. It was found that the average unit shaft

resistance increases by the increase of pile diameter. This has been explained by the

increase of the mobi lized (6d$&ve .

2- A chart is established to evaluate the (6d4,,),,, lcnowing the pile diameter, D and

rm.

3- For batter piles. the increases or decrease of pile capacity with the increase of pile

inclination depends on the value of "$", such that if "@" > 30 the shaft resistance

increases with the increase of pile inclination. On the other hand. if "Y' < 30 the shaft

resistance decreases.

4- A method for predicting the shaft resistance for vertical and battered piles is

presented with help of design charts.

5- For pile subjected to uplift, the pile - soi1 angle of friction "6" has more effecr on the

shaft resistmce as compared to the angle of shearing resistance "@**.

6- Design chart is presented to evaluate the ratio between uplift and Compression shaft

resistance capacity knowing "L.0" and "SI@".

4.2 RECOMMENDATIONS FOR FURTHER RESEARCH

To investigate the case of IateralIy loaded piles and piles subjected to negative shaft

resistance.

To study the critical depth for batter piles.

Field data are needed to examine the shaft resistance for piles under tension and batter

piles.

Examine the shaft resistance of vertical and batter piles in sand subjected to

compression and uplift to a group of piles.

The effect of pile diameter on the unit shaft resistmce should be investigated

experimentally by using wide range of pile's diarneter

to study the effect of the shape of the pile's base on piles subjected to uplift.

To study the failure mechanism associated with shaft resistance of vertical and batter

piles in sand subjected to compression and uplift.

1- Alawneh, Ahmed Shlash, Malkawi, Abdailah 1. Husein and Al-Deeky, Husein (1999),

"Tension Tests on Smooth and Rough Model Pile in Dry Sand," Canadian

Geotechnical Journal, 36, 1999, pp(746-755).

2- Azzouz, Amr S., Baligh, Mohsen M. and Whittle, Andrew J. (1990), "Shaft

Resistance of Pile in Clay," J. Geotech. Engrg, ASCE, 116, No2 pp.(205-221).

3- Chattopadhyay, B. C., and Pise, P. J. (1986). "Uplift Capacity of Piles in Sand," J.

Geotechnicai Engrg, ASCE, 112, No. 9 pp. (888 - 904).

4- Beringen, F. L., Windle, D., and Van Hooydonk, W. R. (1979). "Results of Loading

Test on Driven Pile in Sand." Recent development in the design and construction of

piles, ICE, London, England, 2 13-235.

5- Das, B.M (1989). "ültirnate uplift capacity of piles and piles groups in granular

soil", The International Conference on piling and deep foundations, London.

6- De Nicola, Anthony and Randolph, Mark F. (1993), "Tensile and Compressive

shaft Capacity of Pile in Sand," J. Geotech. En=., ASCE, 119 No. 12 pp(1952-

1973).

7- Feda, J. (1976). "Shaft resistance of piles", Sixth European Conference on Soi1

Mechanics and Foundation Engineering, Vienna.

8- Foray, B., Balachowski, L. and Colliat, J-L., "Bearing Capacity of Model piles

Driven into dense Overconsoiidated Sand," Canadian Geotechnicai Jownal, 35,

pp(374-385).

9- Hanna, A. M. And Afram, A. (1986). "hl1-w!t Cnpacity of Single Batter Piles in

Sand", Canadian Geotechnicd Journiil, Vol. 23, No.3, pp(387-393)

10- Ismael, h b i l F. and Al-Sanad, Hassan A. (1986). "Uplift Capacity of B o r d Piles in

Calcareous Soil," J. Geotech. Engrg, ASCE, 112 No. 10 pp(928-939).

I l - Kaihawy, Fred H., Kozera, David W. and Withiam, James L.(1979), "Uplift Testing

of Mode1 Drilled Shafts in Sand," J. Geotech. Engrg., ASCE, 120, No.8 pp.(1362-

138 1).

12- Kraft, Leland M., Focht, John A. and Arnerasinghe, Srinath F. (198 1), "Friction

Capacity of Pile Driven into Clay," J. Geotech, Engrg, ASCE, Vo1.107, No. GT11,

~~(1521-9541).

13-Lehane, B. M., Jardine, R. J., Bond, A. J. and Frank, R. (1993), "Mechanisms of

Shaft Friction in Sand from Instrurnented Pile Tests," J. Geotech. Engrg., ASCE,

1 19 NO. 1, pp.(19-35).

14-Mansur, C. I., and Kaufman, R. 1. (1958). "Pile Tests, Low-SiU Structure, Old

River, Louisiana." Trans., ASCE, 123, pp (7 15-743).

15- Meyerhof, G.G. (1973). "Uplift Resistance of Inclined Anchors and Piles", Proc.

8" Int. Conf. On Soil Mech. And Foundn. Engrg.. Moscow, Vol. 2.1, pp.(167-172).

16-Miller, G. A. and Lutenegger, A. J. (1997). " Influence of pile plugging on Shaft

resistance in Overconsolidation Clay" I. Geotech. Engrg., ASCE 123 No.(6),

~~~(525-533) .

17- Mochtar, Indrasurya B. and Edil, Tuncer B. (1988), "Shaft Resistance of Mode1 Pile

in Clay." J. Geotech. Engrg., ASCE, Vol. 1 14, No. 1 1, pp(1227-1243).

l&Randolph, M. F. and Murphy. B. S., ''Shaft capacity of Driven Piles in Clay".

Offshore Technology Conference 1985, no 4883.

lPRandolph, M. F., Dolwin, J. and Beck, R. (1994). "Driven Piles in Sand"

Géotechnique 44, NO. 3, pp- (427448).

20- Robinsky, E. 1. And Momson, C. F. (1964), '' Sand Displacement and Compaction

Around Model Friction Piles" Canadian Geotechnical Journal, 1, No.2, pp(8 1-93).

21-Tejchman, A. (1976). "Skin Resistance of Tension Pile", Sixth European

Conference on Soi1 Mechanics and Foundation Engineering, Vienna.

12- Tsien, S.I.(1986). "Shaft Friction Resistance of Long pipe piles Driven Into dense

sands", Paper OTC 5 150 presented at the Annual Offshore Technology Conference.

Documents

2001 - nlc-bnc.ca · At-rest Iateral earth pressure coefficient Initial in- situ vertical effective stress Upper Iirnit of the lateral stress coefficient Lirniting incremental unit