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~ w - u ~ - e / r r q x m y o f t t # United States Gov! rnmnt

MISCELLANEOUS PAPER GL-88-28

AXIAL RESPONSE OF THREE VIBRATORY AND THREE IMPACT DRIVEN H-PILES IN SAND

b

Larry M. Tucker, Jean-Louis Briaud

Briaud Engineers 1805 Laura Lane

College Station, Texas 77840

August 1988

Final Report

Approvyd For Pub l~c Release D t s t r ~ b u t ~ o n U-I rn~ted

f . \ - , - r I . . l , a . y Branch

- . ! c ! ,-~.-,i.:ir cb_nfEr !?, \ : . . < , ,. L ! , I , , L

U,S, Arhly t!, - . - . :;;; ir;eiiment Station . - . . ; , . - y .,., , ...c,L. i;., - . . :C-?,!ppI

Prepared for US Army Engineer Division Lower Mississippi Valley

Vicksburg, Mississippi 391 80-0080

Under Contract No. DACW39-88-MO-421

Monitored by Geotechnical Laboratory US Army Engineer Waterways Experiment Station PO Box E.31, Vicksburg, Mississippi 39180-0631

Destroy this report when no longer needed. Do not return i t to the originator.

The findings in this report are not to be construed as an official Department of the Army position unless so designated

by other authorized documents.

The contents of t h ~ s report are not to be used for advertls~ng, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of

such commercial products.

r /-

U n c l a s s i f i e d - - SECURITY CLASSIFICATION OF T ~ . S PAGE

M i s c e l l a n e o u s Paper G L - 8 8 - 2 8

p i l e s i n Sand

l a p s e a f t e r d r i v i n g was a l s o s t u d i e d . The p i l e s were i n s t r u m e n t e d s o tha: b o t h p i l e t i p l o a d s a n d l o a d t r a n s f e r a l o n g t h e p i l e c o u l d be d e t e r m i n e d .

DD Form 1473, JUN 86 Prev~our editions are obsolete. SECUPITY CLASSIFICATION OF THIS PAGE

U n c l a s s i f i e d

PREFACE

This report was prepared by Mr. Larry M. Tucker and Dr. Jean-Louis

Briaud, College Station, Texas, under contract to the US Army Engineer Water-

ways Experiment Station (WES), Vicksburg, Mississippi, for the US Army Engi-

neer Division, Lower Mississippi Valley. The report was prepared under Con-

tract No. DACW39-88-MO-421.

This report was reviewed by Mr. G. Britt Mitchell, Chief, Engineering

Group, Soil Mechanics Division (SMD), Geotechnical Laboratory (GL), WES.

General supervision was provided by Mr. Clifford L. McAnear, Chief, SMD, and

Dr. William F. Marcuson 111, Chief, GL.

COL Dwayne G. Lee, EN, is Commander and Director of WES. Dr. Robert W.

Whalin is Technical Director.

TABLE OF CONTENTS

BACKGROUND . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1

T H E S O I L . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

THE PILES AND LOAD TEST PROCEDURES . . . . . . . . . . . . . . . . 11

LOAD TEST RESULTS . . . . . . . . . . . . . . . . . . . . . . . . 1 9

R e s i d u a l S t r e s s e s . . . . . . . . . . . . . . . . . . . . . . 1 9 L o a d T e s t R e s u l t s . . . . . . . . . . . . . . . . . . . . . . 1 9 P i l e D r i v i n g A n a l y z e r R e s u l t s . . . . . . . . . . . . . . . . . 52

DISCUSSION OF THE RESULTS . . . . . . . . . . . . . . . . . . . . 5 3

Top L o a d - S e t t l e m e n t C u r v e s . . . . . . . . . . . . . . . . . 5 3 . . . . . . . . . . . . . . . . . . . . . . L o a d D i s r r i b u t i o n 5 6

. . . . . . . . . . . . . . . . . . . . . . . . L o a d T r a n s f e r 5 8 . . . . . . . . . . . . . . . . . . . . . . . E f f e c t o f T ime 5 8

. . . . . . . . . . . . . . . . . CONCLUSIONS AND RECOMMENDATIONS 6 6

. . . . . . . . . . . . . . . . . . . . . . . . . . . . REFERENCES 6 8

iii

F i g u r e

1

2

3

4

5

6

7

8

9

10

I 1

I'

LIST OF FIGURES

Page

L o c a t i o n o f B o r i n g s and I n s t r u m e n t a t i o n . . . . . . . . 4

P r o f i l e s o f S t a n d a r d P e n e t r a t i o n T e s t Blowcounts . . . . 5

CPT P r o f i l e s f o r P o i n t R e s i s t a n c e . . . . . . . . . . . 6

CPT P r o f i l e s f o r F r i c t i o n R e s i s t a n c e . . . . . . . . . . 7

Net L i m i t P r e s s u r e P r o f i l e . . . . . . . . . . . . . . . 8

F i r s t Load Modulus P r o f i l e . . . . . . . . . . . . . . . 9

. . . . . . . . . . . . . . . . . R e l o a d Modulus P r o f i l e 10

. . . . . . . . . . . . L o c a t i o n o f P i l e I n s t r ~ m e n t a t i o n 12

. . . . . . . . . . . . . . . . . . T e s t P i l e L o c a t i o n s 1 3

. . . . . . . . . . . . . . I m p a c t P i l e D r i v i n g Records 17

. . . . . . . . . . . . . V i b r a t o r y P i l e D r i v i n g Records 18

. . . . . . . . . . . L o a d - S e t t l e m e n t Curve f o r P i l e 11 2 1

. . . . . . . Raw Load V e r s u s Depth P r o f i l e s f o r P i l e 11 22

. . . . C o r r e c t e d Load Ver sus Depth P r o f i l e s f o r P i l e 11 23

I n t e r p r e t e d Load Versus Depth P r o f i l e s f o r P i l e 11 . . . 24

. . . . . . F r i c t i o n V e r s u s Movement Curves f o r P i l e 11 2 5

P o i n t R e s i s t a n c e Versus Xovement Curve f o r P i l e 11 . . . 26

. . . . . . . . . . . L o a d ~ S e t t l e m e n t C u r v e f o r P i l e l I R 27

. . . . . . Raw Load V e r s u s Depth P r o f i l e s f o r P i l e 1 I R 28

C o r r e c t e d Load Ver sus Depth P r o f i l e s f o r P i l e 1 I R . . . 29

I n t e r p r e t e d Load Ver sus Oepth P r o f i l e s f o r P i b e 1 I R . . 30

. . . . . . F r i c t i o n V e r s u s Movement Curves f o r P i l e 1 I R 3 1

P o i n t R e s i s t a n c e Versus Hovement Curve f o r P i l e 1 I R . . 32

. . . . . . . . . . . L o a d - S e t t l e m e n t Curve f o r P i l e 1V 33

. . . . . . . Raw Load V e r s u s Depth P r o f i l e s f o r P i l e 1 V 34

Figure

2 6

2 7

2 8

2 9

3 0

3 1

3 2

3 3

3 4

3 5

3 6

3 7

3 8

3 9

4 0

4 1

4 2

4 3

4 4

4 5

4 6

4 7

Page

Interpreted Load Versus Depth Profiles for Pile 1V . . . 35

Friction Versus Movement Curves for Pile 1V . . . . . . 36

. . . Point Resistance Versus Movement Curve for Pile 1V 37

. . . . . . . . . . . Load-Settlement Curve for Pile 1VR 38

. . . . . . Raw Load Versus Depth Profiles for Pile 1VR 39

Interpreted Load Versus Depth Profiles for Pile 1VR . . 40

. . . . . . Friction Versus Movement Curves for Pile 1VR 41

Point Resistance Versus Movement Curve for Pile 1VR . . 42

. . . . . . . . . . . Load-Settlement Curve for Pile 2 1 4 3

Raw Load Versus Depth Profiles for Pile 21 . . . . . . . 44

. . . . Corrected Load Versus Depth Profiles for Pile 21 45

Interpreted Load Versus Depth Profiles for Pile 21 . . . 46

. . . . . . Friction Versus Movement Curves for Pile 21 47

Point Resistance Versus Movement Curve for Pile 21 . . . 48

. . . . . . . . . . . Load-SettLement Curve for Pile 2V 49

. . . . . . . . . . . Load-Settlement Curve for Pile 31 50

Load-Settlement Curve for Pile 3V . . . . . . . . . . . 51

. . . . . . . . . . Comparison of Load-Settlement Curves 54

Friction Versus Depth Profiles . . . . . . . . . . . . . 57

Comparison of Point Load Transfer Curves . . . . . . . . 5 9

. . . . . . . . . Normalized Point Load Transfer Curves 60

Normalized Friction Transfer Curves for Impact DrivenPiles . . . . . . . . . . . . . . . . . . . . . . 62

Normalized Friction Transfer Curves for Vibratory DrivenPiles . . . . . . . . . . . . . . . . . . . . . . 63

Pile Capacity at 0.25 in Settlement Versus Time . . . . 64

. . . . . . . . . . . Pile Ultimate Capacity Versus Time 64

LIST OF TABLES

Table Page

. . . . . . . . . . . . . . . 1 Load Test Program Summary 15

2 Specifications for Delmag D22 Impact Hammer . . . . . . 16

3 Specifications for ICE-216 Vibratory Driver . . . . . . 16

. . . . . . . . . . . . . 4 Pile Driving Analyzer Results 52

. . . . . . . . . . . . . 5 Analysis of Pile Test Results 55

BACKGROUND

I n t h e s p r i n g and summer o f 1986 a s e r i e s of v e r t i c a l l o a d t e s t s

were c a r r i e d o u t on i n s t r u m e n t e d p i l e s d r i v e n i n sand a t H u n t e r ' s P o i n t

i n San F r a n c i s c o . The F e d e r a l Highway A d m i n i s t r a t i o n s p o n s o r e d two

p r o j e c t s on impact d r i v e n p i l e s : one on t h e t e s t i n g of f i v e s i n g l e p i l e s

and one on t h e t e s t i n g o f a f i v e p i l e group (Ng, B r i a u d , Tucker 1988a ;

1 9 8 8 b ) . Then, t h e Lower M i s s i s s i p p i V a l l e y ~ j i v i s i o n ( W D ) of t h e Corps

o f E n g i n e e r s o p e r a t i n g th rough t h e USAE Waterways Experiment S t a t i o n

(WES) sponso red a p r o j e c t on t h e compar ison o f impact d r i v e n p i l e s and

v i b r a t o r y d r i v e n p i l e s . S u b s e q u e n t l y , t h e Deep Foundat ion I n s t i t u t e

d r o v e a number o f p i l e s w i t h v a r i o u s v i b r a t o r y hammers t o compare t h e

hammers' e f f i c i e n c i e s .

T h i s r e p o r t i s a n a n a l y s i s o f t h e p i l e l o a d t e s t s sponso red by t h e

W D t h r o u g h WES comparing impact and v i b r a t o r y d r i v e n p i l e s . The s i t e

i s c h a r a c t e r i z e d , t h e l o a d t e s t s a r e d e s c r i b e d , t h e l o a d t e s t s r e s u l t s

a r e a n a l y z e d and d i s c u s s e d , and recommendations and c o n c l u s i o n s a r e

made.

THE SOIL

The soil has been described in detail by Ng et al. (1988a). Below

a 4 in thick asphalt concrete pavement is a 4.5 ft thick layer of sandy

gravel with particles up to 4 inches in size. From 5 ft to 40 ft depth

is a hydraulic fill made of clean sand (SP). Below 40 ft, layers of

medium stiff to stiff silty clay (CH) are interbedded with the sand down

to the bedrock. The fractured serpentine bedrock is found between 45 £ E

and 50 ft depth. The water table is 8 ft deep

Many tests have been performed at the site including: standard

penetration tests with a donut hammer and a safety hammer, sampling with

a Sprague-Henwood sampler, cone penetrometer tests with point, friction

and pore pressure measurements, preboring and selfboring pressuremeter

tests, shear wave velocity tests, dilatometer tests and stepped-blade

tests. The CPT, SPT and stepped-blade tests were performed beiore and

after driving and testing of the FNWA test piles. The location of sel-

ected soundings are shown on Figure l. The corresponding profiles are

shown on Figures 2 through 7. The hydraulic fill has the following

average properties:

Friction angle Water content Dry unit weight

D60 D l ~ SPT blow count CPT tip resistance PMT net limit pressure Shear modulus (from shear wave velocity measurements)

32' to 35O 22.6 % 100 pcf 0.8 mm 0.7 mn 15 bpi 65 tsf 7 tsf

400 tsf

10 F E E T .

S STEP BLADE TESTS S P T TEST BORINGS

C CONE PENETROMETER TESTS D DILATOMETER TESTS E EXTENSOMETER P PIEZOMETER P M PREBORING PRESSUREMETER TESTS S P SELFBORING PRESSUREMETER TESTS

Figure 1. Location of Borings and Instrumentation

SPT N VALUE (BLOWS/FT>

Figure 2. P r o f i l e s o f Standard Penetration Tes t Blowcounts

5

,-" _ _ _ _ _ _"." -_._l _ l l < _ _ n --, 3- I F - ---_* -- --.---- -- .----- - -

LOCAL CONE FRICTION Cksf)

++ CPT 2

x CPT 3

AVERAGE

CPT T e s t s P e r f o r - med w i t h S t a n d a r d E l e c t r i c C o n e .

Figure 4. CPT Profiles for Friction Resistance

7

"7,---.- u;-ar*.r..-71 -P-TT".*VW-----.--------- - -

NET LIMIT PRESSURE 1 (kPo>

e-----+ PBPMT PC: -4 PRESSUREMETER

Figure 5. Net Limit Pressure Profile

8

FIRST L O A D MODULUS Eo (MPa)

Figure 6 . F i r s t Load Modulus P r o f i l e

3

RELOAD MODULUS E r (MPo)

0 10 20 30 40 50 60 70 80 90 100 0

PBP?lT E r

5

*----- * SBP?lT E

16 PRESSUREMETER

15

20

25

30

35

40

45

5Q

55

Figure 7 . Reload Modulus P r o f i l e

10

THE PILES AND M A D TEST PROCEDURES

Three HP14x73 s t e e l H p i l e s were u s e d i n t h i s program. They were

a l l embedded 30 f t be low t h e ground s u r f a c e ; however , a 4 . 5 f t d e e p , 1 4

i n d i a m e t e r h o l e was d r i l l e d p r i o r t o p i l e i n s e r t i o n f o r t h e impac t

d r i v e n p i l e s , making t h e t r u e p i l e embedment e q u a l t o 2 5 . 5 f t . F o r t h e

v i b r a t o r y d r i v e n p i l e s a h o l e was d r i l l e d t h r o u g h t h e 4 i n t h i c k a s p h a l t

l a y e r o n l y , making t h e embedment e q u a l t o 2 9 . 5 f t . Each p i l e had two

a n g l e s ( 2 . 5 x 2 . 5 x 3/16 i n c h e s ) welded t o t h e s i d e s o f t h e p i l e web a s

p r o t e c t i o n f o r t h e i n s t r u m e n t a t i o n .

The f i r s t p i l e was one of t h e s i n g l e p i l e s u s e d i n t h e FHWA program

( r e f e r r e d t o a s p i l e 1 ) . P i l e 1 was i n s t r u m e n t e d w i t h s e v e n l e v e l s o f

s t r a i n gauges and a t e l l t a l e a t t h e p i l e t i p ( F i g u r e 8 ) . T h i s p i l e was

c a l i b r a t e d b e f o r e d r i v i n g and t h e p i l e s t i f f n e s s was measured f o r u s e i n

t h e d a t a r e d u c t i o n . The measured v a l u e o f p i l e s t i f f n e s s ( A E ) was

614908 k i p s . T h i s v a l u e was used f o r a l l t h r e e p i l e s . P i l e d r i v i n g

a n a l y z e r measurements were o b t a i n e d d u r i n g t h e d r i v i n g o f p i l e 1 w i t h a n

impact hammer. P i l e 1 was then l o a d t e s t e d i n compress ion 30 d a y s a f t e r

i t was d r i v e n (FHWA p r o g r a m ) : t h i s i s l o a d t e s t 11. P i l e 1 was t h e n

r e t e s t e d a t 6 7 days a f t e r d r i v i n g : t h i s i s l o a d t e s t 1 I R . A f t e r p i l e 1

was r e t e s t e d , t h e p i l e was r e s t r u c k w i t h a n impac t hammer and p i l e d r i v -

i n g a n a l y z e r measurements were o b t a i n e d . P i l e 1 was t h e n e x t r a c t e d and

v i b r o d r i v e n a b o u t 30 f t from t h e impact t e s t ( F i g u r e 9 ) . I t was l o a d

t e s t e d a t 33 days a f t e r d r i v i n g ( l o a d t e s t 1V) and a g a i n a t 63 d a y s

a f t e r d r i v i n g ( l o a d t e s t 1VR). A f t e r l o a d t e s t 1 V R t h e p i l e was s t r u c k

w i t h a n impac t hammer and p i l e d r i v i n g a n a l y z e r measurements were ob -

t a i n e d .

PILE 1 PILE 2

TELL TALE 7

GAGES

LCOVER ANGLSS

1 STRAIN GAGE

f i POTENTIOMETER

CTRAIh' GAGE

TELL TALE

F i g u r e 8. Location of Pile Instrumentation

I0 F E E T

Figure 9 . T e s t P i l e Locat ions

The second p i l e i ~ i l e 2 ) was ins t rumented w i t h two l e v e l s o f s t r a i n

gauges : one a t t h e mid-po in t and one a t t h e p i l e t i p ( F i g u r e 8 ) . P i l e 2

was impact d r i v e n and t e s t e d a t 65 days a f t e r d r i v i n g : t h i s i s l o a d t e s t

21. P i l e 2 was then e x t r a c t e d and v i b r o d r i v e n and t e s t e d a t 64 days

a f t e r d r i v i n g . Th i s i s l o a d t e s t 2V. A f t e r l o a d t e s t 2V, t h e p i l e was

s t r u c k w i t h a n impact hammer and p i l e d r i v i n g a n a l y z e r measurements were

o b t a i n e d .

The t h i r d p i l e ( P i l e 3 ) was n o t i n s t r u m e n t e d . I t was impact d r i v e n

and t e s t e d a t 12 days a f t e r d r i v i n g : t h i s i s l o a d t e s t 31 . P i l e 3 was

t h e n e x t r a c t e d and v i b r o d r i v e n . I t was t e s t e d a t 1 2 days a f t e r d r i v i n g :

t h i s i s l o a d t e s t 3V. Table 1 summarizes t h e e i g h t load t e s t s p r e s e n t e d

i n t h i s r e p o r t .

The impact d r i v e n p i l e s were i n s t a l l e d u s i n g a Delmag D22 d i e s e l

hammer a t f u l l t h r o t t l e . A l l r e s t r i k e measurements x e r e a l s o o b t a i n e d

u s i n g t h i s hammer. The hammer was r a t e d a t approx imate ly 40 ,000 f t - l b s

maximum e n e r g y . D e t a i l s of the hammer a r e g iven i n Table 2 . The d r i v -

i n g r e c o r d s f o r t h e impact d r i v e n p i l e s a r e shovn i n Figure 1 0 .

The v i b r a t o r y d r i v e n p i l e s were i n s t a l l e d w i t h a ICE-216 v i b r a t o r y

hammer. D e t a i l s of the hammer a r e g iven i n Table 3 . The p e n e t r a t i o n

r a t e s v e r s u s dep th records f o r these p i l e s a r e shown i n F igure 11.

The l o a d t e s t procedure has been d e s c r i b e d i n d e t a i l by Ng e t a l .

(1988) . I n g e n e r a l , t h e t e s t loads were a p p l i e d i n increments of 10

p e r c e n t o f t h e e s t i m a t e d u l t i m a t e l o a d . Each l o a d s t e p was h e l d f o r a t

l e a s t 30 m i n u t e s , wi th the load be ing moni tored c o n t i n u o u s l y . A l l r e a d -

i n g s from e l e c t r o n i c a l l y monitored i n s t r u m e n t s were recorded e v e r y 5

m i n u t e s . The d a t a was s t o r e d on f loppy d i s k f o r d a t a r e d u c t i o n .

Table 1. Load T e s t Program Summary

T e s t P i l e s

1 I - FHWA P i l e ( Impact)

1 I R - FHWA P i l e ( Impact)

1 V - FHWA P i l e ( V i b r a t o r y )

1VR - FHWA P i l e ( V i b r a t o r y )

2 1 - New P i l e ( Impact)

2V - New P i l e ( V i b r a t o r y )

3 1 - New P i l e ( Impact)

3V - New P i l e ( V i b r a t o r y )

30 Day t e s t

67 Day t e s t

33 Day t e s t

63 Day t e s t

65 Day t e s t

64 Day t e s t

1 2 Day t e s t

13 Day t e s t

Notes :

A . 11, l I R , 1 V and 1VR - Seven s t r a i n gauge l e v e l s

B . 2 1 and 2V - Two s t r a i n gauge l e v e l s

C . 31 and 3V - No s t r a i n gauges

Table 2 . S p e c i f i c a t i o n s f o r Delmag D22 Impact Hammer

Rated energy 39,700 f t - l b s Ram weight 4 , 8 5 0 l b s Blows/minute 42 - 60 Maximum explos ive

p r e s s u r e on p i l e 158,700 l b s Working weight 11 ;275 l b s Drive Cap weight 1 , 5 0 0 l b s

Table 3 . S p e c i f i c a t i o n s f o r ICE-216 V i b r a t o r y Dr iver

E c c e n t r i c moment 1000 i n - l b s Frequency 400-1600 vpm Amplitude 1/4 - 3/4 inches Power 115 HP P i l e clamping f o r c e 50 t o n s Line p u l l f o r e x t r a c t i o n 30 t o n s Suspended weight with clamp 4825 l b s Length 47 inches Width 16 i n c h e s Throa t wid th 1 2 i n c h e s Height w i t h clamp 78 i n c h e s Height w i t h o u t clamp 68 i n c h e s

PENETRATION BMWCOUNT (blows/f t )

(ft> PILE 1 PILE 2 PILE 3

1 RUN NA* RUN

TOTAL 9 6 13 1

* Not a v a i l a b l e

Figure 1 0 . Impact P i l e Dr iv ing Records

P i l e 1 P i l e 2 P i l e 3

Rate o f Rate o f Rate o f

Depth Time Penetration Time Penetration Tim Penetration

( f t ) ( s e c ) ( f t / m i n ) ( s e c ( f t /min) ( s e c ) ( f t /min)

Figure 11. Vibratory P i l e Dr iv ing Records

LOAD TEST RESULTS

Residual Stresses

Residual driving stresses were measured for pile 11. The stress

profile was not monitored between load test 11 and test 1IR. Therefore

the residual stress profile after driving was also used for load test

1IR. Since additional residual stresses are usually induced due to a

compression test, this profile is slightly in error. The residual

stress profile is the first load profile shown in Figure 14.

An attempt was made to record the residual driving stresses for

pile 21. However, the readings obtained were judged unreliable. There-

fore, the residual stress profile from pile 11 was used in reducing the

load test data for pile 21 (Figure 14).

The vibratory driven piles were assumed to have no residual driving

stresses. No attempt was made to verify this. However, published data

substantiate this assumption (Hunter and Davisson, 1969).

Load Test Results

The raw data from the floppy disks was reduced co obtain the fol-

lowing information:

Load-settlement curve at the pile top

Load versus depth profiles - a. raw data b. including residual loads c. interpreted profile

Load transfer curve (friction and point)

The number of plots possible for a given load test depends upon the

amount of instrumentation on the pile

As stated above, three sets of load versus depth profiles are plot-

ted for those piles instrumented with strain gauges. The first set of

p r o f i l e s w i l l b e t h e raw d a t a a s measured d u r i n g the t e s t . S i n c e a l l

i n s t r u m e n t a t i o n was ze roed j u s t b e f o r e t h e l o a d t e s t , t h e s e p r o f i l e s do

n o t i n c l u d e r e s i d u a l s t r e s s e s .

A s e c o n d s e t o f p r o f i l e s i s shown f o r t h o s e p i l e s d r i v e n w i t h a n

impac t hammer which i n c l u d e the r e s i d u a l l o a d s i n the p i l e d > ~ e t o d r i v -

i n g . T h i s s e t o f p r o f i l e s i s n o t shown f o r t h e v i b r a t o r y d r i v e n p i l e s

s i n c e i t h a s been a s s m e d t h a t no r e s i d u a l s t r e s s e s a r e i n l x c e d due t o

i n s t a l l a t i o n .

The t h i r d s e t o f p r o f i l e s i s t h e i n t e r p r e t e d l o a d v e r s u s d e p t h

c u r v e s . The measured d a t a shows some i r r e g u l a r i t i e s vh ich cay be due t o

d r i f t i n t h e r e a d i n g s , t empera tu re f l u c t u a t i o n o r gauge r n a l f * ~ n c t i o n . A

gauge r e a d i n g was o m i t t e d e n t i r e l y i f i t was known t h a t t he gauge was

d e f i n i t e l y m a l f u n c t i o n i n g . This was t h e c a s e w i t h the gaugs a t a d e p t h

o f 25 f t f o r p i l e 1 V and lVR, and f o r b o t h gauge l e v e l s on p i l e 2 V . Any

o t h e r i r r e g u l a r i t i e s were smoothed by f i t t i n g a second o r d e r po lynomia l

c u r v e t h r o u g h t h e d a t a . These c u r v e s a r e shown a s t he t h i r d s e t o f l o a d

v e r s u s d e p t h p r o f i l e s . Other i n t e r p r e t a t i o n s a r e obv ious ly p o s s i b l e .

However, t h e f i t of t h e c u r v e s matches q u i t e w e l l wi th what one would

draw m a n u a l l y .

The r e s u l t s f o r l o a d t e s t 11 a r e g i v e n i n F i g u r e s 1 2 :hrough 1 7 ;

l o a d t e s t 1IR r e s u l t s a r e shorn i n F i g u r e s 18 through 2 3 ; load t e s t l V

r e s u l t s a r e shown i n F i g u r e s 24 th rough 2 8 ; l o a d t e s t 2VR r e s u l t s a r e

shown i n F i g u r e s 29 through 3 3 ; l o a d t e s t 21 r e s u l t s a r e shot+.n i n F i g -

u r e s 34 t h r o u g h 39 . L o a d - s e t t l e m e n t c u r v e s a t t h e p i l e t o p a r e shown i n

F i g u r e s 40 t h r o u g h 42 f o r l o a d t e s t s 2 V , 31 and 3 V r e s p e c t i v e l y .

TOP L O A D (KIPS)

0 50 1 0 0 1 SO O

30 BAY 'BEST

Figure 1 2 . Load-Settlement Curve for Pile 11

TOP LOAD (KIPS)

Figure 18. Load-Settlement Curve f o r Pile 1 I R

TOP LOAD (KIPS)

Figure 24. Load-Settlement Curve for Pile 1V

(3S

W

33NV

1SIS

3rJ df

l llNn

TOP LOAD (KIPS)

0 SO 100 150 200 0

. 5

63 DAY TEST

0

i H V 1

C Z W I W d t- C W

1.5 a 0 I-

2

2. 5

Figure 29 . Load-Sett lement Curve f o r P i l e 1VR

65 DAY TEST

Figure 34. Load-Settlement Curve for Pile 21

TOP LOAD (KI PSI

O 50 150 ZOO 0

. 5

64 DAY TEST

1

1.5

2

2. 5

Figure 40. Load-Settlement Curve for Pile 2V

49

TOP LOAD (KIPS)

Figure 41. Load-Settlement Curve for Pile 31

5 0

TOP LOAD (KIPS)

0 50 1 DO 150 200

13 DAY TEST

Figure 42. Load-Settlement Curve for Pile 3 V

Pile Drivine Analyzer Results

The pile driving analyzer (PDA) consists of the dynamic monitoring

of strain gauges and accelerometers attached to the pile close to the

top. The strain measurements are used to obtain force measurements as a

function of time, and the accelerometer measurements are integrated to

obtain velocity versus time. From these two measurements various para-

meters may be calculated, including the maximum energy delivered to the

pile and the static resistance of the pile by the CASE method (Rausche

et al., 1985). This static resistance represents the PDA capacity pre-

diction.

Pile driving analyzer measurements were made on pile 1 (driven with

the impact hammer) for both initial driving and for restrike after the

load tests were performed, and on piles 1 and 2 (driven with the vibra-

tory hammer) for restrike after the load tests were performed. The

results are presented in Table 4.

Table 4. Pile Driving Analyzer Results (from Holloway, 1987)

Pile Blowcount Maximum Maximum Estimated Force Energy Capacity* (kips) (kip-ft) (kips)

1 I ** 12/12 in. 340 - 5 10 5-15 140 - 165

IT*** 6/6 in. 350 - 505 10-17 145 - 200

1V*** 7/6 in. 300-415 4-13 120- 140

2V*** 14/12 in. 355 - 520 5-11 125 - 150

* Case method capacity assumes a damping constant J=0.25 ** Initial driving

*** Restrike

DISCUSSION OF THE RESULTS

Top Load-Settlement Curves

The top load-settlement curves for the eight load tests are shown

together in Figure 4 3 . Two main observations can be made. First, in

all cases the vibratory driven piles have a lower initial stiffness than

the impact driven piles. Second, the impact driven piles show more

consistent response between piles than the vibratory driven piles.

In an effort to quantify these observations four measurements have

been made from the load-settlement curves. First, the ultimate load has

been defined as the load corresponding to a settlement of one-tenth of

the equivalent pile diameter plus the elastic compression of the pile

under that load as if it acted as a free-standing column. This line has

been drawn on Figure 4 3 . Second, the load at a settlement of 0.25 in

has been obtained from the load-settlement curves. Third, the settle-

ment at one-half the defined ultimate load has been obtained. Fourth,

the piles' stiffness response has been calculated as one-half the de-

fined ultimate load divided by the settlement occurring at that load.

These four items are tabulated in Table 5 for the eight load tests.

Table 5 shows that there is only one percent difference in the

average ultimate load between the impact driven piles and the vibratory

driven piles. However, the coefficient of variation of the ultimate

loads for the vibratory driven piles is 4 . 3 times higher than that of

the impact driven piles.

The second column of Table 5 shows that at a settlement of 0.25 in

the impact driven piles carry 33 percent more load than the vibratory

driven piles. The coefficient of variation of this load for the vibra-

TOP LOAD (KIPS)

0 SO 1 OD I50 200

Figure 4 3 . Comparison of Load-Settlement Curves

5 4

Table 5. Analysis of Pile Test Results

-

Pile Load at Load at Settlement at Initial D/10 + PL/AE 0.25 in. Qul t/2 Stiffness

(kips) (kips) (in) (kips/in)

3 1 160 120 0.088 909

Average 16 6 124 0.094 8 9 4

Standard Deviation 7.5 5.3 0.0075 9 3

Coefficient of Variation 0.045 0.043 0.081

Average 164 9 3 0.195

Standard Deviation 32

Coefficient of Variation 0.195 0.182 0.446

Impact 1.01

Vibratory

tory driven piles is 4.2 times higher than that of the impact driven

piles.

The settlement at one-half the ultimate load for the vibratory

driven piles is over two times larger than that of the impact driven

piles, and the coefficient of variation is 5.5 times larger.

The initial stiffness response of the pile, defined as one-half the

ultimate load divided by the settlement at that load, for the impact

driven piles is 1.91 times that of the vibratory driven piles. The

coefficient of variation of this stiffness for the vibratory driven

piles is 3.6 times that of the impact driven piles.

Load Distribution ----

The load distribution of the vibratory driven piles differs greatly

from that of the impact driven piles. By comparing Figures 15, 21, 26,

31, and 37 it can be seen that at max5,mum load the impact driven piles

carry approximately 51% of the load in point resistance, whereas the

vibratory driven pile carries only 13% of the load in point resistance.

The reload test on the vibratory driven pile (Figure 31) shows that the

point resistance has increased to 29% of the total load. This indicates

that the difference in the driving process causes a different soil

reaction, but the difference becomes less upon repeated loading.

The unit friction profiles at maximum loading are shown in Figure

44 for the five instrumented pile tests. Again in can be seen that

there is a definite difference in soil reaction between the impact

driven and vibratory driven piles; and that the difference becomes less

pronounced upon repeated loading.

Load T r a n s f e r

The H - p i l e p r e s e n t s a p rob len when comput ing u n i t t i p r e s i s t a n c e

and u n i t f r i c t i o n v a l u e s : m a t i s t h e f a i l u r e s u r f a c e ? One p o s s i b l e

a s sumpt ion i s t h a t t h e p i l e f a i l s a l o n g a r e c t a n g l e which e n c l o s e s i h e

H - p i l e , w i t h a s o i l p l u g forming between t h e f l a n g e s . Another p o s s i b i l -

i t y i s t h a t t h e p i l e f a i l s a l o n g the s o i l - p i l e i n t e r f a c e , w i t h no s o i l

p l u g f o r m i n g . P r e v i o u s r e s e a r c h has shown t h a t a b e t t e r a s sumpt ion may

be t h a t t h e f a i l u r e s u r f a c e i s i n between t h e p r e v i o u s two a s s u m p t i o n s

w i t h a s o i l p l u g f i l l i n g h a l f t h e a r e a be tween t h e f l a n g e s (Kg e t a l . ,

1 9 8 8 ) . For t h e HP14x73 p i l e s used i n t h i s s t u d y t h i s a s sumpt ion g i v e s

2 t h e f o l l o w i n g p r o p e r t i e s : Pe r ime te r = 7 0 . 4 7 i n , T i p a r e a = 1 0 9 . 8 i n .

T h i s a s s u m p t i o n i s u s e d f o r a l l f u r t h e r a n a l y s e s .

F i g u r e 45 shows t h e u n i t t i p r e s i s t a n c e v e r s u s t i p movernent c u r v e s

f o r t h e f i v e i n s t r u m e n t e d p i l e s . F igu re 46 shows t h e same c u r v e s w i t h

t h e t i p r e s i s t a n c e n o r m a l i z e d by d i v i d i n g by t h e maximum t i p r e s i s t a n c e .

These two f i g u r e s show a fundamentally d i f f e r e n t r e a c t i o n between t h e

v i b r a t o r y d r i v e n p i l e s and the impact d r i v e n p i l e s : The t i p r e s i s t a n c e

of t h e v i b r a t o r y d r i v e n p i l e s i s zuch lower t h a n t h a t of t h e impac t

d r i v e n p i l e s , and t h e s l o p e o f the c u r v e i s d i f f e r e n t . However, t h e

d i f f e r e n c e i n s h a p e a l m o s t v a n i s h e s upon r e l o a d i n g .

The s h a p e o f t h e t i p r e s i s t a n c e c u r v e o f t h e i n i t i a l l o a d i n g o f t h e

v i b r a t o r y d r i v e n p i l e s u g g e s t s t h a t t h e s a n d immedia t e ly under he p i l e

p o i n t i s i n i t i a l l y l o o s e b u t d e n s i f i e s a s t h e p i l e i s l o a d e d . I n d e e d ,

a t h i g h e r l o a d s t h e t i p r e s i s t a n c e b e g i n s t o i n c r e a s e a t a f a s t e r r a t e ,

r a t h e r t h a n r e a c h i n g a l i m i t i n g va lue a s t h e o t h e r t e s t s show. By com-

p a r i n g t h e c u r v e s f o r P i l e 11 and l I R , i t c a n b e s e e n t h a t t h e impac t

d r i v e n p i l e s do n o t undergo such a change i n b e h a v i o r be tween i n i t i a l

l o a d i n g and r e l o a d i n g .

F i g u r e s 47 and 48 show t h e n o r m a l i z e d f r i c t i o n movement c u r v e s f o r

t h e impact d r i v e n p i l e s and v i b r a t o r y d r i v e n p i l e s , r e s p e c t i v e l y . F i g -

u r e 47 shows a g a i n t h a t t h e impact d r i v e n p i l e s a r e v e r y c o n s i s t e n t i n

t h e i r r e s p o n s e and t h a t no change i n b e h a v i o r o c c u r s be tween i n i t i a l

l o a d i n g and r e l o a d i n g . However, F i g u r e 48 shows t h a t t h e v i b r a t o r y

d r i v e n p i l e e x h i b i t s a g r e a t change i n b e h a v i d r between i n i t i ' a l l o a d i n g

and r e l o a d i n g . The f i v e c u r v e s f o r t h e i n i t i a l l o a d i n g have a much

s o f t e r i n i t i a l r e s p o n s e t h a n t h e r e l o a d i n g c u r v e s . A l so t h e i n i t i a l

l o a d i n g c u r v e s become s o f t e r a s t h e d e p t h i n c r e a s e s , whereas t h e r e l o a d

c u r v e s become s t i f f e r a s t h e d e p t h i n c r e a s e s . The r e l o a d i n g c u r v e s a l s o

e x h i b i t a p a t t e r n which matches t h e impact d r i v e n p i l e s v e r y w e l l

E f f e c t o f T d -

P i l e s 11 and 1 V were t e s t e d a b o u t 31 d a y s a f t e r d r i v i n g and t h e n

r e t e s t e d a b o u t 65 days a f t e r d r i v i n g . The p l o t s o f u l t i m a t e l o a d v e r s u s

t ime f o r two c r i t e r i a a r e shown i n F i g u r e s 49 and 50 . The t r e n d g i v e n

by t h o s e two f i g u r e s does n o t a l l o w t o c o n c l u d e t h a t t h e r e i s a n

i n c r e a s e i n c a p a c i t y v e r s u s t i m e . Indeed F i g u r e 49 shows a n i n c r e a s e i n

s t i f f n e s s b u t F i g u r e 50 shows a d e c r e a s e i n c a p a c i t y f o r t h e v i b r a t o r y

d r i v e n p i l e s ; f o r t h e impact d r i v e n p i l e s F i g u r e 49 shows an i n c r e a s e

w h i l e F i g u r e 50 shows a s l i g h t i n c r e a s e . A t Lock and D a m 26 t h e

c a p a c i t y o b t a i n e d i n t h e l o a d t e s t was 67% h i g h e r t h a n t h e c a p a c i t y

p r e d i c t e d by t h e wave e q u a t i o n method on t h e a v e r a g e . T h i s c a n be

e x p l a i n e d by a 67% a v e r a g e g a i n i n c a p a c i t y o f t h e p i l e s be tween d r i v i n g

and l o a d t e s t i n g o f t h e p i l e s ( 1 week) . Note t h a t t h e s a n d a t Lock and

TIME (DAYS)

Figure 49. Pile Capacity at 0.25 in Settlement Versus Time

TIME (DAYS)

Figure 50. Pile Ultimate Capacity Versus Time

Dam 26 had a n average of 7 . 5 % p a s s i n g t h e #200 s i e v e whi le t h e sand a t

H u n t e r ' s P o i n t had OX p a s s i n g t h e {I200 s i e v e .

I n t h e c a s e o f H u n t e r ' s P o i n t s e v e r a l f a c t o r s i n f l u e n c e t h e change

of c a p a c i t y , one of which i s the e f f e c t o f t ime . The o t h e r s i n c l u d e t h e

i n f l u e n c e of s o i l h e t e r o g e n e i t y and t h e i n f l u e n c e o f t h e f i r s t l o a d t e s t

on t h e second load t e s t . I n o r d e r t o i s o l a t e t h e e f f e c t o f t ime one

s o l u t i o n would be t o use i n t e g r i t y t e s t i n g t o o b t a i n t h e v a r i a t i o n o f

s t i f f n e s s v e r s u s t ime . Another s o l u t i o n would be t o use a s e r i e s o f

l o a d t e s t s more c l o s e l y spaced i n t ime performed on t h e same p i l e o v e r a

l o n g e r p e r i o d of t ime ( e g . 1 d a y , 4 d a y s , 15 d a y s , 40 d a y s , 100 d a y s ) .

CONCLUSIONS AND RECOMMENDATIONS

The main c o n c l u s i o n s t o be drawn from t h i s s t u d y a r e t h e f o l l o w i n g :

- V i b r a t o r y d r i v i n g of p i l e s l e a d s t o approx imate ly t h e same

maximum l o a d a t l a r g e d i s p l a c e m e n t s , b u t t o a l a r g e r s e t t l e -

ment a t working l o a d s .

- The l o a d d i s t r i b u t i o n i s i n f l u e n c e d g r e a t l y by the d r i v i n g

p r o c e s s . For the p i l e s i n t h i s s t u d y , impact d r i v i n g l e d t o a

p o i n t r e s i s t a n c e which was 51% o f the t o t a l load a t maximum

l o a d i n g compared t o 13% f o r v i b r a t o r y d r i v i n g .

The l o a d t r a n s f e r cu rves a r e a l s o a f f e c t e d by the d r i v i n g

p r o c e s s . V i b r a t o r y d r i v i n g l e d t o l o a d t r a n s f e r cu rves which

r e q u i r e d much l a r g e r movements t o r e a c h maximum l o a d i n g . Th i s

a c c o u n t s f o r the f i r s t c o n c l u s i o n above r e g a r d i n g l a r g e r seE-

t l e m e n t s a t working l o a d s b e i n g obse rved f o r v i b r a t o r y d r i v e n

p i l e s .

The e f f e c t s of v i b r a t o r y d r i v i n g l i s t e d above a r e l e s s e n e d

upon r e l o a d i n g of the p i l e . Upon r e l o a d i n g , a v i b r a t o r y d r i -

ven p i l e c a r r i e s a l a r g e r p e r c e n t a g e o f the l o a d i n p o i n t

r e s i s t a n c e ( 2 9 % ) and t h e l o a d t r a n s f e r cu rves t a k e on t h e same

shape a s t h e impact d r i v e n p i l e s .

- The d a t a show t h a t f o r impact d r i v e n p i l e s t h e r e i s a t r e n d

towards a s l i g h t i n c r e a s e i n c a p a c i t y v e r s u s t i m e . For

v i b r a t o r y d r i v e n p i l e s however, t h e d a t a does n o t show any

c l e a r t r e n d .

The f o l l o w i n g recommendations a r e made based on t h e r e s u l t s o f t h i s

s t u d y :

- A s e r i e s of l o a d t e s t s should be performed i n a n a t u r a l sand

d e p o s i t t o v e r i f y t h e r e s u l t s found i n t h i s s t u d y . The t e s t

program shou ld i n c l u d e longer p i l e s ( a t l e a s t 50 f t l o n g ) t o

de te rmine i f t h e same behav io r o c c u r s .

- An a t t e m p t shou ld be made t o l o a d t e s t p i l e s which have been

i n s t a l l e d w i t h a v i b r a t o r y hammer and then tapped w i t h an

impact hammer. T h i s procedure may y i e l d the speed of i n s t a l l -

a t i o n of t h e v i b r a t o r y hammer w i t h t h e s t i f f e r i n i t i a l r e s -

ponse of t h e impact d r i v e n p i l e s .

I n o r d e r t o i s o l a t e t h e e f f e c t of t ime on t h e v a r i a t i o n of t h e

p i l e s t i f f n e s s response i n t e g r i t y t e s t i n g could be u s e d . Th i s

would have t h e advantage o f b e i n g performed on t h e same p i l e ,

and t h e l o a d s a r e smal l enough n o t t o change t h e s o i l

s t r u c t u r e around t h e p i l e .

I n o r d e r t o i s o l a t e the e f f e c t of t ime on the v a r i a t i o n o f t h e

p i l e c a p a c i t y a s e r i e s of load t e s t s more c l o s e l y spaced i n

t ime performed on t h e s a m e . p i l e o v e r a longer p e r i o d of t i m e .

For example, a s e r i e s of t e s t s c o u l d be performed a t 1 d a y , 4

d a y s , 15 d a y s , 40 days and 100 days a f t e r d r i v i n g . Th i s would

have t h e advantage of b e i n g performed on the same p i l e and

would i n c l u d e enough l o a d t e s t s t o be a b l e t o a s s e s s t h e

e f f e c t of one l o a d t e s t on subsequent l o a d t e s t s .

REFERENCES

Holloway, D.M., "Dynamic Monitoring Program Results, FHWA Vibratory. Hammer-Pile Testing, Hunters Point, California," Report to Geo/Re- source Consultants, 1987.

Hunter, A.H., Davisson, M.T., "Measurements of Pile Load Transfer," Performance of Deep Foundations, ASTM STP 444, American Society for Testing and Materials, 1969, pp. 106-117.

Ng, E . S . , Briaud, J.-L., Tucker, L.M., "Pile Foundations: The Behavior of Piles in Cohesionless Soils," FHWA Report FHWA-RD-88-080, 1988.

Ng, E.S., Briaud, J.-L., Tucker, L.M., "Field Study of Pile Group Action in Sand," FHWA Report FHWA-RD-88-081, 1988.

Rausche, F . , Goble, G.G., Likins, G.E., "Dynamic Determination of Pile Capacity," Journal of Geotechnical Engineering, ASCE, Vol. 111, No. 3, March 1985.