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7~~CO MISCELLANEOUS PAPER GL-88-28
i AXIAL RESPONSE OF THREE VIBRATORY ANDof EngneersTHREE IMPACT DRIVEN H-PILES IN SAND
by
AD-A199 126 Larry M. Tucker, Jean-Louis Briaud
Briaud Engineers1805 Laura Lane
College Station, Texas 77840
0z0
Xi
3-VKA)I
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Final Report
M Approve~d For Public Release. Distribution Unlimited
DTICELECT
SEVO 21988H
Proparod tor US Army Engineer DivisionLower Mississippi Valley
Vicksburg, Mississippi 39180-0080Undnr Contract No. DACW39-88-MO-421
or-itored by Geotechnical LaboratoryUS Army Engineer Waterways Experiment Station
LABORATOR P0 Box 631, Vicksburg, Mississippi 39180-0631
88 9 2 0 5
Destroy this report when no longer needed. Do not returnit to the originator.
The findings in this re1 ort are not to be construed as an officialDepartment of the Army position unless so diesignated
by othe - authorized documents.
The contents of thi. report aTe 01, toC be Used foCI
advertising, publicationf, or prornotioral purooseS.
C;iation of trade names does not constitute anofficial endlorsement or approval of the iOst of
such commefcial products.
Unclassified
SECURITY CLASSIFICATION OF THIS PAGEForm AW oved
REPORT DOCUMENTATION PAGE OMBNo. 0704O
la. REPORT SECURITY CLASSIFICATION lb. RESTRICTIVE MARKINGSUnclassified
2a. SECURITY CLASSIFICATION AUTHORITY 3 DISTRIBUTION /AVAILABILITY OF REPORT
2b. DECLASSIFICATIONDOWNGRADING SCHEDULE Approved for public release;
distribution unlimited4. PERFORMING ORGANIZATION REPORT NUMBER(S) S. MONITORING ORGANIZATION REPORT NUMBER(S)
Miscellaneous Paper GL-88-28
6a NAME OF PERFORMING ORGANIZATION 6b. OFFICE SYMBOL 7a. NAME OF MONITORING ORGANIZATION(if applicable) USAEWES
Briaud Engineers Geotechnical Laboratory6c. ADDRESS (City, State, and ZIP Code) 7b. ADDRESS (City, State, and ZIP Code)
1805 Laura Lane PO Box 631College Station, TX 77840 Vicksburg, MS 39180-0631
Ba. NAME OF FUNDING/ SPONSORIG_ - b. OFFICE SYMBOL 9. PROCUREMENT INSTRUMENT IDENTIFICATION NUMBERORGANIZATION (If applicable)
See Reverse LKVD Contract No. DACW39-88-MO-421Br. ADDRESS (City, State, and ZIP Code) Q" SOURCE OF FUNDING NUMBERS
PROGRAM PROJECT TASK WORK UNITELEMENT NO. NO. NO. CCESSION NO.
See Reverse I I I F11. TITLE (Include Security Classifncaion)
Axial Response of Three Vibratory and Three Impact Driven H-piles in Sand12. PERSONAL AUTHOR(S) ' 'Tucker, Larry M.; Briaud, Jean-Louis
13a. TYPE OF REPORT i3b. TIME COVERED 14. DATE OF REPORT (Vear,AonthOay) 15. PAGE COUNTFinal report FROM TO August 1988 78
16. SUPPLEMENTARY NOTATIONAvailable from National Technical Information Service, 5825 Port Royal Road,Springfield, VA 22161
17. COSATI CODES 18. SUBJECT TERMS (Continue on reverse if necessary and identify by block number)FIELD GROUP SUB-GROUP Axial loading, Impact hammers, S
H-piles Vibratory hammers . q
19, A!I ACT (Continue on reverse if necessary and identify by block number)
A research program to compare the ultimate axial capacity of vibratory and impactdriven H-piles in sand was conducted at a San Francisco, CA, site. The effects of time-lapse after driving was also studied. The piles were instrumented so that both pile tiploads and load transfer along the pile could be determined. ., " . . "'-.
20. DISTRIBUTION/AVAILABILITY OF ABSTRACT 21, ABSTRACT SECURITY CLASSIFICATIONE3UNCLASSIFIED/UNLIMITED 0'-1 SAME AS RPT. E DTIC USERS Unclassified
22a. NAME OF RESPONSIBLE INDIVIDUAL 22b TELEPHONE (Include Area Code) 22C. OFFICE SYMBOL
DO Form 1473, JUN 86 Previous editions are obsolete. SECURITY CLASSIFICATION OF THIS PAGE
Unclassified
,\.\
,\ %
Unclassified
89CUOIV CILAIFICA1ON OF THIS RZafE
8a. & 8c. NAME AND ADDRESS OF FUNDING/SPONSORING ORGANIZATIONS AND ADDRESSES (Continued).
US Army Engineer Division, Lower Mississippi ValleyP0 Box 80Vicksburg, MS 39180-0080
Unclasifie
SICIAITYCLASIFIATIO OFTHISPAG
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 III, Chief, GL.
COL Dwayne G. Lee, EN, is Commander and Director of WES. Dr. Robert W.
Whalin is Technical Director.
nes~iot.n For
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TABLE OF CONTENTS
Page
BACKGROUND. .............................. 1
THE SOIL. ............ ................... 3
THE PILES AND LOAD TEST PROCEDURES ................... 11
LOAD TEST RESULTS...........................19
Residual Stresses ......................... 19Load Test Results ......................... 19Pile Driving Analyzer Results ................... 52
DISCUSSION OF THE RESULTS.......................53
Top Load-Settlement Curves....................53Load Distribution ......................... 56Load Transfer ........................... 58Effect of Time.................... . .. 58
CONCLUSIONS AND RECOMMENDATIONS....................66
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LIST OF FIGURES
Figure Page
i Location of Borings and Instrumentation ... ........ 4
2 Profiles of Standard Penetration Test Blowcounts .... 5
3 CPT Profiles for Point Resistance ..... ........... 6
4 CPT Profiles for Friction Resistance ..... .......... 7
5 Net Limit Pressure Profile ....... ............... 8
6 First Load Modulus Profile ....... ............... 9
7 Reload Modulus Profile ........ ................. 10
8 Location of Pile Instrumentation ..... ............ 12
9 Test Pile Locations ...... .................. . 13
10 Impact Pile Driving Records ..... .............. . 17
11 Vibratory Pile Driving Records .... ............. ... 18
12 Load-Settlement Curve for Pile 1I ... ........... . 21
13 Raw Load Versus Depth Profiles for Pile 1I ........ ... 22
14 Corrected Load Versus Depth Profiles for Pile 1I .... 23
15 Interpreted Load Versus Depth Profiles for Pile 1I 24
16 Friction Versus Movement Curves for Pile 1I . ...... . 25
17 Point Resistance Versus Movement Curve for Pile 1I 26
18 Load-Settlement Curve for Pile IIR ... ........... ... 27
19 Raw Load Versus Depth Profiles for Pile IIR ...... ... 28
20 Corrected Load Versus Depth Profiles for Pile IIR 29
21 Interpreted Load Versus Depth Profiles for Pile IIR 30
22 Friction Versus Movement Curves for Pile fIR ........ ... 31
23 Point Resistance Versus Movement Curve for Pile fIR 32
24 Load-Settlement Curve for Pile 1V ... ........... . 33
25 Raw Load Versus Depth Profiles for Pile 1V ......... ... 34
iv
N N N
Figure Page
26 Interpreted Load Versus Depth Profiles for Pile IV . 35
27 Friction Versus Movement Curves for Pile IV . ...... . 36 %
28 Point Resistance Versus Movement Curve for Pile IV 3. . 37
29 Load-Settlement Curve for Pile lVR ... ........... ... 38
30 Raw Load Versus Depth Profiles for Pile lVR . ...... . 39
31 Interpreted Load Versus Depth Profiles for Pile lVR 40 0
32 Friction Versus Movement Curves for Pile 1VR ........ . 41
33 Point Resistance Versus Movement Curve for Pile lVR 42
34 Load-Settlement Curve for Pile 21 ... ........... . 43 0
35 Raw Load Versus Depth Profiles for Pile 21 ........ . 44
36 Corrected Load Versus Depth Profiles for Pile 21 . .. 4. 45
37 Interpreted Load Versus Depth Profiles for Pile 21 45 .. ,
38 Friction Versus Movement Curves for Pile 21 . ...... . 47 O
39 Point Resistance Versus Movement Curve for Pile 21 . 48
40 Load-Settlement Curve for Pile 2V ... ........... . 49
41 Load-Settlement Curve for Pile 31 ... ........... . 50 %
42 Load.3,tlemeut CuA.re foi rile 3V ..... ........... 51
43 Comparison of Load-Settlement Curves .. .......... ... 54
44 Friction Versus Depth Profiles .... ............. ... 57
45 Comparison of Point Load Transfer Curvez.. .......... 59
46 Normalized Point Load Transfer Curves .. ......... . 60
47 Normalized Friction Transfer Curves for ImpactDriven Piles ........ ...................... . 62
48 Normalized Friction Transfer Curves for VibratoryDriven Piles ........ ...................... . 63
49 Pile Capacity at 0.25 in Settlement Versus Time . . . . 64
50 Pile Ultimate Capacity Versus Time ... ........... ... 64
0
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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
~Vi
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BACKGROUND
In the spring and summer of 1986 a series of vertical load tests
were carried out on instrumented piles driven in sand at Hunter's Point
in San Francisco. The Federal Highway Administration sponsored two
projects on impact driven piles: one on the testing of five single piles
and one on the testing of a five pile group (Ng, Briaud, Tucker 1988a;
1988b). Then, the Lower Mississippi Valley Division (LMVD) of the Corps 4
A4.of Engineers operating through the USAE Waterways Experiment Station
(WES) sponsored a project on the comparison of impact driven piles and
vibratory driven piles. Subsequently, the Deep Foundation Institute
drove a number of piles with various vibratory hammers to compare the Jft,
hammers' efficiencies.
- This report is an analysis of the pile load tests-sponsored by the
LMVD through WES comparing impact and vibratory driven piles. The site A
is characterized, the load tests are described, the load tests results
are analyzed and discussed, and recommendations and conclusions are
made.
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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 ft
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 before and
after driving and testing of the FHWA test piles. The location of sel-
ecte-d soundings are shown on Figure 1. The corresponding profiles are
shown on Figures 2 through 7. The hydraulic fill has the following
average properties:
Friction angle 320 to 350Water content 22.6 %
Dry unit weight 100 pcf
D60 0.8 mm
D10 0.7 mmSPT blow count 15 bpfCPT tip resistance 65 tsf
PMT net limit pressure 7 tsfShear modulus (from shearwave velocity measurements) 400 tsf
3
3%
10 FEET
C5 C4 ci c1o3
II IB2"' 0I I I I HH
DZ PM
ClOt E5 C102C3 B7
6O4 E3 E2 8 P4 B30
P5B 5 SP DI P1 P2 P3
IIIF I H B4 H
El B C2
JF J
S STEP BLADE TESTS%B SPT TEST BORINGS
C CONE PENETROMETER TESTSD DILATOMETER TESTSE EXTENSOMETERP PIEZOMETERPM PREBORING PRESSUREMETER TESTSSP SELFBORING PRESSUREMETER TESTS
Figure 1. Location of Borings and Instrumentation
5) .1'
4k
SPT N VALUE (BLOWS/PT)
0 10 20 30 40 so 60
5
10
15BoigB
20 X_ y. Average N Value
_SPT Tests Per-formed with aDonut Hammer.
25
40
454
455
CONE TIP RESISTANCE (kef)
0 100 200 300 400 S00 6000
10
15 0 CPT1I
X CPT 2
*CPT 3
20 ---- AVERAGE
(43CPT Tests Per-
25 formed with a
a. Standard Elec-
W( tric Cone.
'30
35-'4p
40
45
50
Figure 3. CPT Profiles for Point Resistance
6
LOCAL CONE FRICTION (kef)
0 .51 1.5 2 2.5 3
100
15 * CPT 2
X CPT 3
AVERAGE
CPT Tests Perfor-c. med with Standard
Electric Cone.
400
45
50,
Figure 4. CPT Profiles for Friction Resistance
7
-s~ww~* v\A~W\%
NET LIMIT PRESSURE P1* (kPo)
0 250 500 750 1000 1250 1500
0
- PBPMT P5L.------ SBPMT P220
P RES SUR EMETER10
15
20
. 25-
0. 30w
35
40
45
50
5 5 , ,I I I ,II I £ I, l , , , ,,, l , , l9.
Figure 5. Net Limit Pressure Profile
8
FIRST LOAD MODULUS Eo (MPa)
0 2 4 6 8 100
5 ~-4PBPMT E
PRESSUREMETER10
200
1L 5
200
IL 30w
35
40
450
Figure 6. First Load Modulus Profile
9
111 ISO$ ''
RELOAD MODULUS Er" (MPa)
0 10 20 30 40 50 60 70 80 go 1000
-4 PBPMT E
5 0 ......... 00 SBPMT E
-------- - SBPMT Er
10 PRESSUREMETER
15
20
LL 25ML
I-a 30w
35
40
45
50 ._
Figure 7. Reload Modulus Profile
10I
THE PILES AND LOAD TEST PROCEDURES
Three HP14x73 steel H piles were used in this program. They were -
all embedded 30 ft below the ground surface; however, a 4.5 ft deep, 14
in diameter hole was drilled prior to pile insertion for the impact
driven piles, making the true pile embedment equal to 25.5 ft. For the
vibratory driven piles a hole was drilled through the 4 in thick asphalt
layer only, making the embedment equal to 29.5 ft. Each pile had two %
angles (2.5 x 2.5 x 3/16 inches) welded to the sides of the pile we' as
protection for the instrumentation.
The first pile was one of the single piles used in the FHWA program
(referred to as pile 1). Pile 1 was instrumented with seven levels of
strain gauges and a tell tale at the pile tip (Figure 8). This pile was
calibrated before driving and the pile stiffness was measured for use in
the data reduction. The measured value of pile stiffness (AE) was
614908 kips. This value was used for all three piles. Pile driving
analyzer measurements were obtained during the driving of pile 1 with an
impact hammer. Pile 1 was then load tested in compression 30 days after
it was driven (FHWA program): this is load test 1I. Pile I was then
retested at 67 days after driving: this is load test IR. After pile 1
was retested, the pile was restruck with an impact hammer and pile driv-
ing analyzer measurements were obtained. Pile I was then extracted and
vibrodriven about 30 ft from the impact test (Figure 9). It was load
tested at 33 days after driving (load test IV) and again at 63 days
after driving (load test IVR). After load test IVR the pile was struck
with an impact hammer and pile driving analyzer measurements were ob-
tained.
111
4 • TELL
TALESTRAINGAGES
0 - --- 77-./ //,7/_
1",, /, ,- ./ .
/I COVER7 ANGL2 S
5
10 STRAIN GAGE
POTENTIOMETER
ii
2)
STRAIN GAGE
TELL TALE
30
PILE 1 PILE 2
351
Figure 8. Location of Pile Instrumentation
12
10 FEET
iiH H
I II NH %
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Fiur 9. Tes Hil Loaton
II I H3
The second pile (Pile 2) was instrumented with two levels of strain
gauges: one at the mid-point and one at the pile tip (Figure 8). Pile 2
was impact driven and tested at 65 days after driving: this is load test
21. Pile 2 was then extracted and vibrodriven and tested at 64 days
after driving. This is load test 2V. After load test 2V, the pile was
struck with an impact hammer and pile driving analyzer measurements were
obtained.
The third pile (Pile 3) was not instrumented. It was impact driven
and tested at 12 days after driving: this is load test 31. Pile 3 was
then extracted and vibrodriven. It was tested at 12 days after driving:
this is load test 3V. Table 1 summarizes the eight load tests presented
in this report.
The impact driven piles were installed using a Delmag D22 diesel
hammer at full throttle. All restrike measurements were also obtained
using this hammer. The hammer was rated at approximately 40,000 ft-lbs
maximum energy. Details of the hammer are given in Table 2. The driv-
ing records for the impact driven piles are shown in Figure 10.
The vibratory driven piles were installed with a ICE-216 vibratory
hammer. Details of the hammer are given in Table 3. The penetration
rates versus depth records for these piles are shown in Figure 11.
The load test procedure has been described in detail by Ng et al.
(1988). In general, the test loads were applied in increments of 10
percent of the estimated ultimate load. Each load step was held for at
least 30 minutes, with the load being monitored continuously. All read-
ings from electronically monitored instruments were recorded every 5
minutes. The data was stored on floppy disk for data reduction.
14
IN "
Table 1. Load Test Program Summary
Test Piles
II - FHWA Pile (Impact) 30 Day test
IR - FHWA Pile (Impact) 67 Day test
lV - FHWA Pile (Vibratory) 33 Day test
lVR - FHWA Pile (Vibratory) 63 Day test
21 - New Pile (Impact) 65 Day test
2V - New Pile (Vibratory) 64 Day test
31 - New Pile (Impact) 12 Day test
3V - New Pile (Vibratory) 13 Day test
Notes: , j ,
A. 1I, hIR, 1V and lVR - Seven strain gauge levels 'J
B. 21 and 2V - Two strain gauge levels
C. 31 and 3V - No strain gauges c-A,
15
'j,- N, %
Table 2. Specifications for Delmag D22 Impact Hammer
Rated energy 39,700 ft-lbsRam weight 4,850 lbsBlows/minute 42-60
Maximum explosivepressure on pile 158,700 lbs
Working weight 11,275 lbs
Drive Cap weight 1,500 lbs
V
Table 3. Specifications for ICE-216 Vibratory Driver
Eccentric moment 1000 in-lbsFrequency 400-1600 vpm
Amplitude 1/4 - 3/4 inches
Power 115 hPPile clamping force 50 tonsLine pull for extraction 30 tons .Suspended weight with clamp 4825 ibs N
Length 47 inches '
Width 16 inchesThroat width 12 inchesHeight with clamp 78 inches-.Height without clamp 68 inches
16
w%
PENETRATION BLOWCOUNT (blows/f t) )
(ft) PILE 1 PILE 2 PILE 3 ,
1 RUN NA* RUN2
3
464
10 1 41P 2 412 2 4
13 3 414 2 415 2 4
16 2 417 2 5
18 2 419 2 420 2 6
21 2 622 4 623 6 624 5 825 7 826 7 9'
27 8 0
28 0 9
29 21 4130 12 61
TOTAL 96 131,'r
*Not available ;
Figure 10. Impact Pile Driving Records
22 4 6
17 8
'630 12-11
'.' -',- ,,r- :, -l , , . L • ,.l" ,- - . . ' ' ', • , ' "-" :' " . " . . " ,: - " - .0 .
Pile 1 Pile 2 Pile 3
Rate of Rate of Rate of
Depth Time Penetration Time Penetration Time Penetration
(ft) (sac) (ft/min) (sac) (ft/min) (sac) (ft/min)
0
1
2 03
5 1.9
6
7 6.7 25.0
8
9 4 15
10 12 10 9 12
11 12.2 43.6 18 12 14 12
12 23 12 19 12
13 16.8 26.1 28 10 23 15
14 22.7 10.2 34 12 29 10 015 28.4 10.5 39 12 34 12
16 34.6 9.7 44 12 38 15
17 39.0 13.6 49 12 42 15
18 45.1 9.8 54 12 46 15
19 58 15 49 20
20 63 12 53 15
21 57.2 14.9 66 20 58 12
22 61 15.8 69 20
23 73 15 61 40?
24 76 20 64 20
25 70 20 79 20 67 20
26 83 15 70 20 •
27 86 20 73 20
28 89 20 76 20
29 92 20 80 15
30 85 20 96 15 85 12
Figure 11. Vibratory Pile Driving Records
18
LOAD TEST RESULTS
Residual Stresses
Residual driving stresses were measured for pile 11. The stress
profile was not monitored between load test 1I and test IIR. Therefore
the residual stress profile after driving was also used for load test
IIR. 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 II 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 to obtain the fol-
'owing 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
19
-V
profiles will be the raw data as measured during the test. Since all
instrumentation was zeroed just before the load test, these profiles do
not include residual stresses.
A second set of profiles is shown for those piles driven with an
impact hammer which include the residual loads in the pile due to driv-
ing. This set of profiles is not shown for the vibratory driven piles
since it has been assumed that no residual stresses are induced due to
installation.
The third set of profiles is the interpreted load versus depth
curves. The measured data shows some irregularities which may be due to
drift in the readings, temperature fluctuation or gauge malfunction. A
gauge reading was omitted entirely if it was known that the gauge was
definitely malfunctioning. This was the case with the gauge at a depth
of 25 ft for pile IV and IVR, and for both gauge levels on pile 2V. Any
other irregularities were smoothed by fitting a second order polynomial
curve through the data. These curves are shown as the third set of load
versus depth profiles. Other interpretations are obviously possible.
However, the fit of the curves matches quite well with what one would
draw manually.
The results for load test 1I are given in Figures 12 through 17;
load test IR results are shown in Figures 18 through 23; load test IV
results are shown in Figures 24 through 28; load test 2VR results are
shown in Figures 29 through 33; load test 21 results are shown in Fig-
ures 34 through 39. Load-settlement curves at the pile top are shown in
Figures 40 through 42 for load tests 2V, 31 and 3V respectively.
20
TOP LGO (KIPS)
a 50 100 I50 200
PILE 1.5- IMPACT
30 DAY TEST
zw
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Figure 12. Load-settlement Curve for Pile 1I
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TOP LOAD (KIPS)
0 50 100 I50 200
. / PILE IIMPACT
;Sl
67 DAY TEST
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Figure 18. Load-Settlement Curve for Pile IIR
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TOP LOAD (KIPS) 100 .........200
PILE I.5 -VIBRATORY
33 DAY TE-ST
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Figure 24. LoadSettlement curve fo i 1
rder,
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37
TOP LOAD (KIPS)
O 5o I00 150 200
PILE IVIBRATORY63 DAY TEST
zwxw-j
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Figure 29. Load-Settlement Curve for Pile MV
38
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.5 S5 DAY TEST
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50
TOP LOAD (KIPS)
a so 100 I50 2000
PILE 3-5 VIBRATORY
13 DAY TEST
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I-51
Pile Driving 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 EstimatedForce Energy Capacity*
(kips) (kip-ft) (kips)
li** 12/12 in. 340-510 5-15 140-165
ii*** 6/6 in. 350-505 10-17 145-200
IV*** 7/6 in. 300-415 4-13 120-140
2V*** 14/12 in. 355-520 5-11 125-150
S* Case method capacity assumes a damping constant J=0.25
** Initial driving*** Restrike
52
,P
DISCUSSION OF THE RESULTS
Top Load-Settlement Curves •
The top load-settlement curves for the eight load tests are shown
together in Figure 43. 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 43. 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..rg-,.
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-
53
f % % A
TOP LOD (KIPS)
0 50 100 150 200
22
I-I
-NJ
.5
I VR
.j 2V
1.54
D/1 +. N.. - . "'N/ AS *S N
Table 5. Analysis of Pile Test Results
Pile Load at Load at Settlement at InitialD/10 + PL/AE 0.25 in. Qult/2 Stiffness
(kips) (kips) (in) (kips/in) .'
II 160 120 0.104 769
IIR 170 126 0.094 904 P6%
21 175 131 0.088 994
31 160 120 0.088 9,,9
Average 166 124 0.094 894
Standard
Deviation 7.5 5.3 0.0075 93
Coefficientof Variation 0.045 0.043 0.081 0.104
1V 180 102 0.181 497
IVR 145 110 0.103 704
2V 130 71 0.184 353
3V 200 90 0.313 319
Average 164 93 0.195 468
StandardDeviation 32 17 0.087 175
Coefficientof Variation 0.195 0.182 0.446 0.374
Impact1.01 1.33 0.48 1.91
Vibratory
55
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 maximum 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 a
pronounced upon repeated loading.
56
In
/ ,S-.c
,-4.
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Zw 1 /_1
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57.
-- - ---/ %
Load Transfer
The H-pile presents a problem when computing unit tip resistance
and unit friction values: WVIdL is the failure surface? One possible
assumption is that the pile fails along a rectangle which encloses the
H-pile, with a soil plug forming between the flanges. Another possibil-
ity is that the pile fails along the soil-pile interface, with no soil
plug forming. Previous research has shown that a better assumption may
be that the failure surface is in between the previous two assumptions
with a soil plug filling half the area between the flanges (Ng et al.,
1988). For the HP14x73 piles used in this study this assumption gives
.2the following properties: Perimeter - 70.47 in, Tip area = 109.8 in
This assumption is used for all further analyses.
Figure 45 shows the unit tip resistance versus tip movement curves
for the five instrumented piles. Figure 46 shows the same curves with
the tip resistance normalized by dividing by the maximum tip resistance.
These two figures show a fundamentally different reaction between the
vibratory driven piles and the impact driven piles: The tip resistance
of the vibratory driven piles is much lower than that of the impact
driven piles, and the slope of the curve is different. However, the
difference in shape almost vanishes upon reloading.
The shape of the tip resistance curve of the initial loading of the
vibratory driven pile suggests that the sand immediately under the pile
point is initially loose but densifies as the pile is laded. Indeed,
at higher loads the tip resistance begins to increase at a faster rate,
rather than reaching a limiting value as the other tests show. By com-
paring the curves for Pile 11 and lIR, it can be seen that the impact
58
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-~~~ ~~~~~ r.~- -. . - .
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driven piles do not undergo such a change in behavior between initial
loading and reloading.
Figures 47 and 48 show the normalized friction movement curves for
the impact driven piles and vibratory driven piles, respectively. Fig- 'r
ure 47 shows again that the impact driven piles are very consistent in
their response and that no change in behavior occurs between initial
loading and reloading. However, Figure 48 shows that the vibratory
driven pile exhibits a great change in behavior between initial loading
and reloading. The five curves for the initial loading have a much
softer initial response than the reloading curves. Also the initial
loading curves become softer as the depth increases, whereas the reload
curves become stiffer as the depth increases. The reloading curves also
exhibit a pattern which matches the impact driven piles very well.
Effect of Time
Piles 1I and 1V were tested about 31 days after driving and then
retested about 65 days after driving. The plots of ultimate load versus
time for two criteria are shown in Figures 49 and 50. The trend given
by those two figures does not allow to conclude that there is an
increase in capacity versus time. Indeed Figure 49 shows an increase in
stiffness but Figure 50 shows a decrease in capacity for the vibratory
driven piles; for the impact driven piles Figure 49 shows an increase
while Figure 50 shows a slight increase. At Lock and Dam 26 the
capacity obtained in the load test was 67% higher than the capacity .
predicted by the wave equation method on the average. This can be. I-.
explained by a 67% average gain in capacity of the piles between driving
and load testing of the piles (1 week). Note that the sand at Lock and
61
* b. -- - In
____ ____ ____ ____ ____ ____ __ I-~1**~* . ( I ' 'I I I0
N4
U,
uw I
'-4
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31 21 IR
- 100IVRwU) 3V
z x2V ?
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'"U.
w
oL 10 t I I a ,10 100 ,
TIME (DAYS)
Figure 49. Pile Capacity at 0.25 in Settlement Versus Time
300
I21
0.
LI
10 10
xa-L
1%2
-1 60
C
U
U %w
101II I
10 100
TIME (DAYS)
Figure 50. Pile Ultimate Capacity Versus Time
64
0Dam 26 had an average of 7.5% passing the #200 sieve while the sand at
Hunter's Point had 0% passing the #200 sieve.
In the case of Hunter's Point several factors influence the change
of capacity, one of which is the effect of time. The others include the
influence of soil heterogeneity and the influence of the first load test
on the second load test. In order to isolate the effect of time one
solution would be to use integrity testing to obtain the variation of
stiffness versus time. Another solution would be to use a series of r
load tests more closely spaced in time performed on the same pile over a
longer period of time (eg. I day, 4 days, 15 days, 40 days, 100 days).
.N
%'. ,.'.
654
N
65 1N%' ,~4.~.' W~ q ?
CONCLUSIONS AND RECOMMENDATIONS
The main conclusions to be drawn from this study are the following:
- Vibratory driving of piles leads to approximately the same
maximum load at large displacements, but to a larger settle-
ment at working loads.
- The load distribution is influenced greatly by the driving
process. For the piles in this study, impact driving led to a
point resistance which was 51% of the total load at maximum
loading compared to 13% for vibratory driving.
- The load transfer curves are also affected by the driving
process. Vibratory driving led to load transfer curves which
required much larger movements to reach maximum loading. This
accounts for the first conclusion above regarding larger set-
tlements at working loads being observed for vibratory driven
piles.
- The effects of vibratory driving listed above are lessened
upon reloading of the pile. Upon reloading, a vibratory dri-
ven pile carries a larger percentage of the load in point
resistance (29%) and the load transfer curves take on the same
shape as the impact driven piles.
- The data show that for impact driven piles there is a trend
towards a slight increase in capacity versus time. For
vibratory driven piles however, the data does not show any
clear trend.
66
The following recommendations are made based on the results of this
study:
- A series of load tests should be performed in a natural sand
deposit to verify the results found in this study. The test
program should include longer piles (at least 50 ft long) to
determine if the same behavior occurs.
An attempt should be made to load test piles which have been
installed with a vibratory hammer and then tapped with an
impact hammer. This procedure may yield the speed of install-0
ation of the vibratory hammer with the stiffer initial res-
ponse of the impact driven piles.
In order to isolate the effect of time on the variation of the
pile stiffness response integrity testing could be used. This
would have the advantage of being performed on the same pile,
and the loads are small enough not to change the soil
structure around the pile.
* In order to isolate the effect of time on the variation of the
pile capacity a series of load tests more closely spaced in
time performed on the same pile over a longer period of time.
For example, a series of tests could be performed at 1 day, 4
days, 15 days, 40 days and 100 days after driving. This would
have the advantage of being performed on the same pile and
would include enough load tests to be able to assess the .,-,._
effect of one load test on subsequent load tests.
67%WAN
REFERENCES
Holloway, D.M., "Dynamic Monitoring Program Results, FHWA Vibratory
Hammer-Pile Testing, Hunters Point, California," Report to Geo/Re- 9
source Consultants, 1987.
Hunter, A.H., Davisson, M.T., "Measurements of Pile Load Transfer,"Performance of Dee, 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 PileCapacity," Journal of Geotechnical Engineering, ASCE, Vol. 111, No.
3, March 1985. P
U,,
WR
68