Identifying High Pile Rebound Soils Using CPT Pore Water
Pressure Measurements: Case Studies in Florida
Authors
Paul J. Cosentino1, Ph.D., P.E.
Edward H. Kalajian2, Ph.D., P.E
Fauzi Jarushi3
Ryan Krajcik 4
1. Corresponding Author, Professor of Civil Engineering, Florida Institute of
Technology, Melbourne, FL 32901. Phone 321 674-7555, FAX 321 674-7565,
([email protected])
2. Professor of Civil Engineering and Associate Dean, College of Engineering,
Florida Institute of Technology, Melbourne, FL 32901. Phone 321 674- 8020
([email protected])
3. Ph.D Candidate in Civil Engineering, Florida Institute of Technology, Melbourne,
FL 32901,([email protected])
4. MS. Graduate Research Assistant, ([email protected])
Figures and Tables and Title Page Words = -710
Abstract (244) words
Text (4297) Words not including Abstract
Tables 2 or 500 Words
Figures 10 or 2500 Words
Grand Total (7550) Words Including Title, Figures, Tables and References
Revised on 11/15/2012
TRB 2013 Annual Meeting
Paper revised from original submittal.
1
ABSTRACT
At certain depths during large diameter displacement pile driving, rebound well over 0.25 inch
was experienced and followed by a small or zero set during each hammer blow. High pile
rebound (HPR) soils may stop the pile driving and results in a limited pile capacity. The
overburden depth at which HPR occurred is typically greater than 50 ft. In some cases, rebound
leads to pile damage, delaying the construction project, and the requiring foundations redesign.
HPR was evaluated at six Florida sites, during driving of square precast, prestressed
concrete piles driven into saturated, fine silty to clayey sands and sandy clays. Pile Driving
Analyzer (PDA) deflection versus time data, recorded during installation, was used to develop
correlations between cone penetrometer (CPT) pore-water pressures
, pile displacements and
rebound. Fifteen CPT tests with pore-water pressure measurements (CPTu) were evaluated and
comparisons were made to HPR from nine piles at the six sites. At four sites where piles
experienced excessive HPR with no or minimal set, the pore pressure
yielded very high
positive values of more than 20 tsf. However, at the site where the pile rebounded, followed by an
acceptable permanent set, the measured pore pressure
pressure
ranged between 5 and 20 tsf. The pore
exhibited values of less than 5 tsf at the site where no rebound was noticed. In
summary, direct correlations between CPTu pore pressure
and rebound were produced, which
leading to identify soils that produce HPR.
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Paper revised from original submittal.
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INTRODUCTION
At numerous sites throughout the state, the Florida Department of Transportation (FDOT)
contractors and engineers have experienced serious pile installation problems while driving large
diameter displacement piles (e.g., 18-in, 24-in, and 30-in) (1,2) with diesel and air hammers.
During these installations, high pile rebound (HPR) occurred; followed by a small or no
permanent-set. Soils referred to herein as “high rebound soil” stop the pile driving and result in
limiting pile capacity (1).
Pile rebound is defined as the upward elastic pile displacement that occurs during a
hammer blow. Figure 1 shows a typical pile-top displacement versus time record for a single
hammer blow. The maximum initial downward motion is termed "DMX," and is the sum of
elastic and plastic deformations of the pile and soil system. The final value of the displacement is
the permanent pile penetration for the blow, termed "set." Rebound is the difference between the
pile maximum displacement and final set. High rebound describes the situation where the set (i.e.,
plastic soil deformation) represents a small portion of the maximum displacement and the
rebound (i.e., recovered elastic deformation) constitutes the majority of the displacement.
In some cases, rebound lead to pile damage, delaying the construction project, and
requires foundation redesign (1). Schedule delays ranged from 15 minutes to several weeks with
cost overruns more than 20,000 dollars was reported (3).
HPR has occurred during pile driving of high displacement concrete and steel piles with
different dimensions (2). FDOT considers that excessive rebound takes place when there it is
greater than 0.25 inch per hammer blow (4).
HISTORY OF PORE WATER PRESSURE ON HPR
Murrell et al. (5) presented a case history of HPR, which occurred during the construction of a
new ferry terminal in coastal North Carolina. The 20-inch, square 70 ft long, Prestressed Concrete
Pile (PCP) were designed to support an over water structure. The authors describe the high
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Paper revised from original submittal.
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rebound using the term “Bounce”. Pile bounce was observed at overburden depth of 53 ft
(elevation -43ft) when the piles penetrated into saturated, firm to stiff, fine-grained soils that
originate from marine formations along the southeastern coast of the United States.
Excess pore water pressures at shoulder or behind the tip
obtained during CPTu at the
bouncing depth were greater than 20 tsf. When the blow counts during pile driving were at 303
blows per foot (bpf), the pile displacement became zero. The driving process was then stopped
for two hours and restrike was then carried out; however, an additional 2.5 ft of pile length was
driven with blow counts of 73 bpf, 112 bpf, and 87 blows/6 in. Then the driving was again halted
when large rebound resulted in zero set. In order to achieve the pile capacity, and overcome pile
rebound, after four days the pile was driven using a hammer with a larger ram and a short stroke.
Hussein et al. (2) presented a case study related to HPR during driving of PCP for the
State Road 528 Bridge over the Indian River, Florida. A group of 30-inch square PCP with a
length of 115 ft and 18-inch circular hollow core were used to support the bridge. The piles
rebounded when they penetrated into hard soils consisting of saturated medium dense sand with
silt (SP-SM) to fine silty sand (SM) to clayey sands and sandy clays (SC). The authors believe
that that the incompressible water in the soil near and below the pile tip produced excessive pore
pressure during the driving process which caused the tip to exert an upward force on the pile
causing it to rebound. However, no analytical proof of this conclusion is available.
Likins et al. (6) analyzed three sites with pile rebound between 0.4 and 1 inches. He
determined that the only common geotechnical parameter observed at each site was the fully
saturated soils. Therefore, research focused on analyzing the dynamics of pile driving.
Preliminary analysis using the basic wave equation was conducted for each site. The author then
modified the results to match field data acquired by CAPWAP (Case Pile Wave Analysis
Program). It was proposed that the only reasonable cause of the HPR was the buildup of excess
PWP beneath the pile tip. It was also clear through testing, that pile capacities decreased when
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Paper revised from original submittal.
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high quake/rebound occurred. Findings from the work indicate that high quake lowers the pile
capacity by a factor of 3. Field observations often lead to a false interpretation that the hammer is
not large enough for the pile, and in cases where the hammer size is increased, the pile can be
damaged. Likins and Garland (6) conclude that alternative pile designs, such as hollow piles,
should be considered as an effective way to avoid high soil quake.
DYNAMIC (PDA) TESTING
During the driving of test piles, electronic measurements such as ram velocity, stroke, blow
count, and penetration were determined using PDA sensors. This data was used to clarify the pile
movement per blow.
Figure 1 shows a typical HPR PDA data. The plot, with displacement in inches on the
vertical axis, and time in milliseconds on the horizontal axis, shows a maximum displacement
(DMX) of 1 inches, a set of 0.11 inches, thereby yielding a rebound of 0.89 inches.
Maximum Displacement
(in)
1
0.8
0.6
0.4
0.2
0
-0.2
0
20
40
60
80
100
120
140
160
180
200
220
Time (Milliseconds)
FIGURE 1 Typical PDA Pile Top Displacement Versus Time Diagram From One Hammer Blow
For FDOT HPR site.
In addition to the digital set in the PDA output (DFN or dSet) which is not used for this
study because it is recorded in short time of 200 milliseconds, the number of hammer blows per
foot is used to produce an average inspector set (iSet) per blow. The maximum displacements and
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Paper revised from original submittal.
5
iSet were subtracted to determine the rebound per hammer blow (i.e., DMX-iSet =Rebound).
Plots for each of the case studies were developed relating elevations to DMX, iSet and rebound
from the PDA data. The elevation associated with the start of the PDA data corresponded to the
depth at which pile driving commenced, which was below the ground surface because piles at
these sites were set into predrilled holes.
CPTu AND PORE WATER PRESSURE DISSIPATION TESTING
Electrical friction cone tests were performed in soundings by hydraulically advancing the cone
penetrometer while signals were digitally recorded using the Hogentogler standard recording
system. The CPTu soundings were conducted using 10-cm2 piezocones, with porous filter
element type 2 located at shoulder or behind the tip
.
The CPTu test procedure followed ASTM D5778 "Electronic Friction Cone and
Piezocone Penetration Testing". During testing, digital channels were used to record the tip,
friction, inclination and designated pore water pressure
every 2 inches. The rod insertion speed
was 0.75 in/sec. Tests were conducted until refusal of the CPT rig or desired depth was met.
At desired depths (rebound and non-rebound soils), pore-water pressure dissipation tests with
time were performed during the CPTu soundings to obtain dissipation time.
SITE DESCRIPTION
Six sites in Central Florida listed below were evaluated by comparing PDA output to CPTu pore
pressure
. Each of these sites contained a number of instrumented piles, allowing nine piles to
be analyzed at the six sites. Site 1 through 4 displayed HPR with no or minimal set, site 5
displayed HPR with an acceptable set and site 6 displayed no HPR.
1. Intersection of I-4 and SR408 (Anderson Street Overpass).
2. Intersection of SR50 and SR436 Overpass (SR50/SR436 Overpass).
3. Intersection of I-4 and US.Highway192 (I-4/US.192 Ramp CA).
4. Intersection of I-4 and Osceola Parkway (I-4 /Osceola Parkway).
5. Intersection of I-4 and SR408 (Ramp B).
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Paper revised from original submittal.
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6. Intersection of SR 417 and International Parkway.
SOIL PROFILES AND PROPERTIES
Split-barrel and Shelby tube samples were obtained in order to establish the soil profile. The soil
samples were classified in accordance with Unified Soil Classification System (USCS) (ASTM
D-2488). At each site, a generalized soil profile was developed from the SPT boring closet to the
rebounded pile.
Soils profiles are presented in Figures 2 to 9. Sand was the predominate soil at the HPR
sites consistently representing over 50 percent of the soil. The soil strata where HPR occurred can
be classified as one of the following groups: SC, SM-SC, SM, CL, SP-SM, SP-SC and CH. Most
HPR layers had high fines content with a natural moisture content less than the liquid limit. The
soils plotted near the A-line on the Cassagrande plasticity chart. These soils displayed an olive
green to light green color with visual descriptions ranging from clayey and silty fine sands, to
highly plastic clays with low permeability coefficient. A summary of the soil properties from
each of the case studies is presented in Table 1. In reviewing Table 1, the following can be
observed:

Rebound occurred at overburdens depths of greater than 50 ft;

Soils in the rebound layers typically contained silts and clays;

Soils in the rebound zone were dense to very dense or stiff to hard;

Permeability coefficient estimated using the time for 50% dissipation from CPTu
dissipation test ranged between 4.1E-05 and 6.84E-08;

HPR soils had an obtained t50 and calculated permeability coefficient from Parez and
Fauriel (6) in the range of silt to clay soils;

Average CPT sleeve friction in the rebound soils was greater than 1.5 tsf while in the no
rebound soils averaged less than 1 tsf;

Most HPR soils exhibited CPT cone resistance of greater than 100 tsf.
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Paper revised from original submittal.
7
TABLE 1 Summary of Soil Properties at HPR Sites
Site Description
1
2
3
5
6
Elevation
(ft)
Soil Type
(USCS)
FC
(%)
NM
(%)
Physical Properties
LL
PI
K
(%)
(%)
(cm/s)
CPT
t50
b
(tsf)
(tsf)
180 470
0.8
60
6.84E08
2150
3
200
NA
2.7E-05
18
0.5
75
155
NP
110
NP
50
60
NP
NP
2
150
38
31
NA
NP
NP
NP
NP
NP
NP
5
20-90
1000
2150
25
2200
13
500
1200
50
1.5
0.8
21-47
2.7E-05
1.4E-05
6.84E08
1.2E-07
6.6E-08
4.1E-05
4.2E-07
1.4E-07
7.5E-06
4.94E06
0.5
2
1
60
130
60
2.5
100
1
100
70
2.5
100
(sec)
No
74 to 15
SP-SM,
SM,
CL, SM-SC
Yes
15 to -10
SM, SC,
CL& CH
No
45 to 28
Yes
No
28 to 17
60 to 40
CH, SM &
SP
CH
SP&SP-SM
Yes
30 to 20
SM
No
Yes
No
65 to 40
40 to 20
60 to 32
SP&SP-SM
SM
SP&SP-SM
>40
<20
2550
25
25
30
Yes
32 to 0
SM
50
47
NP
NP
No
50 to 25
SM & SC
25
6
4
18
Yes
15 to 8
SM
37
28
NP
NP
20
29
NP
NP
NA
NA
1
100
20
23
NA
NA
13
NP
NP
NA
200
600
2
0.5
1.5
150
40
NA
1.3E-06
3.4E-07
<20
22-50
47
18
1.5E-06
4.6E-07
>40
30
50
40
86
13
42
30
53
NA
55
31
Anderson overpass
SR 50/SR 436
Overpass
Pier
6
Pier
7
I-4 /US.192
Ramp CA
Pier
8
4
Rebound
Observed?
I-4 /Osceola Parkway
I-4/ SR 408
Ramp B
SR417 /International
Parkwaya
No
90 to30
Yesc
30 to 0
SP, SP-SM,
SP-SC, CH
SC
No
-
SM
100
NOTE: USCS=Unified Soil Classification System; FC= % fines content; NM= natural moisture content; LL= Liquid Limit; PL =Plasticity index;
K= Permeability coefficient; = sleeve friction;
= cone resistance; NP= non-plastic; NA=not available; ano rebound site; bduring CPT
c
dissipation test; rebound followed by an acceptable permanent-set.
PILES AND DRIVING EQUIPMENT
A summary of pile driving information obtained from the case histories is presented in Table 2. It
includes information such as site description, pile description, pile spacing, hammer characteristic
and energy, driving blow counts, rebound amount and elevations. As the information suggests,
there are several common characteristics among the HPR sites:

Piles were displacement piles ranging between 18 and 24 inches;

Tested and production piles were longer than 70 ft;

Piles were spaced at 6 to 11 ft (2.5B to 4.5B);

Piles were set into predrilled hole with varying depth;

Pile driving hammers were single acting;

Rebound occurred in Central Florida sites (Site 1 to 5) between elevations 35 to -10 ft;
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Paper revised from original submittal.
8

Average pile driving blow counts in the rebound layers was greater than 100 blows/ft
while in the no rebound sites were less than 50 blow/ft.
TABLE 2 Pile Driving Information Summary
Site
Description
1
2
3
4
5
6
Pile size
and type
Anderson Street
Overpass
SR 50/SR 436
overpass
Pier
6
I-4 /
Pier
US.192
7
Pier
8
I-4/ Osceola
Parkway
I-4/ SR 408
(Ramp B)
SR 417
/International
Parkway
24-in
SPCP
HP
( 14 x
89)
24-in
SPCP
24-in
SPCP
24-in
SPCP
24-in
SPCP
24-in
SPCP
18-in
SPCP
24-in
SPCP
Hammer
Model
Type
Ram
Wight
(kips)
Hammer
Rate
Energy
(ft-k)
Average
BL
(blows/ft)
7 (3.5B)
Delmag
D62-22
13.67
90.50
120
NA
ICE I-30
6.6
105
8 (4B)
106
7 (3.5B)
112
9 (4.5B)
100
6 (3B)
95
6 (3B)
100
NA
100
5 (2.5B)
Pile
Length
(ft)
Pile
Spacing
(ft)
124
a
APE
D62-42
ICE
120 S
ICE
120 S
ICE
120 S
ICE
120 S
Delmag
D36-32
APE
D46-42
b
Total
BL
Rebound
Elevation
(ft)
135
3674
15 to -10
71.4
NA
NA
13.7
154
143
526
2599
26 to 17
1.1
12
120
220
3108
35 to 25
0.6
12
120
140
5183
35 to 20
0.6
12
120
111
4431
30 to 15
1.25
12
120
105
2687
15 to 8
0.9
7.94
84
50
3101
30 to 0
0.5
13.7
154
42
1797
5 to 0
0.25
C
MAX
Rebound
(in)
1.4
No Rebound
Note: SPCP=square prestressed concrete pile; B= pile diameter; asingle acting; baverage driving blow counts in the rebound layer;
ctotal pile driving; BL= blow counts; NA= not available.
RESULTS AND DISCUSSION
Site 1 Anderson Street Overpass
The approximate ground surface elevation (GSE) at the site was 104 ft. The piles were designed
as 24-inch square PCP, 124 ft long. Severe HPR problems occurred between elevation 15 and -10
ft during installation of the displacement piles at Pier 6 located on the east end of the overpass. As
a result, the foundation were redesigned using low displacement steel H-piles. Rebound occurred
only during installation of the concrete piles.
Three CPTu tests were conducted near he rebounded piles. Figure 2 shows the variation
of pore pressure
and PDA pile displacement with elevation. An increase in pore pressures
ranged between 1 and 10 tsf in the no HPR soils above elevation 15 ft, to more than 20 tsf in the
rebound soils from elevation 15 to near 0 ft. By comparing the PDA rebound, iSet and pore
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9
pressure in Figure 2b and 2c, it is evident that when the pore pressure is approximately 30 tsf, the
pile iSet became zero.
Elev. GSE 104ft Soil Layers
(ft)
100
Fine Sand (SP)
90
Pile Displacements
and Rebound (in)
0 0.5 1 1.5 2
0
Pore Pressure
U2 (tsf)
10 20 30
40
Predrilled
Depth
Sand with Silt (SP-SM)
80
70
60
50
40
30
20
10
0
Silty Sand (SM)
Sand with Silt (SP-SM)
Clay (CH)
Silty Clay Fine Sand (SM-SC)
Silty Clay with some Shell (CL)
Silty Clay Fine Sand (SM-SC)
Silty Sand (SM)
Sand with Silt (SP-SM)
Clayey Sand (SC)
Silty Clay Fine Sand (SM-SC)
Sandy Clay (CL)
Green Clay (CH)
-10
Pier 6 Pile 6 DMX
Pier 6 Pile 6 Rebound
Pier 6 Pile 6 iSet
CPTu-4
CPTu-5
CPTu-602
(a)
(b)
(c)
FIGURE 2 (a) generalized soil profile, (b) PDA diagrams, and (c) CPTu pore-water pressure
For Site 1 Anderson Street Overpass.
Site 2 SR50/SR436 Overpass
Twenty-four inch square, PCP piles were installed to support the overpass at the intersection.
These piles were 105 ft long with a GSE of 98 ft. Due to practical refusal of 20 blows per inch,
several piles did not reach the specified minimum tip elevation of 15.6 ft, corresponding to a
depth of 82.4 ft. Figure 3b shows the observed PDA rebound varied from 0.25 to 1 inch, and was
first encountered at an elevation of 26 ft and continued to increase until driving terminated at 18
ft.
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Two CPTu were performed at this site to a depth of 80 ft. By matching the PDA data and
the pore pressure in Figure 3 elevation 26 to 18 ft, the pile displacement decreased as the pore
pressure reached a very high value of more than 20 tsf. A peak pore pressure was recorded at
elevation 23 ft, corresponding to a significantly decrease in displacement at the same elevation.
Elev. GSE 99ft Soil Layers
(ft)
100
90
80
70
Silty Fine Sand (SM)
Fine Sand (SP)
Silty Fine Sand (SM)
Fine Sand (SP)
Fine Sand with silt
(SP-SM)
Silty Fine Sand (SM)
Pile Displacements
and Rebound (in)
0
1
2
3
4
Pore Pressure
U2 (tsf)
0 10 20 30 40
Predrilled
Depth
Fine Sand (SP)
60
50
Silty Fine Sand (SM)
Fine Sand (SP)
Silty Fine Sand (SM)
40
Clay (CH)
Silty Fine Sand (SM)
Fine Sand (SP)
30
Silty Fine Sand (SM)
20
Sandy Fat Clay (CH)
10
EB 4 WB Pile 5 DMX
EB 4 WB Pile 5 Rebound
EB 4 WB Pile 5 iSet
CPTu-1
CPTu-5b
(a)
(b)
(c)
FIGURE 3 (a) Generalized Soil Profile, (b) PDA Diagram and (c) CPTu pore-water pressure
For Site 2 SR50/SR436 Overpass.
Site 3 I-4/US.192
The approximate GSE at the site was 90 to 106 ft. The support piling for the bridge piers
consisted of 24-inch square PCP 95 ft long. Many of the piles with tip elevations between 25 and
5 ft experienced rebound ranging between 0.5 and 1.25 inch per hammer blow (see Figures 4b, 5b
and 6b). Three CPTu tests were conducted each about 40 ft from nearest HPR piles; (i.e., pile 16
pier 6, pile 10 pier 7 and pile 11 pier 8). These three piers were located approximately 200 ft
apart. Large rebound, followed by low displacement was observed during driving.
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Pier 6 Pile 16
The pore pressure versus elevation plot near pier 6 is shown in Figure 4c. By comparing
the PDA results and the pore pressure in Figure 4b and 4c, it is evident that in the overlying zones
with minimal rebound above elevation 35 ft, the pore pressure varied between 1 and 4 tsf, while
the rebound soil below elevation 35 ft yielded very high positive values of more than 20 tsf. In
the rebound zone elevation below elevation 30 ft, the final permanent-set decreased, approaching
near zero as the pore pressure reached 29 tsf and as the pore pressure decreased to less than 5 tsf
at elevation 25 ft, the pile displacement increased resulting in an acceptable permanent-set.
Elev. GSE 106ft Soil Layers
(ft)
100
Sand with silt to Silty
Sand (SM)
90
80
Pile Displacements
and Rebound (in)
0 0.25 0.5 0.75 1
Pore Pressure
U2 (tsf)
0
10 20 30 40
Predrilled
Depth
Sand with Silt (SP-SM)
70
60
50
40
Fine Sand (SP)
Silty Sand (SM)
30
20
10
Pier 6 Pile 16 DMX
Pier 6 Pile 16 Rebound
CPTu-4
Pier 6 Pile 16 iSet
(a)
(b)
(c)
FIGURE 4 (a) Generalized Soil Profile, (b) PDA diagram and (c) CPTu pore-water pressure
for Site 3 I-4/US.192 (Ramp CA Pier 6).
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Pier 7 Pile 10
At this location, the pore pressure increases between elevations 32 and 25 ft corresponding to
large rebounds, and lower permanent-set. Comparing PDA pile displacements and pore pressure
in Figure 5, shows the pile penetration ceased when the pore pressure exceeded 20 tsf. After the
pore pressure decreased below elevation 25, the rebound decreased and permanent-set increased.
Elev. GSE 106ft Soil Layers
(ft)
Pile Displacements
and Rebound (in)
0
0.25 0.5 0.75
Pore Pressure
U2 (tsf)
1
0
10 20 30 40
Sand with Silt (SP-SM)
100
Silty Sand (SM)
90
Sand with Silt (SP-SM)
Silty Sand (SM)
80
Sand with Silt (SP-SM)
Predrilled
Depth
70
60
50
40
Fine Sand (SP)
Sand with Silt (SP-SM)
Silty Sand (SM)
30
20
10
0
Pier 7 Pile 10 DMX
Pier 7 Pile 10 Rebound
CPTu-3
Pier 7 Pile 10 iSet
(a)
(b)
(c)
FIGURE 5 (a) Generalized Soil Profile, (b) PDA Diagram and (c) CPTu pore-pressure
3 I-4/US.192 (Ramp CA Pier 7).
for Site
Pier 8 Pile 11
As shown in Figure 6b, large rebound between elevation 28 and 18 ft, resulted in very low
permanent-set. For the same elevation, the pore pressure yielded an increase of more than 20 tsf
and as the pore pressure decreased below elevation 20 ft a slight increase occurred. Using the
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findings from the PDA analysis and pore pressure at the three piers, it is demonstrated that the
increase in pore pressure is accompanied by very small pile displacement in high pile rebound
soils.
Elev. GSE 90ft
(ft)
90
80
70
60
50
Pile Displacements
and Rebound (in)
Soil Layers
0
0.5
1
1.5
Pore pressure
U2 (tsf)
2
0
10 20 30 40
Fine Sand (SP)
Sand with Silt
(SP-SM)
Predrilled
Depth
Fine Sand (SP)
Sand with Silt (SP-SM)
40
30
Silty Sand (SM)
20
10
0
-10
Sandy Limestone
Pier 8 Pile 11 DMX
Pier 8 Pile 11 Rebound
CPTu-2
Pier 8 Pile 11 iSet
(a)
(b)
(c)
FIGURE 6 (a) Generalized Soil Profile, (b) PDA diagram and (c) CPTu pore-water pressure
Site 3 I-4/US.192 (Ramp CA Pier 8).
for
Site 4 I-4/Osceola Parkway
The bridge pier supports consisted of 24-inch square PCP 95 ft long. Pier 2, pile 8 had high blow
counts due to HPR. Rebound over 0.5 inch occurred between elevations 15 and 0 ft, as shown in
Figure 7b.
One sounding was performed at this location approximately 25 ft from the HPR piles.
The data indicated similar trend to the data from ramp CA at the I-4/US.192 interchange. Very
high pore pressure, reaching 30 tsf, existed from elevations 18 ft to 8 ft. By comparing the PDA
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Paper revised from original submittal.
14
data and pore pressure in Figure 7, it can be shown that at these elevations, pore pressure in
excess of 20 tsf correlated to large rebound and small permanent-set.
Elev. GSE 92ft
(ft)
90
Sand with Silt (SP-SM)
80
Silty Sand (SM)
70
Pore pressure
U2 (tsf)
Pile Displacements
and Rebound (in)
Soil Layers
0 0.25 0.5 0.75 1 1.25
0
10 20 30 40
Predrilled
Depth
Fine Sand (SP)
60
Sand with Silt (SP-SM)
50
40
Silt with sand (ML)
Silty Sand (SM)
Clayey Sand (SC)
30
20
Silty Sand (SM)
10
0
Tan Sandy Limestone
-10
Pier 2 Pile 8 DMX
Pier 2 Pile 8 Rebound
Pier 2 Pile 8 iSet
CPTu-1
(a)
(b)
(c)
FIGURE 7 (a) Generalized soil profile, (b) PDA Diagram, and (c) CPTu Pore-Water Pressure
Site 4 I-4/ Osceola Parkway (Ramp D2).
for
Site 5 I-4 and SR408 Interchange (Ramp B)
Two piles were driven as instrumented test piles; pile 5 pier 2 and pile 2 end bent 1. These piles
were 100 ft long PCP 18-inch square piles.
Three sounding were conducted near the two test piles. The increase of pore pressure
(Figure 8c) encountered during CPTu testing, ranged between 10 and 17 tsf. It correlates to small
amount of rebound followed by an acceptable permanent-set.
TRB 2013 Annual Meeting
Paper revised from original submittal.
15
Elev. GSE 105ft Soil Layers
(ft)
100
90
80
Silty Fin Sand (SM)
Pile Displacements
and Rebound (in)
0 0.25 0.5 0.75 1
Pore Pressure
U2 (tsf)
0 5 10 15 20
Predrilled
Depth
Fine Sand(SP)
Fine Sand With Clay (SP-SC)
70
Fine Sand With Silt(SP-SM)
60
Sand With Clay (SP-SC)
50
Clayey Fine Sand (SC)
40
Clay (CH)
30
Clayey Fine Sand (SC)
20
10
0
Pier 2 Pile 5 DMX
Pier 2 Pile 5 Rebound
Pier 2 Pile 5 iSet
CPTu-B109
CPTu-B118
CPTu -A1-105A
(a)
(b)
(c)
FIGURE 8 (a) Generalized Soil Profile, (b) PDA diagrams (b and c) and (d) CPTu pore-water
pressure
for Site 5 I-4/SR408 Interchange (Ramp B).
Site 6 SR417 /International Parkway
Two piles instrumented with PDA sensors were tested at this site. These piles were 24-inch
square, PCP’s and 100 ft in length. A small amount of rebound was observed (Figure 9b and 9c )
followed by a large undergoing set, however, the piles met driving specifications set forth by the
FDOT (i.e., less than 0.25 inch rebound per blow).
Three CPTu soundings were conducted near the two test piles. Pore pressure increased
from an average in the overlying soils of-0.3 tsf to less than 5 tsf where pile experienced a small
amount of rebound. Figure 9d shows this increase in the pore pressure and rebound (Figure 9c)
between elevation 10 and 0 ft. This data is also consistent with the finding previously described,
TRB 2013 Annual Meeting
Paper revised from original submittal.
16
that rebound increases with pore pressure, soil layers with pore pressures less than 5 tsf
determined during the CPT are not likely to cause any HPR.
Elev. GSE 75ft Soil Layers
(ft)
70
60
50
40
30
Silty Sand (SM)
Fine Sand (SP)
Sand with silt (SP- SM)
Pile Displacements
and Rebound (in)
0
0.5
1
1.5
Pile Displacements
and Rebound (in)
2
0
Predrilled
Depth
0.5
1
1.5
2
Pore Pressure
U2 (tsf)
0 1 2 3 4 5
Predrilled
Depth
Sandy Fat Clay (CH)
Sand with silt (SP- SM)
Elastic silt (MH)
Sand with silt (SP- SM)
Silty Sand (SM)
20
10
0
-10
ClayeyFine Sand (SC)
Silty Fine Sand (SM)
EB 1 Pile 14 DMX
EB 2 Pile 5 DMX
EB 1 Pile 14 Rebound
EB 2 Pile 5 Rebound
EB 1 Pile 14 iSet
EB 2 Pile 5 iSet
CPT1
CPT2
CPT4
(a)
(b)
(c)
(d)
FIGURE 9 (a) Generalized Soil Profile, (b and c) PDA Diagrams, and (d) CPTu pore-water
pressure
for Site 6 SR417/International Parkway.
EFFECT OF PILE SIZE, PILE SPACING AND HAMMER TYPE
The driven HPR piles were 18 to 24 inches in diameters and longer than 70 ft in length. Driven
piles at sites 1 through 4 were 24 inches in diameter and 100 ft long. Piles at these sites
experienced rebound of over 0.65 to 1.50 inches with near zero set while the soils at same
elevation exhibited CPTu pore pressures
of more than 20 tsf. In contrast, soils at site 6 where
similar size piles were driven, produced pore pressures
of less than 5 tsf, and rebound of less
than 0.25 inches followed by a large set. No conclusions can be reached on the effect of pile size
on HPR.
TRB 2013 Annual Meeting
Paper revised from original submittal.
17
The driven piles at the six sites were placed in groups of 12 to 20 piles and were spaced
at 5 to 9 ft (2.5B to 4.5B) as summarized in Table 2. At site 6, where no rebound was observed,
the driven piles were placed at 5 to 6 ft (2.5B to 3B) intervals. At sites where excessive rebound
was observed (sites 1 to 4), the group of piles were placed at 6 to 9 ft (3B to 4.5B) intervals.
Because both HPR and no HPR occurred with similar pile spacings, it can be concluded HPR is
not a function of pile spacing.
Single-acting hammers were used at HPR sites. The hammers were selected based on
standard recommendations for sufficient driving capabilities according to the project
requirements. However, due to excessive rebound at site 1, the engineers recommended hammers
with heavier rams to overcome rebound at the site. Even with heavier rams, the piles at this site
could not be driven. The piles at this site were redesigned and replaced with steel H piles.
Consequently, the data analyses of the hammer type did not provide any clear findings.
POSSIBLE REASON FOR HPR
During pile driving process, piles undergo elastic compression from the hammer blow, and spring
back to their original configuration when the hammer retracts. The soil below the pile tip is also
compressed because of the hammer blow, and will attempt to push the pile back up. The sum of
elastic and plastic deformations of the pile and soil system are referred as rebound. When contact
shear resistance along the pile shaft exists, the pile is prevented from recovering its original
configuration (8).
The authors believe that as the piles penetrated into very dense silty fine sand HPR soils,
excessive positive pore water pressures were produced under the pile tip. This pressure extends
laterally and vertically (9, 10) causing a resistance stress to the point that large diameter piles
could not penetrated the stratum. At the same time, the pore pressures along the shaft decreased
producing very low effective stress and minimal shaft resistance. The combination of the
extremely high tip resistance and minimal or no shaft resistance in relatively dense silty sands
TRB 2013 Annual Meeting
Paper revised from original submittal.
18
produced HPR for the 24 inch square piles in this investigation. No analytical proof of this
conclusion is presented.
CORRELATIONS BETWEEN REBOUND AND CPT PORE PRESSURE
Linear correlations between the pile rebound, permanent-set and the maximum pore pressure, are
presented in Figure 10. These correlations were developed within the HPR zone using CPTu pore
pressure
and both rebound or inspector permanent-set at the same elevation (e.g., Maximum
pore pressure at site 1 is 33 tsf and corresponding rebound at the same depth is 1 in and the iSet is
0.13 in). Figure 10a has plots of rebound and set versus pore pressure while 10b presents the
same variables versus the ratio of pore pressure
pressure
divided by the calculated (hydrostatic)
. The data from this study plus the data presented by Murrell et al. (5) was
combined. It consistently produced strong linear correlations with regression coefficients R2 of
0.6 or higher. The permanent-set decreased and rebound increased as pore pressure increased.
Rebound versus either pore pressure or
⁄
nearly plots through the origin, indicating rebound
would equal approximately 2.5 % of the CPTu
or 5.5 % of the
⁄
ratio. Slightly higher
correlation coefficients in Figure 10b indicate increased agreement between HPR and the
⁄
ratio. The data from Murrell et al. (5) agrees with the results of this study.
TRB 2013 Annual Meeting
Paper revised from original submittal.
19
Present Study
Murrell et al.(2008)
Excludes Murrell, R² = 0.77
Includes Murrell, R2=0.60
y = 0.0254x + 0.0281
1.2
Present Study
0.8
iSet (in)
Rebound (in)
1.6
0.8
0.4
Murrell et al.(2008)
Excludes Murrell, R² = 0.72
Includes Murrell, R2=0.69
y = -0.0141x + 0.5102
0.6
0.4
0.2
0
0
0
5
10
15
20
25
30
35
0
5
10
15
20
25
30
35
Pore Pressure, U2 (tsf)
Pore Pressure, U2 (tsf)
(a)
0.8
Excludes Murrell, R² = 0.70
Includes Murrell, R2=0.73
y = 0.055x - 0.0004
1.2
Excludes Murrell, R² = 0.73
Includes Murrell, R2=0.78
y = -0.0295x + 0.5172
0.6
iSet (in)
Rebound (in)
1.6
0.8
0.4
0.4
0.2
0
0
0
4
8
12
16
20
U2 /U0
0
4
8
12
16
20
U2 /U0
(b)
FIGURE 10 Correlation between Rebound, Permanent-iSet and (a) CPTu pore water pressure, and
(b) Ratio of CPTu pore pressure
and hydrostatic pressure ( ).
CONCLUSIONS AND RECOMMENDATIONS
The overburden depth at which HPR occurred was typically greater than 50 ft. Large
displacement piles predrilled to 25 ft and driven at numerous Central Florida locations have
recorded rebound values over 1 to 1.5 inches per hammer blow. These problems generally
occurred in soils that did not display any unusual properties during routine soil site investigations.
In general, HPR soils displayed an olive green to light green color with visual descriptions
ranging from dense clayey and silty fine sands, to hard highly plastic clays with very low
permeability. Most HPR layers had high fines content, with a natural moisture content less than
the liquid limit.
TRB 2013 Annual Meeting
Paper revised from original submittal.
20
There was a large increase in the CPTu pore pressure
values from near zero or negative
pressure to high positive pore pressures in all the HPR zones identified by the PDA data. This
increase in pore pressure, in conjunction with variations in the strength, stiffness and soil
composition may be the combination of geotechnical properties that could identify the potential
for high pile rebound. Good correlations between rebound, permanent-set and pore pressure
indicated that permanent-set decreases and rebound increases linearly with either pore pressure
⁄
or
.
Geotechnical engineers can expect to encounter HPR problems when driving
displacement piles if the CPTu pore pressure
is greater 20 tsf. It is possible to drive piles
through saturated fine silty sand to sandy silt or clayey sand if pore pressure
while pile driving difficulty may increase if
TRB 2013 Annual Meeting
is less than 5 tsf;
ranged between 5 and 20 tsf.
Paper revised from original submittal.
21
ACKNOWLEDGMENT
The authors gratefully acknowledge the Florida Department of Transportation for their support
for this project. The generous help of Peter Lai, Dr. David Horhota, Kathy Gray, Mr. Brian
Bixler, and Mr. Hipworth Robert is greatly appreciated. Special thanks go to consultants at
Ardaman & Associates, Mr. Zan Bates and from GRL, Mr. Mohamad Hussein, who all provided
valuable expertise and reliable services. Finally, sincere thanks go to the graduate students,
Thaddeus J. Misilo III, Yeniree Chin Fong and Katie Davis, for their efforts.
TRB 2013 Annual Meeting
Paper revised from original submittal.
22
REFERENCES
1. Cosentino, P. Kalajian, E. Misilo, T, Chin Fong, Y. Davis, K., Jarushi F., Bleakley A., Hussein
M. H., and Bates, Z.. Design Phase Identification of High Pile Rebound Soils. Technical
report, Contract BDK81 Work Order 977-01, Florida Department of Transportation, 2010.
2. Hussein, M.H., Woerner, W. A., Sharp, M. and Hwang, C. Pile Driveability and Bearing
Capacity in High-Rebound Soils. ASCE GEO Congress CD-ROM, Atlanta, GA, 2006.
3. Chin Fong, Y. Identifying Soils the Produce High Pile Rebound. Technical report, Florida
Institute of Technology, 2010
4. FDOT. Standard Specification for Road and Bridges Section 455. 2010.
5. Murrell, Kyle L., Canivan, Gregory J., Camp, William M. III. High and Low Strain Testing of
Bouncing Piles. Proceedings of the 33rd Annual and 11th International Conference on Deep
Foundations, 2008. article #1603; publication #85 (AM-2008).
6. Likins, Garland E. Pile Installation Difficulties in Soils with Large Quakes. In G.G. Globe,
editors, Proceedings of Symposium 6 at the 1983 ASCE Convention, May 18, 1983,
Philadelphia, PA, 1983. ASCE Geotechnical Engineering Division.
7. Parez, L. and Faureil, R., 1988. Le piézocône. Améliorations apportées à la reconnaissance de
sols. Revue Française de Géotech, Vol. 44, 13-27
8. Seo, H., Yildirim,I., and Prezzi, M. Assessment of the Axial Load Response of an H Pile
Driven in Multilayered Soil. J. of Geotech. Geoenviron. Eng.,135(12),1789-1804.
9. Bingjian, Zhu. Study of the Pore Water Pressure Variation Rule in Saturated Soft Soil Caused
by Prestressed Concrete Pile Penetration. IEEE, 2011,756-59.
10. Robertson, P. K.,Woeller, D., and Gillespie, D. Evaluation of Excess Pore Pressures and
Drainage Conditions around Driven Piles using the Cone Penetration Test with Pore Pressure
Measurements.Canadian Geotechnical Journal, 1990, 27(2): 249-254.
TRB 2013 Annual Meeting
Paper revised from original submittal.