Identifying High Pile Rebound Soils Using CPT Pore Water Pressure Measurements - Case Studies in...

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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) wordsText (4297) Words not including Abstract

Tables 2 or 500 WordsFigures 10 or 2500 WordsGrand 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 ranged between 5 and 20 tsf. The pore

pressure 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.




2

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 her ein 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




3

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




4

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.

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

-0.2

0

0.2

0.4

0.6

0.8

1

0 20 40 60 80 100 120 140 160 180 200 220

M a x i m u m D

i s p l a c e m e n t

( i n )

Time (Milliseconds)




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).




6

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.




7

TABLE 1 Summary of Soil Properties at HPR Sites

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;

Site DescriptionRebound

Observed?

Elevation

(ft)

Soil Type

(USCS)

FC

(%)

Physical Properties CPT

NM

(%)

LL

(%)

PI

(%)

K

(cm/s)

t50

(sec)b

(tsf)

(tsf)

1 Anderson overpass

No 74 to 15SP-SM,

SM,

CL, SM-SC

<20 22-50 47 181.5E-06

4.6E-07

180 -

4700.8 60

Yes 15 to -10SM, SC,

CL& CH>40

30

50

40

86

13

42

6.84E-

082150 3 200

2SR 50/SR 436

Overpass

No 45 to 28CH, SM &

SP30 53 NA NA 2.7E-05 18 0.5 75

Yes 28 to 17 CH >40 55 155 110 2.7E-05 5 1.5 50

3I-4 /US.192

Ramp CA

Pier

6

No 60 to 40 SP&SP-SM <20 31 NP NP 1.4E-05 20-90 0.8 60

Yes 30 to 20 SM25-

5021-47 NP NP

6.84E-

08

1000

21502 150

Pier

7

No 65 to 40 SP&SP-SM 25 38 NP NP 1.2E-07 25 0.5 60

Yes 40 to 20 SM 25 31 NP NP 6.6E-08 2200 2 130

Pier

8

No 60 to 32 SP&SP-SM 30 NA NP NP 4.1E-05 13 1 60

Yes 32 to 0 SM 50 47 NP NP4.2E-07

1.4E-07

500

1200

2.5 100

4 I-4 /Osceola Parkway

No 50 to 25 SM & SC 25 6 4 18 7.5E-06 50 1 100

Yes 15 to 8 SM 37 28 NP NP4.94E-

0670 2.5 100

5I-4/ SR 408

Ramp B

No 90 to30SP, SP-SM,SP-SC, CH

20 29 NP NP NA NA 1 100

Yesc 30 to 0 SC 20 23 NA NA NA NA 2 150

6SR417 /International

Parkwaya No - SM 40 13 NP NP1.3E-06

3.4E-07

200

600

0.5

1.5100

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

dissipation test; crebound followed by an acceptable permanent-set.




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

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

Site

Description

Pile size

and type

PileLength

(ft)

PileSpacing

(ft)

aHammer

Model

Type

RamWight

(kips)

HammerRate

Energy

(ft-k)

bAverageBL

(blows/ft)

CTotal

BL

ReboundElevation

(ft)

MAXRebound

(in)

1Anderson StreetOverpass

24-in

SPCP124 7 (3.5B)

Delmag

D62-2213.67 90.50 135 3674 15 to -10 1.4

HP

( 14 x

89)

120 NA ICE I-30 6.6 71.4 NA NA No Rebound

2SR 50/SR 436

overpass

24-in

SPCP105 8 (4B)

APE

D62-4213.7 154 143

526

259926 to 17 1.1

3I-4 /US.192

Pier

6

24-in

SPCP106 7 (3.5B)

ICE

120 S12 120 220 3108 35 to 25 0.6

Pier 7

24-inSPCP

112 9 (4.5B)ICE

120 S12 120 140 5183 35 to 20 0.6

Pier

8

24-in

SPCP100 6 (3B)

ICE

120 S12 120 111 4431 30 to 15 1.25

4I-4/ OsceolaParkway

24-inSPCP

95 6 (3B)ICE

120 S12 120 105 2687 15 to 8 0.9

5I-4/ SR 408

(Ramp B)

18-in

SPCP100 NA

Delmag

D36-327.94 84 50 3101 30 to 0 0.5

6SR 417/International

Parkway

24-in

SPCP100 5 (2.5B)

APE

D46-4213.7 154 42 1797 5 to 0 0.25

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.




9

pressure in Figure 2b and 2c, it is evident that when the pore pressure is approximately 30 tsf, the

pile iSet became zero.

(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.

-10

0

10

20

30

40

50

60

70

80

90

100

Elev. GSE 104ft Soil Layers(ft)

Green Clay (CH)

Fine Sand (SP)

Sand with Silt (SP-SM)


Silty Sand (SM)Sand with Silt (SP-SM)

Clay (CH)

Silty Clay Fine Sand (SM-SC)

Silty Clay Fine Sand (SM-SC)

Silty Clay with some Shell (CL)

Silty Sand (SM)

Clayey Sand (SC)

Silty Clay Fine Sand (SM-SC)Sandy Clay (CL)

0 0.5 1 1.5 2

Pier 6 Pile 6 DMX

Pier 6 Pile 6 Rebound

Pier 6 Pile 6 iSet

Predrilled

Depth

Pile Displacements

and Rebound (in) 0 10 20 30 40

Pore Pressure

U 2 (tsf)

CPTu-4

CPTu-5

CPTu-602




10

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.

(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.

10

20

30

40

50

60

70

80

90

100

Elev. GSE 99ft Soil Layers

(ft)

Sandy Fat Clay (CH)

Silty Fine Sand (SM)

Fine Sand (SP)

Silty Fine Sand (SM)Clay (CH)


Fine Sand (SP)Silty Fine Sand (SM)

Fine Sand (SP)


Fine Sand with silt

(SP-SM)



0 1 2 3 4

EB 4 WB Pile 5 DMX

EB 4 WB Pile 5 Rebound

EB 4 WB Pile 5 iSet

Predrilled

Depth

Pile Displacements

and Rebound (in)0 10 20 30 40

Pore Pressure

U 2 (tsf)

CPTu-1

CPTu-5b




11

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.

(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).

10

20

30

40

50

60

70

80

90

100

Silty Sand (SM)

Fine Sand (SP)


Sand with silt to Silty

Sand (SM)


(ft) 0 0.25 0.5 0.75 1

Pier 6 Pile 16 DMX


Pier 6 Pile 16 iSet

Predrilled

Depth

Pile Displacements

and Rebound (in)

0 10 20 30 40

Pore Pressure

U 2 (tsf)

CPTu-4




12

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.

(a) (b) (c)

FIGURE 5 (a) Generalized Soil Profile, (b) PDA Diagram and (c) CPTu pore-pressure for Site

3 I-4/US.192 (Ramp CA Pier 7).

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

0

10

20

30

40

50

60

70

80

90

100

Silty Sand (SM)


Fine Sand (SP)


Silty Sand (SM)


Silty Sand (SM)



(ft)0 0.25 0.5 0.75 1

Pier 7 Pile 10 DMX


Pier 7 Pile 10 iSet

Predrilled

Depth

Pile Displacements

and Rebound (in)

0 10 20 30 40

Pore Pressure

U 2 (tsf)

CPTu-3




13

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.

(a) (b) (c)

FIGURE 6 (a) Generalized Soil Profile, (b) PDA diagram and (c) CPTu pore-water pressure for

Site 3 I-4/US.192 (Ramp CA Pier 8).

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

-10

0

10

20

30

40

50

60

70

80

90

Silty Sand (SM)

Sandy Limestone


Fine Sand (SP)

Sand with Silt

(SP-SM)

Fine Sand (SP)


(ft)0 0.5 1 1.5 2

Pier 8 Pile 11 DMX


Pier 8 Pile 11 iSet

Pile Displacements

and Rebound (in)

0 10 20 30 40

Pore pressure

U 2 (tsf)

CPTu-2

Predrilled

Depth




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.

(a) (b) (c)

FIGURE 7 (a) Generalized soil profile, (b) PDA Diagram, and (c) CPTu Pore-Water Pressure for

Site 4 I-4/ Osceola Parkway (Ramp D2).

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.

-10

0

10

20

30

40

50

60

70

80

90


(ft)

Tan Sandy Limestone

Silty Sand (SM)

Clayey Sand (SC)

Silty Sand (SM)

Silt with sand (ML)


Fine Sand (SP)

Silty Sand (SM)


0 0.250.50.75 1 1.25

Pier 2 Pile 8 DMX


Pier 2 Pile 8 iSet

Pile Displacements

and Rebound (in)

Predrilled

Depth

0 10 20 30 40

Pore pressure

U 2 (tsf)

CPTu-1




15

(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,

0

10

20

30

40

50

60

70

80

90

100


(ft)

Clayey Fine Sand (SC)

Clayey Fine Sand (SC)

Clay (CH)

Sand With Clay (SP-SC)

Fine Sand With Silt(SP-SM)

Fine Sand With Clay (SP-SC)

Fine Sand(SP)

Silty Fin Sand (SM)

0 0.25 0.5 0.75 1

Pier 2 Pile 5 DMX


Pier 2 Pile 5 iSet

Predrilled

Depth

Pile Displacements

and Rebound (in)

0 5 10 15 20

CPTu-B109

CPTu-B118

CPTu -A1-105A

Pore Pressure

U 2 (tsf)




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.

(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.

-10

0

10

20

30

40

50

60

70


(ft)


ClayeyFine Sand (SC)

Silty Sand (SM)

Sand with silt (SP- SM)

Elastic silt (MH)

Sandy Fat Clay (CH)



Silty Sand (SM)

Fine Sand (SP)

0 0.5 1 1.5 2

EB 1 Pile 14 DMX

EB 1 Pile 14 Rebound

EB 1 Pile 14 iSet

Predrilled

Depth

Pile Displacementsand Rebound (in)

0 0.5 1 1.5 2

EB 2 Pile 5 DMX

EB 2 Pile 5 Rebound

EB 2 Pile 5 iSet

Predrilled

Depth

Pile Displacementsand Rebound (in)

0 1 2 3 4 5

Pore PressureU 2 (tsf)

CPT1

CPT2

CPT4




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




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 divided by the calculated (hydrostatic)

pressure . 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 R 2 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.




19

(a)

(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.

0

0.4

0.8

1.2

1.6

0 5 10 15 20 25 30 35

R e b o u n d ( i n )

Present Study Murrell et al.(2008)

Excludes Murrell, R² = 0.77

Includes Murrell, R2=0.60

y = 0.0254x + 0.0281

Pore Pressure, U 2 (tsf)

0

0.2

0.4

0.6

0.8

0 5 10 15 20 25 30 35

i S e t ( i n )

Pore Pressure, U 2 (tsf)

Present Study Murrell et al.(2008)



y = -0.0141x + 0.5102

0

0.4

0.8

1.2

1.6

0 4 8 12 16 20

R e b o u n d ( i n )



y = 0.055x - 0.0004

U 2 /U 0

0

0.2

0.4

0.6

0.8

0 4 8 12 16 20

i S e t ( i n )



y = -0.0295x + 0.5172

U 2 /U 0




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 is less than 5 tsf;

while pile driving difficulty may increase if ranged between 5 and 20 tsf.




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.




22

REFERENCES

1. Cosentino, P. Kalajian, E. Misilo, T, Chin Fong, Y. Davis, K., Jarushi F., Bleakley A., HusseinM. H., and Bates, Z.. Design Phase Identification of High Pile Rebound Soils. Technicalreport, 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 desols. 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 PileDriven 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 PressureMeasurements.Canadian Geotechnical Journal, 1990, 27(2): 249-254.

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