Assessing Adhesion of Driven Pipe Piles in Clay Using Adaptation of ...

[Pages:13]Assessing Adhesion of Driven Pipe Piles in Clay Using Adaptation of Stress History and Normalized Soil Engineering Parameter Concept

Steven R. Saye, M.ASCE1; Dan A. Brown, M.ASCE2; and Alan J. Lutenegger, M.ASCE3

Abstract: This paper presents a method to estimate the side resistance of a driven displacement-pipe pile in clay using the stress history and normalized soil engineering parameter (SHANSEP) concept. The side resistance is treated as an adhesion, and this adhesion is normalized to the effective overburden stress. This normalized adhesion is then related to the soil overconsolidation ratio using an adaptation of the SHANSEP concept to separate the normally consolidated behavior from the overconsolidated behavior. This approach provides a rational means of screening representative measurements of undrained shear strength from measurements that may have been affected by sample disturbance. Assessments of the soil overconsolidation ratio are developed with laboratory odometer test data and an empirical approach using laboratory undrained strength data. A database of pile load tests screened for the effects of incomplete set-up and soil-property data screened for the effects of sample disturbance is used to evaluate the normalized side resistance and the relationship of normalized side resistance to overconsolidation ratio. DOI: 10.1061/(ASCE)GT.1943-5606.0000842. ? 2013 American Society of Civil Engineers.

CE Database subject headings: Cohesive soils; Pipe piles; Clays; Driven piles; Adhesives; Stress history; Soil consolidation.

Author keywords: Cohesive soil; Pipe piles; Side resistance; Side adhesion.

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Introduction

The axial resistance of piles in cohesive soil is most often estimated using empirical correlations of side resistance with total stressstrength parameters, i.e., undrained shear strength su. Such an approach can provide a reliable indication of pile resistance if the method is developed through extensive local experience in a specific geologic formation with a consistent method of determining su and applied in a manner that is faithful to the original empirical calibration to piles of similar type, size, and embedded length. However, such empirical methods suffer from variability and inconsistency and often show poor correlations with long-term axial resistance when applied broadly to a wide range of diverse geologic conditions. Factors affecting the use of empirical correlations with su include variability related to sample disturbance, inconsistent test methods used to determine undrained shear strength, the effects of in situ state of stress due to overconsolidation, pile installation methods, and other factors. Attempts to develop a practical approach using effective stress-strength parameters have not achieved broad acceptance due to the relatively complex nature of the problem of predicting the effects of pile installation on the state of stress at the pile-soil interface as well as the difficulty in

1Senior Geotechnical Engineer, Kiewit Engineering Co., Kiewit Plaza, Omaha, NE 68131 (corresponding author). E-mail: steve.saye@

2President, Dan Brown & Associates, LLC, 300 Woodland Road, Sequatchie, TN 37374. E-mail: dbrown@

3Professor, Dept. of Civil and Environmental Engineering, Univ. of Massachusetts, Amherst, MA 01003-5205. E-mail: lutenegg@ecs.umass.edu

Note. This manuscript was submitted on April 26, 2011; approved on September 20, 2012; published online on December 14, 2012. Discussion period open until December 1, 2013; separate discussions must be submitted for individual papers. This paper is part of the Journal of Geotechnical and Geoenvironmental Engineering, Vol. 139, No. 7, July 1, 2013. ?ASCE, ISSN 1090-0241/2013/7-1062?1074/$25.00.

determining effective stress-strength parameters of the remolded soil at the interface.

The stress history and normalized soil engineering parameter (SHANSEP)?based approach (Ladd and Foott 1974)described in this paper provides the means to address many of the limitations of conventional empirical correlations of axial resistance with su. In this approach, the average long-term side resistance of driven pipe piles qs is treated as an undrained adhesion that is normalized to the average effective overburden stress s9vo along the length of the pile and related to the average overconsolidation ratio (OCR) using the SHANSEP concept (Ladd and Foott 1974). Model pile load-test data obtained by Steenfeld et al. (1981) are presented to illustrate the application of the SHANSEP concept to pile side-adhesion calculations, and an empirical correlation is developed to relate the average normalized side adhesion qs=s9vo developed from the pile load tests to the average OCR developed from laboratory odometer tests. Pile loadtest data from sites considered normally consolidated are used to assess the normally consolidated normalized side adhesion ?qs=s9vo?NC.

Assessment of the design OCR profile is important, and a combination of approaches is used to select the design OCR profile for pile capacity calculations. From initial assessments of OCR using laboratory odometer tests, this paper presents an approach to assess the OCR with undrained strength data su commonly available from unconsolidated undrained (UU) triaxial compression tests (su UUC) and unconfined compression tests (su UC). The effects of sample disturbance on the laboratory UUC and UC strength data are described, and an approach is presented to screen the data for disturbance. Cone-penetration test data are used to make further assessments of the OCR profile rather than directly assessing qs. The OCR is related to measured normalized side adhesion qs=s9vo from a database of driven piles bearing in clay using both OCR calculated from laboratory su UC and UUC data and OCR values measured using odometer and in situ tests. This paper addresses the long-term capacity of piles reflecting full set-up. The record of load tests was screened to remove data with short delays between driving and

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testing where incomplete set-up was thought to significantly understate the pile capacity.

In clays, the normalized side adhesion for long piles installed without significant interruption described by Semple and Rigden (1984) is shown to be similar to that for short piles, and closed-end piles are similar to open-ended piles. This paper presents two examples of displacement-pile performance to illustrate application of the SHANSEP-based approach.

Calculation Methods to Assess Pile Side Adhesion

The total-stress design methods that relate su to pile adhesion are broadly identified as the alpha method based on work by Tomlinson (1957, 1970), Randolph (1983), and Semple and Rigden (1984) using

the relationship:

qs=su ? a

(1)

where qs 5 measured unit-pile side adhesion, su 5 soil undrained strength measured as UC or UUC, and a 5 empirical correlation

factor developed with pile load-test data.

Tomlinson (1957) considered qs to be an adhesion along the shaft of the pile that approximates the remolded soil strength immediately

after driving and increases to the initial soil strength after consoli-

dation. Vesic (1977) describes this time-related increase in pile capacity

related to pore pressure dissipation and other factors. Subsequently,

Randolph (1983) developed empirical correlations relating a to the

normalized undrained shear strength su=s9vo. Semple and Rigden (1984) later developed additional empirical relationships between a

and su=s9vo presented on Table 1. The writers adapt the database

reported by Semple and Rigden (1984) with calculated OCR values

and assigned OCR values in Table 1 with designations of qs data thought to reflect incomplete set-up and low qs values.

The effective-stress beta method described by Burland (1973),

Esrig et al. (1977), and Esrig and Kirby (1979a, b) assumes that the

failure occurs in the soil near the pile-soil interface and relates qs to

s9vo as

qs=s9vo ? KS tan w9OCRm ? bs9vo

(2)

where qs 5 pile side adhesion, s9vo 5 vertical effective stress, KS 5 lateral stress ratio, s9 5 drained-soil friction angle adjoining the pile, OCR 5 soil overconsolidation ratio, m 5 exponent relating the

increase in normalized side adhesion to the increase in OCR, and b 5 empirical correlation coefficient.

As noted by Sladen (1992), the a and b approaches are related

through the normalized undrained strength and OCR. For values of su=s9vo , 0:7, these two methods diverge and match again at su=s9vo 5 0:15.

Stress History and Normalized Soil Engineering Parameter?Based Approach

In the SHANSEP-based approach, qs is normalized to s9vo and then related to the soil OCR in the same format as the concept for normalized undrained shear strength presented by Ladd and Foott (1974), as presented in Eq. (3):

qs=s9vo

?

? qs

=s9vo

?

NC

?OCR?m

(3)

where qs=s9vo 5 normalized pile side adhesion, ?qs=s9vo?NC 5 normally consolidated normalized pile side adhesion, OCR 5 soil OCR, and m 5 exponent representing the increase in qs=s9vo with increasing OCR.

The relationship of OCR and pile shaft adhesion is demonstrated in model tests of displacement piles penetrating kaolin clay reported by Steenfeld et al. (1981) that were used to develop the Effective Stress Model 4 (ESM4) method described by Kraft (1982). The pile shaft adhesion for the model steel piles was measured for three different OCR conditions. Fig. 1 presents the plot of qs=s9vo versus OCR for these controlled conditions and illustrates the relationship of qs to the soil OCR through this adaptation of the SHANSEP concept. The ordinate intercept is the normally consolidated normalized side adhesion ?qs=s9vo?NC for the clay. The increase in qs=s9vo with increasing OCR is measured as the slope of the log-log plot m. Although some variation in ?qs=s9vo?NC occurs for these test data, the data indicate a relationship between qs=s9vo and OCR that is similar to the SHANSEP concept with values of ?qs=s9vo?NC 5 0:23 and m 5 0:71. Use of the OCR provides a method to address the mode of failure in the correlation in that the normalized su for each mode of failure is expected to be proportional to ?OCR?m.

The relationship of OCR to pile shaft adhesion is demonstrated from the results of the field load tests from the sites summarized in Table 2 and presented in Fig. 2. These data represent observations of the average qs=s9vo developed from published pile load tests of pipe piles that are thought to exhibit complete dissipation of excess pore-water pressure with full set-up prior to testing. High-quality measurements of the average OCR in the supporting clay were obtained using laboratory odometer tests. Most of the tests in Table 2 and Fig. 2 represent Norwegian Geotechnical Institute test sites that were reported by Almeida et al. (1996). These pile load tests referencing the average OCR developed from laboratory odometer tests show that ?qs=s9vo?NC 5 0:20 and m 5 0:7. These tests suggest that the initial OCR profile in the supporting soils has a primary effect on the load-carrying capacity of the pile. Other factors affecting stress conditions around the pile, set-up, and remolding of the soil at the pile interface are thought to be secondary factors affecting the relationship between the pile qs and the OCR.

The data from Fig. 2 suggest that the value of qs=s9vo for piles at soft soil sites would be expected to approach 0.20, although truly normally consolidated stress conditions are relatively rare in nature, and many soft soils exhibit an OCR . 1. For example, Burland (1973) presented data for qs versus the average pile length in soft soil showing qs=s9vo values ranging from 0.2 to 0.4. To evaluate values of ?qs=s9vo?NC using additional pile load-test data for straight-sided piles, the data in Table 3 were assembled from sites where the geologic history shows nearly normally consolidated stress conditions in the bearing soil. The relatively small contribution from end-bearing capacity in these compression tests was calculated as 9suAp, where Ap 5 pile end area. The calculated qs=s9vo values reported by Bjerrum et al. (1969), Dawson (1970), Bozozuk (1972), and Fellenius (2006) for downdrag loads on piles in soft clay are also presented in Table 3 with OCR 5 1 assigned to these tests showing values consistent with the normally consolidated values.

The ?qs=s9vo?NC data summarized in Fig. 3 show a relatively narrow range of values with a general trend of decreasing normalized adhesion with increasing plasticity index Ip. The data suggest an average ?qs=s9vo?NC of 0.20, consistent with the interpretation from the data in Fig. 2. Further evaluation of soil type and the corresponding ?qs=s9vo?NC value appears to be merited for assessment of downdrag loads on piles, but variations in ?qs=s9vo?NC with soil type appear to be a secondary factor affecting the capacity of piles in clay soils.

Overconsolidation Ratio Assessment

In the SHANSEP-based approach, the qs=s9vo calculations require an estimate of the OCR profile. Laboratory odometer tests are considered an important part of this assessment, especially for low-OCR

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Table 1. Summary of Pile Load-Test Results, Laboratory Data, and Sources from Semple and Rigden (1984)

Load test no.

Open or closed

Assigned Shear-strength

Plasticity

L (m) D (mm) L=D . 50

ended

su=s9vo

qs=s9vo

Calc. OCR

OCR

test

a

index

Comments

8

20.4

762

No

6, 20

21.6

457

No

3, 7, 17

19.2

610

No

478, 489

15.2

356

No

491, 493

12.2

356

No

854, 855

43.9

305

Yes

868

96.0

610

Yes

869

73.8

610

Yes

873

22.6

767

No

451

66.4

325

Yes

42

30.5

325

Yes

444, 450

45.7

325

Yes

507, 508

29.0

330

Yes

30

13.7

325

No

150

18.3

325

Yes

45

48.2

610

Yes

844, 846, 848, 851 11.6

114

Yes

856

12.2

168

Yes

325

14.0

351

No

67

39.6

274

Yes

43

30.5

610

Yes

443, 449

22.9

325

Yes

368, 369

25.9

325

Yes

435, 436, 437, 438 25.3

274

Yes

70

14.9

528

No

998

32.0

274

Yes

106

12.8

325

No

547, 549

16.8

610

No

31, 32

13.7

325

No

829, 830

13.1

274

No

495, 497

20.4

610

No

*

9.1

450

No

23, 24

18.3

762

No

Closed Closed Closed Open Open

Open Closed Closed Closed Closed Closed Closed Open Closed

Closed Open Closed Closed Closed

Closed Closed

Closed Closed Open Open Open

0.21

0.21

0.22

0.23

0.24

0.23

0.23

0.23

0.18

0.23

0.13

0.25

0.18

0.26

0.30

0.27

0.14

0.29

0.19

0.35

0.15

0.37

0.38

0.40

0.38

0.43

0.42

0.43

0.47

0.30

0.50

0.30

0.51

0.40

0.56

0.27

0.57

0.57

0.30

0.62

0.35

0.76

0.36

0.79

0.41

0.82

0.43

0.87

0.50

1.15

0.63

1.22

0.58

1.37

0.67

1.98

0.87

2.65

1.35

2.90

,1 ,1 ,1 ,1 ,1 ,1 ,1 ,1 ,1 ,1 ,1

1.12 1.20 1.32 1.45 1.45 1.62 1.75

2.01 2.06 2.06 2.29 2.95 3.09 3.24 3.49 4.95 5.33 6.16 9.76 14.05 15.72

1.3 1.15 1 1 1 1.6 1 1 1.12

2.7

1.9 1.75 2.3 2.01 2.06 2.06 2.29 2.95 3.1 3.25 3.5 5.0 5.3 6.1 9.75 14.0 15.7

U

0.92

60

?

U

0.93

60

?

U

0.99

60

?

U

1.05

60

Laboratory OCR

U

1.00

60

Laboratory OCR

V

0.79

U

0.55

a

U

0.71

a

U

1.13

U

0.52

Disturbed

a

U

0.65

U

0.42

a

U

1.02

Disturbed

U

0.94

Disturbed

U

0.97

Disturbed

U

0.59

20

Disturbed

FV

0.64

60

Laboratory OCR

M

0.62

FV

0.78

30

Vane

U

0.49

U

0.59

30

U

0.52

U

0.56

U

0.48

U

0.52

U

0.52

42

M

0.57

10

Step-tapered

U

0.55

U

0.47

Q

0.49

40

M

0.44

M

0.51

U

0.46

35

Note: U 5 unconfined; M 5 other tests; FV 5 field vane; Q 5 quick triaxial; V 5 laboratory vane. aOversized closure plate.

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Fig. 1. qs=s9vo versus OCR for the Cambridge model pile test in Kaolin Clay (data from Steenfeld et al. 1981 and Kraft 1982)

Table 2. Case Study Sites qs=s9vo versus OCR from Odometer Tests

Load test no.

L (m)

D (m) L=D

Open or closed ended

qs=s9vo

Laboratory OCR

C1j

4.5

CP5f 3.8

CP6d 3.7

CP7d 3.6

C

9

D

9

E

9

F

9

G

9

H

9

I

9

J

9

K

9

Jacked 12.2

0.17 27

C

1.52

24

0.10 37

C

1.83

25

0.10 36

C

1.87

17

0.10 35

O

1.76

17

0.305 29.5

O

0.56

5.0

0.305 29.5

C

0.57

5.0

0.305 29.5

C

0.56

5.0

0.305 29.5

O

0.56

5.0

0.203 44.3

O

0.65

5.0

0.203 44.3

O

0.74

5.0

0.203 44.3

C

0.61

5.0

0.203 44.3

C

0.59

5.0

0.203 44.3

C

0.74

5.0

0.114 107

C

0.34

2.0

A1

5.0?15.0 0.219 46

C

0.265

1.55

B1

5.0?15.0 0.812 12

O

0.23

1.5

A

9.9

0.219 45

C

1.57

22.5

C

14.5

0.219 66

C

1.43

17.5

C

0.225

1.25

1

14.0

0.324 43.2

O

0.21

1.0

15.2

0.356 42

O

0.24

1.3

15.1

0.457 33

C

0.22

1.2

13.1

0.274 48

C

0.67

6.1

24.4

0.219 111.4

C

0.225

1.2

cohesive soils. In situ tests play an increasingly important part in geotechnical studies, but the historical record of pile performance is dominated by su data developed from laboratory strength tests. To incorporate these historical data into the SHANSEP-based approach, the following empirical approach is used to relate su=s9vo to OCR based on the approach described by Ladd et al. (1977):

CPT OCR 13.4 13.7 13.7 13.7

5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 5.5 2.0

1.5 1.5 22.5

17.5

1.0

1.2

6

Liquid limit

75 75 75 75 40 40 40 40 40 40 40 40 40 95

70 70 55

55 41.5 100

38

Plasticity index

50 50 50 50 20 20 20 20 20 20 20 20 20 55

40 40 35

35 18 50

18

Source reference Canons Park, England Almeida et al. (1996)

Cowden, England Almeida et al. (1996)

Hamilton AFB, USA Almeida et al. (1996) Onsoy, Norway Almeida et al. (1996) Tilbrook Grange, England NGI Almeida et al. (1996) Seed and Reese (1955) Annacis Robertson et al. (1985) Empire, LA Azzouz and Lutz (1986) Northwestern NGES Finno et al. (1989)

70

40

Univ. of Houston NGES

O'Neill et al. (1982)

75

50

Blanchet et al. (1980)

OCR

?

"? ?su

=s9vo

? ?OC

#1=m

su=s9vo NC

Symbol Cross Cross Cross Cross Long line Long line Long line Long line Long line Long line Long line Long line Long line Open diamond

Open square Short line

Short line Solid square Solid triangle Solid circle

Open triangle Asterisk

Open circle

(4)

where ?su=s9vo?OC 5 normalized undrained strength for the overconsolidated soil, ?su=s9vo?NC 5 normalized undrained strength for

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Fig. 2. qs=s9vo versus OCR from pile load tests using odometer tests to assess OCR

Table 3. Summary of Pile Load-Test Results, Laboratory Data, and Sources for Nearly Normally Consolidated Sites

Load test no. L (m) D (mm)

See Table 1

7

155

4

53.5 400

Lake St. Peter 24.4 219

1

14.3 324

Pipe pile

15.2 457

Sorenga

53

470

Sorenga

41

500

Heroya

32

500

Heroya

30

300

Berthierville 49

324

Note: DD 5 downdrag.

L=D . 50

No Yes Yes No No Yes Yes Yes Yes Yes

Open or closed ended

C O C C C C C C C C

su=s9vo

0.24 0.25

qs=s9vo

0.225 0.22 0.225 0.21 0.22 0.18 0.23 0.25 0.26 0.2

0.26 0.2 0.2

?qs=s9vo?NC

0.19 0.22 0.2 0.21 0.2 0.18 0.23 0.25 0.26 0.2

0.26 0.2 0.2

Assigned OCR

1.25 1 1.2 1 1.2 1 1 1 1 1

1 1 1

Source/reference adapted from

Seed and Reese (1955) Trenter and Burt (1981) Blanchet et al. (1980) Robertson et al. (1985) Finno et al. (1989) Bjerrum et al. (1969)

Bozozuk (1972); Fellenius (2006) Dawson (1970)

Comments Disturbed su Disturbed su

Disturbed su DD DD DD DD DD

DD DD DD

the normally consolidated soil, OCR 5 overconsolidation ratio, and m 5 exponent relating the increase in the normalized undrained strength to the OCR.

Ladd (1991) showed that the laboratory undrained strength

measurement of soil varies with the type of test, soil type, and OCR.

The data presented in Fig. 4(a) (Koutsoftas and Fischer 1976;

Koutsoftas and Ladd 1985) show the linear relationship of the

normalized su for triaxial compression (TC) using both Ko consolidation (CKo UTC) tests and UUC for tests of alluvium in the Atlantic Ocean offshore of Atlantic City, New Jersey. These data

show that when plotted against OCR obtained from laboratory

odometer tests, the normalized su UUC undrained strength reasonably matches the strength from reconsolidated CKo UTC tests at varying OCR values with the normally consolidated value of su=s9vo 5 0:33. Ladd (1991) presented laboratory strength data for the Ko consolidated, normally consolidated, normalized strength, ?su=s9vo?NC, for triaxial compression, triaxial extension, and direct simple shear

tests with respect to the soil plasticity index Ip. For the triaxial compression mode of failure, ?su=s9vo?NC is reasonably uniform with an average value of 0.32. Summarized in Fig. 4(b) are the su UUC and odometer test data from the sites listed in Table 4 that are used

to develop the following empirical relationship between the OCR

and normalized su UUC strength tests on undisturbed samples:

OCR

?

su=s9vo1=0:8 0:32

(5)

Chen and Kulhawy (1993) present laboratory undrained strength and OCR data for a wide range of soils. The UUC and OCR data are presented in Fig. 4(c), with the trend line for the undisturbed strength data assembled by the writers in Fig. 4(b). The writers have indicated by using a different symbol the data that are considered likely to be affected by sample disturbance, consistent with the data in Fig. 4(b) and Eq. (5).

All these results suggest that the use of disturbed strength data would erroneously result in a lower calculated OCR and qs=s9vo values than undisturbed data. Odometer tests (considered less susceptible to sample disturbance than su UC and UUC tests) and in situ tests are valuable additions to the site-characterization programs and tools to improve the OCR and qs=s9vo assessments. A discussion of sample disturbance follows.

Sample Disturbance and Low su Values

Disturbance of the samples for UUC and UC tests leads to unreliable and potentially highly variable assessments of su and a. Errors related to sample disturbance are considered especially important at

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Fig. 3. Pile load test data ?qs=s9vo?NC versus Ip

Fig. 4. (a) Normalized undrained shear strength versus OCR: AGS site (data from Koutsoftas and Ladd 1985 and Koutsoftas and Fischer 1976); (b) assessment of OCR using the normalized undrained shear strength: screened UUC, UC, and odometer data; (c) su=s9vo versus laboratory OCR using UUC (data from Chen and Kulhawy 1993)

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Table 4. Data for the Empirical Correlation to Assess OCR with UUC and UC Strength Data Screened for Sample Disturbance

Laboratory

Laboratory

Site

Depth (m) su (kPa) s9vo (kPa) su=s9vo OCR

Site

Depth (m) su (kPa) s9vo (kPa) su=s9vo OCR

AGS clay

Koutsoftas and Fischer (1976)

AMS

4

Unpublished

5.2

7.9

9.5

ACNJ

8.2

Unpublished

Bangkok Clay

2.2

Moh et al. (1972)

3

3.6

5

7.5

Beaumont clay

1.5

O'Neill and Reese

3

(1972)

4.5

6.1

Beaumont clay

6.1

Woodward-Clyde

7.7

Consultants

(1982)

1.5

5.6

5.8

Beaumont clay

7

University of Houston

O'Neill (2000)

Chicago Till HDR 4

8.8

Finno and

Chung (1992)

Northwestern NGES-Finno 9.8

et al. (1989)

Finno et al. (1989)

3.2

Cowden, England

4

Lehane and Jardine

5

(1994)

6.4

7

8

9.3

GEB VBC

13

Unpublished

1.02

0.89

1.46

1.7

1.8

2.28

2.37

3.35

4.42

19

26

0.69

17

31

0.56

23

42

0.55

28

48

0.59

26

69

0.38

34 24 29 28 33 2.2 2.4 2.6 2.8 1.6 1.8

1.1 1.1 0.9 125

29

1.17

33

0.71

35.3 0.83

43

0.64

59

0.57

0.62 3.55

1.25 1.92

1.88 1.38

2.18 1.28

1.5 1.07

2

0.91

0.31 3.45

1.08 1

0.94 0.94

92

1.36

29

86

0.34

40 113

0.36

145

67

2.16

110

76

1.4

95

88

1.08

120 105

1.14

90 112

0.8

110 124

0.89

105 139

0.76

47 102

0.46

3.7 Leda clay Kabir (1988)

3.9 RRC

4.25 75 54 1.4

5.2

45 62 0.73

6.8 8.9 8.1 9 11.1 15.2 26 2.9 2.2 1.9 1.9 1.4

4.7 3.1 2.6 2 1.65 21.5 9 6.5 5.2 5.7 5.3

5.5

7.6

SLS

4.3

5.8

9.3

Plum Point, Arkansas 8.8

Unpublished

3.7

Quiros et al.

20

(1983)

40

60

80

Ramalho-Oritago

2

et al. (1983)

3

4

St. Alban

2.6

La Rochelle et al.

4

(1974)

4.8

5.5

6.2

7

7.7

8.4

9.4

Storz Expressway

1.7

45 65 0.69 50 85 0.59 25 39 0.64 40 49 0.82 45 80 0.56 33 96 0.34 24 60 0.42 70 110 0.64 110 230 0.48 160 405 0.4 205 580 0.35

5.1 6.4 0.8

5.7 9.6 0.59 6.2 12.8 0.48 16 22 0.73 16 32 0.5 19 34 0.56 24 36 0.67 25 40 0.63 22 44 0.5 27 46 0.59 29 48 0.6 32 52 0.62 0.8 0.47 0.8

21.5 Omaha, NE 5.7 Unpublished 5.7 Station 264 6.4 Tilbrook Grange Lambson et al. 1.2 (1993)

1.15

3.2

0.8 0.67 0.6

5.2

35 44 0.39

5.9

36 49 0.37

9.4

43 68 0.38

4.7 360 72 5

7.5 560 108 5.2

8.5 420 122 3.45

9.5 430 135 3.2

11

460 152 3

12.2 450 170 2.65

12 8.5 5.5 6.5 4 3.8 2.7 1.55

13

440 180 2.45

13.2 400 185 2.15

15.2 420 205 2.05

17

340 230 1.5

19

390 252 1.55

22.5 530 300 1.76

24

680 320 2.12

25.5 670 335 2

28.5 540 380 1.42

6.9

3

3 1.85 2.9 3.05 2.1 1.2 1.4 2.55 1.75 1.4 1.3 3.1

2.3 2.1 2.27 1.7 1.82 1.94 1.95 1.93 2.06 2.08 2.11 3.4

2.3 1.6 1.5 1.2 34 23 22 19 16 12

12 11.8 10

8.5 8 11 12 9.5 7

OCR values less than about 2. Direct measurement of the OCR with

odometer tests is considered to provide the most reliable means to

assess OCR because these results are believed to be less sensitive to disturbance than the triaxial shear and unconfined compression tests. Odometer test data are particularly desirable to define the OCR value where OCR , 1:5.

Disturbance of samples is a concern for all laboratory test data. The effects of significant sample disturbance limit the usefulness of

the empirical correlations developed with measured strength data.

The writers have attempted to address this issue by assigning an OCR of 1 for sites where the reported su=s9vo is less than 0.3 and using laboratory odometer test data to assess OCR instead of the

laboratory su data. To help identify disturbed samples and poorquality laboratory strength tests, the su data can be normalized to s9vo, and values of su=s9vo from the su UUC tests of less than 0.3 are considered disturbed (recognizing that in rare occurrences soils

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could be underconsolidated). The measurement of volumetric strains during reloading to s9vo described by Andresen and Kolstad (1979) also can be used to assess the specimen quality to help eliminate significantly disturbed specimens from consideration and to rank the quality of the laboratory test results. In nearly normally consolidated soils, in situ tests can provide a reliable means to characterize the site conditions with less uncertainty related to sample disturbance; correlations with in situ test results may be used to assess the OCR profile for pile design, particularly where laboratory odometer tests confirm the OCR assessment made with the in situ test correlations.

qs=r9vo in Overconsolidated Soils: su Reference Data

The data available from pipe pile-load tests in overconsolidated cohesive soils where su data have been reported provide a basis to extend the SHANSEP method to these conditions. Semple and Rigden (1984) reported pile load-test data relating laboratory su data to the measured average qs of driven pipe piles installed entirely in clay. The average qs is related to the average s9vo at middepth of the pile. The data from Semple and Rigden (1984) are presented in Table 1 with the reported average undrained strength data, the type of strength test, index property tests when reported, and the OCR calculated from the su UUC tests using Eq. (5). Where available, the laboratory OCR from odometer tests was used. These su data were screened to remove undrained strength results considered disturbed in cases where su=s9vo was less than 0.3, and Table 1 shows that about half the strength data were either eliminated, assigned an OCR 5 1, or assigned a higher OCR based on the odometer data. The average screened su=s9vo data then are used to calculate an average OCR using Eq. (5). The screened data are identified in Table 1 as the writers' assigned OCR column. The qs values also were screened for the effect of incomplete set-up due to short wait times between installation and testing. Data considered reliable are identified in Table 1 as the writers' assigned qs=s9vo column. These values of qs=s9vo versus OCR are combined with the data from Table 2 reflecting the laboratory odometer test results to develop the relationship in Fig. 5. The calculated OCR values developed with the screened su=s9vo data combined with the qs=s9vo data correspond well with the data developed from laboratory odometer tests and expand the empirical assessment of the exponent m to yield the empirical relationship

qs=s9vo ? 0:19?OCR?0:7

(6)

Incorporation of Cone-Penetration Test Data into the Stress History and Normalized Soil Engineering Parameter?Based Approach

Almeida et al. (1996) present cone-penetration test (CPT) and piezocone test (CPTu) data for many of the sites presented in Table 2. Whereas Almeida et al. (1996) develop a direct relationship between uncorrected cone resistance qc or corrected cone resistance qT and qs, the SHANSEP-based approach uses the CPT/CPTu data first to evaluate the OCR profile and then to evaluate qs=s9vo using Eq. (6). The OCR values developed from the CPT/CPTu data are related to the measured qs=s9vo in Fig. 6 for the sites described by Almeida et al. (1996) and others. These data fit reasonably well to the trend line for Eq. (6), which is based on the OCR values developed from laboratory odometer tests and correlations with the laboratory su data.

Open-Ended Piles and Closed-End Piles, Long Piles, and Short Piles

When the concepts described in this paper are applied to available test-pile data in cohesive soils, the effects of closed-end conditions and pile length do not appear to significantly affect qs. Fig. 7 presents the screened data from Tables 1 and 2 sorted as either full-displacement (closed-end) or partial-displacement (open-ended) piles. No significant variations are seen in the relationship between qs=s9vo and OCR between the two pile types. Fig. 8 presents the screened data from Tables 1 and 2 sorted by pile length. The long piles (length/diameter . 50) follow the same trend line as the short piles (length/diameter , 50), suggesting that the available data do not provide a reason to separate the evaluation of qs for pile length, as previously recommended by Semple and Rigden (1984). Three long piles from Table 1 with qs=s9vo , 0:18 (Load Tests 868, 451 and 444, 450) were plotted in Fig. 8 with a designation o?. These data were excluded from the trend line for length variations in Fig. 8. Other factors appear to affect the capacity of these piles.

The long piles reported by Peck (1961), designated 444, 450, and 451 in Table 1 represent the pile tests at Drayton, North Dakota.

Fig. 5. Screened qs=su versus OCR from odometer tests with calculated OCR using undisturbed UC and UUC strength data (data from Semple and Rigden 1984)

JOURNAL OF GEOTECHNICAL AND GEOENVIRONMENTAL ENGINEERING ? ASCE / JULY 2013 / 1069

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