Final report: interpretation of cone penetration tests for pile design applications at the Georgia Department of Transportation [June 2009]

Contract Research
GDOT PROJ NO. 07-21 Final Report
INTERPRETATION OF CONE PENETRATION TESTS FOR PILE DESIGN APPLICATIONS AT THE GEORGIA DEPARTMENT OF TRANSPORTATION
Susan E. Burns, Ph.D, P.E. Associate Professor
School of Civil and Environmental Engineering Georgia Institute of Technology
Contract with Department of Transportation
State of Georgia
Georgia Department of Transportation Office of Materials and Research 15 Kennedy Drive Forest Park, Georgia 30297-2599
June, 2009
The contents of this report reflect the views of the authors who are responsible for the facts and accuracy of the data presented herein. The contents do not necessarily reflect the official views or policies of the Department of Transportation of the State of Georgia. This report does not constitute a standard, specification, or regulation.
i

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
Acknowledgements
The author thanks Neoma Cole for her assistance with data gathering, and Professor Paul Mayne for constructive discussions through the course of this project.
ii

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
Executive Summary
The goal of this project is to outline procedures to design pile foundations based on piezocone (CPT or PCPT) penetration test data. The piezocone test is an in situ test that records three independent readings during a sounding: tip resistance qc , sleeve friction f s , and pore water pressure u2 . The substantial level of detail provided by a cone sounding makes it an excellent tool for profiling the stratigraphy of a soil deposit. This is especially true in light of the excess pore water pressure generated in fine-grained materials during CPT penetration, facilitating the distinction between coarse and fine grained soil deposits.
After the soil types in a profile have been identified, two primary approaches to CPT based axial capacity pile design can be applied: 1) the indirect or rational method and 2) the direct method. The rational method relies on evaluation of soil properties from CPT data, followed by application of traditional pile design methods. This report outlines procedures for design based on the beta method, which was originally developed for effective stress analysis, but is applicable in all soil types (Mayne, 2007). This report also outlines the steps in the CPT based design method known as the direct method, where the cone is modeled as a mini-pile. Cone data provided by the Georgia Department of Transportation (GDOT) was analyzed using both methods, with a step-bystep procedure given in the report. Finally, this report also outlines the steps required for development of the pile load-displacement curve and illustrates the methodology using examples from previous GDOT reports (GDOT Research Project 2021, Mayne, 2003; Mactec, 2005). Keywords: Piezocone penetration test, pile design, classification, rational method, direct method
iii

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
Table of Contents
Acknowledgements............................................................................................................. ii Executive Summary ........................................................................................................... iii List of Symbols ................................................................................................................. vii Piezocone Penetration Testing............................................................................................ 1
Introduction..................................................................................................................... 1 Tip Resistance Correction............................................................................................... 2 Application of tip resistance correction to GDOT cone data.......................................... 3 Soil Classification Using Piezocone Penetration Tests ...................................................... 9 Method 1: Robertson and Campanella (1983) ................................................................ 9 Method 2. Robertson et al. (1986) ............................................................................... 10 Method 3. Robertson (1990) ......................................................................................... 12 Application to CPT classification ................................................................................. 15 Soil Classification Thomas County Borehole B-1........................................................ 19 Soil Classification Summary......................................................................................... 22 Soil Properties from Cone Testing.................................................................................... 23 Effective stress friction angle........................................................................................ 24 Undrained Shear Strength ............................................................................................. 25 Overconsolidation Ratio in Sands................................................................................. 28 Coefficient of lateral earth pressure (Ko) ...................................................................... 28 Summary ....................................................................................................................... 29 Pile Design Using CPT Methods ...................................................................................... 30 Static Methods of Pile Design ...................................................................................... 31
-Method .................................................................................................................. 31 -Method................................................................................................................... 31 Rational CPT Method ................................................................................................... 32 Axial Capacity from CPT Measurements- Direct Method ........................................... 34 Driven and Drilled Piles in Sand .............................................................................. 34 Drilled Shafts in Sand ............................................................................................... 38 Pile Displacement Methods .............................................................................................. 40 Davisson Capacity ........................................................................................................ 42 Steps in CPT Based Design .............................................................................................. 44 Examples........................................................................................................................... 46 Soil Parameters and Pile Design Using Rational Method ............................................ 46 Soil Parameters and Pile Design Using Direct Method ................................................ 47 Load Displacement Curves ........................................................................................... 48 Piedmont Geology Deep Foundations: Coweta County ........................................... 48 References......................................................................................................................... 51 APPENDIX A................................................................................................................... 54
iv

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
List of Tables
Table 1. Sample Cone Tip Resistance Correction State Route 3: CPT-21........................ 5 Table 2. Sample Cone Tip Resistance Correction State Route 3: CPT-11........................ 8 Table 3. Pile Materials and Installation Effects Modifiers (from Mayne 2007).............. 32 Table 4. Bearing capacity factor kc for LCPC Method* ................................................. 35 Table 5. Pile categories for LCPC Direct CPT Method................................................... 36 Table 6. Eslami and Fellenius (1997, 2006) Side Friction Coefficient as a Function of Soil Type (Figure from Mayne, 2007).............................................................................. 38
v

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
List of Figures
Figure 1. Measurements recorded with the piezocone penetrometer. ............................... 1 Figure 2. Water pressure effect on cone tip resistance. ..................................................... 2 Figure 3. Piezocone Penetration Data (CPT-21, Ochlocknee River, Thomas County, Georgia). ............................................................................................................................. 4 Figure 4. Piezocone Penetration Data (CPT-11, Ochlocknee River, Thomas County, Georgia) .............................................................................................................................. 6 Figure 5. Piezocone Penetration Data (CPT-11, Ochlocknee River, Thomas County, Georgia), magnified from 12.0 to 14.0 meters.................................................................... 7 Figure 6. Robertson and Campanella Classification (1983). Figure from Mayne (2007). ........................................................................................................................................... 10 Figure 7. Robertson et al. Classification (1986). Figure from Mayne (2007). ............... 12 Figure 8. Robertson classification (1990) Normalized cone resistance versus friction ratio. Figure from Mayne (2007). .................................................................................... 14 Figure 9. Robertson classification (1990). Normalized cone resistance versus porewater pressure parameter. Figure from Mayne (2007). ............................................................. 14 Figure 10. CPT Classification for CPT-1 according to Robertson and Campanella (1983). ........................................................................................................................................... 16 Figure 11. Classification for CPT-1 according to Robertson et al. (1986) - FR.............. 17 Figure 12. Classification for CPT-1 according to Robertson et al. (1986) Bq. ............ 17 Figure 13. Classification for CPT-1 for Robertson (1990) - FR...................................... 18 Figure 14. Classification for CPT-1 for Robertson (1990) - Bq....................................... 19 Figure 15. Visual classification of Thomas County PCPT data (CPT 1). ....................... 20 Figure 16. Borehole log B-1, Thomas County, Georgia.................................................. 21 Figure 17. Comparison of visual cone classification method with borehole records. ..... 22 Figure 18. Effective stress friction angle as a function of normalized tip stress. Figure from (Mayne 2007). .......................................................................................................... 25 Figure 19. Undrained shear strength as a function of overconsolidation ratio. Figure from (Mayne 2007). .......................................................................................................... 26 Figure 20. Preconsolidation stress as a function of net cone resistance. Figure from (Mayne 2007).................................................................................................................... 27 Figure 21. Bearing factor as a function of effective stress friction angle (figure from Mayne, 2007). ................................................................................................................... 33 Figure 22.Bustamante and Gianeselli (1982) method: (a) for clays, and (b) for sands. Figure from Mayne (2007)................................................................................................ 36 Figure 23. Eslami and Fellenius (1997, 2006) method to determine the soil type for unit side resistance. (Figure from Mayne, 2007). ................................................................... 37 Figure 24. . Load-deflection curve for Coweta County drilled shaft foundation (Mayne, 2003). ................................................................................................................................ 50
vi

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
List of Symbols
an net area ratio d = foundation diameter fb base resistance f p unit side resistance f s sleeve friction (measured on the sleeve behind the cone tip and pore pressure
element) qb unit end bearing qc tip resistance (stress exerted on the tip of the cone during penetration) qt corrected cone tip resistance s relative movement su undrained shear strength ub pore water pressure ( ub position is measured behind the cone tip) uo hydrostatic pore water pressure u2 pore water pressure ( u2 position is measured behind the cone tip) wt pile vertical displacement under axial compression A = cross-sectional area of the pile Ab area of base B width of pile CK factor to account for installation effects CM factor to account for pile material type Cse = side correlation coefficient D = Pile diameter or width (cm) E = Modulus of elasticity of the pile Eb = soil modulus below foundation base ( Eb = EsL for a floating pile) E p = pile modulus (concrete plus reinforcing steel) EsL = soil modulus along pile shaft at level of base Esm = soil modulus at mid-depth of pile shaft I p = displacement influence factor L = pile length Nc bearing capacity coefficient *Nc = 9.33 for circular and square foundations N kt bearing factor Nq bearing factor
vii

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

OCR

=



' p
' v

overconsolidation ratio

Pt = applied axial load at the top of the shaft

Q = applied load

Qb pile end bearing Q f pile skin or side friction Qs pile skin or side friction Qult pile ultimate load capacity Se = Elastic compression of total pile length (cm) S f = movement of pile top (cm) factor used in total stress analysis for pile design

= Ki tani' factor used in effective stress analysis for pile design

' effective stress friction angle

atm atmospheric pressure = 1atm = 100kPa 1tsf 14.7 psi



' p

preconsolidation pressure

vo total overburden stress

' vo

effective overburden stress

s = Poisson's ratio of soil

FR = f s qt (%)

friction ratio

Bq

=

u2 - u0 qt - vo

porewater pressure parameter

Fr

= qt

fs - vo

x100%

normalized friction ratio

Ko

=

' ho
' vo

Coefficient of lateral earth pressure

Qt

=

qt - vo '
vo

Normalized cone resistance

qt1

=



qt atm





' vo
atm

0.5

Normalized corrected

cone tip resistance



=

db d

=

eta

factor

( db =diameter

of

base;



=1

for

straight

shafts)

= EsL = xi factor ( = 1 for floating pile and < 1 for end bearing pile) Eb

viii

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

* = Esm = rho ( * = 1 for uniform soil and * = 0.5 for simple Gibson soil) E sL



=

2(1 +

s

)

Ep E sL

= lambda factor



=

ln[0.25

+

(2.5

*

(1

-

s

)

-

0.25

](

2L d

)

=

zeta

factor

L

=

2 2(

)

0.5



L d



=

mu

factor

Unit Conversions
1kPa = 1kN / m2 = 0.145 psi 1psi = 6.9kPa 1tsf 1bar = 100kPa = 0.1MPa 1atm = 101.3kPa = 14.7 psi = g (Unit weight in N/m3 = density in kg/m3 x 9.81 m/s2)
w = unit weight of water = 62.4 lb/ft3; 9.81 kN/m3

(1 N = 1 kg-m/s2)

ix

Piezocone Penetration Testing

Introduction

Cone penetration testing is an in situ investigation method developed to enhance soil profiling in a minimally invasive manner. The piezocone is pushed hydraulically from the soil surface at a rate of 2 cm/s, and is instrumented to measure the interaction between the penetrometer and the soil/pore fluid. Three measurements are typically taken during piezocone penetration: tip resistance qc (stress exerted on the tip of the cone during penetration), sleeve friction f s (measured on the sleeve behind the cone tip and pore pressure element), and pore water pressure u2 (water pressure generated during penetration u2 position is measured behind the cone tip). Note, the pore water pressure can be measured in several locations, including on the cone face ( u1 position) or behind the friction sleeve ( u3 position), but the u2 position is the preferred location for measurement because it allows for correction of the cone tip resistance measurement.

fs

u2

qc

Figure 1. Measurements recorded with the piezocone penetrometer.

1

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
One of the most useful applications for the cone penetration test is for identification of soil profiles. The piezocone, which includes a pore pressure transducer to measure the pore water pressure during penetration, is especially useful for identifying strata of sand versus clay.
Tip Resistance Correction
The cone tip resistance measurement ( qc ) that is gathered with the piezocone requires correction due to the pore water pressure that is exerted on unequal end areas in the tip design:
U
qc
Figure 2. Water pressure effect on cone tip resistance. The magnitude of the pore pressure that is exerted on the cone tip is a function of the hydraulic conductivity of the soil deposit that is being penetrated; coarse-grained gravels and sands develop relatively little pore pressure, while finegrained silts and clays can develop very large magnitudes of pore water pressure. Consequently, the correction will be close to zero for tests performed in sand (freely draining materials), but
2

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

can be quite significant during undrained penetration in low hydraulic conductivity soils like clay. The corrected cone tip resistance qt is determined by the following relationship:

qt = qc + (1 - an ) u2

Equation 1

where an = net area ratio, a geometric parameter that is measured for each cone and should be supplied by the manufacturer or contractor. The most recent ASTM procedure governing cone penetration (ASTM D-5778-07) details procedures for laboratory calibration to determine the net area ratio of a cone penetrometer.

Application of tip resistance correction to GDOT cone data
The data gathered by Golder Associates for the State Route 3 Alternate (John B. Gordon Highway) over the Ochlocknee River, Thomas County, Georgia are presented below to illustrate the application of the tip resistance correction. Data from CPT-21 are plotted in Figure 3, with the corrected cone tip resistance qt reported in MPa, the sleeve friction f s and pore water pressure u2 reported in kPa. The cone sounding shows an inter-bedded soil profile, with relatively low pore water pressures developing during the sounding. In a case like this, where the pore water pressure is small, the cone tip resistance correction will also be small, as demonstrated in Table 1. For example, at a randomly chosen depth of 1.98 m, the measured cone tip resistance qc = 1.67 MPa, while the corrected tip resistance qt =1.68 MPa. In this example, the correction is very small, resulting in qc qt Corrected cone tip resistance values for the entire CPT-21 sounding are included in Appendix A.

3

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

qt (MPa)

0

20

0

40

0

0

fs (kPa)

500

1000

1500

u2 (kPa)

0

200 400 600 800

0

5

5

5

10

10

10

Depth (m)

15

15

15

20

20

20

25

25

25

Figure 3. Piezocone Penetration Data (CPT-21, Ochlocknee River, Thomas County, Georgia).

4

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Table 1. Sample Cone Tip Resistance Correction State Route 3: CPT-21

Test: CPT-21

Date: 7/27/2005

Location: Sta 249+53 Lt 72 Cone size: 10 cm2

an = 0.59

GWT = 0 m

Depth

1.98 m

qc measured cone tip resistance

1.67 MPa

u2 pore water pressure

18.29 kPa (0.01829 MPa)

an net area ratio

0.59

qt corrected cone tip resistance

qt = qc + (1 - an ) u2

qt = 1.67MPa + (1 - 0.59) 0.01829MPa

qt corrected cone tip resistance

1.68 MPa

In contrast, in cases where the pore pressures are large, the correction of the cone tip resistance can be important. For example, the data gathered by Golder Associates for the State Route 3 Alternate (John B. Gordon Highway) over the Ochlocknee River, Thomas County, Georgia at CPT-11 are plotted in Figure 4. In this sounding, the amount of fine-grained clays and silts are higher than observed in sounding CPT-21, and, consequently, much higher pore water pressures are generated during the sounding (over 5000 kPa at a depth of 12.5 m). The higher pore pressures in turn lead to a larger correction for the tip resistance, which is illustrated in the magnified tip resistance data gathered between 12 and 14 m (Figure 5 and Table 2).

5

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

qt (MPa)

fs (kPa)

u2 (kPa)

0

10

20

30

0

500

1000

1500

0

2000

4000

6000

0

0

0

qt qc

3

3

3

6

6

6

Depth (m)

9

9

9

12

12

12

15

15

15

Figure 4. Piezocone Penetration Data (CPT-11, Ochlocknee River, Thomas County, Georgia)

6

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

qt (MPa)

0

10

20

30

12.0

12.5

Depth (m)

13.0
qt qc
13.5

14.0
Figure 5. Piezocone Penetration Data (CPT-11, Ochlocknee River, Thomas County, Georgia), magnified from 12.0 to 14.0 meters.

7

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Table 2. Sample Cone Tip Resistance Correction State Route 3: CPT-11

Test: CPT-11

Date: 7/28/2005

Location: Sta 243+56 Lt 78 Cone size: 10 cm2

an = 0.59

GWT = 0 m

Depth

12.8 m

qc measured cone tip resistance

25.5 MPa

u2 pore water pressure

5010 kPa (5.0 MPa)

an net area ratio

0.59

qt corrected cone tip resistance

qt = qc + (1 - an ) u2

qt = 25.5MPa + (1- 0.59) 5.0MPa

qt corrected cone tip resistance

27.6 MPa

8

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
Soil Classification Using Piezocone Penetration Tests
The piezocone penetration test is used extensively for identification of soil without drilling and sampling. While it is advantageous that the cone does not require removal of soil from the subsurface, it can also present problems for classification because there is no physical sample to check for cross-correlation. A variety of classification schemes have been developed to assess soil type on the basis of cone penetration data, but it is important to note that not all methods work in all cases. This work will review the classification schemes that are most commonly used by DOTs in the United States (Mayne 2007):
Method 1: Robertson and Campanella (1983) Method 2: Robertson et al. (1986) Method 3: Robertson (1990)
Method 1: Robertson and Campanella (1983): Simple method that
categorizes soil as a function of the corrected cone tip resistance and the friction ratio. For this method, the corrected cone tip resistance qt is plotted versus friction ratio (FR), where FR = f s qt (%) . The authors then present bounds that delineate sand, silty sand, sandy silt and silt, clayey silt, and clay.
9

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
Figure 6. Robertson and Campanella Classification (1983). Figure from Mayne (2007).
Method 2. Robertson et al. (1986). The advantage to the 1983 method is its
simplicity; however, it is hindered by two factors. First, its predictive ability is limited because it does not incorporate the measured pore water pressure into the classification, and pore water pressure is an excellent measurement for the differentiation between sands and clays. Second, this method does not account for the fact that cone resistance increases as the depth of penetration is increased, due to the influence of the overburden stress as penetration goes deeper. Because the cone resistance increases due to the increased overburden stress, classification schemes that do not account for this would result in an apparent change in classification as the depth increased.
Robertson et al. (1986) added a factor to incorporate the measured pore water pressure into the classification scheme through the addition of the porewater pressure parameter:
10

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Bq

=

u2 - u0 qt - vo

Equation 2

where vo = total overburden stress at the same depth as the cone readings. Classification is performed by plotting the corrected cone tip resistance versus the friction ratio, as well as versus the porewater pressure parameter. The authors delineated 12 zones of soil based on the magnitude of the classification parameters (Figure 7).

11

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
Figure 7. Robertson et al. Classification (1986). Figure from Mayne (2007).
Method 3. Robertson (1990). In another iteration on classification from
piezocone data, Robertson (1990) introduced additional normalization parameters to account for the influence of overburden pressure as the depth of penetration is increased.
12

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Normalized cone resistance

Qt

=

qt - vo '
vo

Equation 3

Normalized friction ratio

Fr

=

qt

fs - vo

x100%

Equation 4

Soil is then classified by plotting the normalized cone resistance versus normalized friction ratio and normalized cone resistance versus porewater pressure parameter (Figure 8 and Figure 9).

13

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Normalized Q = (q t - vo)/vo'

1000 7

100

6

8 9

5

10

4

3

1

2 1

0.1

1

10

Friction Ratio, FR = fs/(qt-vo)

1 = Sensitive Cl a y 2=Or ga ni c
3 = Clays
4=Silt M ixtures
5=Sand M ixtures
6=Sa nds
7=Gravelly Sand
8=Stiff Sand to Clayey Sand 9=Stiff Clays

Figure 8. Robertson classification (1990) Normalized cone resistance versus friction ratio. Figure from Mayne (2007).

1000 7

Normalized Cone Resistance, Qt

6 100

5 4
10 3

1

1

-0.2

0

0.2

0.4

0.6

0.8

1

1.2 1.4

Porewater Pressure Parameter, Bq

Figure 9. Robertson classification (1990). Normalized cone resistance versus porewater pressure parameter. Figure from Mayne (2007).

14

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
While Methods 2 and 3 utilize additional information, sometimes the interpretation of these methods is difficult because the zones indicated by the different parameters may not agree.
Application to CPT classification. The following examples look at the
application of the three classification schemes using the CPT-1 data for the State Route 3 Alternate (John B. Gordon Highway) over the Ochlocknee River, Thomas County, Georgia. Method 1: Robertson and Campanella (1983). For this method, the corrected cone tip resistance qt is plotted versus friction ratio (FR) where FR = f s qt (%) (Equation 5).
15

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

1000

Sands
100
10

Silty Sands

Sandy Silts & Silts Clayey Silts

Clays

Cone Bearing, qt (MPa)

1

0

1

2

3

4

5

6

7

8

Friction Ratio, FR = fs/qt (%)

Figure 10. CPT Classification for CPT-1 according to Robertson and Campanella (1983).

According to this method, the soil ranges from sandy silts to clays.

Method 2. Robertson et al. (1986). This method relies on plotting the corrected cone tip

resistance versus friction ratio and versus the porewater pressure parameter:

Bq

=

u2 - u0 qt - vo

(Equation 2)

Results for CPT-1 data are shown in Figure 11 and Figure 12.

16

Cone Bearing, qt (bar)

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

1000 100

10
9 8 7

10

12

6

5

4

11 3

1
1 0

2

2

4

6

Friction Ratio, FR=fs/qt (%)

1 Sensitive clay 2 Organic soil 3 Clay 4 Silty clay 5 Clayey silt 6 Sandy silt 7 Silty sand 8 Sand to silty sand 9 Sand 10 Gravelly sand 11 Very stiff fine grain 12 Sand to clayey sand
8

Figure 11. Classification for CPT-1 according to Robertson et al. (1986) - FR.

1000

Cone Bearing, q t (bar)

100
5 4 3
10

1

2
1

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Porewater Pressure Parameter, Bq

Figure 12. Classification for CPT-1 according to Robertson et al. (1986) Bq.

17

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
According to Method 2, the soil is classified primarily as sandy silts to clay.

Method 3. Robertson (1990). This method relies on normalized parameters (tip resistance, sleeve friction, and porewater pressure) for classification. Results for CPT-1 data are shown in Figure 13 and Figure 14.

1000 7

100

6

5 10

8 9

Normalized Q = (q t - vo)/vo'

1

0.1

1

10

Friction Ratio, FR = fs/(qt-vo)

Figure 13. Classification for CPT-1 for Robertson (1990) - FR.

18

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
1000 7

Normalized Cone Resistance, Qt

100
6 5 4

10

3

1

1

-0.2

0

0.2

0.4

0.6

0.8

1

1.2

1.4

Porewater Pressure Parameter, Bq

Figure 14. Classification for CPT-1 for Robertson (1990) - Bq.

For Method 3, soils are primarily grouped into groups 6-9, which classifies as clean sand to silty sand, gravelly sand to sand, very stiff sand to clayey sand, and very stiff fine grained soil.
Soil Classification Thomas County Borehole B-1
In addition to the three methods by Robertson, soil classification based on visual analysis of trends in the data from PCPT tests was performed and compared to the driller's log. The data analyzed were from borehole B-1 and cone sounding CPT 1

19

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
(Project #BR-001-00 (363), Thomas County, Station 237+10, 80 ft left). From a simple visual analysis of the data, four distinct layers were identified in the deposit (Figure 15). The borehole data from B-1 are shown in (Figure 16).

0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

qt (MPa)

10

20

30

40

0

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

fs (kPa)

500

1000

1500

0 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14

u2 (kPa)

2000

4000

6000

Figure 15. Visual classification of Thomas County PCPT data (CPT 1).

20

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
Figure 16. Borehole log B-1, Thomas County, Georgia. Comparison of the borehole data with the visual PCPT classification shows two interesting differences: 1) the CPT did not detect the transition from SP SM to SM at a depth of approximately 3.5 m, and 2) the borehole log indicates a transition from MH to SC at a depth of 11.3 m; however, the cone data indicate that transition at 10 m. Some of this variation may be attributable to the inherent variability encountered adjacent to the river setting. In general, however, there is very good agreement between the layering as predicted from the cone data, and that observed through drilling and sampling.
21

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

qt (MPa)

0

10

20

30

40

0

0

0

1

1

2

SP SM SP SM

2

3

3

4

SM

4

5

5

SC

6

6

7

7

8

8

MH

9

9

10

10

11

11

12

12

SC

13

13

14

14

fs (kPa)

500

1000

1500

0

0

1

2

3

4

5

6

7

8

9

10

11

12

13

14

u2 (kPa)

2000

4000

6000

Figure 17. Comparison of visual cone classification method with borehole records.

Soil Classification Summary. None of the currently available classification
methods based on cone data are exact, as demonstrated by the different results of the three methods applied to the same CPT data set in this example. Consequently, local experience and correlation with borings logs is critical to ensure the most appropriate classification scheme is being used in a given soil deposit.

22

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
Soil Properties from Cone Testing
The piezocone penetration test measures tip resistance, sleeve friction, and pore water pressure. While these parameters are used primarily for classification, they can also be used to model soil properties. It is important to note that the translation of cone parameters into soil properties is based on assumptions about the behavior of the soil continuum. Methodologies exist to derive soil properties such as:
Unit Weight Poisson's Ratio Shear Wave Velocity Small Strain Shear Modulus Soil Stiffness Stress History Strength (Effective Stress) Strength (Undrained Shear Strength) Relative Density Lateral Stress Coefficient of Consolidation Hydraulic Conductivity Rigidity Index Fundamentally, the design of foundations relies on the accurate estimation of these properties, so proper evaluation of these properties is critical to the success of the design. For the purposes of this investigation, the work will focus on estimates of stress history, strength (effective stress), strength (undrained shear strength), and lateral stress.
23

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Effective stress friction angle

Several correlations between cone data and the effective stress friction angle in sands are available for analysis. One of the most robust relationships was developed by Kulhawy and Mayne (1990), and correlates effective stress friction angle () in sands with the normalized, corrected cone tip resistance. The following data were gathered from cone penetration tests performed in calibration chambers with 24 sands (Kulhawy and Mayne 1990):

Where:

' = 17.6o +11.0 log(qt1)

Equation 6

qt1

=



qt atm





' vo
atm

0.5

Equation 7

atm = 1atm = 100kPa 1tsf 14.7 psi

24

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Figure 18. Effective stress friction angle as a function of normalized tip stress. Figure from (Mayne 2007).

Undrained Shear Strength

The undrained shear strength (su) is useful for performing total stress analysis (TSA) and in cases where short term, undrained loading is applicable; however, it is important to remember that undrained shear strength is a non-unique measurement that is a function of loading conditions. Traditionally, the undrained shear strength can be estimated from CPT data according to (Mayne 2007):

su

=

(qt

- vo ) N kt

Equation 8

Where Nkt is a bearing factor, which is typically assumed to be approximately 15, but is

the subject of some debate.

Alternatively, the undrained shear strength is also directly related to the

preconsolidation

pressure

(maximum

past

vertical

effective

stress)



' p

,

and

to

the

overconsolidation ratio,

OCR

=



' p



' v

.

It is well established that the undrained shear

25

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

strength, as measured in the direct shear test, can be related to the overconsolidation ratio through the following (Jamiolkowski et al., 1985; Ladd, 1991; Ladd and DeGroot, 2003):



su '
vo

DSS

=

0.22OCR0.8

Equation 9

Or when OCR is small (Trak et al., 1980; Terzahi et al., 1996):

su



0.22

' p

Equation 10

Figure 19. Undrained shear strength as a function of overconsolidation ratio. Figure from (Mayne 2007).

However, in order to obtain an estimate of undrained shear strength, the preconsolidation stress must first be estimated from the cone data. Three methods exist to related preconsolidation pressure to cone data; the most appropriate one is site specific.
Method 1) As a function of net cone resistance (Figure 20) (Mayne 2007):



' p

=

0.33(qt

- vo )

Equation 11

Method 2) As a function of measured pore water pressure (Mayne 2007):

26

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT



' p

=

0.53(u2

- u0 )

Equation 12

Method 3) As a function of tip resistance and pore water pressure (Mayne 2007):



' p

=

0.60(qt

- u2 )

Equation 13

Figure 20. Preconsolidation stress as a function of net cone resistance. Figure from (Mayne 2007).
In summary, in order to estimate undrained shear strength as a function of preconsolidation pressure, a two step procedure must be followed:
1) Determine preconsolidation stress from CPT data (using one of three previous correlations)
2) Convert preconsolidation stress into undrained shear strength It is important to note also that these correlations are developed for intact clays. Care must be taken in cases where the deposit exhibits fissures because most CPT and
27

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

PCPT correlations do not account for the presence of cracks or fissures within the soil mass.

Overconsolidation Ratio in Sands
The stress history in a sand deposit is more challenging to determine due to the relatively small amount of settlement, when compared to a fine grained soil. Mayne (2005) presented a closed form solution for OCR in sands (siliceous in calibration chamber testing) as a function of corrected tip resistance, effective vertical stress, and effective stress friction angle:

OCR

=



' p

' vo

=

0.192 (1 - sin

qt atm 0.22

'

)





' vo



atm

0.31



1 sin ' -0.27



Equation 14

Coefficient of lateral earth pressure (Ko)
The coefficient of lateral earth pressure relates the effective horizontal stress to the effective vertical stress:

Ko

=

' ho
' vo

Equation 15

The coefficient of lateral earth pressure can be evaluated for uncemented sands and low

sensitivity clays according to (Mayne 2007):

K o = (1 - sin ' )OCRsin'

Equation 16

In terms of cone data, Ko can be evaluated from the following relationship developed for

clean sands in calibration chamber testing (Mayne, 2007):

28

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

( ) Ko

= 0.192 qt atm 0.22





atm



' vo



0.31



OCR

0.27

Summary

Equation 17

It is important to note that the derivation of soil parameters from cone data is typically based on either correlations or assumptions about the soil continuum, and as a result, should be referenced with available historical data and local knowledge in all cases involving design.

29

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Pile Design Using CPT Methods

Incorporation of CPT data into the design of pile foundations can proceed according to two primary methods: 1) an "indirect" method in which soil properties are derived from cone data, followed by the application of traditional design methods, or 2) a direct method, in which the cone is modeled as a mini-pile foundation, with scale up for pile design (Mayne 2007). In the latter method, the measured tip resistance is related to the pile end bearing, while the measured sleeve friction is related to the side friction on the pile.
The ultimate load capacity of a pile consists of two components: 1) skin or side friction ( Q f ), and 2) end bearing at the base of the pile ( Qb ). The ultimate capacity then becomes:

Qult = Q f + Qb With the allowable capacity defined as:

Equation 18

Qa

=

Qult FS

Equation 19

The transfer of skin friction is a function of soil type, with higher load transfer occurring

at the surface than at depth. The transfer is non-linear in fine-grained soils, linear in

coarse grained soils, but decreasing with depth in both cases. Two approaches for design

of piles in axial compression will be outlined in the following sections, with methods

drawn from (Mayne 2007).

30

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
Static Methods of Pile Design

-Method
The -method is a total stress analysis (TSA), and is used to model the short term load capacity of piles:

j

Q f =

( u

) i

(su

) i



(

perimeter)



(length)i

i =1

Where j = number of soil layers along the length of the pile.

Equation 20

End bearing is determined from:

( ) Qb = fb Ab = N c su b Ab

Equation 21

Where

f b

= base resistance;

N c

=

bearing

capacity

coefficient,

and

(s u

) b

= undrained

shear strength of soil at base of pile.

-Method
The -method is an effective stress method which can be used for both short term and long term loading, for different soil types. The skin friction is determined by:

( ) j

Qf =



' x

i

tani' ( perimeter)i

(length)i

i =1

Equation 22

Lateral stress can be calculated from the vertical stress through the coefficient of lateral

earth

pressure:

(



' x

=

K

' z

),

which

is

attractive

because

vertical

stress

can

be

calculated

using only depth and unit weight. Substituting into the previous equation:

( ) j

Qf =

Ki



' z

i

tan i' ( perimeter)i

(length)i

i =1

Equation 23

Finally, Ki tani' = is typically substituted as a lumped parameter, yielding:

31

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

( ) j

Qf =

i



' z

i ( perimeter)i (length)i

i =1

End bearing capacity of piles can be determined from:

Equation 24

( ) Qb

=

fb Ab

= Nq



' z

b Ab

Rational CPT Method

Equation 25

This method relies on determining soil properties from the measured CPT data, and then applying them to traditional pile design methods. This analysis will rely on an effective stress method for pile design, commonly known as the method, which has been shown to be applicable to all soil types (Mayne, 2007). The unit pile side resistance can then be calculated by (Kulhawy et al. 1983):

fp

=

CM

C

K

K

o

' vo

tan '

Equation 26

Where CM = factor to account for pile material type and CK = factor to account for

installation effects (Table 3). The values of the coefficient of lateral stress, effective

overburden stress, and effective stress friction angle are determined as described in

previous sections.

Table 3. Pile Materials and Installation Effects Modifiers (from Mayne 2007).

32

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

The unit end bearing (qb = qult) for undrained loading can be calculated from limit plasticity (Vesic 1977):

Undrained loading qb = *Nc su

Equation 27

Where *Nc = 9.33 for circular and square foundations, and su = undrained shear strength

beneath the foundation at a depth from the base of the pile ( z = L ) to the base of the pile

plus pile diameter ( z = L + d ).

For drained loading, the end bearing will be a function of friction angle (Figure

21). In large diameter piles, including drilled shafts, in sands (Mayne, 2007):

Drained, operational limit

qb

=

0.1N

q

' vo

Equation 28

The 10 % reduction factor in the previous equation is to limit the movement of the pile.

Figure 21. Bearing factor as a function of effective stress friction angle (figure from Mayne, 2007).
The total axial compression capacity of the pile is calculated according to:
33

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

#layers
Qs f pi dzi (circular) i-i
#layers
Qs f pi 4lzi (square) i-i
Qb = qb Ab
Qult = Qs + Qb - W

Equation 29
Equation 30 Equation 31
Equation 32

Axial Capacity from CPT Measurements- Direct Method

Alternatively, the prediction of pile capacity from CPT soundings can be performed by modeling the cone as a mini-pile, and scaling the cone data to the pile. Penetration of a cone penetrometer is analogous to the behavior of a pile; consequently, the measured side resistance and tip resistance from cone penetration can be used as the basis for pile design (Bustamante and Gianeselli 1982; Robertson et al. 1988; Poulos, 1989; Eslami and Fellenius, 1997). This approach relies on an estimation of unit end bearing (qb) and unit side resistance (fp) from the tip resistance, sleeve friction, and pore water pressure measurements recorded during the CPT sounding. Multiple methods exist to derive the unit pile parameters from the measured cone data, and they can be categorized as a function of pile type (driven/drilled/bored) and soil type (clay/sand). The most relevant approaches for GDOT are summarized in the following sections; the reader is referred to Mayne (2007) for a comprehensive summary of methods.

Driven and Drilled Piles in Sand

Method 1. This section focuses on the estimation of side friction and end bearing for drilled and driven piles in sand; the LCPC method was developed in 1982 and is a

34

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

widely used method of direct analysis for pile design based on CPT data (Bustamante and Gianeselli, 1982). Unit end bearing for the method is predicted by:

LCPC unit end bearing: qb = kcqc Where kc is a function of pile and soil type (Table 4).

Equation 33

Soil Type

Table 4. Bearing capacity factor kc for LCPC Method*

Nondisplacement Pile

Displacement Pile

Clay and/or Silt

0.40

0.55

Sand and/or Gravel

0.15

0.50

*Frank and Magnan (1995); Bustamante and Frank (1997)

Estimation of the unit side friction ( f p ) has been developed and presented

graphically by Poulos (1989), and is presented in Figure 22, with pile type categories

given in Table 5.

35

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Figure 22.Bustamante and Gianeselli (1982) method: (a) for clays, and (b) for sands. Figure from Mayne (2007).

Table 5. Pile categories for LCPC Direct CPT Method

Pile Category Type of Pile

IA

Plain bored pile, mud bored piles, hollow auger bored piles, case

screwed piles, Type I micropiles, piers, barrettes

IB

Cased bored piles, driven cast piles

IIA

Driven precast piles, prestressed tubular piles, jacked concrete piles

IIB

Driven steel piles, jacked steel piles

IIIA

Driven grouted piles, driven rammed piles

IIIB

High pressure grouted piles (d>0.25 m)< Type II micropiles

* Table from Mayne (2007)

36

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Method 2. Eslami and Fellenius (1997, 2006) proposed a method that is applicable to clays, silts, and sands. The method was developed using data from both driven and bored piles, and evaluates unit end-bearing as:

qb = Cte (qt - ub ) (fully mobilized resistance) Where Cte 1

Equation 34

Unit side friction is obtained from the Eslami and Fellenius method according to:

f p = Cse qe

Equation 35

Where Cse = side correlation coefficient, which is determined from Figure 23 and Table

6.

Figure 23. Eslami and Fellenius (1997, 2006) method to determine the soil type for unit side resistance. (Figure from Mayne, 2007).
37

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
Table 6. Eslami and Fellenius (1997, 2006) Side Friction Coefficient as a Function of Soil Type (Figure from Mayne, 2007)

Method 3. Takesue et al. (1998) proposed the following relationship to estimate the pile side friction ( f p ) of drilled shafts and driven piles in sands and clays from the sleeve friction measurements ( f s ) and excess pore water pressures ( ub ) of a CPT. For type 2 pore water pressure measurements:

For

ub < 300kPa : then

f p

=

f

s

ub 1250

+

0.76

Equation 36

For

ub

> 300kPa : then

f p

=

fs

ub 200

-

0.5

Equation 37

Where ub = ub - uo . The Takesue method is attractive because it allows estimation of

unit pile side resistance in soils that develop negative pore water pressure during

piezocone testing, behavior observed in heavily overconsolidated soils, and in the soils of

the Piedmont.

Drilled Shafts in Sand

Method 4. When compared to clays, the base resistance does not mobilize as quickly in a sand deposit, and will be a function of the relative movement ( s ) with respect to the width of the pile ( B ) (Ghionna et al., 1993; Lee and Salgado, 1999; Mayne and Schneider, 2001; Jamiolkowski, 2003):

38

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Sands:

qb



qt

1.90

+



0.62 s
B



-1

Equation 38

A ratio of movement to diameter is typically taken as: s = 0.1, which yields (Mayne, B

2007):

qb 0.12qt

Equation 39

For drilled shafts in sand, the unit side resistance can be determined by the method

proposed by Fioravante et al. (1995):

Sands:

f

p

(MPa)





qt

(MPa) 274

0.75

Equation 40

Method 5.

39

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Pile Displacement Methods

Estimation of pile displacements under axial load is frequently modeled using elastic theory. The vertical displacement of a pile foundation being loaded by axial compression can be determined from the following relationship (Poulos 1987, 1989; Mayne and Schneider 2001):

wt

=

Qt I p EsL d

Equation 41

Where Qt = applied axial load at the top of the shaft, EsL = soil modulus along the sides

of the pile at full depth, d = foundation diameter, and I p = displacement influence

factor.

The displacement influence factor is dependent on the properties of the pile and

the soil, and is given as follows (Randolph and Wroth 1978, 1979; Poulos 1987; Mayne

and Schneider, 2001):

Ip

=

4(1 + )

1

+

1

4 1 - s

8 tanh(L) L

(1 - s )

L

d





+

4

tanh(L) L

L

d



Where:

Equation 42

d = shaft diameter

L = pile length



=

db d

=

eta

factor

( db =diameter

of

base;



=1

for

straight

shafts)

= EsL = xi factor ( = 1 for floating pile and < 1 for end bearing pile) Eb

40

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

* = Esm = rho ( * = 1 for uniform soil and * = 0.5 for simple Gibson soil) E sL



=

2(1 +

s

)

Ep E sL

= lambda factor



=

ln[0.25

+

(2.5

*

(1

-

s

)

-

0.25

](

2L d

)

=

zeta

factor

L

=

2 2(


) 0.5



L d



=

mu

factor

E p = pile modulus (concrete plus reinforcing steel)

EsL = soil modulus along pile shaft at level of base

Esm = soil modulus at mid-depth of pile shaft Eb = soil modulus below foundation base ( Eb = EsL for a floating pile) s = Poisson's ratio of soil

Elastic theory also provides a means for analyzing the percentage of load that is

applied at the top of the pile, which is transferred to the base of the pile, according to the

following closed form solution (Fleming et al., 1985; Mayne and Schneider, 2001):

4 1

Qb =



(1

-



s

)



cosh(L)



Qt

4



(1

-



s


)

+

4

tanh(L) L

L

d



Equation 43

The nonlinear settlement can be accounted for through use of a modified

hyperbola (Mayne and Schneider, 2001):

41

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

wt

=

QI p

dEmax [1 -

f



Q Qult

]g

Equation 44

Where: Q = P = applied load and Qult = Pult = axial capacity for compression loading

For the simple case of homogeneous soil (E' constant with depth) interacting with a rigid

pile, the displacement influence factor simplifies to (Mayne, 2007):

I =

1

1- 2

1

+

(L / d)

(1+) ln[5 (L / d ) (1-)]

and the percentage of load transferred to the base (or pile toe or tip) is:

Equation 45

( ) Qb = I .
Qt 1 - 2

Equation 46

Davisson Capacity

Once the load displacement curve has been developed, the determination of the load limit is the final criteria. Many definitions for failure load are available, with the Davisson capacity being one of the most frequently applied. In this method, the load limit is defined as follows (Davisson, 1972):

S f = Se + (0.38 + 0.008D) S f = movement of pile top (cm)

Equation 47

D = Pile diameter or width (cm)

Se = Elastic compression of total pile length (cm)

42

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Se

=

QL AE

Q = applied load

Equation 48

L = Total length of pile

A = cross-sectional area of the pile

E = Modulus of elasticity of the pile

While there is some discussion over the magnitude of the offset, the Davisson capacity

remains an attractive method because it applies a quantitative, rather than qualitative,

criteria to the estimation of the load limit of a pile.

43

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
Steps in CPT Based Design
1) Gather tip resistance ( qc ), sleeve friction ( f s ), and pore water pressure ( u2 ) measurements.
2) Correct the cone tip resistance ( qc ) to ( qt ) using the net area ratio ( an ), which is unique to each piezocone.
3) Classify the soil types; typically use multiple classification methods and correlate with boring logs to confirm.
4) Determine CPT based design method: a. Indirect or Rational method i. interpret soil properties based on cone data 1. Stress history 2. strength (effective and undrained) 3. Lateral stress 4. Sands versus clays ii. apply traditional pile design methods b. Direct method (model cone as a mini-pile and scale up) i. Multiple methods available 1. Sand versus clay 2. Installation method ii. Silts
5) Load-displacement behavior
44

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
As with any method that relies on interpretation of soil properties, the design of pile foundations based on piezocone data should be correlated with boring logs and traditional pile design methods.
45

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Examples

Soil Parameters and Pile Design Using Rational Method

The following examples look at the application the relationships to determine soil properties from the data gathered during the CPT-1 sounding for the State Route 3 Alternate (John B. Gordon Highway) over the Ochlocknee River, Thomas County, Georgia. After the soil properties were evaluated from the PCPT data, an evaluation of pile capacity was performed using the rational method of pile design. The results for these calculations are included in an appendix to the report (electronic: spreadsheet).
Step 1. Classify soil (see previous section on classification). Step 2. Correct cone tip resistance to qt (see previous section). Step 3. Estimate effective overburden stress. In this example, a unit weight of 19
kN/m3 (121 lb/ft3) was assumed for the entire soil profile. Step 4. Estimate effective stress friction angle (and normalized tip resistance) according to:

' = 17.6o +11.0 log(qt1)

qt1

=



qt atm





' vo
atm

0.5

Step 5. Estimate Ko and OCR according to:

Equation 6 Equation 7

( ) Ko

=

0.192 qt atm 0.22





atm



' vo

0.31



OCR

0.27

Equation 17

46

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

OCR

=



' p

' vo

=



0.192 qt atm 0.22



(1

-

sin



'

)





' vo



atm

0.31



sin



1 ' -0.27











Equation 14

Step 6. Calculate unit side friction according to:

fp

=

CM

CK

K o

' vo

tan

'

Equation 26

Step 7. Estimate unit side friction in each layer by averaging the values

determined for each layer in Step 6.

Step 8. Sum values for each layer to determine total side friction:

#layers
Qs f pi 4lzi (square) i-i

Equation 30

Step 9. Determine unit end bearing (drained loading):

qb

=

0.1N

q

' vo

Equation 28

Step 10. Calculate total end bearing:

Qb = qb Ab Equation 31

Step 11. Determine total pile capacity:

Qult = Qs + Qb - W Equation 32

Soil Parameters and Pile Design Using Direct Method
Step 1. Classify soil (see previous section on classification). Step 2. Correct cone tip resistance to qt (see previous section). Step 3. Estimate effective overburden stress. In this example, a unit weight of 19
kN/m3 (121 lb/ft3) was assumed for the entire soil profile.

47

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Step 4. Calculate unit side friction according to relationship(s) outlined under

section "Axial Capacity from CPT Measurements- Direct Method".

Step 5. Sum values for each layer to determine total side friction:

#layers
Qs f pi 4lzi (square) i-i

Equation 30

Step 6. Calculate unit end bearing according to relationship(s) outlined under

section "Axial Capacity from CPT Measurements- Direct Method".

Step 7. Calculate total end bearing:

Qb = qb Ab Equation 31

Step 10. Determine total pile capacity:

Qult = Qs + Qb - W Equation 32

Load Displacement Curves
Data gathered for the Final Report for GDOT Research Project 2021 (Mayne, 2003)
was analyzed in order to demonstrate the approach to predicting pile settlement under load. The calculations for this example are included in an Appendix (electronic: spreadsheet).

Piedmont Geology Deep Foundations: Coweta County

Cone soundings were performed adjacent to the I-85 drilled shaft bridge

foundation in Coweta County (Mayne, 2003). Using the methods outlined in the section

titled "Pile Displacement Methods", yielded the following results for the analysis and

prediction:

qb



32Mpa1.90

+

0.62 -1



0.1



=

32Mpa *0.1235

48

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Qb = qb * Ab = 32Mpa *0.1235*0.65m2 = 2.56MN

Average f p = 0.71 fs
Average f p = 87kPa

Qs = f p As = 87kPa 55m2 = 4.78MN

Qt = Qs + Qb = 2.56MN + 4.78MN

From the shear wave velocity data:

sat

1+

1 0.614 + 58.7(log z

+ 1.095) /Vs

Go = Vs2

Eo = 2Go (1 + )

E(MPa) = 20z(m)

E = 20 18 = 360MPa

Finally, applying:

wt

=

Qt I p EsL d

Equation 41

allows evaluation of settlement versus load:

49

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Top Deflection, wt (mm)

Axial Load, Q (kN)

0

2000

4000

6000

8000

0

10

20

30

40

50
Qtotal = Qs + Qb M eas. Total

Pred. Qs M eas. Shaft

Pred. Qb M eas. Base

Figure 24. . Load-deflection curve for Coweta County drilled shaft foundation (Mayne, 2003).

50

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
References
ASTM D-5778-07, Standard Guide for Using the Electronic Cone Penetrometer for Environmental Site Characterization, American Society for Testing and Materials, West Conshohocken, PA.
Bustamante, M. and R. Frank (1997). "Design of Axially Loaded Piles--French Practice," Design of Axially Loaded Piles--European Practice (Proc. ERTC3, Brussels, Belguim), Balkema, Rotterdam, The Netherlands, pp. 161175.
.Bustamante, M. and Gianeselli, L. (1982). "Pile bearing capacity prediction by means of static penetrometer CPT". Penetration Testing, Vol. 2 (Proc. 2nd ESOPT, Amsterdam), Balkema, Rotterdam, 493-500.
Davisson, M.T. (1972). High Capacity Piles, Proceedings of Lecture Series on Innovations in Foundation Construction, American Society of Civil Engineers, Illinois Section, Chicago, March 22, pp. 81-112.
Eslami, A., "Bearing Capacity of Shallow and Deep Foundations from CPT Resistance," Proceedings, GeoCongress (Atlanta, Ga.), American Society of Civil Engineers, Reston, Va., Feb. 26Mar. 1, 2006, 6 pp.
Eslami, A. and Fellenius, B.H. (1997). Pile capacity by direct CPT and CPTu methods applied to 102 cas histories. Canadian Geotechnical Journal 34 (6), 886-904.
Fioravante, V., et al. (1995) "Load Carrying Capacity of Large Diameter Bored Piles in Sand and Gravel," Proceedings, 10th Asian Regional Conference on Soil Mechanics and Foundation Engineering, Beijing, China, 1995.
Fleming, W.G.K., Weltman, A.J., Randolph, M.F., and Elson, W.K. (1985). Piling Engineering, Surrey University Press, Wiley & Sons, New York, 380 p.
Frank, R. and J.-P. Magnan, "Cone Penetration Testing in France: National Report," Proceedings, International Symposium on Cone Penetration Testing, Vol. 3, Swedish Geotechnical Society Report 3:95, Oct. 45, 1995, Linkping, Sweden, pp. 147156.
Ghionna, V. N., Jamiolkowsi, M., Lancellotta, R. and Pedroni, S. (1993). "Base Capacity of Bored Piles in Sands from In-Situ Tests", Proceedings of 2nd International Geotechnical Seminar on Deep Foundations on Bored and Auger Piles (Van Impe ed.), Balkema, Rotterdam, pp. 67 74.
Jamiolkowski, M., C.C. Ladd, J.T. Germaine, and R. Lancellotta, "New Developments in Field and Lab Testing of Soils," Proceedings, 11th International Conference on Soil Mechanics and Foundation Engineering, Vol. 1, San Francisco, Calif., Aug. 1216, 1985, pp. 57154.
Jamiolkowski, M., "Soil Parameters Relevant to Bored Pile Design from Laboratory and In-Situ Tests," Deep Foundations on Bored and Auger Piles, Millpress, Rotterdam, The Netherlands, 2003, pp. 83100.
Kulhawy, F. H. and P. W. Mayne (1990). Manual on Estimating Soil Properties for Foundation Design. Palo Alto, CA, Electric Power Research Institute.
Kulhawy, F.H., C.H. Trautmann, J.F. Beech, T.D. O'Rourke, and W. McGuire, Transmission Line Structure Foundations for Uplift-Compression Loading, Report EL-2870, Electric Power Research Institute, Palo Alto, Calif., 1983, 412 pp.
51

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
Ladd, C.C. and D.J. DeGroot, "Recommended Practice for Soft Ground Site Characterization," Soil & Rock America 2003 (Proc. 12th Pan American Conf., Massachusetts Institute of Technology, Boston), Verlag Glckauf, Essen, Germany, 2003, pp. 357.
Ladd, C.C., "Stability Evaluation During Staged Construction," The 22nd Terzaghi Lecture, Journal of Geotechnical Engineering, Vol. 117, No. 4, 1991, pp. 540 615.
Lee, J.H. and Salgado, R. (1999). Determination of pile base resistance. ASCE Journal of Geotechnical & Geoenvironmental Engineering 125 (8), 673-683.
Mactec (2005). GDOT Technical Report. Mayne, P.W., "Integrated Ground Behavior: In-Situ and Lab Tests," Deformation
Characteristics of Geomaterials, Vol. 2 (Proc. Lyon, France), Taylor & Francis, London, United Kingdom, 2005, pp. 155177. Mayne, P.W., "Class-A Footing Response Prediction from Seismic Cone Tests," Deformation Characteristics of Geomaterials, Vol. 1 (Proc. IS-Lyon, France), Swets and Zeitlinger, Lisse, The Netherlands, 2003, pp. 883888. Mayne, P.W. (2007). Cone Penetration Testing, NCHRP Synthesis 368, Transportation Research Board, Washington D.C., 117 pp. Mayne, P.W. and Schneider, J.A (2001). "Evaluating axial drilled shaft response by seismic cone", Foundations & Ground Improvement, GSP No. 113, (Proceedings, GeoOdyssey 2001), ASCE, Reston/VA, 655-669. Poulos, H.G. (1987). From theory to practice in pile design (E.H. Davis Memorial Lecture). Transactions, Australian Geomechanics Society, Sydney, 1-31. Poulos, H.G. (1989). Pile behavior: theory and application", 29th Rankine Lecture, Geotechnique Vol. 39, No. 3, September, 363-416. Randolph, M.F. and Wroth, C.P. (1978). Analysis of deformation of vertically loaded piles. Journal of the Geotechnical Engineering Division, ASCE, Vol. 104 (GT12), 1465-1488. Randolph, M.F. and Wroth, C.P. (1979). A simple approach to pile design and the evaluation of pile tests. Behavior of Deep Foundations, STP 670, ASTM, 484499. Robertson, P. K. (1990). "Soil classification using the cone penetration test." Canadian Geotechnical Journal 27(1): 151-158.Robertson, P. K. and R. G. Campanella (1983). "INTERPRETATION OF CONE PENETRATION TESTS. PART II: CLAY." Canadian Geotechnical Journal 20(4): 734-745. Robertson, P. K., R. G. Campanella, et al. (1986). USE OF PIEZOMETER CONE DATA, Blacksburg, VA, USA, ASCE (Geotechnical Special Publ n 6), New York, NY, USA. Robertson, P.K., Campanella, R.G., Davies, M.P. and Sy, A. (1988). "Axial capacity of driven piles in deltaic soils using CPT". Penetration Testing 1988, Vol. 2, Balkema/Rotterdam, 919-928. Takesue, K., Sasao, H., and Matsumoto, T. (1998). Correlation between ultimate pile skin friction and CPT data. Geotechnical Site Characterization (2), Balkema, Rotterdam, 1177-1182. Terzaghi, K., R. Peck, and G. Mesri, Soil Mechanics in Engineering Practice, 3rd ed., John Wiley & Sons, New York, N.Y., 1996.
52

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT
Trak, B., P. LaRochelle, F. Tavenas, S. Leroueil, and M. Roy, "A New Approach to the Stability Analysis of Embankments on Sensitive Clays," Canadian Geotechnical Journal, Vol. 17, No. 4, 1980, pp. 526544.
Vesic, A.S., NCHRP Synthesis of Highway Practice 42: Design of Pile Foundations, Transportation Research Board, National Research Council, Washington, D.C., 1977, 68 pp.
53

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

APPENDIX A

Ochlocknee River, Thomas County, Georgia Test: CPT-21
Date: 7/27/2005 Location: Sta 249+53 Lt 72
Cone size: 10 cm2 an = 0.59
GWT = 0 m

Depth
(m)
0.00 0.15 0.31 0.46 0.61 0.76 0.92 1.07 1.22 1.37 1.52 1.68 1.83 1.98 2.13 2.29 2.44 2.59 2.74 2.90 3.05 3.20 3.35 3.51 3.66 3.81 3.96 4.12 4.27 4.42 4.57 4.73 4.88 5.03

qc (MPa)
0.00 0.00 0.41 14.16 14.44 13.65 11.91 8.10 3.59 3.77 2.67 2.14 1.45 1.67 4.58 10.94 17.43 15.72 13.61 13.88 12.14 10.93 11.93 5.92 1.77 0.96 0.62 3.16 2.07 1.21 0.52 3.84 12.15 20.72

fs (kPa)
0.00 0.00 4.40 75.27 117.69 119.41 120.28 97.58 71.72 48.26 45.29 27.58 43.38 52.09 92.70 75.36 70.19 114.34 139.14 131.48 146.42 160.11 160.30 121.42 79.00 33.80 28.63 37.35 47.69 49.99 44.43 41.08 79.48 149.19

u2 (kPa)
-0.19 -0.38 -0.57 6.51 -3.16 -5.17 -8.43 -9.10 -2.30 1.53 5.08 10.44 9.00 18.29 21.16 12.93 6.99 3.16 6.22 -10.05 -14.08 -15.23 -9.10 -12.54 -9.77 -8.43 -6.70 -4.69 -3.35 1.82 2.68 4.69 7.76 11.20

u2 (MPa)
0.00 0.00 0.00 0.01 0.00 -0.01 -0.01 -0.01 0.00 0.00 0.01 0.01 0.01 0.02 0.02 0.01 0.01 0.00 0.01 -0.01 -0.01 -0.02 -0.01 -0.01 -0.01 -0.01 -0.01 0.00 0.00 0.00 0.00 0.00 0.01 0.01

qt (MPa)
0.00 0.00 0.41 14.17 14.43 13.65 11.91 8.10 3.59 3.77 2.68 2.14 1.46 1.68 4.59 10.95 17.44 15.72 13.61 13.87 12.13 10.93 11.92 5.91 1.76 0.96 0.62 3.16 2.07 1.21 0.52 3.84 12.16 20.72

54

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Depth
(m)
5.18 5.33 5.49 5.64 5.79 5.94 6.10 6.25 6.40 6.55 6.71 6.86 7.01 7.16 7.32 7.47 7.62 7.77 7.93 8.08 8.23 8.38 8.54 8.69 8.84 8.99 9.14 9.30 9.45 9.60 9.75 9.91 10.06 10.21 10.36 10.52 10.67 10.82 10.97 11.13 11.28 11.43 11.58 11.74 11.89 12.04 12.19 12.35

qc (MPa)
26.46 29.39 31.54 32.14 31.26 29.66 26.33 24.65 22.96 20.91 20.81 19.04 17.73 14.65 15.71 16.61 16.29 15.78 16.03 21.88 28.28 20.72 20.75 22.68 20.92 19.19 18.99 16.97 15.07 4.64 3.34 13.43 15.68 9.49 8.79 7.37 7.82 9.83 8.28 8.23 8.33 10.25 9.72 10.00 11.00 9.04 8.27 7.15

fs (kPa)
219.29 259.03 284.31 306.53 289.48 272.25 258.46 225.32 205.02 187.88 161.64 148.91 137.70 128.32 85.90 117.59 141.73 145.27 145.46 154.75 119.80 131.67 93.94 87.24 121.42 128.41 91.74 77.76 69.43 121.52 145.75 214.41 422.88 400.66 354.60 321.37 273.59 379.59 406.98 355.08 328.65 352.49 455.25 401.91 480.14 383.43 329.80 286.61

u2 (kPa)
14.75 16.95 18.29 18.67 16.28 13.89 11.68 10.15 7.85 5.75 4.12 3.83 5.46 3.64 2.97 5.84 6.80 6.22 7.85 12.35 12.35 14.46 15.61 20.11 20.30 19.34 19.92 20.88 20.01 16.85 8.33 63.58 240.74 177.83 128.89 112.04 101.60 60.52 68.09 61.38 67.89 69.91 74.41 73.35 70.48 85.80 89.82 82.26

u2 (MPa)
0.01 0.02 0.02 0.02 0.02 0.01 0.01 0.01 0.01 0.01 0.00 0.00 0.01 0.00 0.00 0.01 0.01 0.01 0.01 0.01 0.01 0.01 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.06 0.24 0.18 0.13 0.11 0.10 0.06 0.07 0.06 0.07 0.07 0.07 0.07 0.07 0.09 0.09 0.08

qt (MPa)
26.46 29.39 31.55 32.15 31.27 29.67 26.33 24.66 22.97 20.91 20.81 19.04 17.74 14.65 15.71 16.61 16.29 15.78 16.04 21.88 28.29 20.72 20.76 22.69 20.93 19.20 19.00 16.98 15.08 4.64 3.34 13.46 15.77 9.56 8.84 7.42 7.86 9.85 8.31 8.25 8.36 10.28 9.75 10.03 11.03 9.07 8.31 7.18

55

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Depth
(m)
12.50 12.65 12.80 12.95 13.11 13.26 13.41 13.56 13.72 13.87 14.02 14.17 14.33 14.48 14.63 14.78 14.94 15.09 15.24 15.39 15.55 15.70 15.85 16.00 16.16 16.31 16.46 16.61 16.76 16.92 17.07 17.22 17.37 17.53 17.68 17.83 17.98 18.14 18.29 18.44 18.59 18.75 18.90 19.05 19.20 19.36 19.51 19.66

qc (MPa)
5.92 7.01 11.59 9.12 10.69 10.79 11.42 11.87 13.50 14.08 11.52 11.76 11.34 13.97 13.26 13.70 15.37 11.55 11.37 11.06 10.50 10.09 10.46 12.88 13.20 13.38 14.68 9.35 8.56 7.97 7.23 7.55 9.66 12.48 9.96 11.32 10.89 12.01 18.21 21.42 14.17 11.85 12.97 13.92 13.06 14.52 26.53 22.80

fs (kPa)
292.55 253.10 412.34 398.75 457.16 520.84 509.06 528.89 635.18 912.12 664.39 523.52 474.68 595.63 646.38 716.58 767.71 553.30 501.11 490.10 459.08 357.00 347.61 357.86 634.41 473.92 880.04 473.54 338.42 320.03 320.80 302.12 319.46 539.42 475.36 522.28 566.61 410.62 528.22 1134.95 580.98 451.51 435.42 503.51 499.87 535.40 883.49 1275.91

u2 (kPa)
71.72 75.65 94.13 135.98 157.81 184.91 228.96 249.26 270.33 253.86 256.16 254.34 249.74 248.79 292.55 283.83 253.48 275.69 273.59 275.98 271.67 255.68 244.29 259.80 232.41 280.77 220.54 199.66 197.65 204.54 199.28 205.41 238.92 181.08 230.40 307.97 330.37 372.80 334.11 261.43 545.55 515.48 542.29 594.96 577.05 511.94 615.45 172.18

u2 (MPa)
0.07 0.08 0.09 0.14 0.16 0.18 0.23 0.25 0.27 0.25 0.26 0.25 0.25 0.25 0.29 0.28 0.25 0.28 0.27 0.28 0.27 0.26 0.24 0.26 0.23 0.28 0.22 0.20 0.20 0.20 0.20 0.21 0.24 0.18 0.23 0.31 0.33 0.37 0.33 0.26 0.55 0.52 0.54 0.59 0.58 0.51 0.62 0.17

qt (MPa)
5.95 7.04 11.63 9.17 10.76 10.86 11.52 11.97 13.61 14.19 11.62 11.86 11.44 14.07 13.38 13.82 15.47 11.67 11.48 11.17 10.61 10.20 10.56 12.99 13.30 13.50 14.77 9.43 8.64 8.05 7.31 7.63 9.76 12.56 10.06 11.44 11.03 12.16 18.34 21.52 14.39 12.06 13.19 14.16 13.30 14.72 26.78 22.87

56

Final Report: Interpretation of Cone Penetration Tests for Pile Design Applications at GDOT

Depth
(m)
19.81 19.97 20.12 20.27 20.42 20.57 20.73 20.88 21.03 21.18 21.34 21.49 21.64 21.79 21.95 22.10 22.25 22.40 22.56 22.71 22.86 23.01 23.17 23.32 23.47 23.62 23.78 23.93 24.08 24.23

qc (MPa)
20.56 16.29 15.38 15.28 21.70 23.63 23.15 23.25 22.65 23.59 24.83 24.17 23.90 24.33 24.35 24.97 25.69 24.42 20.99 20.40 21.71 15.46 17.04 19.24 20.00 18.07 12.45 17.67 13.92 8.88

fs (kPa)
1117.81 1109.96 874.58 713.42 888.18 666.21 371.65 371.36 449.79 410.53 338.99 369.92 376.05 322.33 334.68 340.72 436.86 502.74 600.71 582.32 678.08 909.25 522.95 384.38 321.85 505.90 703.65 816.84 899.29 504.18

u2 (kPa)
365.42 316.20 279.33 219.96 165.09 101.51 53.43 47.78 54.20 52.86 39.84 35.43 36.20 28.25 26.24 25.28 36.96 40.51 64.83 83.12 113.86 261.33 153.98 82.93 73.07 94.71 160.78 239.11 265.93 101.60

u2 (MPa)
0.37 0.32 0.28 0.22 0.17 0.10 0.05 0.05 0.05 0.05 0.04 0.04 0.04 0.03 0.03 0.03 0.04 0.04 0.06 0.08 0.11 0.26 0.15 0.08 0.07 0.09 0.16 0.24 0.27 0.10

qt (MPa)
20.71 16.42 15.50 15.37 21.77 23.67 23.17 23.27 22.67 23.61 24.84 24.19 23.91 24.34 24.36 24.98 25.70 24.44 21.02 20.43 21.75 15.56 17.10 19.27 20.03 18.11 12.52 17.77 14.03 8.92

(Robertson and Campanella 1983; Robertson and Campanella 1983; Robertson, Campanella et al. 1986; Robertson 1990; Mayne 2007)
Kulhawy, F. H. and P. W. Mayne (1990). Manual on Estimating Soil Properties for Foundation Design. Palo Alto, CA, Electric Power Research Institute. Mayne, P. W. (2007). Cone Penetration Testing. Washington DC, Transportation Research Board: 117. Robertson, P. K. (1990). "Soil classification using the cone penetration test." Canadian Geotechnical Journal 27(1): 151158. Robertson, P. K. and R. G. Campanella (1983). "INTERPRETATION OF CONE PENETRATION TESTS. PART I: SAND." Canadian Geotechnical Journal 20(4): 718-733. Robertson, P. K. and R. G. Campanella (1983). "INTERPRETATION OF CONE PENETRATION TESTS. PART II: CLAY." Canadian Geotechnical Journal 20(4): 734-745. Robertson, P. K., R. G. Campanella, et al. (1986). USE OF PIEZOMETER CONE DATA, Blacksburg, VA, USA, ASCE (Geotechnical Special Publ n 6), New York, NY, USA.

57