REVIEW OF CPT BASED DESIGN METHODS FOR ESTIMATING AXIAL
CAPACITY OF DRIVEN PILES IN SILICEOUS SAND
By
Juan Carlos Monz6n A.
B.S. Civil Engineering
University of Florida, 2001
SUBMITTED TO THE DEPARTMENT OF CIVIL AND ENVIRONMENTAL ENGINEERING
IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE DEGREE OF
MASTER OF ENGINEERING IN CIVIL AND ENVIRONMENTAL ENGINEERING
AT THE
MASSACHUSETTS INSTITUTE OF TECHNOLOGY
k4ASSACHUSETS INS
OF TECHNOLOGY
[JUN 7 2006
JUNE 2006
LIBRARIES
02006 Juan Carlos Monz6n A. All rights reserved.
The author hereby grants to MIT permission to reproduce
and to distribute publicly paper and electronic
copies of this thesis document in whole or in part
in any medium now known or hereafter created.
Signature of Author:
Departme
of Civil and EnvironmentaThgjneering
May 26, 2006
A-
Certified by:
A, ,,,,.
Andrew J. Whittle
Professor of Civil and Environmental Engineering
I Thesis Supervisor
A
Accepted by:
AndN4A-hittle
for
Graduate Students
Chairman, Departmental Committee
E
REVIEW OF CPT BASED DESIGN METHODS FOR ESTIMATING AXIAL
CAPACITY OF DRIVEN PILES IN SILICEOUS SAND
By
Juan Carlos Monz6n A.
Submitted to the Department of Civil And Environmental Engineering
on May 26h, 2006 in Partial Fulfillment of the Requirements for the Degree of
Master of Engineering
ABSTRACT
The Cone Penetration Test has been used for more than 30 years for soil exploration purposes. Its
similarities in mode of installation with driven piles provides the potential of linking key variables of pile
design and performance, such as base resistance and shaft friction, to measured cone tip resistance.
Large scale pile load tests, performed in the last two decades, have shown better agreement with recent
CPT based design criteria, than with conventional American Petroleum Institute (API) earth pressure
approach design guidelines. The CPT based design methods provide a more coherent framework for
incorporating soil dilation, pile size effect, pile plugging during installation, and the friction at the pile-soil
interface.
A review, of four recent CPT based design methods and the API design guidelines, for estimating axial
capacity of driven piles in siliceous sands was performed by comparing their predictive performance to six
documented on-shore piles with load tests. First, a detailed site investigation based on CPT data was
performed to validate the provided soil profile, and to evaluate the accuracy of the CPT readings to
identify and classify soil strata. Three piles were selected for further study and axial capacity calculations.
Three of the design methods, UWA-05, ICP-05 and NGI-05, prove to accurately predict axial pile
capacities for on-shore short piles founded on sites where sand dominates. Analysis against a larger and
more detailed database is required to validate their performance in multilayer soil profiles.
Thesis Supervisor: Andrew J. Whittle
Title: Professor of Civil and Environmental Engineering
2
ACKNOWLEDGMENTS
I acknowledge and gratefully thank, Mr. Thomas Shantz, Senior Research Engineer at the California
Department of Transportation (CALTRANS), who kindly provided the information that made the
execution of this thesis possible.
I would like to extend a special thank you to my thesis supervisor, Professor Andrew Whittle, for his
knowledge, critical thinking, enthusiastic interest, and for the time he dedicated to guide and teach me; not
only in this thesis but in my courses at MIT.
A warm thank you goes to my family, for their love, understanding, and support; to my mother for making
this Master possible; and to my grandfather, who introduced me to Civil Engineering, a passion we share.
Special thanks got to Diana Escobar, for her love, inspiration, encouragement, and for the life we are
about to start together.
This thesis is dedicated to the loving spirit of my sister Natalia, and her journey to recovery:
"Hoy no caminas junto a m', pero tus huellas me acompafian a tu encuentro."
3
TABLE OF CONTENTS
AB STRACT .............................................................................................................................................. 2
ACKNOW LEDGM ENTS ......................................................................................................................... 3
TABLE OF CONTENTS .......................................................................................................................... 4
LIST OF FIGURES ................................................................................................................................... 6
LIST OF TABLES ..................................................................................................................................... 7
INTRODUCTION ............................................................................................................................ 8
1.
2.
3.
BACKGROUND ON DESIGN M ETHODS ...................................................................................9
AXIAL PILE CAPACITY - OVERVIEW ..................................................................................... 11
Basic design forraulation ....................................................................................................... 11
DESCRIPTION OF DESIGN M ETHODS .................................................................................... 13
3.1.
4.
4.1.
4.2.
4.3.
4.4.
API-00 .................................................................................................................................... 14
FUGRO-05 ............................................................................................................................. 16
ICP-05 ..................................................................................................................................... 18
NGI-05 ................................................................................................................................... 22
LTW A-05 ................................................................................................................................. 24
CALTRAN S PILE DATA .............................................................................................................. 30
4.5.
5.
5.1.
5.2.
5.3.
5.4.
6.
Load tests ............................................................................................................................... 31
Pile and site data overview .................................................................................................... 32
SOIL-PROFILE CHARACTERIZATION ....................................................................................33
General procedure .................................................................................................................. 33
6.1.
6.2.
7.
Pile-site characteristics report ................................................................................................ 31
CPT profiles ........................................................................................................................... 31
Site interpretation results ....................................................................................................... 38
AX IAL PILE CAPACITY PREDICTION ..................................................................................... 53
Spreadsheet input data ........................................................................................................... 53
7.1.
7.2.
7.3.
General calculation procedure ............................................................................................... 53
Clay layers - Load contribution ............................................................................................. 54
7.5.
Spreadsheet output ................................................................................................................. 55
Pile M IT-4 capacity prediction .............................................................................................. 55
7.6.
Pile M IT- 1 capacity prediction .............................................................................................. 63
7.7.
Pile M IT-5 capacity prediction .............................................................................................. 67
7.4.
SUMMARY OF REVIEW OF CPT DESIGN METHODS...........................................................75
8.
8.1.
Tension loading......................................................................................................................75
8.2.
Compression loading .............................................................................................................
8.3.
API-00....................................................................................................................................77
8.4.
FU GRO-05.............................................................................................................................77
8.5.
ICP-05....................................................................................................................................78
8.6.
N GI-05...................................................................................................................................78
8.7.
U W A -05.................................................................................................................................79
76
CON CLUSION ..............................................................................................................................
80
REFERENCES ........................................................................................................................................
81
9.
APPEN D ICES Appendix A - Site Investigation pile M IT-I ..............................................................
84
Appendix A - Site Investigation pile M IT-1 .......................................................................................
85
Appendix B - Site Investigation pile M IT-5 ..................................................................................
91
Appendix C - Pile-soil profile for pile MIT-3.....................................................................................98
Appendix D - Pile-soil profile for pile M IT-6 ................................................................................
99
Appendix E - MIT-1 - Axial capacity prediction - Second Scenario (Mostly sand profile)...........100
5
LIST OF FIGURES
Figure 3.1 - Three main phases during the history of a driven pile: .......................................................
12
Figure 4.1 - Relative density classification (API 2000).........................................................................
15
Figure 4.2 - FUGRO-05 dimensional parameters...................................................................................
17
Figure 4.3 - Interface friction angle, 5, variation with D50 (Lehane et al. 2005c).................................26
Figure 4.4 - Determination qc using the Dutch averaging technique (Lehane et al. 2005b).................28
Figure 5.1 - Caltrans Test sites (Olson and Shantz, 2004).....................................................................
Figure 6.1 - Comparison of measured
)'
from frozen samples vs. qt (Mayne 2005)............................
30
36
Figure 6.2 - Preconsolidation Stress in Clay from Net Tip Stress (Mayne 2005).................................
37
Figure 6.3 - Pile MIT-4- Pile-soil elevations diagram...........................................................................
41
Figure 6.4 - Pile MIT-4 - Chart A - Vertical profile, CPT readings.....................................................
42
Figure 6.5 - Pile MIT-4 - Chart B - CPT normalized profiles.................................................................
43
Figure 6.6 - Pile MIT-4 - Chart C - Friction angle and relative density for cohesionless layers........... 44
Figure 6.7 - Pile MIT-4 - Chart D (Undrained strength and stress history of clay layers).....................
45
Figure 6.8 - Pile MIT-4 - Chart E - Soil Classification (Robertson and Campanella, 1988).................
46
Figure 6.9 - Pile MIT-1 - Pile-soil elevations diagram..........................................................................
48
Figure 6.10 - Pile MIT-5 - Pile-soil elevations diagram........................................................................
51
Figure 7.1 - MIT 4 - Tension load test and predicted axial capacity......................................................57
Figure 7.2 - MIT-4 - Tension - Axial capacity distribution...................................................................
59
Figure 7.3 - MIT 4 - Compression load test and predicted axial capacity.............................................
60
Figure 7.4 - MIT-4 - Compression - Axial capacity distribution..........................................................
62
Figure 7.5 - MIT-1 - Tension load test and predicted axial capacity ...................................................
64
Figure 7.6 - MIT-I - Tension - Axial capacity distribution...................................................................66
Figure 7.7 - MIT-5 - Tension load test and predicted axial capacity ...................................................
69
Figure 7.8 - MIT-5 - Tension - Axial capacity distribution...................................................................71
Figure 7.9 - MIT-5 - Compression load test and predicted axial capacity ............................................
73
Figure 7.10 - MIT-5 - Compression - Axial capacity distribution........................................................
74
6
LIST OF TABLES
Table 4-1 - Timeline of the development of design methods for offshore piles (Chow 2005)................13
Table 4-2 - Coefficients of lateral earth pressure, Kf..............................................................................14
Table 4-3 - API RP 2A (2000) design parameters for Cohesionless Siliceous Soil ..............................
15
Table 5-1 - Available information matrix ..............................................................................................
30
T able 5-2 - CPT soundings .........................................................................................................................
32
Table 5-3 - Site inform ation ........................................................................................................................
32
Table 5-4 - Pile properties...........................................................................................................................
32
Table 5-5 - Load-deflection tests ................................................................................................................
32
Table 7-1 - MIT-4 - Coverage of pile embedment per layer .................................................................
55
Table 7-2 - Pile MIT-4 - Pile axial capacity overview ............................................................................
56
Table 7-3 - Pile MIT-1 - Pile axial capacity overview based on profile derived in Section 6.2.2...... 63
Table 7-4 - MIT-5 - Coverage of pile embedment per layer.................................................................
67
Table 7-5 - Pile MIT-5 - Pile axial capacity overview ............................................................................
67
Table 8-1 - Summary of prediction of total pile capacity in Tension .....................................................
75
Table 8-2 - Summary of prediction of total pile capacity in Compression............................................
76
7
1.
INTRODUCTION
Historically, pile design in sands has been based on an earth pressure approach, and described by simple
linear relationships for the unit shaft friction and unit base resistance. In both cases, the approach imposes
limiting values at some 'critical depth' expressed either in absolute terms or normalized by the pile
diameter (Randolph 2003). This approach has been incorporated into the American Petroleum Institute
(API) offshore pile designs guidelines since 1969.
The Cone Penetration Test (CPT), and piezocone penetration test (PCPT), have been widely used in
geotechnical site investigations for more than 30 years. In these tests, soil profiling is based on continuous
measurements of cone resistance (q), sleeve friction (f,) and pore pressures generated at the tip or base (u,
or u 2 respectively) of the cone as it penetrates the soil at a constant rate. These tests trace its origins to the
work of Wissa and Torstensson in 1975 (Baligh et al. 1980).
The similarities in mode of installation of driven piles and CPT probes indicated that further development
of the CPT method should improve the pile design methods. Early attempts at correlating CPT
measurements to pile capacities was performed by Bustamante and Gianeselli (1982), and has evolved to
link cone tip resistance (qg) to pile's base resistance and shaft friction resistance.
Large scale pile load tests performed in last two decades have advanced the understanding of driven piles
in sand, as they have identified the gradual degradation of shaft friction at any given depth as the pile is
driven progressively deeper (Randolph 2003). The results of the load test differ significantly from
predictions based on conventional API design criteria but show good agreement with those based on more
recent CPT based design criteria.
The present document provides a comparative review of five design methods for estimating axial capacity
of piles in siliceous sands. The design methods comprise four recent (2005) CPT based design methods,
and the API earth pressure approach.
The current review compares the predictive performance of the proposed CPT design methods using data
for six well documented on-shore piles and load tests. Chapters 2 to 4 present an overview of methods
used to estimate axial pile capacity in sands and the four proposed CPT design methods. Chapters 5 and 6
describe the site conditions and soil profile interpretation based on CPT data. Chapters 7 and 8 apply and
compare the proposed CPT design methods to estimate the capacity measured in the pile load tests.
8
2.
BACKGROUND ON DESIGN METHODS
In the last two decades, a series of load tests were performed on driven piles at sufficiently large scale to
obtain reliable pile load test data in very dense sand for development of improved offshore pile design
criteria for North Sea type conditions and to contribute to the definition of new Eurocodes. These load
tests were part of a European initiative called EURIPIDES, designed to provide more confidence and less
conservatism for new design guidelines for offshore pile foundations (Zuidberg & Vergobi, 1996).
The Euripides program comprised of a highly instrumented (0.76 m) diameter driven pile that was tested
at one location, extracted and redriven and tested at a second location. Static compression and tension tests
(30 MN) were performed at three penetration depths (30.5 m, 38.7 m and 47.0 m) at the first location, and
at one penetration depth (46.7 m) at the second location. The latter series of tests was repeated after 1.5
years. Further background to the Euripides tests can be found in Zuidberg & Vergobi (1996).
The results of the EURIPIDES load tests revealed that the American Petroleum Institute (API) offshore
pile designs guidelines were very conservative and underestimated the pile load capacities in dense sands.
These findings confirmed earlier results obtained from load tests performed by Saudi Aramco in Ras
Tanajib in the Arabian Gulf in 1985 (Helfrich et al., 1985; Stevens and Al-Shafei, 1996). In this program a
highly instrumented pile was driven to 17 m depth and tested. After pulling the pile, a casing was driven to
17 m below ground level, the soil plug removed and the instrumented test pile was driven through this
casing to 25 m depth. Subsequently, another series of static compression and tension tests was performed.
The tests results differed significantly from predictions based on conventional offshore design criteria
given in API RP2A. However, good agreement was obtained with predictions made with more recent,
CPT-based design criteria (Helfrich et al. 1985).
In 2001, the results of EURIPIDES became public, and together with the progress in Cone Penetration
Tests (CPT) site investigations methods, led to the development and/or confirmation of recently proposed
design methods that improved the predictions of the API recommendations, particularly for dense
siliceous sands. These methods were ICP and NEW FUGRO.
Between 2002 and 2004, API funded a project and appointed Fugro N.V. to compile pile load tests results
into a large database, with the objective of comparing and revising those results against the API guidelines
for design of offshore piles; the NEW FUGRO method; and the ICP method that had been successfully
applied in foundation designs of 14 North Sea platforms since 1996.
9
At the end of 2004, the API project was completed; it concluded that the API design guidelines were very
unreliable; it provides less conservatism for increasing length/diameter ratio, and more conservatism with
increasing relative density. For the ICP method it concluded that it was reasonably reliable, in particular
for compression capacity; slightly unconservative for piles in tension; and conservative for end bearing.
In early 2005, the API piling sub-committee, requested Prof. Lehane from the University of Western
Australia (UWA), to conduct an independent evaluation of the existing API recommendations (API-00)
for offshore structures, and those given by the recently proposed design methods for estimating axial
capacity in driven piles, namely: Imperial College (ICP-05), Fugro (FUGRO-05), and the Norwegian
Geotechnical Institute (NGI-05) for axially loaded piles in sand. This review, which was conducted by
Lehane et al. (2005a,b,c), included the compilation of a significantly larger database of pile load tests than
employed in the development of the 3 'new' CPT based design methods and highlighted limitations of
these methods.
The review of the 3 CPT design methods by Lehane et al (2005a,b,c) led to development of the UWA-05
method, and the publication of a comprehensive study that evaluates the performance of the design
methods against a large load pile test database that combines the API and UWA information (Lehane et al.
2005a).
10
3.
3.1.
AXIAL PILE CAPACITY - OVERVIEW
Basic design formulation
The ultimate capacity of a pile, defined as
Qui, is the load that will cause a pile to fail. The value of Qut
(Equation 3-1) is the sum of the contribution of the ultimate shaft resistance Qsf, and the ultimate end
bearing resistance Qbf, minus the weight of the pile.
Quit = Qsf + Qbf -Weight
(3-1)
The ultimate shaft resistance of a pile, Qsf, is the sum of the unit shaft friction applied along the embedded
surface of the pile (Equation 3-2).
Qf
r dz
= 7D
(3-2)
The unit shaft friction is defined as the product of the horizontal effective stresses at the failure condition
and the mobilized friction coefficient along the pile's length (Equation 3-3). The mobilized friction
coefficient is defined as the tangent of the pile-soil friction angle, (6):
T f = a-' h . tan 5
( 3-3 )
The ultimate end bearing resistance, Qbf, is the maximum load that a pile can mobilize at its tip. It is
calculated as the product of the ultimate unit end bearing stress, qbf, and the pile's base area, Ab. The
ultimate unit end bearing stress will be reached at large displacements, therefore the practical definition of
ultimate is often taken as the unit end bearing capacity at a displacement of 10% the pile diameter, qbo.I.
This definition is summarized in Equation 3-4.
g *
Qbf
(34)
2
The pile's base area, Ab, corresponds, for the case of closed-ended piles, to the actual physical area of the
pile. In the case of open-ended piles, the formation of a plug must be evaluated, as to determine if the unit
end bearing stress acts solely on the annulus of the pile, or on the soil plug formed in the interior of the
pile during driving. The failure mechanism of the plug can occur either through shear failure of the soil
against the pile's internal surface, or as a bearing failure of the plug's tip. Recommendations to assess the
formation of the plug in an open-ended pile are provided in Lehane et al. (2002) and Paik et al. (2001).
11
The general form of Equation (3-1) for an open-ended pile can be re-written as:
Quit = Qsf+Qbf - Weight =(AD - Jv dz)+ /,Z
J qboA -Weight
(3-5)
From the previous equations it can be noted that the difficulty in calculating the ultimate pile capacity
depends on the estimation of the stress parameters
qbf
(or qzo.1) and -ref (or c-'h). This estimation is
challenging because it is influenced on several factors that inherently affect the initial state of stresses in
the soil and that are difficult to quantify. These factors include, but are not limited to: the direction of
loading, soil disturbance due to type of pile installation, pile's properties, size effects, set-up time, etc.
Figure 3.1 provides schematic drawings, of the main phases in the lifetime of a pile, that illustrate some of
the mentioned factors for the case of driven piles.
(a)
(b)
(c)
Figure 3.1 - Three main phases during the history of a driven pile:
(a) installation; (b) equilibration; (c) loading (Randolph, 2003)
12
DESCRIPTION OF DESIGN METHODS
4.
The present section will introduce the formulations and describe the characteristics of the five design
methods, for estimating axial capacity in driven piles in siliceous sands, being reviewed in this document.
(Lehane et al. 2005a)
The design methods can be classified in two groups:
i)
Existing API recommendations for offshore structures(API-00), which are based on an earth
pressure approach.
ii)
Recent CPT based design methods, namely:
"
Fugro, named hereafter (FUGRO-05)
"
Imperial College, named hereafter (ICP-05)
*
Norwegian Geotechnical Institute, named hereafter (NGI-05)
0
University of Western Australia, named hereafter (UWA-05)
The following figure presents a timeline of the history and development of the design methods.
Method
Dates
Notes
API
1969 -2005
Earth pressure approach
ICP
1996 -2005
Class-A prediction for EURIPIDES
NGI
1999 -2005
Developed using the NGI database and EURIPIDES
FUGRO
2001 - 2005
Developed using EURIPIDES and the Fugro database
2005
of open-ended piles using the ICP expression as a
base
Developed using an expanded database
UWA
Introduces the use of the IFR to calculate area ratio
for shaft capacity of open ended piles based on cavity
expansion models.
Uses FFR for base capacity of open-ended piles.
Table 4-1 - Timeline of the development of design methods for offshore piles (Chow 2005)
13
4.1.
API-00
The design method identified as API-00, corresponds to the recommendations included in the American
Institute of Petroleum manual for offshore pile design, namely: API 2000.
4.1.1.
Shaft resistance
The total shaft resistance of the pile is defined by the integral of the unit shaft friction along the pile shaft,
as indicated in equation (3-3). The unit shaft friction is expressed using a Coulomb friction approach that
in general relates the frictional force between two surfaces to the perpendicular normal force applied and
modifies it by a friction coefficient. The friction factor corresponds to the roughness of the contact
materials. Following this approach, the unit shaft friction (tr) is defined as the local effective horizontal
stress on the pile - expressed in terms of the corresponding effective vertical stress (c' 0o) multiplied by a
coefficient of lateral earth pressure (Kf) - and modified by the friction coefficient that corresponds to the
tangent of the friction angle (6) between the soil and pile wall. The previous definition is summarized in
equation (4-1), where the coefficient of lateral earth pressure and the friction coefficient are grouped into a
term named as beta (P).
(4-1)
'f = Kf ' tan 5 -- 'v0 = ).al - V- f
It can be noted in equation (4-1), that the value of the unit shaft friction (trf) increases proportionally to the
vertical stress(a',0 ), nevertheless the API-00 design method limits the unit shaft friction (Tflim) to the
values indicated in Table 4.3.
Open ended or
Closed end or
unplugged piles
plugged piles
Compression
0.8
1.0
Tension
0.8
1.0
Table 4-2 - Coefficients of lateral earth pressure, Kf
The friction angle (6) between the soil and the pile is specified for different densities of non-cohesive
materials in Table 4.3. Classification of a material under a given density can be performed from the angle
of internal friction or the relative density of the material, as indicated in Figure 4.1, which is included into
the API (2000) guidelines.
14
*, angle of internal friction
Q*
#120
0*
Vly LOOsM
Loose
300
4
3
0
Dense
Mwwln
Dann
45*
Very
Dens
250
"h waerl
Tabls
200
-150
Sand Below
the w*We
Table
100
50
0
0
40
so
80v
RELATIVE DENSITY, %
20
1W
Figure 4.1 - Relative density classification (API 2000)
Density
Very loose
Soil
Soil-Pile
Limiting Skin
Friction
angle, 6
Friction, tflim
2
Limiting Unit End
Nq
Bearing,
qbo.iI1m
2
[kips/ft ]
[kPa]
8
40
1.9
67
12
60
2.9
1.7
81.3
20
100
4.8
30
2
95.7
40
200
9.6
35
2.4
114.8
50
250
12
Description
[degrees]
[kips/ft ]
[kPa]
Sand
15
1
47.8
20
1.4
25
Sand-silt
Loose
Medium
Silt
Sand
Loose
Medium
Sand-silt
Silt
Dense
Medium
Sand
Dense
Sand-silt
Dense
Sand
Very Dense
Sand-silt
Dense
Gravel
Very Dense
Sand
Table 4-3 - API RP 2A (2000) design parameters for Cohesionless Siliceous Soil
15
4.1.2.
Open ended vs. closed end piles
The calculations of the axial capacity of a driven pile must consider the condition of the pile at its tip. For
the case of a closed-end pile it is clear that the end bearing area corresponds to the physical area of the
pile, in this case no internal shaft friction is possible.
In the case of an open ended driven pile, the condition at the tip must be evaluated for two scenarios:
"
The pile is plugged at its tip. For this case the contribution of the plug must be evaluated by
comparing the end bearing capacity of the plugged end area and the shaft friction of the column of
soil against the inner area of the pile. The smallest value will control.
"
The pile is unplugged at the tip, in this case the end bearing area corresponds to the physical
annular end area of the pile.
4.1.3.
End bearing capacity
The tip resistance of a pile is calculated from the unit end bearing capacity of the soil times the end
bearing area of the pile in contact with the soil.
The unit end bearing capacity is calculated by modifying the effective vertical stress by a dimensionless
bearing capacity factor Nq, (included in Table 4.3) as expressed in equation (4-2). Recall that the unit end
bearing capacity for the API-00 method is defined as the base resistance for a pile tip displacement
equivalent to 10% of the outer diameter of the pile.
qbo.1 = Nq -a ' 0 < qbO.1 11
(4-2)
The maximum limiting values of unit end bearing capacity (qo.iiim) for different densities are tabulated in
Table 4.3; Nq values are also included.
4.2.
FUGRO-05
The Fugro-05 design method was developed by Fugro Engineers B.V. for the Fugro Group, an
engineering support company that specializes in geotechnical, survey, and geoscience services
(www.fugro.com).
16
Shaft resistance
4.2.1.
For compression loading the unit shaft friction is defined as:
C
0.05
Zf
=O.O8.q
Pa
Pa
-0.9
)"
R
0.05
rf =0.08 -q
for h/R* > 4
(4-3)
for h/R* < 4
(4-4)
R*
I
C )4R*)
(4).0.9
aO*
h
Pa
For tension loading the unit shaft friction is defined as:
. =0.15 -M
-0.85
max
-'
r,=0.045.q
hPa
L
C
,4
(4-5)
where:
z
q, = cone tip resistance
C-'vo = vertical effective stress at depth z
h
=
distance measured from the pile tip,
Pile
length
h = pile length - depth z
R
=
-.b
4- 2R=D
outside radius of pile (D/2)
Ri= inside radius of pile (Di/2)
R* = equivalent radius = (R2 -R12) 0.
R* = R for closed end piles
Figure 4.2 - FUGRO-05 dimensional parameters
4.2.2.
End bearing capacity
The unit end bearing is related to the average cone tip resistance (q, ) and area ratio (Ar). The cone
resistance at the tip should be averaged over a distance ± 1.5 pile diameters from the pile tip following
the recommendations presented by Bustamante & Gianeselli (1982)
qO 1-=
Pa
where:
8.5.- -C-
-- >0.5
A,
(4-6)
Pa)
q = cone tip resistance averaged over a distance ± 1.5 D from the pile tip
Ar = area ratio = 1 -(Di/D) 2 ; Di = 0 for closed end piles
17
ICP-05
4.3.
The ICP design method was developed from field measurements with the Imperial College Pile at the
University of the same name in London, UK. The shaft capacity equations were based on measurements
made using a closed-ended instrumented pile and soil mechanics principles. The equations were later
revised to include hypotheses made for open-ended piles and confirmed in full scale load tests. The ICP
method has been used in the industry since 1996 and has been validated on a database of 65 pile tests
(Chow 2005).
4.3.1.
Shaft resistance
The method provides distinct approaches for calculating the unit shaft resistance based on the axial
loading condition of the pile.
Pile under COMPRESSION loading
if
= 0-',f-tan , = (-'r,
+A
-'rd
tan t5,
(4-7)
where
5=
constant volume interface friction angle
O'rf = radial effective stress at failure = (O-'rc +A
-'rd
C're= radial effective stress after installation and equalization
A
U',d
= change in radial stress next to the shaft during axial loading of the pile
The value of the constant volume interface friction angle should be measured directly in laboratory
interface shear tests, but may be estimated as a function of mean effective particle diameter (D 50) (Figure
4.3.)
The radial effective stress after installation and equalization (a're ) is defined for this method as follows:
at', =0.029 -
a 0
Pa
.
,8
max
(4-8)
R3
where:
ge = cone tip resistance from CPT
('),
= vertical effective stress at depth z
h = distance measured from the pile tip; h = pile length - depth z
18
R
=
outside radius of pile
Ri= inside radius of pile
R* = equivalent radius = (R2 -Ri 2 )O-; R* = R for closed end piles
For the case of piles with a non-circular cross section (closed-end), the value of R* corresponds to the
radius of a circle with equivalent base area to that of the non-circular pile:
R*=
(4-9)
where:
A = gross sectional area of pile (non-circular)
This assumption is only validfor unit shaftfriction, i.e. perimeter calculations, and should be modified
for unit end bearingcapacity area calculations,please refer to correspondingsections!
The change in radial stress (A a',d) is related to dilation at the pile interface during loading. This dilation
(lateral expansion) can be calculated using a cylindrical cavity expansion analogy.
ACT',
= 2G
Ar
(4-10)
-
R
where
A r = interface dilation, it is estimated at approximately 0.02mm for a lightly rusted steel pile.
G = shear modulus of the soil
R = outside radius
Lehane et al. (2005a) suggest to determine the shear modulus from the small strain shear modulus
(i.e. G = GO), and indicate that this can be estimated as a function of the cone tip resistance from Baldi et
al. (1989):
Go = q
.0203 +0.001257 -1.2lx0-5q
and )r=q/('vo pa) 0 5
(4-11)
It was found during the calculation phases of this study that Equation (4-11) produced "jumps" for certain
values of cone resistance (qc) which corresponded to a ratio of log(q/a'vo) = 2.11. This unusual behavior
was verified by comparing Equation (4-11) with the data provided in the original paper by Baldi et al.
(1989). It was calculated that the equation that best fitted the data presented in a figure in that paper
(Figure 5 -
Q, vs. Go correlation
for uncemented predominantly quartz sands) is of the form:
19
-0.7503
Go = q, .1504.1.
(4-12)
c
In this study, Equation (4-12) was used in substitution of Equation (4-11) for calculating the small strain
modulus.
Pile under TENSION loading
Vf = a.(0.8 - a',+A a',d) tan 5,
(4-13)
where
a = 1.0 for closed-end piles and 0.9 for open end piles
Refer to previous section for description of other factors in equation (4-13).
4.3.2.
End bearing capacity
Closed-endpiles
The unit end bearing is considered in this method as a function of the average cone tip resistance (qc)
and pile-cone diameter ratio (D/DcpT). The cone resistance at the tip should be averaged over a distance
± 1.5 pile diameters from the pile tip following the recommendations presented by Bustamante et al.
(1982).
The formula for the normalized unit end bearing follows:
qbo.
/(qc)= max
I - 0.5 log( DU
, 0.3
( 4-14 )
where:
q = cone tip resistance averaged over a distance ±1.5 D from the pile tip
Dcr = 0.036 m
20
/
Equation (4-14) sets a lower bound to the ratio
1-0.5log
q* II
) at a value of 0.3, one can calculate by setting
D ) = 0.3, that the maximum pile diameter that satisfies this equation is D = 0.9 m, meaning
(DCPr
that the development of the method, and hence its applicability, is limited up to this value.
For the case of piles with a non-circular cross section (closed-end), the method considers that the value of
the unit end bearing (qo.1) does not vary due to area size or shape effects at the pile tip (i.e. area ratio, Ar),
therefore the method recommends to calculate the unit end bearing, as follows:
qbO.
/(q
(4-15)
0.7
Open-ended piles
The method defines two possible states of an open-end pile, completely plugged or unplugged. The
criteria to determine if a pile should be considered as plugged is indicated in the next equations:
Di < 0.2 (Dr-30)
(4-16)
Di< 0.083- -Pa
( 4-17 )
DCPT
where:
Di= inside diameter of the pile in meters
Dr = relative density expressed in percentage
*
Plugged piles
Given that a plugged condition in the pile tip is estimated by the previous method, the unit end bearing
capacity (qo.1) can be calculated with the following equation:
qbo./(qc)= max 0.5 - 0.2 5 log(D
,0.15, Ar
(4-18)
where:
Ar = area ratio = 1-(Di/D) 2
/
Equation (4-18) sets a lower bound to the ratio qbO. I
) at a value of 0.15, one can calculate that the
maximum pile diameter that satisfies this equation is D = 0.9 m, equal to the limit set forth by the method
for closed-end piles.
21
*
Unplugged piles
In the case of an unplugged open-end pile, this design methods assumes that the unit end bearing is
provided by the annular pile area alone (no contribution of the inside shaft resistance) and it is a function
of the average cone tip resistance and the area ratio of the pile (a size effect factor):
qbO.I/(q)
Note by comparing equations (4-18) for the condition of
qbo.
(4-19)
A,
=
0.15 and equation (4-19) that it is
possible for an unplugged pile to have higher unit end area capacity than a plugged pile.
4.4.
NGI-05
The Norwegian Geotechnical Institute (NGI) design method was established from a data base from high
quality pile tests in sand. (Clausen et al. 2005). The method determines the unit shaft resistance in tension
at a point along the pile's shaft as a function of the relative density of the material, the state of effective
vertical stress, the location of the point in relation to the total depth of the pile, and the condition of the
pile tip: rskin tension = f (Dr, a-'yo , z/zti, , open/closed tip)
The method assumes that the unit shaft resistance of the pile in compression is related to the tension case
by a correlation factor of 1.3:
Tfcompression=
1.3 x tf tension
The unit end bearing capacity is defined for the NGI design method as a function of the cone resistance,
the relative density, and the condition of the pile tip: qtip = f (q; , Dr, open/closed tip)
4.4.1.
Shaft resistance
The unit shaft resistance along the pile is given as:
=Dr
Ztip
-
Fd
- Fj, - F.,
-F
(4-20)
The unit shaft resistance is set to have a lower limiting value given for each point along the pile as:
Tf (z)> 0.1- ',
(4-21)
where:
zei,= pile tip depth
22
pa = atmospheric pressure, expressed in units corresponding to the desired unit shaft resistance
FD. = 2.1(Dr-0.1) 1 7 , with Dr expressed in fractions.
Fload =
1.0 for tension and 1.3 for compression
F
=
1.0 for driven open ended piles, and 1.6 for closed-end piles
Fmat
=
1.0 for steel and 1.2 for concrete
Fsig
(a'vW/pa)~
25
calculated at the depth (z) of the point of interest.
The method introduces a ratio of z/zti,. This value relates the depth of any point along the pile shaft to the
depth of the pile tip. The values of depth should be measured from the top soil elevation, not the pile
head. This ratio includes an effect of reduction of the side friction with depth. This effect is related to the
friction fatigue of the material around the pile. As the pile is driven deeper into the soil, the upper layers
of soil will experience more disturbance from the passing pile than the lower layers.
The NGI method calculates the relative density (Dr) from the cone resistance, (qe):
Dr =0.4- ln
1
c
22(o', pa )O.P
_
(4-22)
The previous equation can provide values of Dr > 1, these values should be used. NGI also developed a
best fit relationship to correlate standard penetration test values (NI) to cone resistance equivalence. The
correlation is as follows:
qc =2.8 - N, -Pa
(4-23)
The measured N 1 values correspond to blow counts corrected for a reference confining pressure of 1 atm,
as introduced by Peck et al. (1974):
N =CN - N
where:
CN = 0.77log
(4-24)
20
( 'YV (TSF)
N = Standard penetration resistance measured in the field (Blows/ft)
4.4.2.
End bearing capacity
The unit end bearing capacity is defined for the NGI design method as a function of the cone resistance at
the pile tip level (q,up), the relative density (Dr), and the condition of the pile tip: open or closed end.
23
For the case of a driven closed-end pile the unit end bearing capacity is expressed as:
=- 0.8
(4-25)
'''
1+ Dr
q
For the case of a driven open-end pile the unit end bearing capacity is calculated from the smallest value
of the core resistance (internal side friction of the plug-pile and base resistance of the annulus of the pile),
and the base resistance of a plugged condition.
The core resistance is calculated assuming that the state of stress of the soil against the pile annulus
corresponds to cone resistance, qg, and that the value of internal side friction of the plug-pile interface is
equal to 3 times the external value of the unit shaft resistance.
The end base resistance of the plugged portion of the pile is expressed as:
qbo.1 =
'0.7
(4-26)
l+3D,.
4.5.
UWA-05
The UWA-05 method was developed at the University of Western Australia, at Perth, Lehane et al.
(2005b). It was proposed based on the findings of a review process of the previously described CPT based
design methods, performed at UWA at request of the API sub-committee on piling (Lehane et al., 2005a)
and against a wider load test database that comprised 231 tests.
4.5.1.
Shaft resistance
The method provides the same approach for calculating the unit shaft resistance for compression and
tension loading, the only difference being the reduction of the shaft resistance by 25% for the case of the
tension loading.
Vf = af'
ta
=
','d
(4-27)
where
'rf = local shear stress at failure along the pile shaft
5,
= constant volume interface friction angle
24
O'fr
= radial effective stress at failure = (a'rc +A
-'rd)
a'c= radial effective stress after installation and equalization
A u'rj = change in radial stress due to loading stress path
f/fe = 1 for compression loading and 0.75 for tension loading
The value of the constant volume interface friction angle (8cv) is related to the relative roughness of the
steel and the soil (Uesugi et al. 1986) and it should be measured directly in laboratory interface shear
tests, but it may be estimated as a function of mean effective particle diameter (D 50 ) indicated in
Figure 4.3.
The radial effective stress after installation and equalization is defined for this method as follows:
a'
=0.03 -q - Ar,f 0 3. maxC,2
]-0-5
(4-28)
where:
qc = cone tip resistance from CPT
Areff = effective area ratio = 1 - IFR(Di/D) 2
IFR = Incremental Filling Ratio
Di= inside pile diameter. (Di = 0 for closed ended piles)
D
=
outside pile diameter
h
=
distance measured from the pile tip; h = pile length - depth z
A simplified approximation for IFR averaged for the last 20 pile's diameters of penetration is considered
to be a function of the pile inside diameter (Di) is given as:
Dj: expressed in meters
IFRavg = min 1L1,JJ
(4-29)
The change in radial stress is assumed for this method to be minimal for full scale offshore piles, it can be
expressed using a cylindrical cavity expansion analogy:
Ar
A-'rd = 4G--
D
(4-30)
where
A r = interface dilation, it is estimated at approximately 0.02mm for a lightly rusted steel pile.
25
G = operational shear modulus of the soil ( G = G. is assumed). The method suggests to
determine the shear modulus from an equation based on Baldi et al. (1989):
G=q, .185*q
= (q
qclN
(4-31)
1 Nj0.
(432)
a )05
a
For the case of piles with a non-circular cross section (closed-end), the value of R* corresponds to the
radius of a circle with equivalent base area to that of the non-circular pile.
32 Employed for
databaseovaluation
I
Li I
11
30
T
26-
24e-1r4-4
e4c-4
t+o+
I
I
I
i
I1II
-
l
|
|
F
I
-
F1
I
1I
liii
LLt[I42
1T-T11
III'III
I
-
i
I- -
26ILJ~44L
22
I
I- I
I..4
1-4
FT
1 TT17F117
-r-
I
i i|
III!
I
l
i
i
I i
I
l
i
i
I
i
i
I Il
11111||
20
0.01
0.1
1
10
Median Grain Size, D5o (mm)
Figure 4.3 - Interface friction angle, 8, variation with D 50 (Lehane et al. 2005c)
The UWA-05 and ICP-05 share the same basic formulation for calculating unit shaft frictions (e.g.
equation 4.27 and 4.8 respectively), but differ in the estimation of the degree of soil displacement caused
by pile installation. In the UWA-05 method, the final degree of displacement is expressed in terms of an
effective area ratio, A,,eff, (Equation 4-28). This ratio accounts for the degree of displacement that is
imparted to any given soil strata during pile installation, i.e. the displacement experienced by that strata
when it was located in the vicinity of the tip during driving. The effective area ratio is unity for closed-
ended piles; for open-ended piles, this ratio accounts for the soil displacement due to the pile material
itself and the additional displacement imparted when the pile is partially plugging or fully plugged
during installation (Lehane et al. 2005c).
26
4.5.2.
End bearing capacity
In this design method the unit end bearing is determined in a general case for open and closed ended piles
without the explicit consideration by the user of a plug formation at the pile's tip. In this regard the
method is user independent. The unit end bearing capacity for a displacement, 6 = 0.1 D, at the head of
the pile is given by:
= 0.15 +0.45 -A,,,
qbO.
(4-33)
where
q = cone tip resistance averaged using the Dutch method. See Figure 4.4.
In the Dutch method, the pile outside diameter (D) should be used for closed-end piles, while an effective
diameter must be used for open-end piles.
The effective diameter should be calculated using this equation:
D= D (Arb,eff
(4-34)
where:
Arb,ff= effective area ratio, which is unity for a closed-ended or fully plugged pile.
Arbeff
=1 - FFR -(D /D) 2
(4-35)
FFR = Final Filling Ratio, measured at the end of pile driving, and averaged over a distance of 3
diameters from the pile tip.
An approximate formula for estimating FFR as a function of the pile internal diameter (Di), is given by:
0.2~
FFR =min 1, 1.
Di: expressed in meters
(4-36)
Lehane & Randolph (2002), have shown that, if the length of the soil plug is greater than 5 internal pile
diameters (5Di), the plug will not fail under static loading, regardless of the pile diameter.
27
Procedure:
Cone resistance qc
1 = Average q. over a
distance of yD below the pile
tip (path a-b-c). Sum q,
values in both the downward
2
e
0
(path a-b) and upward
(path b-c) directions. Use
actual q values along path a-b
?
and the minimum path rule
along path b-c. Compute q.,
for y values from 0.7 and 4.0
and use the minimum q.
values obtained.
48D
qc2 = Average q. over a
distance of SD above the pile
tip (path c-e). Use
the minimum path rule as
for path b-c in the q%
Envelope of
minimum q, values
c
I
b
,a
6
computations. Ignore
any minor 'x' peak
depressions if in sand,
but include in
minimum path if in clay.
F
i-
Figure 4.4 - Determination q, using the Dutch averaging technique (Lehane et al. 2005b)
The authors of the UWA design method indicate that the Dutch averaging procedure provides similar
results (q, ) as the procedure of averaging the cone tip resistance over a distance ± 1.5 pile diameters
from the pile tip recommended by Bustamante et al. (1982), given that the values of qc do not vary
significantly at the pile tip.
For offshore conditions the CPT profiles are often not continuous, and therefore the UWA authors present
a conservative approach for averaging q, , Figure 4.4:
qC = (qca, --
cby
)2
(4-37)
where:
qca = is the minimum value of qc over the depth interval extending from the pile tip to a depth of
between 0.7 D* to 4 D* (D* as in equation 4-34)
qcb =
is the average qc value from the tip of the pile to a height of 8 D* above it.
28
Simplified UWA-05 desian method
4.5.3.
The UWA methods presents a simplified version of the method applicable to offshore piles with diameter
equal or larger to 1.00 m. For this dimension the incremental filling ratio (IFR) is equal to unity, and the
stress loading path tends to zero (A cr'rd ~ 0), and equation (4-27) takes the form of equation (4-38) in
compression and equation (4-39) in tension.
Shaft friction in compression
4.5.4.
F(h~ \-0.5
,2
L D JJ]
0.3
=0.03 -q, - A,m.3 Max
(-8
( 44-8
Shaft friction in tension
4.5.5.
=0.75-0.03 - q - ,.3 [max
,52)]
(4-39)
where:
q,= cone tip resistance from CPT
Ar
4.5.6.
=
area ratio = 1 - (Di/D) 2
D
=
outside pile diameter
h
=
distance measured from the pile tip; h= pile length - depth z
End bearing
qbo.1
/(qc = 0.15 +0.45 -Ar
(4-40)
where
2
Ar = area ratio = 1-(Di/D)
Di= 0 for closed-end piles.
29
5.
CALTRANS PILE DATA
The California Department of Transportation (Caltrans) gathered information from hundreds of pile load
tests performed since the 1960's on driven piles, and adjusted it to create a data set of 319 tests performed
on 227 piles at 75 bridge sites (Olson and Shantz, 2004). Most of the tests were performed in heavily
populated areas along the California coast (Figure 5.1).
Eureka
San
Rosa
0
PC
ento
ac
0 Mode
Bay
Area oSalins
*P
Visalia
an
0
Figure 5.1 - Caltrans Test sites (Olson and Shantz, 2004)
Mr. Thomas Shantz, Senior Research Engineer at Caltrans, kindly provided data from 6 project sites in
Los Angeles and San Francisco for this research project.
The information provided included site characteristic reports, CPT soundings, and pile load-deflection test
results. The following table provides a summary of the available information for each of the six sites,
arranged under an arbitrary numbering system (MIT #) that will be used in this document to reference the
pile information in a brief manner.
MIT ID
1
2
3
4
5
6
MITID
ride lcatonCPT
Bridge location
North East Conn. OC, Br. No. 57-783F
Los Coyotes Diagonal, Br. No. 53-1193S
Rte 2/5 Separation Bent 10, Br. No. 53-527L
SFOBB Bent E31R, Br. No. 33-0025
Mission Ave. Via., Br. No. 57-1017R/L Bent 2L
La Cienega-Venice Sep. Bent 5, Br. No. 53-2791S
Sounding
UTC-40
-
UTC-27
UTC-09
UTC-37
UTC-28
Site report &
Load Test
38-01
56-01
62-01
86-01/02
87-01/02
88-01
Table 5-1 - Available information matrix
30
5.1.
Pile-site characteristics report
The report, written in MathematicaC format, is an overview of the pile and site characteristics for any
given site. First, it discusses the agreement between available data, e.g. SPT tests, boring logs, laboratory
testing, driving records, CPT soundings; and provides general comments on the results of the load tests,
the pile behavior, and on any other relevant information.
Next, a data quality assessment is done by assigning grade values to the data relative to a rating criteria
developed for the database. This rating has qualitative meaning only within the Caltrans dataset, therefore
it will not be considered in this study.
A description of the pile physical properties and dimensions; and soil profile follows. The parameters
reported for each layer include: Undrained Strength (psf), set to zero for sands; N values, set to zero for
clays; and unit weights (pcf).
Finally, a prediction of axial pile capacity based on SPT N values correlations is presented. For
calculation purposes, the report estimates the N values of clays based on a correlation with the undrained
strength (Olson and Shantz, 2004).
5.2.
CPT profiles
The cone penetration test (CPT) profiles provide continuous readings at 0.05 m depth increments for tip
resistance (q), sleeve friction (fs), and shoulder pore pressure (u 2) for all of the sites. The data is presented
in an Excel spreadsheet where the
1s
column describes the depth in (meters), the 2d column the tip
resistance in (tsf), 3" column the sleeve friction in (tsf), and the 4h column the shoulder pressure, u2 , in
(psi). The data was transformed into SI-units for the purpose of this study.
5.3.
Load tests
Load-displacement pile tests were provided for each site. Piles MIT-4 and MIT-5 included both up-lift
and compression readings. The remaining piles only included up-lift load tests.
31
Pile and site data overview
5.4.
MIT
ID
CPT
Sounding
No.
1
2
3
4
5
6
Top of
Sounding
Elevation
(ft)
Top of
Sounding
Elevation
(m)
35
0
361
14
36
88
10.67
0.00
110.06
4.27
10.98
26.83
UTC-40
-
UTC-27
UTC-09
UTC-37
UTC-28
Table 5-2 - CPT soundings
MIT
ID
Surface
Elevation
Watertable
depth
Watertable
Elevation
Footing
elevation
Pile top
elevation
Pile Tip
Elevation
(m)
(m)
(m)
(m)
(m)
(m)
13.11
14.94
13.72
13.26
10.37
16.46
-6.71
-10.67
94.97
-12.96
-1.83
8.23
7.32
5.79
110.52
0.30
9.45
25.30
6.40
4.27
108.69
0.30
8.54
24.70
4.88
-0.61
97.56
0.30
6.40
19.97
1.52
4.88
11.13
0.00
2.13
4.73
8.54
6.10
110.06
3.05
10.67
27.13
1
2
3
4
5
6
Pile
embedment
length
(m)
Table 5-3 - Site information
MTPile
Tip
D type
Pile
MIT
ype ile Tip
________
1
2
3
4
5
6
PP 16x0.5
PP 14x0.44
HP 10x57
Steel
Square conc.
HP 14x89
____
open
open
open
open
closed
open
length
engt
WallAra
Pile
Stick
upk embeded Pile width thicness Perimeter
up
length
Area
Wih
Weigh
(in)
(in)
(in)
(in)
(cm)
(in)
(M2)
(kN)
14.02
16.46
15.55
13.26
11.28
17.07
0.91
1.52
1.83
0.00
0.91
0.61
13.11
14.94
13.72
13.26
10.37
16.46
0.41
0.36
0.25
0.61
0.36
0.36
1.27
1.12
0.00
1.27
0.00
0.00
1.28
1.12
1.03
1.91
1.12
1.45
0.0157
0.0121
0.0108
0.0238
0.0993
0.0168
16.86
15.23
12.90
24.17
26.38
22.01
Table 5-4 - Pile properties
MIT
ID
Load Test Test location
1.27
No.
1
2
3
4
5
6
38-01
56-01
62-01
86-01/02
87-01/02
88-01
North East
Los Coyotes
2-5 Sep
Bent E31 R
Mission Ave
La Cienega
Uplift (mm)
2.54 5.08
(KN)
(KN)
1068
1313
356
1246
490
1513
1068
1522
356
1358
614
1780
I
Compression (mm)
2.54 5.08
1.27
(KN)
(KN)
I (KN)
(KN)
1068
1558
356
1358
614
1958
0
0
0
2493
1148
0
0
0
0
2737
1148
0
0
0
0
2737
1148
0
Table 5-5 - Load-deflection tests
32
6.
SOIL-PROFILE CHARACTERIZATION
The first analytical task undertaken in this study was to interpret various soil parameters for each of the
six sites based on the CPT soundings, and assess the accuracy of those results to confirm the applicability
of the CPT method.
General procedure
6.1.
a) Collect all data pertaining to each of the six sites and reference it according to Table 3. Given that
the CPT soundings and the borehole information included in the Pile-site characteristicsreport
were referenced to different elevations, it was necessary to superimpose and align all the data
relative to a fixed datum. This was done by drawing each profile to scale in Autocad. Each sketch
includes elevations for: the CPT sounding, the surface, the top of pile, the bottom of the footing,
the watertable, the tip of the pile, and for each of the soil layers described in the borehole log. For
each of the soil layers descriptive information included the soil type, unit weight, standard
penetration blow counts (N), and undrained shear strengths.
b) Draw profile of vertical stresses ( a,.; a',O; assuming hydrostatic pore pressures, u.) based on
quoted unit weights of the borehole logs.
c)
Draw CPT profiles for tip resistance, sleeve friction, and shoulder pore pressure (u 2) readings.
d) Draw normalized CPT profiles: i) qc-ayo/J',
0
, ii) f,/q, and u 2/qc.
e)
Detect locations of clean sands, which will occur at Au = (u-u0 )
f)
Detect fine grain deposits, as evidenced by high values of u 2/qc (>0.7) and low values of q.
g)
Label soil layers as probable sands or clays.
h) Calculate the friction ratio (f,/(qt-cor)
0 and relative high values of q.
* 100%) and classify the soil deposits according to the chart
developed by Robertson & Campanella (1988).
i)
Develop correlations of tip resistance vs. depth for various relative densities, Dr. (Jamiolkowski et
al. 2001). Details are provided in section 6.1.2.
j)
Develop correlations of tip resistance vs. depth for various angles of effective friction, j'
(Mayne 2005). Details are provided in section 6.1.3.
k) Calculate maximum effective past pressure for clay layers (For correlations of q, and a'p; Mayne,
2005).
1)
Calculate undrained shear strength (su Dss) for estimated OCR as per Ladd (1991).
m) Calculate cone resistance coefficient Nk~ (qt-avo)/su for clay layers.
n) Graph previous results against depth, and compare them to reference values and correlations.
33
o) Iterate with more detail where applicable to classify definite soil layers.
p) Label interpreted soil profile and compare it to Caltrans profile
q) Repeat cohesionless materials graphs for relative density (i) and friction angle (j), assigning to the
clay layers a value of zero for q.
r)
Repeat graphs (k),(l),(m); for clay layers assigning a value of qe equal to zero for the sand
deposits.
s)
Draw interpreted soil profile with calculated soil identity parameters (s",
', Dr, etc.), and compare
it to Caltrans profile.
6.1.1.
Soil classification
It was mentioned in the preceding heading that the soil profiles were classified using the chart developed
by Robertson and Campanella (1988) for CPT tests. The input parameters of the log chart are based on
the CPT readings, were the abscissa corresponds to the Friction Ratio, and the ordinate to the Normalized
Cone Resistance:
Friction ratio:
"
-100%
(6-1)
(q, o-,)
Normalized cone Resistance:
q'
-
(6-2)
For the sake of this study, and to allow a more expedient sorting of the many data points available for
each site, the soil classification chart was digitized. This permitted superposition of the data points on top
of the digitized chart.
6.1.2.
Cohesionless layers
The relative density (D,) and the angle of effective friction (4') were determined for the cohesionless
layers present in each site. These parameters, not only provide information that allows classification of
the soil deposits, but also they are input parameters of the API-00 and NGI-05 design methods review
herein.
The relative density (D,) was calculated using an empirical equation proposed by Jamiolkowski et al.
(2001), based on the earlier worked of Schmertmann (1976). This correlation relates the relative density
(D,) to the cone tip resistance (q,) and to in-situ the mean effective geostatic stress:
34
O'm =
3
1+2KO )- a'
(6-3)
where:
KO ~0.40
and a', should be expressed in [kPa] to input equation 6-13.
Om'
The relative density equation was developed for unaged, uncemented silica sands of low to moderate
compressibility, and can be rearranged to calculate the tip resistance as a function of vertical effective
stress (thus depth) for selected values of relative density (equation 6-3). The results can be plotted in
design charts with a family of curves representing the range of the relative density, the outcome illustrated
in Figure 6.6.
qC
=eC2D,
.C 0 .(Y
:)c
(6-4)
where:
C2
=
2.96, C1 = 0.46, C0 * = 300
Dr
=
relative density (in decimals)
K,~0.40
qe and am' are expressed in [kPa]
The angle of effective friction (#') was assessed in a similar manner as the relative density. Design charts
were developed for each site, by means of an equation (6-5) proposed by Mayne (2005) based on
empirical CPT relationships developed from statistical analyses of data measured in a calibration
chamber.
#'=17.6* + I
- log(
U- 1
( 6-5 )
Mayne (2005) concludes that the empirical equation compares well to measured data obtained from
results of undrained triaxial compression tests performed on high quality samples at four river sites
(Mimura 2003). The following figure illustrates the comparison.
35
50
IN Yodo River
X Natori River
451
-
a)
4)
Tone RiverI---------40 Edo River
a
*K&M90
40
351 - --
-- -
#'(deg}= 17.6 +11.0. -10
30
0
. ..200
100
.
-
300
Normalized Tip Stress, qt1
Figure 6.1 - Comparison of measured
#'
from frozen samples vs. qt (Mayne 2005)
The transformed equation that allows plotting the cone tip resistance against the vertical effective stress
for given values of angles of effective friction is presented:
(
'17.6*
q ~=o,1i
(6-6)
11'
where:
qt and avo' are expressed in units of atmospheres.
Figure 6.6 includes the design charts calculated for pile MIT-4.
6.1.3.
Fine grain (Clay) layers
Three parameters were determined for identification of the clay layers, these were: overconsolidation
ratio, undrained shear strength, and cone resistance coefficient. The details of their required calculations
follows.
The maximum effective past pressure (a'p) for clay layers was determined using an analytical formulation
developed by Mayne (2005) on the basis of spherical cavity expansion theory and critical state soil
mechanics concepts. The formulation relates the overconsolidation ratio (OCR = Zi) in clays to CPT
V0
parameters in the following simplified form for intact clays:
36
o-'P = 0.33-(q, -o-)
[[kPa]
(6-7)
Mayne (2005), indicates that the validity of equation (6-7) was confirmed by statistical analysis of
piezocone-oedometer data in a variety of clays. Figure 6.2 illustrates the agreement in the data.
100W0
ow
1100
tit
1000
100
10000
Net Cone Restdtmice, q,-a,
(IWO.)
Figure 6.2 - Preconsolidation Stress in Clay from Net Tip Stress (Mayne 2005)
The undrained shear strength (su) was calculated following the empirical equation presented by Ladd and
Foot (1974) and Ladd (1991), which correlates a power function of the overconsolidation ratio (OCR
=
a,'/ av') and the effective stress of the clay; to its undrained shear strength ratio.
=S-OCR m
((
(6-8)
I/DSS
where:
S = undrained strength ratio of K0 normally consolidated clay
m= is an empirical coefficient
Extensive correlations (Ladd, 1991) show S = 0.22, and m = 0.80.
The cone resistance coefficient (Nk) is proportional to the ratio of the net tip resistance and the undrained
shear strength as indicated in the following equation.
NkNk
(
t - avoJ
*
(6-9)
SU
Empirical correlations established from undrained shear strength measured in direct simple shear tests
(su
DSs)
report values of Nk that vary in a range of 15 ± 5. The quoted range for Nk implies that the
37
undrained strength can vary is as much as 50% (Whittle, 2005). Nevertheless, in this study, the cone
factor,
Nk,
is used to confirm the existence of clay deposits based on piezocone readings that provided
results within the mentioned range, and not to provide insight on the value of the undrained shear
strength, which was estimated beforehand. Under this premise, the applicability of Nk in this investigation
is validated
Site interpretation results
6.2.
The outcome of the interpretation of the soil profiles is presented in a set of charts and a diagram that
illustrate the main findings of the investigation, and that define the profile that will be used for predicting
the axial pile capacity for the methods under consideration in this study. The site investigation
information for each pile location consists of the following documents:
*
Pile-soil elevations diagram
*
Chart A - Vertical profile, CPT readings
*
Chart B - CPT normalized profiles
*
Chart C - Internal friction angle and relative density graphs
*
Chart D - Undrained strength (se) Cone Resistance Factor (Nk), Overconsolidation Ratio (OCR)
*
Chart F - Soil Classification as per Robertson and Campanella (1988)
For the sake of illustration, a detailed description of the site interpretation results for pile MIT-4 will be
presented in the main body of this document, whereas for the remaining piles only a summary will be
presented, their corresponding set of detailed charts can be found in the Appendices.
6.2.1.
Pile MIT-4
Section 6.2 - Site investigation results, indicated that six diagrams are produced as the result of the site
interpretation for each pile. These diagrams are included in this section for pile MIT-4 with a detailed
description of their main findings. The descriptive sequence of the interpreted soil profile and the
presentation of the diagrams will start at the pile top and move toward its tip.
Pile MIT-4 is a 13.26 m long, 0.61 m in diameter open-ended steel pipe (Figure 6.3). The pile top is
located at elevation (El.+0.30
in),
under approximately 4 meters of a hard material that comprises a
38
compacted fill. This layer acts on the pile solely as overburden. The water table elevation provided by
Caltrans is near the pile top at elevation (El. +0.3 m), (Figure 6.3).
Below the fill, there is a 4 m thick recognizable layer of sand (El. +0.30 m to El -3.88 in). In this layer the
pore pressures readings (u 2), Figure 6.4d, indicate that the excess pore pressures created by the piezocone
penetration is almost zero (Au = u 2-u0 ~ 0),which is typical behavior of clean sands; additional
confirmation, is provided by the high readings of the tip resistance (qc) in Figure 6.4b; and the low values
of the normalized pore pressure factor (u 2/qc) in Figure 6.5c. Review of the relative density (Dr) and angle
of internal friction (b') correlations of section 6.1.2, are presented in Figures 6.6a and 6.6b, respectively.
These data indicate that the layer comprises two recognizable subunits. The first layer (El. +0.42 m to
El. -1.23 m) exhibits "lower strength" compared to the denser layer below (El. +1.23 m to El -3.88 in),
Figure 6.3. The Robertson and Campanella (1988) soil classification ranks these layers as group 6: Sands
- Clean sand to silty sand, as can be appreciated in Figure 6.8b for their corresponding elevations. The
interpretation of this layer as sand matches almost identically with the profile interpreted by Caltrans,
Figure 6.3.
From elevation (El. -3.88 m and El. -9.43 m) there is a layer where the tip resistance readings drop to
small values, while excess pore pressures develop (Figure 6.4b and 6.4d). For this layer the normalized
pore pressure factor (u2/qc) in Figure 6.5c reaches ratios higher than 0.4. The previously described
behavior is expected for clay layers. The existence of a clay layer is confirmed by the calculated
undrained shear strength, of approximately 45 kPa (Figure 6.7b), which is very close to the values
measured in laboratory UU-tests by Caltrans and included in Figure 6.3. The cone resistance factor for
this layer (Nk
=
15) are exactly on the average of the reported values in the literature (Aas et al. 1986).
Robertson and Campanella (1988) classify this layer as group 3: Clays - Clay to silty clay. Figure 6.8b
illustrates that there is very small variation in the input parameters for the soil classification, and that the
values are clustered together well into the clay groups (Groups 3 and 4); providing un ambiguous
evidence of the existence of clay (Figure 6.8).
Below the clay layer, (i.e. below El. -9.43 m) there are 4 meters of variable tip resistance (Figure 6.4a)
that indicate the existence of a layer of increasing density, with traces of a weaker material (e.g. El. -12.00
m). The readings of excess pore pressures (Figure 6.4d) indicate that this layer does not effectively
dissipate the excess pore pressure created by the piezocone probe, thus indicating that the layer is not a
clean sand. The normalized pore pressure factor (u2/qc) included in Figure 6.5c, decreases rapidly from
ratios of 0.4 to almost zero, indicating that the presence of cohesionless materials increases with depth.
39
This appreciation is confirmed by the classification of Robertson and Campanella (1988). From elevation
El.-9.43m to El.-10.93 m it ranks the layer as group 5: Sand mixtures, from El.-10.93 m to El. -11.98 m as
group 6: Sands, then from El. -11.98 m to El. -12.13 m as group 3: Clays, and at the bottom of the layer
from El. -12.13 to El. -13.38 as group 6: Sands, as indicated in Figure 6.8b. From the previous description
it is concluded that this layer comprises a sand matrix that increases its density with depth, with an
embedded thin clay layer at El. -12.00 m. The relative density (Dr) and angle of internal friction (')
correlations (Figure 6.6a and 6.6b) provide the means for subdividing the sand matrix into three sublayers that match the elevations described in the Robertson and Campanella (1988) classification and that
are illustrated in Figure 6.3. The embedded clay layer at El. -12.00 m is thin but exhibits stiff properties.
The calculated measured of undrained shear strength (Figure 6.7b) varies between 150 kPa and 300 kPa,
but given the small of the clay layer, a lower value of 150 kPa is assigned to this layer. The Caltrans soil
profile fails to recognize this clay layer, this is expected, as its site exploration was performed during the
execution of the standard penetration test, in which sampling occurs at intervals larger than the clay layer.
It should be noted that the pile tip is located in this sand matrix layer, at elevation -12.96 m.
From El. -13.38 m to El. -15.08 m, the cone tip resistance increases continuously, indicating the presence
of sands. This is confirmed by the normalized pore pressure factor (u2/qc) in Figure 6.5c, where the ratios
are equal to zero. Robertson and Campanella (1988), Figure 6.8b, classify this layer as group 6: Sands.
The relative density is estimated using the Jamiolkoski et al. (2003) correlation at 80%. The angle of
internal friction is estimated at 43 degrees (Figures 6.6a and 6.6b).
At the bottom of the CPT exploration data a 0.5 m thick clay layer can be identified on top of the
beginning of a sand layer. The clay layer is identified by the low values of cone resistance (Figure 6.4a)
and by the Robertson and Campanella (1988) classification. Figure 6.3 includes both the Caltrans and the
interpreted profile, together with the significant pile elevations and characteristics.
40
Pile - ID # 4
Type of pile:
End condition:
Diameter:
Thickness:
Base area of pile:
Perimeter:
Weight of pile:
CPT Top
Surface
Steel pipe pile
Open ended
0.61 m
0.5" (1.27 cm)
0.0238 m2
1.91 m
24.17 kN
CALTRANS Soil Profile
+4.27
Soil
type
Ysail
N
Su
[kN/m3]
[bpf]
[kPa]
-
19
-
-
+3.05
Interpretation based on CPT
+4. 27
57
+2. 7
+2.
2.75
Top of pile
Bott. footing
Water table
+0.30
Fill
I
. ,-
q
18.8
-
-
Soil
*
Dr
su
type
[0]
[o
[kPa]
Fill
-
-
-
Clay
-
-
20
Sand
40
60
-
Sand
38
50
-
Sand
40
55
-
Clay
-
-
42.50
Sand
38
40
-
Sand
40
65
-
+0. 42
+0.30
-1.2 3
Sand
18.4
21
-
-3.96
0.61
-3.8 8
--
D)
Clay
13.26
Elevations
(m)
14.9
-
42.50
-9.15
-9.4 3
Sand
19.5
26
-
-10. 93
-11.59
Pile tip
Sand
20.4
43
-
-
-
150
43
80
-
Sand
43
80
-
-15. 08 7T
Clay
-15. 4
-15. 63 jSand
-
-
125
38
45
-
-13. 38
Sand
-15.63
-15.85
Cla
Sand
-12.96
-13.72
CPT Tip
-11. 98
-12. 13
20.4
49
-
Figure 6.3 - Pile MIT-4- Pile-soil elevations diagram
41
MIT-4
MIT-4
0
MIT-4
MIT-4
0
60,000
500
1000
5.
5
5
-100
5
4.
4
4
4
200
0
400
20,000
I
40,000
I
400
I
3
3
2
2
1
1
I
I
I
0*
0
-1 -
-1
-3.
-4
d
-5.
I
,
-5
C- -6-
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
-6
-7.
-7
-8
-8
-9
-9
I
'
-10
-11
I
I
I
I
I
I
I
-13-14-
I
I
-12
-12
,
--
U0
'
'
-15-
-15
-16-
-16
- - - uO ---
s'vo --
svo, kPa]
1
1
0
-3
-4
-4
-5
-5
-6
-6
-7
-7
-8
-8
-9
-9
-10
-10
-11
-11
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
-
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
-3
I
I
-
-2
-2
1400
*
S
U
I
*
I
I
I
I
I
I
I
I
I
I
I
£
-12
-12
-13
-13
I
I
-14-
-14
I
I
-15
-15
-16
-16
I
I
I
I
-13
-14
2
I
-10
-11
2
I
I
I
[j
3
-1
-3
-4
3
0
-2
-2
I
I
900
I
I
I
I
I
I
I
I
-Tip resistance (qc), kPa
-Sleeve
friction (fs), kPa]
-
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
*
I
I
I
Pore pressure (u2) - - - uo, kPa
Figure 6.4 - Pile MIT-4 - Chart A - Vertical profile, CPT readings
42
MIT-4
0
100
200
300
MIT-4
MIT-4
400
0.000
500
5
5-
4
4-
3
3
2
2.
0.050
0.100
0.150
-0.100
0.150 0.400 0.650 0.900
1
0
0
-1
E
-4
-2-
-3 -
-3
-4
-4-
-5U
-5 -
-6
-6-
-7
-7-
w
-8
-9
-2
-10
-11
-12
-12-13
-13-
-13
-14
-14
-14
-15
-15-
-15
-16
-16
-16
I-(qc-sv)/s'vo I
- -fsqc
|---
u2/qc
|
Figure 6.5 - Pile MIT-4 - Chart B - CPT normalized proffies
43
MIT-4 - Correlation z vs q, [kPa] for various D,
(Jamiolkowski 2003)
MIT-4 - Correlation depth vs qc [kPa] for various 0'
(Mayne 2003)
0
10,000
20,000
30,000
40,000
50,000
0
60,000
10,000
20,000
30,000
40,000
50,000
60,000
5
4
3
2
4
3
2
1
1:~
V
0
-1
0
-11
:T6
-2
-3-4C
0
-4-5
-5
-6
-6
-31
a)
-8
-9
-10
-11
-124
-13
-144
-15
-16
-8
-10
-11
-12-
A
-13
-14
-15
4
-16
34 36 38
-30
- 38
-46
42
40
-32
40
-- 048
46 =0'(*)
44
- - -34
i
42
qc, kPa
--
50%
0.1
0.5
40%
36
44
'
0.9
60%
80%
70%
-
0.2
-
0.3
0.4
0.8
-
0.7
qc,kPa
0.6
1
100% =D,
90%
Figure 6.6 - Pile MIT-4 - Chart C - Friction angle and relative density for cohesionless layers
44
MIT-4 -SuDSS
MIT-4
100
0
0
400
300
200
100
200
MIT-4 - OCR
MIT-4 - Nk
20
10
0
300
0
5-
30
5
5
4
4
4.
4
3
3-
3-.
2
2
2
0
0-
0
I
3
3
-1
-1
-2
-2
-2
-3
-3-
-3
-5 -
11
-74
-4
-7-
-7.
-50
-8
-8
-61
-9I
-4
-9
-9
-5
-10
-10
-11
-11
-112
0
13
-
-3
-13
-13
o'vo
-14
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
-12
-12
-12
I
I
-,-
-10
20
I
-,
-6
-6
I
I
I
15
-4
-5
0
-8I
I
I
I
1
-6
I
I
-3
-1
10
I
I
-2
4
-
5
-14
I
I
-15
-15
- - - U0
-s'vo
-
svo
-16
-16
-16
-16
su Caltrans
su Interpreted, kPa
-Cone
Resistance Factor
E~i~
Figure 6.7 - Pile MIT-4 - Chart D (Undrained strength and stress history of clay layers)
45
1000
::1q 7
MIT-4 - Soil Classification
(Robertson & Campanella, 1988)
I
8
.-
11 1 Vl
I-
94
0
5
4
>
3
.U
100
K 1-4
5e
-U
0c
Cu 10
0
E
0
3--
Cu
1
0.1
-k i i
-L
--L -L;;
10
1
Friction Ratio
1. Sensitive Fine Grained
2. Organic Soils -Peats
3. Clays - Clay to silty clay
4. Silt mixtures - Clayey silt to silty clay
5. Sand mixtures - Silty sand to sandy silt
6. Sands - Clean sand to silty sand
7. Gravelly sand to sand
8. Very stiff sand to clayey* sand
9. Very stiff fine grained*
*Heavily overconsolidated or cemented
fIs/(qc-v
0)
-L -
-
-1
61.616
1
0
-1
-2
-3
-4
-5
-6
-7
-8
I
1 ,1
IN ak
-
-9
-10
-11
-12
-13
-14
-15
-16
.- ,
I II
I
0
I II
IlI
1I 1 1I1I Iti
,,
- ,
IiI
I IIi l
T7 "T 1_-
I
r-r-
I
I
r,
fs/(qc-svo)
-
-i-i,
ri
- - , - -,
* r
I II I I Il
I I t i ll
il
I
100
10
---
M l
IIt l
I II]
1 11 1 ]
IIl l I I I II
I
1
I I
i ll
ti l
- - .6. -6 .6 1 61.
1 .1
W -6
-L~
I II
SI
2
At~ 1
1
-
-j
1000
10000
(qc-sv)/s'vo
Figure 6.8 - Pile MIT-4 - Chart E - Soil Classification (Robertson and Campanella, 1988)
46
6.2.2.
Pile MIT-1
In pile MIT-1 the CPT readings end just beneath the tip, providing enough data to interpret the profile
along the pile's length. This pile is a 13.11 m long open-steel pipe pile with a diameter of 0.41 m (Figure
6.9)
There is a poor agreement between the Caltrans and the author's interpreted profile, specifically in the
location and width of the clay layers. The Caltrans profile indicates that the site consists mostly of sand
layers with one clay deposit of approximately 1.20 m thick, located below elevation -3.35 m. This clay
layer corresponds to 9.3% of the total pile's embedded length (13.11 m). In contrast, the interpreted
profile indicates the existence of seven clay layers that equate a total thickness of 9.43 m or 72% of the
pile's embedded length (Figure 6.9). Refer to Appendix B for detailed site investigation charts.
The disagreement between the two interpretations arises due to the peculiar behavior of the site
investigation data, which borderlines the definition between sands and clays for many of the encountered
layers. The findings can be summarized as follows:
*
Most of the cone tip resistances (q) indicate the existence of soft deposits. Few layers exhibit
high values of qc commonly found in clean sand deposits.
"
The measured pore pressure (u 2) is shifted from zero into negative values indicating the existence
of fine grained deposits. The u 2 profile increases with depth following a slope that resembles the
assumed hydrostatic pore pressure and for most of the site Au = (u-uO)
*
constant.
The ratio u2/qc does not provide conclusive results, on the contrary, most of the readings are low,
between - 10% and +10% suggesting the existence of coarse deposits, quite the opposite to the
measured pore pressures u 2 . There are a few "peaks" that confirm the existence of fine grained
deposits where pore pressure created by the CPT cone were not dissipated.
*
The measure sleeve friction (f,) is relatively constant along the entire site, with the exceptions of
the clay layer at elevation +4.00 m and the sand layers at the pile's tip.
*
The relative density and angle of internal friction were preliminary calculated for the entire length
of the pile, as if all the layers were sand, the results indicated that most of the pile encounters
loose material and confirmed the existence of the clean clay layer (very low values of Dr).
*
The Robertson and Campanella (1988) soil classification ranks most of the site as: "Silt mixtures
- Clayey silt to silty clay", it also confirms that there are clean sands at the pile's tip and a few
layers of clean clays (Please refer to Appendix for detailed chart).
47
9
The calculated values of undrained shear strength and cone factor are slightly higher than the
typical values of clay layers, but in range of the expected accuracy of their predictions.
*
It was concluded that the site is dominated by materials classified as silt mixtures.
*
It was noted that the soil profile follows a repetitive layering pattern; a sand layer, on top of a
silty clay layer, and so on. The layers are relatively thin, and could potentially conduct water
efficiently, thus explaining the resemblance of the measured pore pressures (u 2) to the assumed
hydrostatic condition.
0
The shift of the u 2 profile into negative values can be arguably explained to occur because of the
existence of a clay layer at exactly the location of the start of the shift. This layer can hinder the
supply of water to lower layers.
Pile - ID # 1
Type of pile:
End condition:
Diameter:
Thickness:
Base area of pile:
Perimeter:
Weight of pile:
CPT Top
Steel pipe pile
Open ended
0.41 m
0.5" (1.27 cm)
0.01 57 m2
1.28 m
16.86 kN
+10.6 7 --T-
-
Top of pile
ysoI
[kN/m3l
N
Su
[M*A
[kPal
+8.54
19
-
-
Fill
18.8
-
-
+7.82
+7.57
+7.42
0.92
Bottom of
footing
Sand
19.6
11
-
Water table +4.87
(m)
-
0.41
+5.27
+4.62
+4.42
Elevations
Sand
20.04
28
-
Sand
20.1
21
-
Sand
19.6
11
-
-2.13
-
-
Sand
34
20
-
-
90
4~-
1-ana
34
20
Clay
-
-
-
-
90
34
30
-
Clay
-
-
90
Sand
36
35
-
Clay
-
-
60
150
Clay
20.1
27
-3.23
-3.35
Clay
-4.57
-5.18
-5.79
Sand
Sand
Sand
-7.01
18.8
20.4
19.8
20.9
-
50
18
72
35.91
-
Sand
38
Clay
Sand
40
an
40
60
Clay
-
-
125
Clay
Sand
-
-
90
42
70
-
Clay
-
-
175
Sand
44
80
-
45
-1.08
-2.28
Sand
-6.88
Fill
+0.12
13.11
-6.71
[kPa
+0.61
14.03
Pile tip
CPT tip
SU
1%]
+3.27
+2.13
0L
U-
Dr
+6.37
+6.17 -Sand
+6.40
+6.40
0
[01
+8.67
+8.54
+7.32
Soil
type
+10.67
+10.67
-
-
Surface
Interpretation based on CPT
CALTRANS Soil Profile
Soil
type
-4.10
-4.98
-5.38
-6.23
-6.88
175
-l -o
Figure 6.9 - Pile MIT-1 - Pile-soil elevations diagram
48
The interpreted site profile for pile MIT-I concluded that 72% of its length is comprised of silt mixtures,
and not of sand materials, which is the scope of this thesis. Nevertheless, this pile will be considered into
the calculation stage that follows in the next chapter, in order to provide more insight into the
interpretation of the soil profile using piezocone data.
6.2.3.
Pile MIT-5
Pile MIT-5 is a 0.36 m wide, 11.26 m long, square closed-ended concrete pile. The pile has a length of
embedment of 10.35 m after its tip, located at El. -1.83 m (Figure 6.10).
The surface elevation at the pile location is El. +10.67 m., slightly lower than the location were the CPT
test was performed and that is about 10 m away. The bottom of the footing, which is the effective pile top,
is located at elevation El. +8.54 m. The water table is located at El. +6.40 m (Figure 6.10).
The overburden layer comprises of a 2.5 m deep fill layer with a unit weight of 18.80 kN/m 3 as reported
by Caltrans (Figure 6.10).
Below the fill, from elevation +8.54 m to + 4.53 m, three distinct layers of sand are encountered. These
layers exhibit typical cohesionless behavior: the measured cone tip resistance values are relatively high;
the excess pore pressures created by the piezoprobe cone are almost zero (Appendix B - Chart A); and the
normalized pore pressure factor (u2/qc) is close to zero (Appendix B - Chart B). Robertson and
Campanella (1988) define these layers from higher to lower elevation as Sand mixtures, Sand, and Sand
mixtures, respectively. The calculated measured relative density and angle of internal friction, confirms
that the layer in the middle (El. +7.73 to El. +5.5 8) is denser than the two boundary layers. Figure 6.10
presents their calculated soil properties.
Under the sand layers, from elevation El. +4.53 m to El. +1.38 m, an interlayer system of sands and clays
is encountered. This repetitive pattern can be clearly identified from the piezocone data:
*
The average values of the cone tip resistance drop, in comparison to the previous sand layers.
There is an increase in variability in the cone tip measurements, the low values correspond to the
clay layers, and the high values to the sand materials. (Appendix B - Chart A).
49
"
Excess pore pressures develop and follow an constant average trend. At the location of the sand
layers, the excess pore pressures reduce, and therefore "peaks" occur, i.e. El. +3.25 m (Appendix
B - Chart A).
"
The normalized pore pressure factor varies significantly, from values of 0.4 typical in clay, to
values near to zero and common to sands. (Appendix B - Chart B).
"
The calculated values of cone factor (N) for the clay layers varies from 15 to 22, a range that is
common to clays (Aas et al. 1986). (Appendix B - Chart D).
"
The calculated relative densities calculated for the sand layers classify them as medium dense
sands, with an average value of 40% (Appendix B - Chart C).
"
Confirmation of the classification of this soil layers is provided by means of Robertson and
Campanella (1988) in Chart D of the Appendix B.
Figure 6.10 summarizes the soil properties for this interlayer system.
From elevation El. +1.38 m until the tip of the CPT sounding at elevation El. -1.62 m, four sand layers are
identified. The classification of these layers as sand conforms to the cone tip measurements readings that
exhibit a constant increase from elevation E. +1.38 m downward. For that same location the excess pore
pressures measurements, and the normalized pore pressure factors drop to zero. (Appendix B - Chart A
and Chart B). The definition of four different layers, corresponds to their increase in relative density,
which can be clearly identified from the calculated values of relative density as per Jamiolkowski et al.
(2003) in Appendix B - Chart C. The upper layer exhibits Dr = 40%, while the lowest layer an average
value or 70%.
At the tip of the CPT sounding, i.e. El. -1.62 m, the values of cone tip resistance drop and excess pore
pressures develop, nevertheless, the normalized pore pressure factor remains with values close to zero. It
can be argued that the underlying material below the previously described sands, is clay. There is not
enough information to confirm this assumption.
In general terms, the Caltrans profile and the interpreted profile, agree on the location of the upper group
of layers of sand, as well on the lower group. (i.e. El. +8.54 m to El. +4.53 m, and El. +1.38 m to El. -1.62
m respectively) as indicated in Figure 6.10. Both interpretations agree, for both of those sand group
layers, on an increasing trend of sand strength with depth. This fact can be identified by comparing the
calculated relative densities and angles of internal friction with the reported Caltrans N-values (Figure
6.10)
50
The Caltrans profile fails at identifying the interlayer system of sand and clay materials between elevation
El. +4.53 m and El. +1.38 m.
Please refer to the Appendix B for the detailed site investigation charts.
Pile-ID#5
Type of pile:
End condition:
Diameter:
Thickness:
Base area of pile:
Perimeter:
Weight of pile:
Square concrete pile
Closed ended
0.36 m
0.0993 m2
1.12 m
26.38 kN
CALTRANS Soil Profile
+10.98
+10.67
CPT Top
Surface
Top of pile
Bottom of
footing
Soil
ysoil
type
oimzl
[bpfl
+10.98
-- a
1
+10.67
+9.45
Fill
18.80
Sand
19.8
8
Sand
19.8
8
Sand
20.1
14
Sand
19.8
9
0.91
+8.54
0.36
a
0
Ia0
-
+4.57
Sand
+3.96
10.35
7
19.8
Sand
+0.91
+0.30
0
-0.30
-0.91
(in)
CPT tip
Pile tip
-1.62
-1.83
-1.52
-3.05
-
-
-
Sand
38
45
-
Sand
40
55
-
Sand
38
40
-
-
155 F-
+5.58
+5.49
12
20.1
+2.44
Elevations
+7.73
+6.71
+6.40
Fill
+8.54
+8.54
+7.62
Water table
Interpretation based on CPT
Dr
Su
Soil I '
[% I [kPaJ
[0]
type
N
'
Sand
20.4
20
Sand
Sand
Sand
Sand
20.4
28
20.4
35
20.4
56
20.4
34
Sand
20.4
+4.
+4.38
+3.83
+3.13
+2.73
+2.38
+2.18
+1.38
+0.98
+0.28
-0.12
-
Sand
36
30
Clay
Sand
-
-
110
38
45
-
JSand
36
30
-
Clay
-
-
100
Sand
38
40
-
and
Sand
40
41
60
65
-
Sand
41
70
-
-
-1.62
I
12
I
Figure 6.10 - Pile MIT-5 - Pile-soil elevations diagram
51
6.2.4.
Pile MIT-2
The "Pile-site information report" provided for pile MIT-2 did not agree with the CPT readings. It was
found that those CPT readings correspond to a different site, and therefore this pile will not evaluated in
this study.
6.2.5.
Pile MIT-3
For this pile the CPT readings cover 74% of the total length of the pile measured from the top. The scope
of this document requires for axial prediction purposes that the CPT data should cover at least the entire
length of the pile, therefore this pile will not be considered in the axial capacity predictions of this study.
Please refer to the Appendix for the detailed site investigation charts.
6.2.6.
Pile MIT-6
For this pile the CPT readings cover 69% of the total length of the pile measured from the top. The scope
of this document requires for axial prediction purposes that the CPT data should cover at least the entire
length of the pile, therefore this pile will not be considered in the axial capacity predictions of this study.
Please refer to the Appendix for the detailed site investigation charts.
52
7.
AXIAL PILE CAPACITY PREDICTION
One of the features of the piezocone data is that they provide a continuous penetration record that can be
incorporated directly into the design process for pile foundations. In this study, the piezocone data are at
0.05 m intervals through the length of the pile. This resolution provided 300 to 400 calculation data points
for each pile. To take advantage of this information, and to avoid averaging techniques for each soil layer,
a spreadsheet program was developed in Microsoft's Excel. The spreadsheet was designed to efficiently
process the CPT readings, compare and relate the elevation datum, and predict the axial capacity of each
pile for the 5 methods under consideration in this thesis.
This chapter presents the results of the predicted axial capacity, for piles MIT-4, MIT-5 and MIT-1,
calculated following the guidelines of the CPT design methods described in Chapter 4. The predictions
include tension and compression type of loading for each pile. First, the calculation procedure is
described, followed by the graphical representations of the results.
7.1.
Spreadsheet input data
The spreadsheet requires the input of:
*
The characteristics of the pile: dimensions, elevations, and material properties.
*
The site description: surface and water table elevations, and height of overburden material.
*
The CPT readings: tip resistance, sleeve resistance, shoulder pore pressure.
*
The classification of each data point as either cohesionless (sand), or fine grained (clay) material.
The classification of the soil follows the procedure described in Chapter 6.
General calculation procedure
7.2.
The calculation procedure performed by the spreadsheet can be summarized in these steps:
*
Insert input data as indicated in section 7.1
*
Compare the input elevations and adjusts them to a common datum
*
Determine width of overburden layer, defined as soil that contributes to the vertical stress but has
no effect on the side friction of the pile.
"
Assign unit weights for each layer (a default value y = 19 kN/m 3 is used if no data is provided)
"
Assign interface friction angle (6,)for ICP and UWA method. (default value, 6, = 29
0
, if no
data available)
53
*
Calculate relative density (Dr) for the NGI method and compare it with the prediction by
Jamiolkowski et al. 2001 (Section 6.1.2).
*
Calculate small strain modulus for ICP and UWA methods, compare results (Section 4.3.1)
*
Calculate unit shaft friction for cohesionless materials
*
Calculate unit shaft friction due to contribution of clay layers (Section 7.3)
*
Calculate shaft pile capacity for five design methods
*
Calculate end bearing capacity for 10% pile diameter displacement (qbo.1) for 5 design methods
*
No plug formation was considered in excess to those guidelines included in the design methods
.
Average tip resistance over ± 1.5 D for calculation of tip resistance
*
Average tip resistance following the Dutch method for the UWA method (Section 4.5.1)
*
Calculate pile tip resistance
*
Display figures for unit shaft capacity and axial load distribution for both tension and
compression loading
*
Calculate pile's weight
*
Display predicted axial pile capacities minus pile weight on corresponding measured loaddeformation test curves
7.3.
Clay layers - Load contribution
The approach adopted for calculating the contribution of clay layers to the shaft pile resistance was to
estimate the unit shaft resistance (-rf) from the CPT's cone tip resistance (q) and control the result, by
comparing it to the unit shaft resistance as calculated from the undrained strength.
Lehane et al. (2000) indicate that the unit shaft resistance, ry, varies approximately between the ratios of
qg/20 to qt/50 in (kPa). The precise ratio was estimated by calculating the unit shaft resistance following
the guidelines of the American Petroleum Institute for cohesive soils (API, 1993) that are based on
Randolph and Murphy (1985):
)
rf =0.5 -(sn - O)05
for su/a'vo < 1
(7-1
r0 =0.5 -s'
for su/a'v. > 1
(7-2)
0.25
It was found that unit shaft friction contributed by the clay layers in pile MIT-4 best fitted the ratio qt/25.
54
In pile MIT-5 the best comparison was achieved by the ratio q,/50. Both values fall within the limits
indicated by Lehane et al. (2000).
Spreadsheet output
7.4.
The spreadsheet produces a summary of the predicted axial pile capacities for each of the five methods at
each pile site, the output includes:
*
Table summarizing pile's axial capacity predictions (e.g. Table 7-2)
*
Plot of the predicted and measured axial pile capacity under tension (e.g. Figure 7.1)
"
Diagram of axial load distribution and unit shaft friction for tension loading without correcting
for pile's weight (e.g. Figure 7.2)
"
Plot of the predicted and measured axial pile capacity under compression (e.g. Figure 7.3)
"
Diagram of axial load distribution and unit shaft friction for compression loading without
correcting for pile's weight (e.g. Figure 7.4)
7.5.
Pile MIT-4 capacity prediction
Pile MIT-4 is a 0.61 m in diameter steel open-ended pipe with an embedded length of 13.26 m. Section
6.2.1 presented the site interpretation for pile MIT-4, its corresponding soil profile and soil properties are
included in Figure 6.3. The following table (7-1) summarizes the soil profile by main soil groups, as sand
and clay; it is evident that the pile is surrounded by more sand layers than clays', but in very close
proportion. This table, when compared with the estimated shaft resistance for each soil group, will
provide information on the relative contribution of the normalized friction, i.e. average layer pressures on
the shaft of the pile.
Layer
Thickness
(%)
(M)
Sand
7.56
57%
Clay
5.70
43%
13.26
100%
Pile embedment:
Table 7-1 - MIT-4 - Coverage of pile embedment per layer
It must be indicated that only external shaft friction was considered in the pile capacity predictions. Some
of the design methods claim to include plug formation into their formulation (e.g. UWA-05 and ICP-05);
55
therefore, to provide and unbiased evaluation of their performance, no analysis on plug formation was
considered.
The following table summarizes the predicted pile capacity for each of the five design methods under
tension and compression loading. It includes the predicted load for each soil group layer (kN) and its
contribution to the total load as percentage (%). For compression loading, the estimated tip bearing
capacity is indicated separately. Table 7-2 provides the value of the load test, the ratio of calculated axial
load to measured load (QcaIc/Qtest), and an average of the predictions of all design methods.
Load condition
API-00
(kN)
FUGRO-05
ICP-05
NGI-05
UWA-05
(kN)
(kN)
(kN)
(kN)
Load Test Averages
(kN)
Tension
Sand - shaft
843
62%
1103
68%
824
62%
579
53%
870
63%
844
62%
Clay - shaft
508
508
508
508
508
508
38%
Weight of pile
Pile capacity:
Qcalc/Qtest
=
32%
38%
-24
1326
-24
1587
-24
1307
47%
-24
1063
0.977
1.169
0.963
0.783
37%
38%
-24
1353
1358
1327
0.997
1.000
0.978
Compression
Sand-shaft
843
23%
1384
35%
1120
36%
753
27%
1159
40%
1052
32%
Clay - shaft
508
508
508
508
508
508
14%
Tip bearing
Weight of pile
Pile capacity:
Qcalc/Qtest=
13%
16%
2361
64%
-24
3688
2024
52%
-24
3891
1455
48%
-24
3059
1508
55%
-24
2745
1240
43%
-24
2883
2737
1.347
1.422
1.117
1.003
1.053
1.000
18%
17%
16%
1718
52%
3253
1.188
Table 7-2 - Pile MIT-4 - Pile axial capacity overview
The first conclusion that can be drawn by comparing Table 7-1 and Table 7-2, is that the sands layers
provide a higher load resistance per unit area than the clay layers. This can be identified by comparing the
coverage of each layer and its load contribution, e.g. the sand layers in pile MIT-4 cover 57% (Table 7-1)
of the pile's length, but in average, they provide 62% of the pile axial capacity in tension (Table 7-2).
This is not surprising, as the identified clay layer (El. -3.88m to El. -9.43m) has a relatively low undrained
shear strength (Figure 6.3).
The variation of the ratio (Qcaic/Qtest) in tension is smaller than in compression; in tension the average of
the ratios of prediction to measured values is 0.978, while in tension it is 1.118 (Table 7-2). The increase
in variation in the compression mode is caused by the uncertainties that are involved in predicting a plug
56
formation at pile's tip. The calculated average contribution of the tip is 52% of the load loading capacity
of the pile in compression (Table 7-2).
Each mode of loading, i.e. tension and compression, will be analyzed in further detail with the
presentation of the spreadsheet results in the next sections.
7.5.1.
Tension loading
The predictability of the design methods will be presented in this section by introducing the spreadsheet
results illustrated in Figure 7.1 and Table 7.2.
The pile test load-displacement measured curve includes the results of the predicted axial pile capacities
(Figure 7.1). It can be seen in Figure 7.1, that the behavior of the pile in up-lift is somewhat ductile. It
starts picking up load at an increasing rate, yielding is reached at a displacement of approximately, 6 = 20
mm, and a measured load of 1358 kN. In terms of pile diameters, the yielding displacement corresponds
to a ratio of 5/D = 3.28%; in terms of pile length: 5/L = 0.15%. The first unloading-reloading cycle
included in Figure 7.1 suggests that the plastic deformation at yielding should be close to 15 mm. Note
that the slope of the unloading cycles are very flat compared to the original loading slope.
MIT-4 - Pile Load Test Tension (ID 86-02)
0
200
400
5.
600
800
1000
I
1_
I
.
Load (kN)
1400
1200
I
.
I
_
I_ .
1600
_ __.
5
10
1E
20
-
Load test:138k
API
FUGRO
20
--
25
--- NGI
-O-UWA
A- ICP
: 1326 kN
:1587 kN
:1307 kN
:1063 kN
:1353 kN
30
40
Figure 7.1
-
MIT 4 - Tension load test and predicted axial capacity
57
Three methods (UWA, ICP and API) provide very close estimates of the total axial capacity, on the other
hand, NGI under predicts the capacity and FUGRO over predicts it (Figure 7.1).
Figure 7.2 provides the predicted shaft capacity under tension and the corresponding unit shaft friction.
The following observations can be made:
"
API-00 under predicts the contribution of the lower sand layers, this is indicated by the low shaft
friction between El. -11.00 m and El. -13.00 m in Figure 7.2b, and the load axial contribution of
those layer in Figure 7.2a. Under prediction is expected as this method imposes a limiting value
of unit shaft friction. The opposite conclusion can be drawn for the upper layer of sand (Figure
6.3) near the pile top, where the API-00 method over predicts the contribution of those layers in
comparison to the other methods. This behavior is expected, as the API-00 does not account for
friction fatigue effects.
"
Overall API-00 provides a good prediction of the pile axial capacity QcaIc/Qtest= 0.977 (Table 7-2)
"
FUGRO-05 provide an upper bound prediction along the entire length of the pile (Figure 7.l a),
this behavior is accentuated at the pile tip where the FUGRO method excludes friction fatigue
considerations for elevations less than h = 4R* (Equation 4-5).
*
NGI-05 follows a similar trend as API-00 for the lower sand layers (Figure 7.2a), but it differs in
the upper layers, where it becomes more conservative. In terms of total capacity NGI-05 is most
conservative of all methods with a ratio of Qalc/Qtest= 0.783 (Table 7-2).
"
ICP-05 and UWA-05 provide very similar results of total predicted capacity (Table 7-2). They
follow a common trend in axial load distribution, but differ in the contribution of the sand layer
between elevations, EL. -11.00 m and EL. -12.00 m (Figure 7.2).
"
All of the methods predict that the lower sand layer (i.e. below El. -9.43 m), contribute to 50% of
the total axial capacity of the pile. These layers have a total thickness of 3.50 m (27% of the total
embedded length of the pile).
"
The methods provide greater variation in calculated unit shaft friction in sands with increasing
relative density, as can be observed by comparing the soil profile in Figure 6.3 and Figure 7.2b.
In the upper looser sands, the variation is less than 15 kPa, while at the tip it exceeds 100 kPa.
58
MIT-4 - Unit shaft friction - Tension - SAND+CLAY [kPa]
MIT-4 - Axial load distribution - Tension - SAND+CLAY [kN]
0
200
400
1200
1000
800
600
1400
1600
1.00
1.00
-1.00
-1.00
-3.00
-3.00
-5.00
-5.00
E
C
0
0
1800
-7.00
--
U.1
I
-9.00
I
I
A I+
FurI
C
-
~
I--
W
I
I
I
I
I
-9.00
II
-
-11.00
I
I
400
I
I
I
I
350
300
250
200
150
100
-7.00
I
I
I
50
-Aa- I Fgo
~i
lP-
'-
G -.-
W
-11.00
-13.00
-13.00
-15.00
-15.00
Figure 7.2 - MIT-4 - Tension - Axial capacity distribution
59
7.5.2.
Compression loading
The pile load test under compression for pile MIT-4 is presented in Figure 7.3, the predicted axial
capacities are also included. The behavior of the load-displacement curve is ductile, with small elastic
deformation (e.g. 4 mm after the first unloading cycle). The yielding load is reached at an approximate
displacement at the pile head of 8 = 25 mm (Figure 7.3). This displacement equates to 8/D = 4.1%, which
is considered low given that the methods are based on a ratio of 6/D = 10%. Nevertheless, this state is not
conclusive; based on the deformations read during the load test, it can be argued, that the maximum
displacement was not reached, due to hardening of the load-deformation response. This argument could
validate the results of the UWA-05 and the ICP-05 method that slightly over predict the pile capacity
(Figure 7.3).
The variation of the prediction is higher for the compression mode than in tension, because: i) the API-00
method considers that the calculated unit shaft friction in tension and compression is equal, on the other
hand the CPT based methods allow Ts in compression to be higher than -, tension; ii) Plug formation was
assumed, in other words, no analysis of plug formation was performed in addition to that incorporated in
each method. The UWA-05 and the ICP-05 include formulations that analyzes this problematic condition,
i.e. if the plug is formed, and if so, if it is full or partial.
MIT-4 - Pile Load Test Compression (ID 86-01)
0
500
1000
1500
2000
2500
3000
Load (kN)
3500
4000
0
5-e
E
10
E
--- Load test
-API
15
-0- FUGRO
- -ICP
-S
20
NG
-0-UWA
:2737 kN
:3688 kN
:3891 kN
:3059 kN
:2745 kN
:2883 kN
-
-
-
-
25
Figure 7.3
-
MIT 4 - Compression load test and predicted axial capacity
60
From the analysis of Figure 7.3 and 7.4 further conclusions can be made:
*
The API-00 over estimates the resistance of the unit shaft friction for the upper sand layers
(similar to the tension mode), and consistently under estimates the shaft friction at depth, for the
lower sand layers (Figure 7.4b). The reasons for this behavior were discussed in the tension
section, and apply also to compression given that this method does not differentiate in modes of
loading.
*
API-00 predicts an axial capacity for fully plugged mode of 3688 kN (Table 7-2), more than
double of the unplugged condition (1536 kN).
*
API-00 follows the similar axial distribution, but it is offset by the tip resistance (Figure 7.4a).
*
FUGRO-05 provides an upper bound prediction for compression, primarily due to over
estimating the contribution of the lower sand layers (El. -11.00 m to El. -13.00 m).and for tip
resistance (Figure 7.3a).
*
NGI-05 provides the best prediction of load capacity in the compression mode, with a variation
ratio of QcaIc/Qtest= 1.003 (Table 7-2). Its estimation of the tip capacity seems to be consistent with
more refined methods that account for plug formation (UWA and ICP). The estimation of the
shaft resistance is low, thus its overall performance is conservative (Figure 7.3a).
*
The ICP-05 and UWA-05 methods provide, again for compression, very close results. Their
computed variation ratios of Qcalc/Qtest differ by 5% (Table 7-2). The differences in predictions
can be traced to the tip bearing, 1455 kN and 1240 kN, respectively (Table 7-2).
.
Both methods, ICP-05 and UWA-05, find that the pile is fully plugged. The ICP-05 method
calculates the tip resistance based on q
= cone tip resistance averaged over a distance +1.5 D
from the pile tip, while the UWA-05 method calculates it using the Dutch technique
(section4.5.2). In pile MIT-4 the Dutch method provides lower average tip resistance.
*
The ICP-05 limits the resistance at the tip, qbo.1, for the case of pile MIT-4 being plugged to 0.15*
q, (equation 4-18), while the UWA-5 method allows a higher stress of almost double this value.
Nevertheless, the UWA-05 method provides overall lower tip resistance due to lower average q,
obtain using the Dutch method.
*
Note that despite the high variation in predictions, the variation at the pile tip (e.g. El. -13.00) is
almost identical as the variation of the total axial capacity at the top (Figure 7.4a).
61
MIT-4 - Unit shaft friction distribution - Compression SAND+CLAY [kPa]
MIT-4 - Axial load distribution - Compression - SAND+CLAY [kN]
1.00
1000
500
0
.
1500
I
-1.00
-3.00
-3.00
100
-5.00
-7.00
200
I
I
I
I
I
I
I
I
300
400
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
500
I
I
I
I
I
I
I
I
I
-5.00
w
0
,
I
I
0
4-
. .
I
-1.00
E
C
.
1.00
I
I
4000
3500
3000
.
I .
I
2500
2000
I
I
I
I
I
I
-7.00
--
A
urI-e
ICP
--
N
l--U
A
-9.00
-9.00
-11.00
-11.00
-13.00
-13.00
I
-API --- Fugro -~-lCP -w--NGI -.-UWA
-15.00
-15.00
Figure 7.4 - MIT-4 - Compression - Axial capacity distribution
62
7.6.
Pile MIT-1 capacity prediction
In section 6.2.2 the results of the site interpretation for pile MIT-i were presented. The interpretation
indicated the existence of cohesionless materials (28%) along the pile's embedded length and abundant
layers of fine grained materials. This interpretation disagreed with Caltrans' profile, which assumed
cohesionless materials for almost the entire profile (97%) as indicated in Figure 6.9 . Pile MIT-I was
nevertheless, considered into the axial capacity calculations included in the present chapter with the
purpose of providing further information on the piezocone's site investigation accuracy.
Pile MIT-1 is an open-ended steel pipe with a diameter of 0.41 m. The load test provided for this pile
included up-lift mode of loading only, and indicated a maximum load of 1068 kN (Figure 7.5).
Two predictions were performed for pile MIT-1, the first followed the interpreted profile of this study,
where clay dominates; the second included a more "subjective" approach in which if only slight
disagreement or indication of probable sands materials could be argued, that data point was assumed as
sand. The second scenario turned out to provide a lower bound to the predictions, with low average value
of axial capacity under tension (800 kN). Appendix E includes axial capacity prediction charts for the
second scenario (i.e. mostly sand profile).
Under the first scenario (interpreted - clay dominated), the axial capacities were over predicted, but in a
much closer range to the measured load test value. The ratios of predicted load to measured load included
in Table 7-3 for the design method confirm this statement (variation is less than 17%).
Load condition
FUGRO-05
ICP-05
NGI-05
UWA-05
Load Test
(kN)
(kN)
(kN)
(kN)
(kN)
281
23%
953
77%
-17
1217
313
25%
953
75%
-17
1249
256
21%
953
79%
-17
1192
193
17%
953
83%
-17
1128
264
22%
953
78%
-17
1200
1068
1197
1.139
1.169
1.116
1.056
1.123
1.000
1.121
API-00
(kN)
Averages
Tension
Sand-shaft
Clay-shaft
Weight of pile
Pile capacity:
Qcalc/Qtest=
261
21%
953
79%
Table 7-3 - Pile MIT-1 - Pile axial capacity overview based on profile derived in Section 6.2.2
The fact that the second scenario (mostly sand profile) significantly under predicts the measured axial
capacity, substantiates the interpretation of the soil profile proposed in this thesis. Here, the higher pile
63
capacity of MIT-i is due to the existence of strong clay layers not identified in the original Caltrans
databse (Figure 6.9).
It is important to notice that the predicted axial capacity for the sand layers varies as much as 100 kN
among the design methods, this means a variation of as much as 50% for the lowest prediction. This
variation is considered high for a profile with an interpreted sand cover of only 28% of the pile's length.
The origins of this variation are explored next.
7.6.1.
Tension loading
The load-displacement curve for the uplift test is presented in Figure 7.5, it includes the axial load
predictions from the five design methods, which over predict the capacity of pile MIT-1.
Load (kN)
MIT-1 - Pile Load Test Uplift (ID 38-01)
200
0
400
600
800
1000
1200
0.00
5.00
Load test -1068
10.00
IAP
A
1
15.00
-
---
LFUGRO
A
ICP
X-- NGI
UWA
--
:1249 kN
:1192 kN
:1128 kN
-: 1200kN
- -
20.00-
25.00
Figure 7.5 - MIT-1 - Tension load test and predicted axial capacity
Pile MIT-I experienced a very brittle behavior. After the 4' millimeter of displacement the pile "failed"
for a load of 1068 kN (Figure 7.5). Recalling that the estimated contribution of the clay layers is 953 kN
(Table 7.3), that means that the sand layers provide only around 115 kN of load capacity. Pile MIT-I has
a perimeter of 1.28 m, therefore the corresponding unit side friction for that load is 91 kN/m of pile
length. The sand layers in the profile are very thin, usually less than a 1 meter in width, but at the tip,
64
there at two layers that could potentially provide the required unit shaft friction. These layers are located
at elevation -5.00 m and -6.00 m (Figure7.6). Their location seems to prove the brittle failure during the
pile test. After the clay layers have reached their capacity, the sand layers beneath the clay have to resist
the additional axial load. The failure occurs abruptly once the small contribution of the sand layers at the
tip is reached and all of the previous layers have reached their capacity i.e. no load distribution occurs.
Figure 7.6 provides the predicted shaft capacity under tension and the corresponding unit shaft friction.
The following observations can be made:
*
FUGRO-05 provides the lowest shaft friction for loose sands (Elevation +6.50 m, +5.00 m, and 0)
*
FUGRO-05 provides the highest shaft friction for dense sands, as can be seen at the increase in
load distribution at the pile tip (Elevation -6.50 in).
"
API-00 provides the lowest shaft friction for dense sands, this supports the findings of the many
authors that on that basis developed the design methods being revised here.
"
The limiting shaft frictions imposed by the API-00 method at each sand layer are not reached.
*
UWA-05 and ICP-05 provide almost identical axial distribution curves and unit shaft friction, and
therefore total axial capacity.
"
Plug formation is expected to happen in pile MIT-1. Weak materials are overlying a stiff layer at
the pile's tip. Weak and loose materials will collapse inside the pile and act as overburden on the
plug near the tip.
"
The incremental filling ratio (IFR) for the UWA-05 method is 0.76, suggesting that the pile is
partially plugged.
"
The NGI-05 method includes a limit on the minimum value on the calculated unit shaft friction, it
corresponds to 10% of the effective vertical stress. This limit controls for most of the pile's
length, from the pile's top to an elevation of -2.70 m where the first medium dense sands are
encountered.
*
The location of the clay layers can be identified in the graphs, they occur where the unit shaft
frictions coincide.
"
The calculated unit shaft friction among the five methods varies in proportion to the increase in
relative density. The upper loose sand layers vary in less than 10 kPa, while the lower denser
layers vary in as much as 150 kPa.
"
In general, for pile MIT-1, the FUGRO-05 method provides the highest estimate of capacity, and
the API-00 the lowest.
65
MIT-I
0
-
MIT-1 - Unit shaft friction - Tension - SAND+CLAY [kPa]
Axial load distribution Tension SAND+CLAY [kNI
-
200
400
-
600
800
1000
150
100
50
200
250
300
7.00
I
I
6.00
4.00
3.00
2.00
0 0.00
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
1.00
I
I
I
I
I
5.00
-
0
1200
7.00
I
I
I
I
I
I
I
I
w -1.00
I
I
I
-2.00
I
-3.00
I
I
-4.00
I
I
6.00
5.00
I
I
4.00
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
3.00
2.00
1.00
0.00
-1.00
-2.00
-3.00
-4.00
-5.00
-5.00
-6.00
-6.00
-7.00
-7.00
-API
-a-
Fugro -~--ICP -- u-- NGI -.---UWA
-=
-on
-API
-Fugro
-ICP
NGI -
UWA
Figure 7.6 - MIT-1 - Tension - Axial capacity distribution
66
7.7.
Pile MIT-5 capacity prediction
Pile MIT-5 is a square concrete pile 10.35 m long (embedment) and 0.36 m wide (Figure 6.10). The
distribution of main soil groups in the pile's embedded length is presented in Table 7-4. Pile MIT-5 offers
the most interesting pile from the point of view of the scope of this thesis, since the profile is dominated
by sand layers (81%).
Layer
Thickness
(%)
(M)
Sand
Clay
8.35
2.00
81%
19%
Pile embedment:
10.35
100%
Table 7-4 - MIT-5 - Coverage of pile embedment per layer
The pipe-soil elevations profile in Figure 6.10 summarizes the soil interpretation for pile MIT-5. In
general terms, three strata are found. An upper group of sand layers (El. +8.54 m to El.+4.53 in), a mixed
layer system of sand and clays between El.+4.53 m to El.+1.38 m, and a lower group of sand layers with
increasing relative density (Dr) with depth, from El.+1.38 m and to the pile's tip. For further detail on the
site interpretation please refer to Appendix B. The results of the calculated axial capacity predictions for
pile MIT-5 are shown in Table 7-5, its analysis follows in the next page.
Load condition
Tension_
API-00
FUGRO-05
ICP-05
NGI-05
UWA-05
Load Test
(kN)
(kN)
(kN)
(kN)
(kN)
(kN)
530
81%
128
19%
-26
632
610
83%
128
17%
-26
712
562
81%
128
19%
-26
664
546
81%
128
19%
-26
648
554
81%
128
19%
-26
656
614
662
1.028
1.159
1.080
1.068
1.000
1.078
530
35%
128
8%
895
53%
128
8%
678
54%
128
10%
710
59%
128
11%
739
58%
128
10%
710
863
664
439
373
403
548
Averages
Tension
Sand -shaft
Clay - shaft
Weight of pile
Pile capacity:
Qcalc/Qtest =
1.055
561
81%
128
19%
Compression
Sand-shaft
Clay - shaft
Tip bearing
58%
Weight of pile
Pile capacity:
QcalcQtest =
39%
35%
31%
52%
128
9%
32%
39%
-26
1495
-26
1687
-26
1245
-26
1211
-26
1270
1148
1381
1.302
1.469
1.084
1.054
1.106
1.000
1.203
Table 7-5 - Pile MIT-5 - Pile axial capacity overview
67
The axial capacity predictions of pile MIT-5 under tension using the four CPT-based methods, are in
good agreement with the quoted load test value capacity reported by Caltrans (614 kN, Table 7-5). The
average variation of the design methods
is 1.078 (i.e. 7.8%, Table 7-5).
Note that in tension, the load distribution between the sand and clay layers follows the same proportion as
the soil distribution coverage around the pile, i.e. the sand layers cover 81% of pile's length (Table 7-4)
and in average for the design methods they provide 81% of the capacity (Table 7-5). This coincidence
suggest that the shaft resistance is uniform in the pile, but later it will be shown that this is not the case.
In compression, there is an increase in the variation of the ratio Qcaic/Qtest = 1.203 compared to the tension
case. All of the proposed design methods over predict the pile capacity. NGI-05 provides the lowest
prediction, and thus closest to the measured value, on the other hand the FUGRO-05 provides the highest
prediction;, almost 50% higher than the measured load capacity (Table 7-5).
ICP-05 and NGI-05 present the most consistent prediction in tension and compression, for both cases,
their ratio of variation Qcaic/Qtest is identical, the very small difference, less than 0.1%, is well below the
accuracy that should be expected in any geotechnical calculation. UWA-05 presents a small variation in
both loading modes, however this variation is less than 4%, and therefore well within the "experimental
accuracy" of this analysis.
On the other hand, the FUGRO-05 and API-00 provide large variation between the tension and
compression modes, with ratios that differ 31% and 27% respectively (Table 7.5).
In the next sections, each mode of loading will be analyzed in more detail and in combination with the
output graphs from the spreadsheet program (Section 7.4).
7.7.1.
Tension loading
The pile-displacement results for Pile MIT-5 are shown in Figure 7.7. The curve includes 3 loading cycles
that reached a maximum load of 614 kN at a displacement of approximately 5 = 24 mm (Figure 7.7). The
curve exhibits a very ductile behavior under tension loading (Figure 7.7). The yielding point is not well
defined, and in the opinion of the author the load test should have proceeded further to allow better
identification of the capacity. In Figure 7.7, at a displacement of 20 mm a load reading close to 600 kN is
68
reached, the next data point occurs at a displacement of 22 mm and a load of 614 kN (Figure 7.7), after
this maximum the load is released an the unloading cycle begins. It can be argued, that additional load
imposed at the pile at a deformation of 22 mm could further increase the load, and repeat the observed
behavior at the previous loading cycle, e.g. at displacement 10 mm. At that location, and after unloading,
the pile was able to pick-up more load (Figure 7.7).
MIT-5 - Pile Load Test Tension (ID 87-02)
0
100
200
300
400
500
600
Load (kN)
700
800
0
5
E
0
10
15 -
20
-V--
Load test :614kN
API
632 kN
FUGRO
:712 kN
A ICP
:664 kN
X NGI
:648 kN
-4-UWA
:656 kN
25
Figure 7.7 - MIT-5 - Tension load test and predicted axial capacity
Details on the load distribution of the design methods are presented in Figure 7.8:
"
Figure 7.8b presents the unit shaft friction profile for pile MIT-5. It can be noted that the stiff
sand layer at the pile tip provides a large contribution to the load capacity. Below El. 0 m, the unit
shaft friction increase steadily to average values of 100 to 200 kPa. In the other graph, in Figure
7.8a, it can be noted that the lower dense sand layer provides almost 60% of the total load
capacity of the pile, i.e. 400 kN.
"
From elevation El.+2.00 m to El.+8.54 m the unit shaft friction presents a uniform decrease of
resistance that equates to a load of approximately 300 kN.
69
*
The contribution of the interlayer system of sand and clay between El.+ 4.53 and El. +1.38 to the
total axial capacity indicates a linear increase (Figure 7.8a), the corresponding average unit shaft
resistance is uniform close to a value of 50 kPa (Figure 7.8b).
"
API-00 provides a lowest value on all the predictions. The contribution of the stiff base sand layer
is limited by the guidelines of this method (Figure 7.8b)
*
FUGRO-05 provides the highest estimate of tensile capacity. At the pile tip, the method over stimates the contribution of the stiff sand layer. The source of this over prediction can be
explained by the fact that the FUGRO-05 method does not include friction fatigue in a zone of 2
diameters from the tip. Given that pile MIT-5 is founded into a stiff sand layer, which is not
corrected by FUGRO-05 the resulting unit shaft friction values are high. FUGRO-05 was
developed from load tests performed in long piles, where the contribution of the small
uncorrected area at the tip doesn't make much difference, but for onshore short piles, this area
greatly influences the results.
"
UWA-05, ICP-05 and NGI-05 follow a similar load distribution, from pile tip to top. These
methods experience the larges difference in the interlayer system previously discussed, e.g. at
El.+ 4.00.
"
Overall, this pile is a good confirmation of the accuracy of most of the design methods for
application in onshore short piles.
70
MIT-5 - Axial load distribution - Tension - SAND+CLAY [kN]
0
100
200
300
400
I
500
600
700
II
MIT-5
800
0
-
Unit shaft friction distribution - Tension - SAND+CLAY
[kPa]
50
100
150
200
300
350
400
I
8.00
-- API -m--Fugro - -lCP --- NGI -+- UWA
8.00
I
6.00
C
250
I II
I
6.00
4.00
4.00
I
I
I
I
II
I
.2
U)
-
A
-
I -
ur
I
+
I
-
GI
-+
W
I
2.00
2.00
0.00
0.00
-2.00
-2.00
Figure 7.8 - MIT-5 - Tension - Axial capacity distribution
71
7.7.2.
Compression loading
Pile MIT-5 is closed-ended, this provides a great opportunity to establish the applicability of the design
methods in their "pure" tip bearing form. (i.e. without any misinterpretations regarding plug formation)
The compression load-displacement test for pile MIT-5 is shown in Figure 7.9 and includes three loading
cycles up to a load of 1148 kN and a displacement of 23 mm. The load curve indicates a brittle behavior,
common for piles bearing on stiff layers at the tip (e.g. sand layer at El. -1.00, Figure 6.9).
The yielding load is reached at an approximate displacement of the pile head of 6 = 15 mm (Figure 7.9).
This displacement equates to 5/D = 4.2%, which is considered low given that the methods are based on a
ratio of 8/D = 10%. This is especially true for the UWA-05, FUGRO-05 and API-00 methods that specify
this limit at the pile tip, which is expected to be less that the measured values at the top. It appears, that
for on-shore piles, this definition of tip bearing resistance corresponding to 8/D = 10% should be revised.
The brittle behavior of the load test, can be explained by comparing the pile-soil profile of Figure 6.9 and
the calculated unit shaft resistance included in Figure 7.10. The pile tip is anticipated to be located at
EL.-1.83 m, just at boundary of the stiff sand layer and a softer material that follows. The CPT sounding
ends at the pile tip and therefore this underlying layer cannot be identified, nevertheless, the Caltrans
profile included in Figure 6.9, classifies that layer as a medium dense sand layer (N=12). As the pile is
loaded, from head to tip, the maximum capacity of all the soil layers is reached (Figure 7.1Gb), the
remaining load is taken as tip resistance by the stiff sand layer (El. -0.12 m to El. -1.62 in). When that
layer reaches its capacity no further distribution of load is possible, and the pile "fails".
The ICP-05, NGI-05 and UWA-05 provide the best predictions in compression, with a variation of less
than 10% to the measured values (Table 7-2). Out of these methods the NGI-05 has the best accuracy for
pile MIT-5. The similarity in their load distribution profile can be noted in Figure 7.1Oa.
The API-00 method performs in exactly the same manner as in the previously described piles. At the top
layers, it tends to predict a higher unit shaft friction resistance (trf). At the lower stiff layers, the design
method restricts its Trf calculated capacity. These limits are smaller than the available capacity that the stiff
sand layers can provide (Figure 7.1Gb).
72
In pile MIT-5, API-00 fails to incorporate into its prediction the influence of the weak layer of sand under
the stiff bearing layer (El. -0.12, Figure 6.9). Its formulation for calculating the bearing pile capacity is
based on effective stresses at the pile tip location, this number is then modified by a bearing capacity
factor to obtain the unit end bearing (Equation 4-2). This approach excludes any averaging technique and
can over estimate the local bearing capacity of a pile resting just above the boundary of a stiff material
overlying a weaker one, as is the case of pile MIT-5 (El. -1.62, Figure 6.9). In this case the bearing factor
is expected to be greatly influenced by the weaker layer and therefore it should be reduced accordingly,
an averaging technique should be recommended.
In pile MIT-5, FUGRO-05 confirms its past performance; it provides an upper bound prediction to the
design methods. The origins of this over estimation was described in the other pile's description. In
summary, FUGRO-05 was developed from load tests performed on open-ended large scale piles. Its
interpolation to small onshore piles fails to accurately predict their behavior at the tip, especially when
there is a presence of a stiff bearing layer.
MIT-5 - Pile Load Test Compression (ID 87-01)
0
500
1000
Load (kN)
1500
0
5
E
E
E
0
-+- Load test
10
--6-
-
Mn
API
FUGRO
- ICP
-V- NGI
4---UWA
S15
:1148kN
:1495 kN
:1661 kN
:1218 kN
:1184 kN
1244 kN
0
25
7s
Figure 7.9
-
MIT-S
-
Compression load test and predicted axial capacity
73
MIT-5 - Unit shaft friction distribution - Compression -
MIT-5 - Axial load distribution - Compression - SAND+CLAY [kN]
0
250
500
750
1000
1250
1500
SAND+CLAY [kPa]
1750
0
100
200
I
I
300
*
400
I
500
600
I
I
700
8.00
8.00
--
-API
API
-'-Fugro
-- Fugro
6.00-
---ICP
ICP
6.00
-- NGI
-- NGI
-
UWA
-- UWA
E 4.00-
4.00
2.00 -
2.00
I
I
I
I
I
I
0.00
-2.00-
-2.00
Figure 7.10 - MIT-5 - Compression - Axial capacity distribution
74
8.
SUMMARY OF REVIEW OF CPT DESIGN METHODS
This Chapter provides a summary of the pile axial capacity predictions, presented in detail in Chapter 7;
and a review of the considerations and limitations that can be drawn for each of the design methods based
on the analysis performed in this thesis for piles.
Two piles were considered for analysis from the results of the axial capacity predictions, namely: MIT-4
and MIT-5. Pile MIT-1 contained mostly clays, and therefore its calculated capacities, included in section
7.6., were used to confirm the CPT based site investigation, and to provide information on the
performance of the design methods. Nevertheless, being the scope of this thesis the review of pile design
methods in sand, its results cannot be included in the present summary
8.1.
Tension loading
Table 8-1 presents the ratios of calculated pile capacity to measured pile capacity (Qcac/Qmeasured) for pile
MIT-4 and MIT-5 under tension. The API design method, based on an earth pressure approach, performs
well, within a variation of
5% of the measured values for the short on-shore piles revised here. The off-
shore design methods provide a greater variation, with a tendency toward the unconservative side (i.e.
Qcalc/Qmeasured >1). The UWA-05, ICP-05 vary in a range from -5% to 10% (Table 8-1), but are considered
acceptable given the Factors of Safety typically used for ultimate capacity of pile foundations
(e.g. F.S.= 2.0). NGI-05 provides great conservatism at Qcac/Qmeasured <0.8. FUGRO-05 has a greater
variation, next to 20%.
Summary of Tension Loading
1.20
-----
---
1.10 ----
-------
- ---
-
-
------
1.00
CY
0.90 ------
-----
-----
0.80 ------------
-------
K-------------
-----------
-- -
---------------
CY 0.70
4
*API-0
5
Pile
0 FUGRO-05 A ICP-05 )KNGI-05 0UWA-05
Table 8-1 - Summary of prediction of total pile capacity in Tension
75
The recognized advantages that the CPT design methods have on the API approach in the off-shore arena
(Lehane et al. 2005a), are not fully utilized for smaller scale, onshore piles.
For example, the API method includes limiting values on the unit shaft friction that tend to over estimate
the effect of the friction fatigue due to driving, and therefore underestimate the contribution of shaft
resistance for many soil layers in off-shore piles. The criterion for assigning this limiting value is based
on the effective stresses (i.e. depth of point of interest). For on-shore piles with lengths shorter than 10-20
m, the imposed limitation is only applicable to the lower soil layers. The advantage that the CPT methods
can provide in tension loading is reduced to a smaller area in the on-shore piles.
8.2.
Compression loading
In compression, three of the CPT design methods - NGI-05, ICP-05, and UWA-05 - provide the best
agreement of calculated to measured load, for both, open-ended piles (MIT-4), and closed-ended piles
(MIT-5) as indicated in Table 8-2.
The API-00 and the FUGRO-05 method provide unconservative results, being FUGRO the design
method in compression with the highest probability of failure,
QcaIc/Qmeasured>1.40,
Table 8-2.
Summary of Compression Loading
1.50
1.40 --
E
o
O1
----
1.30 ---------.20 -- - - 1.10 ----1.10
1.00
0.90
--------
------------------------
-----------------------
- - - - - - - - - - - - - - - - -
A---------------------------
-----
4
*API-00 OFUGRO-05 ,ICP-05
-
- - -
t----------
5
Pile
)KNGI-05 OUWA-05
Table 8-2 - Summary of prediction of total pile capacity in Compression
It was noticed, for the analyzed piles, that the failure load during the compression load tests was achieved
for displacements significantly lower less than 8/D=10%, which is the design criteria of the CPT design
methods. The quality and extent of the load tests, did not allow concluding whether the load test was
terminated before failure was achieved, or that the CPT design methods need to be calibrated for smaller
76
displacement/diameter ratios. Definition of this disagreement will require more detailed loaddisplacement curves.
8.3.
API-00
The main advantages of the API design method, is that it is a simple method, and that it has been applied
in many offshore areas since 1969 (Chow 2005). This historic record proves its quoted conservatism
(Lehane et al. 2005a), and explains the difficulty of adopting a different standard.
In this study it was found that the API-00 provides reliable total axial pile capacities in TENSION. Its
under prediction of the unit shaft resistance of sand layers at depth, is canceled out by over predicting the
contribution of the shallower sand layers. It was noted that API-00 is more conservative with increasing
relative density, i.e. the influence of the limiting shaft friction is greater, compared to the resistance of a
dense sand near the pile tip (e.g. pile MIT-5).
In COMPRESSION, API-00 proves to be very unconservative for open-ended and closed-ended piles.
For the case of open-ended piles, API-00 fails to predict the formation of soil plug, and therefore further
analysis is required by the used to determine if the unit tip bearing is applied to the pile's annulus, the full
plug area, or if the plug is controlled by the coring resistance against the pile's inner walls. For closedended piles, the pile tip bearing is determined locally at the pile tip, with disregard to the surrounding
layers. This can lead to high probability of failure, if the pile is founded on thin, but stiff sand, underlined
by a weak material layer (e.g. MIT-5).
8.4.
FUGRO-05
In the review undertaken in this thesis, the FUGRO-05 design method provided the worst performance,
overestimating the measured capacity by approximately 45% (Table 8-1, and Table 8-2). This method
was developed from empirical results form the Euripides testing program in large scale piles (Zuidberg et
al. 1996), and therefore the limiting values included into its formulations emulate the testing conditions
and dimensions of those load tests. In addition to that, the FUGRO-05 method does not properly deal with
the possibility of a stiff sand layer occurring right at the pile tip (MIT-5 Figure 7.8 and Figure 7.10),
where no reduction of qc for friction fatigue is accounted for. Calibration of the FUGRO-05 for on-shore
piles, is nevertheless possible by adjusting its parameters using a larger database.
77
In COMPRESSION, the FUGRO-05, does not account for the formation of the soil plug. Further analysis
and input by the user is required.
One benefit of the method, is that its formulation and implementation is very simple. It only requires the
input of the pile dimensions and the measured cone tip resistance for the sand layers under consideration.
8.5.
ICP-05
The ICP-05 design method was the pioneer of the CPT design methods. It traces its origins to 1996, it has
been used in 14 projects in North Sea (Chow, 2005), and therefore has a good confidence record. Its
formulation and calculation is more time consuming than the previous two methods. In addition to the
pile properties and the measured cone tip resistance, it requires these input variables: small strain shear
modulus (G0), and the constant volume interface friction angle (6,v). It provides two determine if a soil
plug formation should be considered. Pile tip resistance is provided by three equations, depending on the
plug formation, and pile geometry.
The ICP-05 was developed from a theoretical framework, but adjusted to a database of piles mostly
smaller than 0.9 m in diameter. In this regard, it suits the onshore pile dimensions better than other
methods developed for larger piles.
Its performance in tension and compression loading was satisfactory.
8.6.
NGI-05
The NGI-05 design method performed conservatively for the loading modes explored in piles MIT-4 and
MIT-5.Its formulation is not related directly to the measured cone resistance, qc, but indirectly, because
this parameter is used to calculate the relative density of the sands layers. The calculated relative density
is then incorporated as a factor in the equation for predicting the axial capacity (Equation 4-20).
The calculation procedure of NGI-05 is simple for shaft resistance. Tip bearing requires soil plug
formation considerations, and therefore it is not user independent.
78
This method tends to under predict the unit shaft friction for medium to dense sands layers near the
surface (Figure 7.2 and Figure 7.4). A minimum value of unit shaft friction, tf = 10% the effective vertical
stress, is imposed for this method by equation 4-21. When the water table is located near the pile top, the
resulting unit shaft frictions are too low (Figure 7.2 and Figure 7.4 for pile MIT-4).
8.7.
UWA-05
The UWA-05 design method performed well in this short study. In tension and in compression, openended or closed-ended, its predictions varied less than 10% of the measured load-test values.
The calculation time and effort of this method is the largest of all the methods, but it has the advantage
that it is user independent. It was developed in the same theoretical framework as the ICP-05, and
therefore it follows the same logic and basically the same parameters. One difference is the evaluation of
the formation of a soil plug, which is included intrinsically in the method formulation. Its results in
compression, indicate that its approach is correct.
Its performance both in tension and compression are the most consistent of the design methods (Table 8-1
and Table 8-2) for the short on-shore pile considered in this thesis.
79
9.
CONCLUSION
The execution of this thesis provided a great opportunity to review the applicability and accuracy of the
piezocone (CPT) measurements as a site investigation tool, and their use in predicting axial capacity of
driven piles in siliceous sands.
A detailed site investigation was carried out on a set of on six sites provided by Caltrans (Chapter 5).
Three of these sites have been examined in detail.
Two piles were used for comparing the four off-shore CPT based design methods for predicting axial pile
capacities and the API design criteria; these piles were: MIT-4 and MIT-5. The predictions were
calculated for short on-shore driven piles and compared against the measured load tests.
It was found that a the third test, MIT-1, was performed at a site with more clays than expected
(according to Caltrans database). A revised interpretation of the soil profile was used to compute the pile
capacity; it produced much better estimates of capacity than to those obtained using the original soil
profile.
and that was allegedly founded on sands, was effectively mostly covered by clays. These CPT site
interpretation results were confirmed by calculating the pile axial capacity and compare it to the load test.
The interpreted profile, that include mostly clays, provide a closer and better fit, than the site modeled
with sands only.
The results indicate that of the four off-shore design methods, three of them provide consistent and
conservative results. These methods are: ICP-05, NGI-05, and UWA-05. It was also found that for short
piles (e.g < 20 m) the API-00 design method provides similar results as to CPT-based design methods.
The CPT design methods incorporate a theoretical framework that improves the basic formulation of the
API-00 method. Further comparison of those methods against a larger database should improve their
applicability in both offshore and onshore locations.
This thesis concludes that design guidelines based on CPT measurements allow in depth analysis and
provide detailed information of the soil strata found in a given site. In this sense, they provide the
Geotechnical Engineer the tools to perform a sound and coherent foundation design.
80
REFERENCES
API (1993). "RP 2A-WSD: Recommended Practice for Planning, Designing and Constructing
Fixed Offshore Platforms-working Stress Design 21 edition." American PetroleumInstitute,
Washington D.C.
API (2000), "RP 2A: Recommended Practice for Planning, Designing and Constructing Fixed Offshore
Platform." American Petroleum Institute,Washington D.C.
Aas, G., Lacasse, S., Tunne,T., Hoeg, K. (1986). "Use of in situ tests for foundation design on clay."
Invited lecture ASCE Specialty Conference "in-situ'"Blacksburg
Baldi, G., Belloti, R., Ghionna, V., Jamiolkowski, M., Lo Pesti, D.F.C. (1989). "Modulus of sands from
CPT's and DMT's."12th Internationalconference on soil mechanics andfoundation engineering,
Rio de Janeiro,pp. 165-170.
Baligh M.M., Ladd C.C. (1980). "Cone Penetration in Soil Profiling. Journal of the Geotechnical
Engineering Division." Proceedingsof the American Society of Civil Engineers, Vol. 106, No.
GT4, April, 1980, p.p. 447-461
Bustamante, M., Gianeselli, L. (1982). "Pile bearing capacity prediction by means of static penetrometer
CPT." Proceedingsof the 2 nd European Symposium, Amsterdam, pp. 492-500.
Chow, F. (2005). "Time effects on piles and on their design methods. Presentation in the workshop: Axial
capacity of piles in siliceous sand." InternationalSymposium on Frontiersin Offshore
Geotechnics, Perth, Australia (IS-FOG 2005)
Clausen, C.J.F., Aas, P.M., Karlsrud, K., (2005). "Bearing capacity of driven piles in sand, the NGI
approach". InternationalSymposium on Frontiersin Offshore Geotechnics, Perth, Australia (IS-
FOG 2005)
Helfrich, S.C., Wiltsie, E.A., Cox, W.R., Al Shafie, K.A. (1985). "Pile Load Tests in Dense Sand:
Planning, Instrumentation, and Results." Proceedings,17th Offshore Technology Conference,
Houston, Tex., May 191985, OTC Paper 4847, Vol. 1, pp. 55-64.
Jamiolkowski, M.B., Lo Presti, D.F.C., Manasser, M. (2001). "Evaluation of relative density and shear
strength of sands from CPT and DMT." Soil Behavior and Soft Ground Construction,
Cambridge, GSP No. 119, ASCE, pp. 201-238.
Jardine, F.M., Chow, F.C., Overy, R.F., Standing, J.R. (2005). "ICP design methods for driven piles in
sands and clays." Thomas Telford, London.
Kolk, H.J., Baaijens, A.E., Senders, M. (2005). "Design criteria for pipe piles in silica sands."
InternationalSymposium on Frontiersin Offshore Geotechnics, Perth, Australia (IS-FOG 2005)
Ladd, C.C. (1991). "Stability evaluation during staged construction." Terzaghi Lecture, ASCE Journalof
GeotechnicalEngineering117 (4): p.p. 540-615.
81
Ladd, C.C., Foot, R. (1974). "New design procedure for stability of soft clays." J. of Geot.
Eng. Div., ASCE, GT7, pp. 763-786.
Lehane, B.M, Chow, F.C., McCabe, B.A., Jardine, R.J. (2000). "Relationships between shaft capacity of
driven piles and CPT end resistance." Proceedingsof the Institution of Civil Engineers,
GeeotechnicalEngineering,Vol. 143, No. 2, p.p. 93-101
Lehane, B.M, Randolph, M.F. (2002). "Evaluation of a Minimum Base Resistance for Driven Pipe Piles
in Siliceous Sand." ASCE Journalof Geotechnicaland GeoenvironmentalEngineering,Vol. 128,
No. 3
Lehane, B.M., Schneider, J.A., Xu, X. (2005a). "A Review of Design Methods for Offshore Driven Piles
for Offshore Driven Piles in Siliceous Sand." GEO 05358, University of Western Australia,
Perth.
Lehane, B.M., Schneider, J.A., Xu, X. (2005b). "CPT Based Design of Driven Piles in Sand for Offshore
Structures." GEO 05345, University of Western Australia, Perth.
Lehane, B.M., Schneider, J.A., Xu, X. (2005c) "The UWA-05 method for prediction of axial capacity of
driven piles in sand." Proc. of the InternationalSymposium on Frontiersin Offshore Geotechnics,
Perth, Australia (IS-FOG 2005)
Mimura, M. (2003). "Characteristics of some Japanese natural sands - data from undisturbed frozen
samples". Characterizationand EngineeringPropertiesof NaturalSoils (2), Swets and
Zeitlinger, Lisse, p.p. 1149-1168.
Mayne, P.W. (2005). "Integrated Ground Behavior: In-Situ and Lab Tests. Deformations Characteristics
of Geomaterials." ProceedingsIS Lyon, Taylor & Francis,London, Vol. 2, p.p. 155-177
Meyerhof, G.G. (1976). "Bearing Capacity and settlement of pile foundations." J. Geotech Engr.Div.
ASCE, 102 (3), 195-228
Olson, R.E., Shantz, T.J. (2004). "Axial load capacity of piles in California in cohesionless soils."
Practicesand Trends in Deep Foundations2004, ASCE, GSP 142, Vol 1
Paik, K., Salgado, R., Lee, J., Kim, B. (2003). "Behavior of Open- and Closed-Ended Piles Driven Into
Sands." ASCE Journalof Geotechnicaland GeoenvironmentalEngineering,Vol. 129, No. 4
Randolph, M.F. (2003). "Science and empiricism in pile foundation design." Geotechnique 53, No. 10,
pp.847-875
Randolph, M.F., Cassidy, M., Gourvenec, S., and Erbrich, C. (2005). "Challenges of offshore
geotechnical engineering."Proc. 16'h Int. Conference on Soil Mechanics and Geotechnical
Engineering,Osaka, 123-176.
Randolph, M.F., Dolwin, J., Beck, R. (1994). "Design of driven piles in sand." Geotechnique 44, No. 3,
pp. 427-448.
Randolph, M.F., Murphy, B.S. (1985). "Shaft capacity of driven piles in clay." Proc. 17th Annual
Offshore Technology Conference, Houston, 1, p.p. 371-378.
82
Robertson, P.K., Campanella, R.G. (1988). "Guidelines for Use, Interpretation and Application of the
CPT and CPTU." UBC, Soil Mechanics Series No. 105, Civil Eng. Dept., Vancouver, B.C., V6T
1W5, Canada, 197 pp.
Shantz, T.J. (2006). Email communications April and May 2006.
Schmertman, J.H. (1976). "An Updated Correlation between Relative Density Dr and Fugro-Type
Electric Cone Bearing, qc". ContractReport DACW 39-76 M 6646 WES, Vicksburg, Miss.
Stevens, R.F., Al-Shafei, K.A. (1996). "The applicability of the Ras Tanajib Pile Capacity Method to
Long Offshore piles." ProceedingsOffshore Technology Conference, Houston, Texas, May 1996,
OTC Paper 7974, Vol. 1, pp. 171-180.
Uesugi, M., Kishida, H. (1986). "Influential factors of friction between steel and dry sands". Soils and
Foundations,Vol. 26, No. 2, pp. 33-46
Whittle, A.J. (2005). "Class Notes." MassachusettsInstitute of Technology, MIT - 1.364 Advanced
GeotechnicalEngineering,Chapter 5, p.p. 3-39
Zuidberg, H.M., Vergobbi, P. (1996). "EURIPIDES, load tests on large driven piles in dense silica
sands." Proceedings, 28th Offshore Technology Conference, Houston, Tex., May 1996, OTC
Paper 7977, Vol. 1, pp. 193-206.
83
APPENDICES
84
Appendix A - Site Investigation pile MIT-1
PILE MIT-1 - SITE INTERPRETATION RESULTS
Pile - ID # 1
Type of pile:
End condition:
Diameter:
Thickness:
Base area of pile:
Perimeter:
Weight of pile:
CPT Top
Steel pipe pile
Open ended
0.41 m
0.5" (1.27 cm)
0.0157 m2
1.28 m
16.86 kN
Soil
type
Top of pile
+7.32
N
Su
Soil
*
[bpf
ikPal
type
(*I
-t
19
-
-
-
-
Sand
34
20
J ayd
Clay
34
20
34
30
-
+7.82
Fill
18.8
-
-
+7.42
Sand
. "w
90
+6.37
+6.17
+6.40
+6.40
Water table +4.87
19.6
11
-
Clay
+5.27
+4.62
+4.42
90
35
36
Sand
60
Clay
Elevations
(m)
-0.41
Sand
20.04
28
Sand
20.1
21
i
i
150
Clay
+0.61
14.03
+0.12
13.11
Sand
19.6
11
-2.28
Sand
20.1
27
-5.18
-5.79
-7.01
38
45
Clay
Sand
40
60
40
60
175
-
-3.23
-3.35
-4.57
Sand
-1.08
-2.13
-6.71
-6.88
t
+3.27 i
+2.13
C
Ia.
Pile tip
CPT tip
[% I
Fill
+8.67
+8.54
0.92
Bottom of
footing
Su
kPa
Dr
+10.67
-
+8.54
yso"I
[kNm3j
+10.67
+10.67
Surface
Interpretation based on CPT
CALTRANS Soil Profile
Clay
18.8
Sand
Sand
20.4
19.8
50
18
-4.98
-5.38
Sand
20.9
72
-6.23
-6.88
35.91
-4.10
125
Clay
90
Clay
42
70
Clay
Sand
175
i
44
1 80
-
85
MIT-1a
0
MIT-lb
200
400
0
11 -
11
10
10
10,000
MIT-Ic
20,000
I
I
9
9
8
8
7
7
6
6
5.
5
0
11
I
I
I
I
I
I
200
-
400
10
4
I
I
I
4
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
9
8
6
5
4
I
3
.2
2
]
3
I
I
2
1
1
I
I
I
0
0
I
I
I
I
I
I
I
I
-1
-2
-2
-3
-3 -
I
I
I
-100
0
100 200 300 400
9
8
6
ovo
-4
-5
-5
U0
-6
I
I
I
I
I
I
I
I
I
I
I
1
I
I
I
I
I
I
I
I
I
-1
-7
I--- s'vo - - - uO -svo,
kPa
I
-4
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
-5
I
I
I
-6
I
I
I
-7 -
I
I
I
I
I
-
-
-
I
I
I
I
I
-
0
-1
-2
I
I
I
I
I
I
I
I
I
I
-5
-6
-7
-7
---Tip resistance (qc), kPa
I
I
I
-3
I
I
I
I
I
I
3
1
-3
-6
I
2
-2
4i~IIIiI
I
5
II
-4
I
7
4
I
2
0
-1
800
10
I
I
I
I
I
I
600
11
7
I
I
I
MIT-Id
-
Sleeve friction (fs), kPa
-Pore
pressure (u2) - - - uo, kPa
MIT-i - Chart A - Vertical profile, CPT readings
86
MIT-I
0
100 200 300 400
11
I
1~
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I_
I
I
II
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
9.
I
I
8
I
I
I
7-
I
6-
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
5-
I
I
I
I
I
I
I
I
,1
I
I
I
3-
I
I
I
I
E
S2-
I
I
I
I
1
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
-2-
I
I
I
I
-41
I
I
I
I
I
-5
I
-6I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
-71
8
I
7
6
6
5
(qc-sv)/s'vo
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
3
2
I
I
I
I
I
I
I
I
7
I
I
I
I
I
I
8
I
I
I
I
I
I
I
0-
-
I
-~
-1
I
I
-2
-
-.----I.
I
I
I
I
I
I
I
I
F~I.
I
I
I
-4-
I
I
I
I
I
-5-
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
II
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
-o
-6-
-6
I
-7.
-
I
I
I
I
I
I
-3
I
I
I
I
I
9
4
I
I
I
I
9
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
10
I
I
I
I
I
I
I
I
I
I
.
I
I
I
I
I
I
10
-0.10 0.15 0.40 0.65 0.90
11
5
I
I
~ -I-----I
I
I
I
I
I
I
I
I
I
0.10
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
0.05
I
I
I
I
I
I
I
I
I
I
-3-
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
-
I
-1
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
0-
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
0.00
MIT-1
11
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
500
~
I
I
I
I
10-
4
MIT-I
-7
-fsqc
I
I
I
I
---
I
I
u2qc
MIT-1 - Chart B, CPT normalized profiles
87
MIT-1 - Correlation depth vs qc [kPa] for
various ' - (Mayne 2003)
0
20,000
30,000
40,000
50,000
60,000
0
11
11
10
10
9
9
8
8
7
7
6
6
5
5
4
4
E
3
0
2
CIO
ED
10,000
MIT-1 - Correlation z vs q, [kPa] for various Dr
(Jamiolkowski 2003)
30,000
40,000
50,000
Axx
I
I
I
I
I
I
I
I
I
I
I
I
2
1
0
I
-1
I
0
-1
I
-2
-2
-3
-3
-4
-4
-5
-5
-6
I
-6
I
-7
-7
3436 38
-
20,000
3
I
I
I
1
-
10,000
30
38
46
40
-
42
32
40
48
44
-
- - 34
-'42
qc, kPa
46 =
--
4' [0]
40% 50% 60% 70%
0.1
36
44
--
0.5
0.9
-
-0.2
0.6
1
80%
-
90%
100% = D,
0.3
-m--0.4
'-0.7
0.8
qc,kPa
MIT-1 - Chart C . Friction angle and Relative density graphs for cohesionless materials
88
MIT-1
0
100
MIT-1 -suDSS
200
300
o
400
100
11
11
I
I
I
I
I
10
I
I
I
I
I
10
9
8
I
I
I
9
-
I
I
I
8
I
7
7
200
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
6
6
I
5
5
-
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
4
4
3
I
I
I
I
3
I-I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
0
300
I
I
I
I
I
MIT-1 - OCR
MIT-1 - Nk
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
9I
I
I
I
I
I
I
I
I
I
87.
I
I
I
I
I
I
I
I
I
6-
I
I
2
2
w 1
I
I
I
I
1
4-
I
I
I
I
I
I
I
I
I
I
I
I
3
I
I
I
I
0
0
-1
-1
-2
I
I
I
I
I
I
I
I
-2
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
-I
-4
Ivo
v
'
'I
I
I
I
I
I
I
I
I
I
-5
-5
-6
-6
I
I
I
I
I
I
I
I
I
0
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
:I
-7 .1
Su Interpreted, kPa
I
I
I
I
I
I
I
1
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
2
I
I
0
-2
-3
-4
-5
I
I
I
I
I
I
I
I
I
I
-6
I
I
I
I
:
:I
-4
-5
I
I
I
I
I
I
I
I
I
-6
I
-7 -
-7.
-
I
I
4
-2
I
I
I
I
7
-1
I
I
I
I
I
I
I
8
-1
I
:7 I
I- - - u0 - s'vo ----- svo
I
-3
I
I
-4
-7
1
-3
I'
'
I
I
I
I
I
I
I
I
-3
I
I
I
I
9
3
I
I
I
I
I
I
5
2-
I
I
10
C
0
15
6
I
5
I
I
I
10
I
I
I
5
11
10
I
I
I
0
30
I
I
I
I
I
I
20
I
I
I
I
I
I
10
11
I
--
Cone Resistance Factor
-- OCR
MIT-1 - Chart D, (Undrained strength and stress history of clay layers)
89
1.
1000
7
8
4 k0
N4
MIT-1 - Soil Classification
(Robertson & Campanella, 1988)
I''''I
t:
-9-
11
0
10
1-1
100
9
0
8
7
0
A~
X
(D
6
6
X
5
10
I I I
4
G)
I i I , l li i l i l
3
0
l
IfIi
i
I
Il i
I If ill
I I I I II
2
0*
U
1
0.1
0
10
1
Friction Ratio
1.
2.
3.
4.
5.
1
Sensitive Fine Grained
Organic Soils -Peats
Clays - Clay to silty clay
Silt mixtures - Clayey silt to silty clay
Sand mixtures - Silty sand to sandy silt
6. Sands - Clean sand to silty sand
7. Gravelly sand to sand
8. Very stiff sand to clayey* sand
(
I r M O I- I I I I I Ili
i IiI
i
I I i I
-1
-2
-3
-4
-5
-6
-7
0
1
10
100
1000
10000
9. Very stiff fine grained*
F-- fs/(qc-svo) -- (qc-sv)/s'vo
or
cemented
*Heavily overconsolidated
MIT-1 - Chart E - Soil Classification (Robertson and Campanella, 1988)
90
Appendix B - Site Investigation pile MIT-5
Pile MIT-5 - SITE INTERPRETATION RESULTS
Pile - ID # 5
Type of pile:
Square concrete pile
End condition:
Closed ended
Diameter:
0.36 m
Thickness:
Base area of pile: 0.0993 m2
1.12 m
Perimeter:
26.38 kN
Weight of pile:
CPT Top
Surface
+10.98
+10.67
Top of pile
Bottom of
footing
+9.45
Soil
y-oi
N
Soil
'
Dr
Su
type
[kN/m3]
[bpfq
type
10
[%]
[kPa]
+10.98
+10.67
-
19
Fill
18.80
Sand
19.8
Sand
19.8
Sand
20.1
14
Sand
19.8
9
0.91
-8
+8.54
+8.54
8
+7.62
Water table
+6.40
-0
+3.96
10.35
Sand
Sand
19.8
+0.91
+0.30
-0.30
-0.91
CPT tip
Pile tip
-1.62
-1.83
-1.52...
7
20.1
+2.44 1
(in)
-
-
-
Sand
38
45
-
Sand
40
55
-
Sand
38
40
-
-'
-
+3.83
Sand
36
30
-
+3.13
+2.73
+2.38
+2.18
Clay
-
-
110
Sand
38
45
-
-
-
+8.54
+7.73________
+5.58
+5.49
+4.57
0
Fill
+6.71
0.36
Elevations
Interpretation based on CPT
CALTRANS Soil Profile
12
i
+4.5
4.
-
Sand
36
30
-
Sand
20.4
20
+1.38
Clay
-
-
100
Sand
38
40
-
Sand
20.4
28
+0.28
Sand
20.4
35
Sand
60
65
-
Sand
Sand
Sand
40
41
20.4
56
Sand
41
70
-
20.4_[
34
Sand
20.4
12
-
-1.62
-3.05
Pile-soil elevations profile
91
0
200
100
MIT-5
MIT-5
MIT-5
300
0
0
30,000
20,000
10,000
200
400
MIT-5
600
-100
800
-50
0
50
I
9
I
I
I
I
9
I
100
.
11
I.
. ,
I
I
I
I
10
10
I
9-
8
I
I
I
8
I
I
I
I
7
I
I
I
I
I
I
I
I
I
I
I
I
2
I
I
I
I
I
I
I
I
1
I
6
9
7-
4
I
6-
I
-I
I
3
5I
I
I
4
I
I
3
I
-2
I
I
I
I
I
I
I
I
I
I
I
II
I
I
I31
I
I
I
I
I
I
I
I
0
I
I
I
I
I
I
I
I
I
I
I
-1
I
I
I
uo
II
I
I
'
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
-3
- - - uo ---
s'vo -
-so
-Tip
resistance (qc), kPa
---
Sleeve friction (fs), kPa
I--
Pore pressure (u2) - - - uO, kPa
MIT-5 - Chart A - Vertical profile, CPT readings
92
0.000
300
200
100
0
0.020
11
I
I
I
10-
___
I-
I
I
8
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
8
I
I
7
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
6
I
I
7
I
I
I
I
I
I
I
I
I
I
5
3
I
I
I
2
I
I
I
1
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
0
I
I
I
I
I
I
I
I
I
I
I
-1
5
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
'
-3
0.000
0.020
8
7
I
I
I
I
I
I
I
I
6
1
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
3-
2-
I
I
I
I
1
I
I
I
I
I
I
I
I
I
I
I
0
I
I
2
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
C
I
I
I
'
I
'
I'
-
-2-
-2
-3-
-3
-*- fs/qc
(qc-sv)/s'vo
MIT-5
-
-1
I
I
I
I
I
I
0
I
I
I
I
3
I
I
I
I
I
I
I
I
I
I
5
4
4-
I
I
I
I
I
I
I
-0.020
9
I
I
I
I
I
-2
-0.040
11
10
10
I
I
I
I
I
I
I
I
I
I
I
I
I
I
0.080
I
I
I
I
I
I
I
I
I
I
0.040 0.060
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
9-
I
I
I
C
I
I
I
I
MIT-5
MIT-5
MIT-5
-+-u2/qc
Chart B, CPT normalized profiles
93
MIT-5 - Correlation depth vs q, [kPa] for various Dr
(Jamiolkowski 2003)
MIT-5 - Correlation depth vs qc [kPa] for various
(Mayne 2003)
5,000 10,000 15,000 20,000 25,000 30,000 35,000 40,000
0
40,000
30,000
20,000
10,000
0
11-
11
9
1-I.1
9
x!l
3k1
fEli
7-
-
--
I
6
11
5
0
cc
Q)
flV-kL
E
5
0D
4
I
X
I
A
U~I
Iii
IiU
ii U
___
lA~I
~U
i
i~
==t
A7
IY
'I
ti
I-
3
U
.
K
.
I:
I
- -4-"
U
4 lZLtiZ][I
IL
A 1~1X~X-\-~--~
.1
5-I.a--~--J~I
3
k
I
a d=.;
7
C
I
X
ILI
LS
8
8
6
II
I
I
10
II.
10
I
I
I
I
I
I
I
II
U
2
2
I1
I
1
-u
0
EIE
-1
F
-2
34 36
--
30 -32
0
Iti
38
:I-
-1
-
-
I
I
I
-2
40
34 -"-36 -u-38 --
42
40 -+-42 -44
44
-46
=
-+-48
60%
30% 40% 50%
[*]
-qc,
kPa
-0-0.1
0.2 -"--0.3 --
0.4 --
0.5
- -0.6
70%
-
80%
0.7 -
0.8 -
90% = Dr
0.9
--
1 -.- qc,kPa
MIT-5 - Chart C . Friction angle and Relative density graphs for cohesionless materials
94
MIT-5 - Depth vs Su
MIT-5
0
200
100
100
0
300
MIT-5 -Depth vs
OSS
0
200
11
I
I
I
I
I
I
I
I
I
I
I
20
30
0
11
11
10
10
I
9
9 -
I
I
8
8
7
7
7-
6
6
6
5
5
4
4
3
3-
2
2 8-
1
1
1
0
0
0
0
-1
-1
-1
-1
-2
-2
-2
-3
-3
8
I I
I
ii
E
6-
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
|
1
I
I
I
I
I
I
I
I
1
I
i
I
i
I
I i
I
I i
I
I
I I
Ii
8
5
5I
.
cc
I
I
4
I
SI
SI
9
9 -
E_
I
I
10
10
10
MIT-5 - Depth vs OCR
Nk
I
I
I
I
I
I
I
I
I
I
3-
3
2-
2
Il e i
-2-
I
UO
II
I
VI
-
-3
- - - u0 ---
s'vo -svo
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
I
II
I
I
I
I
I
I
I
I
I
--- su Interpreted, kPa
30
20
10
I
--
-
--
3.
I-
Cone Resistance Factor I
MIT-5 - Chart D, (Undrained strength and stress history of clay layers)
95
MIT-5-Soil Classification (Robertson & Campanella 1988)
MIT-5 - Soil Classification
(Robertson & Campanella, 1988)
1000,
9
11
I I I IillT
10
111111I
I
9
100
I
8
-
1 1
1 1
111
I
1
I I f1i ll
1
I I I I I f ll1
11
,
i
T
1 111
|
i 1 I l II
1
1 11
11 1
I
I I I I I I1II
II
1
1 1 1 11 1
I I I
I11
7
1111I
6
z
10
0
4.,
E
5
0
(U
*
4
1
T
I
I
1
1 1 1 1 111
t I
I
I
I
1111
1 1=911
11 1111
I
I
1t t
I
1 1 1 f1 111
1
I I
I t I I
3
3
0.1
1
2
10
Friction Ratio
1
1
~ ~ ~ ~ ~ ~11 1T-r
~ ---
-- --- 1 l
I i 1
i
i 1 1i 1
0
1. Sensitive Fine Grained
2 . Organic Soils -Peats
3 . Clays - Clay to silty clay
4 . Silt mixtures - Clayey silt to silty clay
5 . Sand mixtures - Silty sand to sandy silt
6 . Sands - Clean sand to silty sand
7 . Gravelly sand to sand
8 . Very stiff sand to clayey* sand
9 . Very stiff fine grained*
-1
-2
-3
0
10
1
---
fs/(qc-svo) --
100
1000
10000
(qc-sv)/s'vo
*Heavily overconsolidated or cemented
MIT-5 - Chart E - Soil Classification (Robertson and Campanella, 1988)
96
I
MIT-5 - Relative Density
MIT-5 - Clay Shaft friction, kPa
8.00
8.00
I
.
I
0
20
I
6.00
C 4.00
0
u
6.00
2.00
...
~~ ~ ~ .~ ~
N .66... .X
.
,
.
.
.
..
.
0.00
-2.00
(0.50)
(0.30)
(0.10)
0.10
I---
0.30
0.50
0.70
Jamiolkowsky - -NGI
0.90
I
1.10
1.30
60
40
-+-
80
100
120
qc/50 --- Su
MIT-5 - Chart F - Comparison of relative density and undrained shear strength
97
Appendix C - Pile-soil profile for pile MIT-3
Pile - ID # 3
Type of pile:
End condition:
Diameter:
Thickness:
Base area of pile:
Perimeter:
Weight of pile:
Top of pile
CPT Elevation.
Surface elevation
Bottom of footing
Steel HP 10x57 pile
Open ended
0.25 m
0.0108 m2
CALTRANS Soil Profile
1.03 m
12.90 kN
Soil
type
ysoil
N
Su
[kN/m3]
[bpfj
[kPa]
Fill
18.06
-
-
Sand
19.6
12
-
Sand
20.4
75
-
Sand
19.6
9
-
Sand
19.6
12
-
Sand
20.1
30
-
Sand
19.9
20
-
Sand
19.08
15
-
Sand
20.06
96
-
Sand
20.1
36
-
Sand
20.1
20
-
Sand
20.1
28
-
Sand
20.3
34
-
+110.52
+110.06
+110.06
1.83
+108.69
+108.69
+107.93
+107.32
+106.10
0)
0)
C
CU
+105.18
+104.57
(U
CU
C
Ia0
Elevations
+103.35
15.55
(mn)
+102.13
13.72
0.25
-
+100.91
+100.00
CPT tip
+98.91
Water table
+97.56
+98.48
+96.95
Pile tip
+94.97
+94.82
98
Appendix D - Pile-soil profile for pile MIT-6
Pile - ID # 6
Type of pile:
End condition:
Diameter:
Thickness:
Base area of pile:
Perimeter:
Weight of pile:
Steel H P 14x89 pile
Open e nded
0.36 m
0.0168 m2
1.45 m
22.01 kN
CALTRANS Soil Profile
Soil
ysovl
N
Su
[kPa]
[bp]
type [kN/m3]
Surface elevation +27.13
CPT Elevation
+27.13
+26.83
1.84
Top of pile
+25.30
0.60
Bottom of footing +24.69
Fill
18.1
-
-
Clay
17.3
0
95.77
Sand
20.1
30
-
Clay
18.1
0
119.71
Clay
17.3
0
95.77
Sand
20.1
30
-
Sand
20.4
59
-
Sandy
20.4
57
-
18.1
20.4
20.4
0
50
65
119.71
20.4
85
-
Gravel
20.4
94
-
Gravel
20.4
151
-
Gravel
20.4
96
-
+24.69
C
+21.65
n
Water table
+19.97
+19.82
0.36
-
+17.99
Elevations
(m)
16.47
+15.85
+15.24
+14.02
CPT tip
+13.48
-L-
gravel
+12.20
+11.59
+10.98
+10.37
Clay
Sandy
gravel
+9.76
Pile tip
+8.23
-
-
+8.54
+7.01
+5.79
99
MIT-1 - SCENARIO 2 PREDICTION - Unit shaft friction - Tension SAND+CLAY [kPa]
MIT-1 - SCENARIO 2 PREDICTION - Axial load distribution Tension - SAND+CLAY [kN]
0
7.00 -
100
200
300
400
500
600
700
800
900
0
1000
50
100
150
200
250
300
7.00
6.00-
6.00
5.00
5.00 -
4.00-
4.00-
3.00
3.00
2.00
2.00-
1.00
1.00 -
.2 0.00
0.00I
iii -1.00 -
-1.00-
-2.00
-2.00
-3.00 -
-3.00
-4.00-
-4.00
-5.00-
-5.00-
-6.00
-6.00-
-7.00.
-7.00
-API
-
Fugro
m ICP - - -x-- NGI --
UWA]
-- API --
Fugro -&- ICP -,- NGI - -- UWA
Appendix E - MIT-1 - Axial capacity prediction - Second Scenario (Mostly sand profile)
100