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Analysis of the Colorado Department of Transportation driven pile data base

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Title:
Analysis of the Colorado Department of Transportation driven pile data base
Creator:
Vinopal, Robert J
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English
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xix, 266 leaves : ; 28 cm

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Subjects / Keywords:
Piling (Civil engineering) -- Databases ( lcsh )
Piling (Civil engineering) ( fast )
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Databases. ( fast )
bibliography ( marcgt )
theses ( marcgt )
non-fiction ( marcgt )
Databases ( fast )

Notes

Bibliography:
Includes bibliographical references (leaves 261-266).
General Note:
Department of Civil Engineering
Statement of Responsibility:
by Robert J. Vinopal.

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|University of Colorado Denver
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|Auraria Library
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All applicable rights reserved by the source institution and holding location.
Resource Identifier:
707494048 ( OCLC )
ocn707494048
Classification:
LD1193.E53 2010m V56 ( lcc )

Full Text
ANALYSIS OF THE COLORADO DEPARTMENT OF
TRANSPORTATION DRIVEN PILE DATA BASE
by
Robert J. Vinopal
B.S. Civil Engineering, University of Colorado Denver, 1999
A thesis submitted to the
University of Colorado Denver
In partial fulfillment
of the requirement for the degree of
Master of Science
Civil Engineering
2010


This thesis for the Master of Science
degree by
Robert J. Vinopal
has been approved
by
Shing-Chun Trever Wang
Brian T. Brady
/// b/20/tf
Date


Robert J. Vinopal (M.S., Civil Engineering)
Analysis of the Colorado Department of Transportation Driven Pile Data Base
Thesis directed by Professor Nien-Yin Chang
ABSTRACT
This thesis presents analyses of the Colorado Department of Transportation driven
pile data base focusing mainly on Grade 50 steel H piles driven into sedimentary
bedrock along the Front Range and steel pipe piles on thick soil deposits. The study
examines representative soil profiles and related soil design parameters, pile static
capacity estimation, evaluation of pile stress during driving, and relationships
between pile driveability and driving resistance. Weak sedimentary rocks along the
Front Range can develop nominal resistance for Grade 50 steel piles with reasonable
penetration lengths. In many typical rock profiles, design pile loads can approach
permissible structural limits without requiring excessive pile length.
For H piles in clay shale and shale, the DRIVEN program yielded conservative
estimates of nominal pile estimate compared to PDA measurements. Models of pile
side (shaft) resistance calculated using the box perimeter of the four sides or the
perimeter of only the two flanges, and end bearing resistance derived using the box
area are recommended for preliminary estimates of H pile length and capacity for the
end of drive condition. In uncemented and partially cemented sandstone, the pile


flange perimeter area/box area and pile box perimeter/box area models have very
similar capacities in DRIVEN. Use of modified SPT derived friction angles for end-
bearing and side friction is recommended.
Pile compressive stress calculated by the wave equation as implemented in
GLRWEAP showed, in general, a satisfactory match with the PDA measured stress.
A value of 80 percent hammer efficiency is recommended in GRLWEAP using 70
and 90 percent of rated combustion pressure. For the database, maximum pile
compressive stress did not exceed 44 ksi over a wide range of pile capacities in
different geologic profiles. Pile driving stress does not appear to be a limiting factor
to utilizing piles in weak rocks along the Front Range with PDA monitoring. Driving
resistance does not show a consistent correlation to pile nominal capacity for the
database as a whole. The absence of overall predictive relationships between nominal
pile capacity measured at re-strike conditions by the PDA and re-strike driving
resistance verifies the necessity of site and hammer specific correlations between
nominal pile capacity measured by the PDA and field driving resistance criteria.
This abstract accurately represents the content of the candidates thesis. I recommend
its publication.
Signed^
'c£i> / O
ien-Yin Chang


ACKNOWLEDGEMENT
This thesis was performed under the supervision of Professor Nien-Yin Chang. The
insight, guidance and support from Professor Chang were an important contribution
to the completion of my study at the University of Colorado Denver. I would also
like to thank Dr. Shing-Chun Trever Wang, Colorado Department of Transportation,
and Professor Brian T. Brady for serving on the final examination committee.
Funding and support for the study was provided through the Research and
Implementation Council of the Colorado Department of Transportation. I appreciate
the access and use of internal construction files from the Colorado Department of
Transportation. Alan Hotchkiss, Colorado Department of Transportation, provided
important data on pile sites and field procedures of pile installation and dynamic
testing.
Civil engineering graduate students Dr. Hien Nghiem and Mr. Quoc Cuong Vu
assisted in drafting and CAPWAP analysis.


FRONTISPIECE
H Pile Installation at Plum Creek Parkway @125, Douglas County,


CONTENTS
Figures.....................................................................x
Tables..................................................................xviii
Chapter
1. Introduction.............................................................1
1.1 Study Background........................................................1
1.2 Objective...............................................................3
1.3 Research Approach.......................................................4
1.4 Engineering Significance................................................5
2. Review of the CDOT Driven Pile Data Base.................................6
2.1 Geologic-Geographic Setting.............................................6
2.2 Rock Terminology........................................................8
2.3 General Geology........................................................10
2.3- 1 Colorado Piedmont...................................................10
2.3- 2 Denver Basin........................................................13
2.3- 3 Raton Basin.........................................................15
2.3- 4 Intermountain Valleys...............................................16
2.3- 5 High Plains in Eastern Colorado.....................................18
2.4 Rock Strength of Bearing Stratum......................................18
vii


2.4-1 Range of Rock Strength in the Front Range..............................20
2.5 General Observations of Rock Profiles in the Front Range, Colorado,
and H Pile Capacity.......................................................23
2.6 Discussion of Grade 50 Steel H Piles Bearing in Expansive Clay Shale.....35
3. Piles Driven into Clay Shale, Shale, or Sandstone.........................41
3.1 Pile Design Loads and Design Resistance...................................41
3.2 Provided Nominal Pile Capacity Measured by the PDA.......................43
3.3 Pile Setup Time..........................................................44
3.4 Maximum Driving Stresses in Piles Measured by PDA........................50
3.5 Hammer Energy Transfer Ratio.............................................57
4. DRIVEN Analysis of Piles in Clay Shale, Shale, Sandstone.................58
4.1 DRIVEN Analysis of Piles in Clay Shale, Shale.............................59
4.2 Selection of Input Parameters for DRIVEN Analysis........................61
4.3 DRIVEN Capacity Estimates for H Piles in Clay Shale, Shale..............67
4.3-1 Effects of Pile Setup Time and SPT Blow Count on DRIVEN Analysis........74
4.4 DRIVEN Analysis of H Piles in Sandstone.................................83
4.5 Selection of Input parameters for DRIVEN Analysis........................86
4.6 DRIVEN Capacity Estimates for H Piles in Sandstone.......................87
5. Piles Driven into Sand, Clay, Gravel.....................................103
5.1 Pile Design Loads and Design Resistance..................................108
5.2 Provided Nominal Pile Capacity Measured by PDA..........................109
5.3 DRIVEN Analysis of Piles in Sand, Clay, Gravel..........................111
viii


5.4 Selection of Input Parameters for DRIVEN Analysis.....................113
5.5 DRIVEN Capacity Estimates for H and Pipe Piles in Sand, Clay, Gravel..114
6. WAVE Equation Analysis of Driven Piles.................................118
6.1 Selection of Input Parameters for GRLWEAP Analysis....................119
6.2 Results of GRLWEAP Analysis...........................................122
6.2- 1 GRLWEAP Analysis of Transmitted Energy...........................122
6.2- 2 GRLWEAP Analysis of Compressive Stress...........................123
6.2- 3 GRLWEAP Analysis of Driving Resistance...........................130
6.3 Observed Driving Resistance...........................................144
7. Discussion of H Pile Length in Front Range Rocks.......................149
7.1 Design Charts for Estimation of H Pile Length.........................149
7.2 Pile Length and Pile Capacity in Front Range Rocks....................154
7.3 Pile Resistance and Penetration Length.................................174
8. Conclusions.............................................................177
Appendix
A. Boring Log Profiles with Pile, Hammer, and Measurement Data............182
B. Data Tables............................................................241
References.................................................................261
IX


FIGURES
Figure
1 Location map of data sites in the investigation..............................8
2 Physiographic sub-provinces of the Great Plains.............................11
3 Bedrock geology of the Denver Basin.........................................15
4 Geologic cross section through the Southern Rocky Mountains.................17
5 Boring log profile of weathered and partially-softened clay shale
gradational to hard clay shale..............................................24
6 Boring log profile of weathered or softened clay shale section
gradational to very hard clay shale or shale................................26
7 Boring log profile of weathered clay shale section
gradational to extremely hard cemented shale................................28
8 Boring log profile of very thick section of hard to very hard clay shale....30
9 Boring log profile of extremely hard, partially to moderately cemented shale....31
10 Boring log profile of thick section of uncemented sandstone.................33
11 Distribution of factored design loads for H-piles and pipe piles
in clay shale, shale, and sandstone.........................................41
12 Range of factored design load and required factored pile resistance
for a resistance factor of 0.7
.42


13 Distribution of required factored resistance for H-piles, pipe piles
in clay shale, shale, and sandstone.........................................43
14 Comparison between required factored resistance and nominal
pile resistance as measured by the PDA......................................44
15 Distribution of setup times at the pile data sites........................45
16 Boring log profile of 24 inch open-end pipe pile with 695 kips capacity...47
17 Boring log profile of 24 inch open-end pipe pile with 1296 kips capacity..48
18 Correlation between maximum pile stress and nominal pile resistance
as measured by the PDA......................................................52
19 Correlation between transferred hammer energy and nominal pile resistance
as measured by the PDA......................................................52
20 Correlation between transferred hammer energy and pile compressive stress
as measured by the PDA......................................................53
21 Wave equation analysis of H 12x74 pile driven through 20 feet of sand
into 20 feet of bedrock.....................................................55
22 Wave equation analysis of H 12x74 pile driven through 20 feet of sand
into 20 feet of bedrock.....................................................56
23 Distribution of hammer energy transfer ratio for all H-piles and pipe piles.57
24 Low displacement piles that can be driven into weak rock....................59
25 Correlation between clay undrained shear strength and friction (adhesion)
factor in steel pipe piles..................................................63
26 Variation in adhesion factor based on geomaterials strength.................64
XI


27 Nominal pile capacity (PDA) verses DRIVEN estimated capacity (EOD)
for total perimeter, tip area model.........................................69
28 Nominal pile capacity (PDA) verses DRIVEN estimated capacity (EOD)
for flange perimeter, box area model........................................70
29 Nominal pile capacity (PDA) verses DRIVEN estimated capacity (EOD)
for box perimeter, box area model...........................................71
30 Nominal pile capacity (PDA) verses DRIVEN estimated capacity (EOD)
for total perimeter, tip area model.........................................73
31 Nominal pile capacity (PDA) verses DRIVEN estimated capacity (EOD)
for box perimeter, box area model and for flange perimeter, box area model..75
32 Nominal pile capacity (PDA) verses DRIVEN estimated capacity (EOD)
for box perimeter, box area model and for flange perimeter, box area model..76
33 Boring log profile for abutment #2, structure K-18-GQ with test pile.........79
34 Boring log profile for abutment #1, structure ADA 120-09.5W308
with test piles..............................................................82
35 Coefficient cct implemented in DRIVEN........................................84
36 Bearing capacity factor implemented in DRIVEN................................84
37 Relationship between maximum unit pile toe resistance and friction angle
for cohesionless soils......................................................85
38 Nominal pile capacity (PDA) verses DRIVEN estimated capacity (EOD)
for flange perimeter/tip area model.........................................90
xii


39 Nominal pile capacity (PDA) verses DRIVEN estimated capacity
(EOD) for total perimeter/tip area model....................................91
40 Nominal pile capacity (PDA) verses DRIVEN estimated capacity
(EOD) for flange perimeter/box area model...................................93
41 Nominal pile capacity (PDA) verses DRIVEN estimated capacity
(EOD) for box perimeter/box area model......................................94
42 Boring log profile for abutment #2, structure F-12-CA with test pile........95
43 Force and velocity records for CAPWAP analysis, structure F-12-CA...........96
44 DRIVEN analysis of 12x74 H-pile in shallow, uncemented
Dawson sandstone, structure H-17-DA abutment #1.............................97
45 Boring log profile for abutment #1, structure H- 17-DA with test pile.......98
46 DRIVEN analysis of 12x74 H-pile in shallow, uncemented
Laramie-Fox Hills sandstone, structure D-17-EA abutment #1..................99
47 Boring log profile for abutment #1, structure D-17-EA with test pile........100
48 Data curves from Meyerhof with end bearing capacity in uncemented
sand compared to end bearing capacity calculated by DRIVEN..................102
49 Boring log profile for abutment #2, structure C-21-BO with test pile........104
50 Boring log profile for abutment #1, structure C-22-BV with test pile........105
51 Boring log profile for pier #2, structure B-27-J with test pile.............106
52 Boring log profile for abutment #2, structure E-12-I with test pile.........107
53 Distribution of factored design loads for H-piles and
pipe piles in sand, clay, gravel
xiii
108


54 Range of factored design load and required factored pile resistance
for a resistance factor of 0.7............................................109
55 Correlation between pile length and nominal pile capacity
measured by PDA...........................................................110
56 Correlation between nominal pile capacity and pile compressive
stress as measured by PDA.................................................110
57 Correlation between nominal pile capacity and pile compressive
stress as measured by PDA.................................................111
58 DRIVEN capacity analysis for 12x74 H pile in uniform sand section
using box perimeter for shaft resistance and box area for tip resistance..112
59 Nominal pile capacity (PDA) verses DRIVEN estimated capacity for box
perimeter-box area for H piles, pile perimeter-closed end for pipe piles..117
60 GRLWEAP program components.................................................120
61 Correlation between measured and calculated Enthru values.................124
62 Range of rated combustion pressure percentage used in GRLWEAP
to match PDA Enthru values................................................124
63 Correlation between measured and calculated compressive stress
for piles in clay shale, shale............................................126
64 Correlation between measured and calculated compressive stress
for H piles in sandstone..................................................127
65 Correlation between measured and calculated compressive stress
for piles in sand, gravel, clay...........................................128
XIV


66 GRLWEAP drivability model for Delmag D 19-42 hammer
in example profile............................................................131
67 GRLWEAP drivability model Delmag D 12-32 hammer
in example profile............................................................132
68 GRLWEAP drivability model for structure B-23-AW, Abutment #1...................134
69 GRLWEAP drivability model for structure C-16-BC, Abutment #1...................136
70 Boring log profile of 24 inch closed-end pipe pile with refusal at 16 feet.....137
71 Initial GRLWEAP drivability model for structure F-18-BK, Pier #3...............139
72 Modified GRLWEAP drivability model for structure F-18-BK, Pier #3..............140
73 Correlation between measured and calculated blow counts........................143
74 Comparison between end-of-initial driving resistance and
re-strike driving resistance..................................................145
75 Correlation between nominal pile capacity and re-strike driving resistance.....146
76 Correlation between nominal pile capacity and re-strike driving resistance.....147
77 Correlation between measured hammer energy and
re-strike driving resistance..................................................148
78 Correlation between measured hammer energy and
re-strike driving resistance..................................................148
79 Design chart for SPT blow count and side resistance............................150
80 Design chart for SPT blow count and end-bearing resistance.....................151
81 Example calculation of estimated pile capacity.................................152
82 Example calculation of estimated pile capacity.................................153
XV


83 Penetration to develop nominal resistance for Grade 36 and
Grade 50 H 12x74 piles with maximum allowable load..........................156
84 Comparison of penetration length and resistance for end of drive
condition between Grade 36 and Grade 50 steel H 12x74 piles.................158
85 PDA nominal resistance verses pile penetration length into clay shale,
shale, and sandstone at the beginning of restrike with varying setup times..159
86 PDA nominal resistance verses pile penetration length into clay shale,
shale, and sandstone at the beginning of restrike with varying setup times..160
87 Boring log profile for abutment #3, structure K-l8-HA with test pile.........162
88 DRIVEN analysis of pile capacity for a 20 foot pile at end of drive..........163
89 Boring log profile for abutment # 1, structure K-18-FB with test pile........164
90 DRIVEN analysis of pile capacity for a 45 foot profile at end of drive.......165
91 Boring log profile for abutment #1, structure ADA 120-07.9E305
with test pile..............................................................166
92 DRIVEN analysis of pile capacity for a 46.5 foot pile at end of drive........167
93 Boring log profile for abutment # 1, structure C-16-CF with test pile........168
94 DRIVEN analysis of pile capacity for a 59 foot pile at end of drive..........169
95 Boring log profile for abutment #1, structure D-17-CT with test pile.........170
96 DRIVEN analysis of pile capacity for a 42 foot profile at end of drive.......171
97 Boring log profile for abutment #1, structure D-l 1 A with test pile.......172
98 DRIVEN analysis of pile capacity for a 68 foot pile at end of drive..........173
XVI


99 Pile capacity with increasing penetration length into clay shale..................175
100 Boring log profile of section at SH 24 pile test site............................176
xvii


TABLES
Table
1 AASHTO 2010 resistance factors for driven piles.............................2
2 Stratigraphic units of the Denver Basin.....................................14
3 General stratigraphy of sediments in Eastern Colorado.......................19
4 Classification of rock material strengths...................................22
5 Summary of DRIVEN axial capacity analysis of four H pile resistance models
compared to measured PDA nominal pile capacity..............................67
6 Pile capacity in very hard Pierre Shale for DRIVEN and PDA...................77
7 Joint-effect factor for drilled shafts in cohesive intermediate geomaterials.78
8 Pile tests at abutment 1, structure ADA 120-09.5W308.........................81
9 Summary of DRIVEN axial capacity analysis of four H pile resistance models
compared to measured PDA nominal pile capacity..............................88
10 Unit shaft resistance from DRIVEN analysis of sand section with <(> of 34.113
11 Summary of DRIVEN axial capacity estimates compared to measured
PDA nominal pile capacity...................................................115
12 Recommended damping values for impact driven piles GRLWEAP.................122
13 Recommended quake values for impact driven piles GRLWEAP...................122
xviii


14 Summary of GRLWEAP compressive stress estimates in piles compared
to PDA compressive stress measurement......................................125
15 Summary of GRLWEAP blow count estimates compared to blow count
at PDA capacity measurement................................................142
16 Pile load, pile number and nominal resistance for example structure.......155
17 Estimated pile lengths, driving stress, and driving resistance
for example structure......................................................157
XIX


1. Introduction
1.1 Study Background
Steel H piles and pipe piles are commonly used in deep foundations for support of
structural loads. Steel H piles consist of rolled wide flange sections that have flange
widths approximately equal to the section depth. Foundation piles transfer structure
load from the pile to the adjacent soil. Load transfer can be by shaft resistance (skin
friction), toe- (end) bearing resistance or a combination of both (Hannigan et al.,
1998). H piles and pipe piles are suitable for end-bearing piles, and as combined
shaft resistance and end-bearing piles. H piles displace a low soil volume during
driving and can be driven more easily through dense granular soil and hard clays than
closed-end piles. Use of cast pile shoes for pile toe reinforcement is typical for H
piles driven into dense sands, gravels, and rock in order to prevent pile damage. H
piles and pipe piles are manufactured in standard sizes, currently of Grade 50 steel.
Prior to the introduction of Grade 50 steel, H piles and pipe piles were constructed of
lower-strength, Grade 36 steel. Grade 36 steel piles bore lower loads and required
less resistance capacity in the supporting soil and rock.
The axial load carrying capacity of a steel pile is limited by the pile section area and
the resistance capacity of the soil. Load and Resistance Factor Design (LRFD)
guidelines have replaced Allowable Stress Design (ASD) design approach for design
1


of bridge structures (AASHTO, 2010). LFRD applies factors to both the load and the
resistance rather than a single global factor of safety. The piles ultimate capacity is
called nominal resistance in the AASHTO LRFD code. The nominal resistance
determination methods (Likins, 2010) for driven piles specified by AASHTO in order
of increasing accuracy are: static analysis, dynamic formula, wave equation analysis,
PDA monitored pile driving (for static load capacity estimate), and static load
testing. Each of these determination methods is assigned a resistance factor by
AASHTO for design purposes (table 1). Higher resistance factors can allow the pile
to bear higher loads resulting in the use of fewer piles, if the soil/rock can provide the
required resistance with reasonable penetration length.
Table 1 AASHTO 2010 resistance factors (R.F.) for driven piles (Likins, 2010).

Dynamic formula (Gates) .40
Wave equation .50
' Dynamic testing i.2% oi 2#} .65
Static testing or 100% dynamic testing . 7 5
Static & 2"A, Dynamic testing .80
2


Static analysis uses geotechnical exploration data such as the Standard Penetration
Test (SPT) or Cone Penetration Test (CPT) and concepts from soil mechanics to
estimate nominal resistance. Due to low accuracy, static analysis is not used to
govern pile installation. Static analyses are suitable as a preliminary design tool to
estimate pile length and installation time. Dynamic formulas, based on hammer
kinetic energy, have a poor prediction accuracy and low resistance factor. AASHTO
recognizes the Gates formula. The wave equation, such as GRLWEAP, simulates
pile driving using a numerical model of the hammer, the pile, and the soil. For a
range of assumed nominal resistances, hammer blow counts are predicted for field
driving resistance. Nominal soil resistance is generally assigned based on SPT or
CPT data. Dynamic pile testing using the Pile Driving Analyzer (PDA) is routinely
used to determine nominal pile capacity by measuring pile force and velocity during
hammer impact. Static load testing is the traditional standard for determining
nominal resistance. Maintaining loads over several days is costly and static load
testing is only performed on very large or critical projects. The quick static load test,
developed through Federal Highway Administration (Likins, 2010) sponsorship, is
less costly, but is applied on only a limited basis.
1.2 Objective
The objectives of this thesis study are to collect and analyze driven pile installation
data and soil resistance profile characteristics from Colorado Department of
Transportation project sites. The study focuses mainly on Grade 50 steel H piles
3


driven into sedimentary bedrock along the Front Range and steel pipe piles on thick
soil deposits. Of interest is the resistance capacity of rock strata along the Front
Range to bear the higher loads enabled by the use of Grade 50 steel piles. This study
considers analysis of representative soil profiles and related soil design parameters,
pile static capacity estimation, evaluation of pile stress during driving, and
relationships between pile driveability and driving resistance. The applicability of the
programs DRIVEN and GRLWEAP to pile analysis are investigated. The analysis
results will be used to assess appropriate resistance factors for piles driven in
sedimentary rocks along the Front Range.
1.3 Research Approach
Research tasks will include the following:
1. Collect data for rock//soil material properties, pile load and resistance design
criteria, and pile driving analyzer (PDA) measurements from internal Colorado
Department of Transportation construction files.
2. Construct subsurface geologic profiles at data sites encompassing the interval of
pile penetration.
3. Review geologic profiles to delineate the range of subsurface rock and soils
profiles based on rock/soil type and strength. Compare typical geologic profiles to
PDA nominal pile resistance and depth of pile penetration.
4. Perform static analysis of pile capacity using the program DRIVEN for four
models of pile resistance distribution at each data site. DRIVEN was developed
4


under sponsorship of the Federal Highway Administration and is widely used by
transportation agencies.
5. Compare nominal pile capacity estimates derived from DRIVEN to PDA measured
pile resistance. Develop empirical input parameters for DRIVEN to improve static
capacity analysis in rock and soil along the Front Range.
6. Investigate predictive relationships between Standard Penetration Test (SPT) data,
commonly collected in site investigation, and nominal capacity for Grade 50 steel H
piles.
7. Evaluate the applicability of the wave equation to estimate hammer energy, pile
stress, and driving resistance in H piles and pipe piles using the program GRLWEAP.
Compare GRLWEAP calculated values to PDA measurements. Develop
recommendations for use of GRLWEAP in rock and soil along the Front Range.
8. Analyze construction records and evaluate safe levels of pile stress and
corresponding hammer energy.
9. Analyze construction records to determine possible relationships between
resistance measured by blow count and nominal pile capacity,
1.4 Engineering Significance
Analysis of the driven pile data base will provide greater understanding of H pile
resistance in sedimentary rocks of varying strength along the Front Range and of pipe
pile resistance in thick soil deposits. If pile resistance developed in rock profiles can
be achieved with reasonable lengths of pile penetration, loads on Grade 50 steel piles
5


can be increased up to the section area capacity to take advantage of the higher
strength of Grade 50 steel verses Grade 36 steel. Additionally, the higher resistance
factors allowed by AASHTO specifications for dynamic pile testing will enable
efficient design loads if rock resistance is sufficient. Improved parameters in static
analysis for predicting nominal pile capacity from SPT data will lead to better
estimates of pile length and of installation time. Evaluation of pile stress, hammer
energy and pile resistance from the database will outline the range of driving
conditions that yield safe levels of pile stress at the required resistance. Back analysis
of existing pile data will lead to recommendations for improvement in pre-installation
estimates of pile stress and driving resistance determined by GRLWEAP (wave
equation).
6


2. Review of the CDOT Driven Pile Data Base
2.1 Geologic-Geographic Setting
The CDOT driven pile data base includes sites that present a wide range of soil and
rock profiles (figure 1). The sites are categorized into two broad categories
depending on the bearing stratum; 1) clay shale-cemented shale-sandstone, and 2)
sand-clay-gravel. Forty-five H-piles and 2 pipe piles bear in clay shale (36) or
sandstone (9) largely along the Front Range with some sites in intermountain valleys.
One H-pile was driven in apparent meta-sedimentary rock. Along the northern Front
Range, clay shales, shales and sandstones are from the Pierre Shale, Fox Hills
Sandstone, Laramie Arapahoe, Denver and Dawson Formations in order of
decreasing geologic age. Sites that bear on clay shale and cemented shale in the
central and southern Front Range and in intermountain valleys are in the Pierre Shale.
H-pile penetration into bedrock ranges from 3 to 31 feet. Eighteen H-piles and pipe
piles bear in sand, clay, or gravel of varying proportion, dominantly on the Eastern
Plains with a few sites in mountain valleys. H-pile and pipe pile length ranges from
22 to 78 feet in sand-clay-gravel sites.
7


. ^ WYOMING
BASIN
GknwoccP
Springs
COLORADO
Grand -
j Junction
! PLATEAU j
SOUTHERN
f
ROCKY
MOUNTAINS
Gunnison
Figure 1 Location map of data sites in the investigation. Marked locations (arrows)
may contain more than 1 site and overlap on this map scale.
2.2 Rock Terminology
Argillaceous (clay-based) rocks in the Dawson, Denver, Arapahoe, Laramie, Fox
Hills and Pierre Shale formations were classified as shale or mudstone by geologists
who originally mapped these rock stratigraphic units. Shales possess fissility, the
tendency to break apart along closely-spaced parallel surfaces. Fissility can be the
result from the parallel orientation of clay particles in the rock fabric or the presence
of finely-spaced laminations. Mudstones lack fissility but possess bedding. For
engineering applications, the geologic classification of argillaceous rocks is
8


incomplete and misleading when applied to geotechnical investigations of foundation
capacity and slope stability (Terzaghi et al. 1996). Mead (1936) introduced an
engineering classification for argillaceous rocks of cemented shale and compaction
shale. Cemented shale is defined as hard rock that deteriorates slowly in the
atmosphere only after long exposure. Recrystallization of the constituent clay
minerals and the precipitation of carbonate or silica cements create adhesion and
bonding in addition to densification caused by compaction. Compaction shale is
lithified from compaction densification and deteriorates rapidly on atmospheric
exposure through slaking, wetting, and desiccation. Peterson (1958) used clay shale
as analogous with compaction shale. Subsequently, the term clay shale or clayshale
has been used extensively in the technical literature by engineers to describe weak
argillaceous rock. As discussed in Botts (1986), many of the argillaceous rock
formations of Tertiary and Cretaceous age in the Rocky Mountain area and on the
Great Plains have engineering properties characteristic of clay shales. The
engineering classification of clay shale and cemented shale does not imply a fissile
structure as per the geologic definition. Thus, sections of clay shales and cemented
shales can include mudstones (Goodman, 1993). Sandstones in the Dawson and Fox
Hills Formations are typically uncemented to weakly-cemented near surface.
Partially- to moderately-cemented sandstones and siltstones occur in the Denver,
Arapahoe, and Laramie Formations. Thin lenses or thick beds of highly cemented
sandstone or siltstone which have unconfined compressive strengths in excess of
100,000 psf occur locally in these formations.
9


2.3 General Geology
Most pile test sites are in the Colorado Pediment and the Raton Basin. A description
of the general geology of the Front Range follows below, summarized from USGS
publications (Trimble, 1980).
2.3-1 Colorado Piedmont
The Colorado Piedmont lies at the eastern foot of the Rockies, (figure 2) largely
between the South Platte River and the Arkansas River. The South Platte on the north
and the Arkansas River on the south, after leaving the mountains, have excavated
deeply into the Tertiary (65- to 2- million-year-old) sedimentary rock layers of the
Great Plains in Colorado and removed great volumes of sediment. At Denver, the
South Platte River has cut downward 1,500 to 2,000 feet to its present level. Three
well-formed terrace levels flank the rivers floodplain, and remnants of a number of
well-formed higher land surfaces are preserved between the river and the mountains.
Along the western margin of the Colorado Piedmont, the layers of older sedimentary
rock have been sharply upturned by the rise of the mountains. The eroded edges of
these upturned layers have been eroded differentially, so that the hard sandstone and
limestone layers form conspicuous and continuous hogback ridges. North of the
South Platte River, near the Wyoming border, a scarp that has been cut on the rocks
of the High Plains marks the northern boundary of the Colorado Piedmont. Pawnee
Buttes are two of many butte outliers of the High Plains rocks near that scarp,
separated from the High Plains by erosion as is Scotts Bluff, farther north in Nebraska.
10


Figure 2 Physiographic sub-provinces of the Great Plains (Trimble, 1980).
11


To the east, about 10 miles northwest of Limon, Colo., Cedar Point forms a west-
jutting prow of the High Plains. The Arkansas River similarly has excavated much of
the Tertiary piedmont deposits and cut deeply into the older Cretaceous marine rocks
between Canon City and the Kansas border. The upturned layers along the mountain
front, marked by hogback ridges and intervening valleys, continue nearly
uninterrupted around the south end of the Front Range into the embayment in the
mountains at Canon City. Extending eastward from the mountain front at Palmer
Lake, a high divide (Palmer Divide) separates the drainage of the South Platte River
from that of the Arkansas River. The crest of the divide north of Colorado Springs is
generally between 7,400 and 7,600 feet in altitude, nearly 1,500 feet higher than
Colorado Springs and more than 2,000 feet higher than Denver. From the crest of the
divide to north of Castle Rock, resistant Oligocene Castle Rock Conglomerate (which
is equivalent to part of the White River Group of the High Plains) is preserved in
many places and forms a protective caprock on mesas and buttes. Much of the terrain
in the two river valleys has been smoothed by a nearly continuous mantle of
windblown sand and silt. Northwesterly winds, which frequently blow with high
velocities, have whipped fine material from the floodplains of the streams and spread
it eastward and southeastward over much of the Colorado Piedmont. Well-formed
dunes are not common, but aligned gentle ridges of sand and silt and abundant
shallow blowout depressions are evidence of the windblown sand. The Colorado
Piedmont elevation is lower than the foothills, but is also slightly lower elevation than
the High Plains to the east. According to current geologic theory, the Piedmont was
12


formed approximately 28 million years, during the broad bowing of the North
American Plate that lifted the continent between present-day Kansas and Utah to its
present elevation of approximately 5000 ft. This uplift resulted in increased stream
flow and rapid erosion on the eastern side of the Rocky Mountains. The erosion
scraped away the top layer of Upper Cretaceous sandstone (which still exists as the
top layer on the High Plains), exposing the underlying layer of Pierre Shale. It was
during this time that the South Platte River, which had previously flowed eastward
across the Plains, rerouted northward along the mountains to join the Cache la Poudre
River.
2.3-2 Denver Basin
The basin starting forming as early as 300 million years ago, during the Colorado
orogeny that created the Ancestral Rockies. Rocks formed during this time include
the Fountain Formation, which is most prominently visible at Red Rocks and the
Boulder Flatirons. The basin further deepened in Tertiary time, between 65 and 45
million years ago, during the Laramide orogeny that created the modern Colorado
Rockies. The deep part of the basin near Denver became filled with Upper Cretaceous
-Tertiary clay shale, sandstone and conglomerate of the Laramie, Arapahoe, Denver,
Dawson and Castle Rock Conglomerate formations (table 2). In the regions to the
north and south of Denver, however, stream erosion removed the Tertiary layers,
revealing the underlying Cretaceous Pierre Shale and Fox Hills Sandstone.
13


Table 2 Stratigraphic units of the Denver Basin (Topper, 2003).
Era System Series Stratigraphic Unit Unit Thickness (feet) Physical Description
viuatcmary m olocene Pleistocene Ail iumm\ U n c o n s o i i cl a i e d g ravel, sand silt, and clay
Oiigocenc Castle Rock Conglomerate u-50 Fme to coarse arkosic sand- stone and conglomerate
tocone Diiwf.cn Formation D I /Hij Sandstone and conglomeratic sandstone with interbedded siltstone and shale
Denver t ofrn.it? on B00-1 00u Shale silty claystone. and interbedded sandstone: beds of lignite and carbona- ceous siltstone and shale common
Upper Anion ooe Formation 400-/00 .Sandstone conglomeratic sandstone and interbedded shale and siltstone
U totaccouv l O'slfTHfi Fotn aii on HJO-OOO Upper part shale silty shale siltstone and interbedded fine sandstone bituminous coal seams common lower part sandstone and shale
1Hills Sandstone 100 TOO Sandstone and siltstone interbedded with shale
Pierre Shale 4 500- 7.000 Shale calcareous silty and dense
The United States Geological Survey estimates that between 1500 and 2000 feet of
sediment were eroded along the Front Range in the last 5 million years (Trimble,
1980) forming the present-day distribution of Cretaceous and Tertiary age rock units
in the Denver Basin which commonly serve as bearing strata for drilled shaft and
driven pile foundations (figure 3). Recent sediments from wind, river and floodplain
deposits mantle the bedrock in areas with varying thickness of gravel, sand and clay.
14


ConuionHM'i.!?!: Denver Fv*;>iivs.-sfM>ri
Oawson f-'orm.iilnn Arapahoe r'onoafrvo P-x-m- Shale
A A .. 00 .)( 3(:l li'S"
Figure 3 Bedrock geology of the Denver Basin (Topper, 2003).
2.3-3 Raton Basin
Volcanism characterizes the Raton section. The volcanic rocks, which form peaks,
mesas, and cones, have armored the older sedimentary rocks and protected them from
the erosion that has cut deeply into the adjoining Colorado Piedmont to the north and
15


Pecos Valley to the south. The south edge of the Raton section in New Mexico is
marked by a south-facing escarpment cut on the nearly flat-lying Dakota Sandstone.
This escarpment is the Canadian escarpment, north of the Canadian River.
Northward for about 100 miles, the landscape is that of a nearly flat plateau cut on
Cretaceous rock surmounted here and there by young volcanic vents, cones, and lava
fields. Near the New Mexico-Colorado border, basaltic lava was erupted 8 to 2
million years ago onto an older, higher surface on top of either the Ogallala
Formation of Miocene age or the Poison Canyon Formation of Paleocene age. These
lava flows formed a resistant cap, which protected the underlying rock from erosion
while all the surrounding rock washed away. The result is the high, flat-topped mesas
such as Raton Mesa and Mesa de Maya that now form the divide between the
Arkansas and Canadian Rivers. The northern boundary of the Raton section in
Colorado is placed somewhat indefinitely at the northern limit of the area injected by
igneous dikes. The eastern boundary of the Raton section is at the eastern margin of
the lavas of Mesa de Maya and adjoining mesas. Driven pile sites in the Raton Basin
bear in the Cretaceous Pierre Shale Formation. The Pierre Shale consists dominantly
of shale with variable amounts of silica and calcite cementation that produces high
SPT blow counts. Thin weathered zones may occur.
2.3-4 Intermountain Valleys
Six pile sites are in intermountain valleys west of the Front Range. The piles bear in
dense gravel or the Cretaceous Mancos Shale and Pierre Shale. One site is in
16


apparent, weathered Precambrian gneiss. Geologic sections in the Rocky Mountains
present a variety of rock types. Ranges of faulted gneiss and granite are separated by
intermountain basins containing Paleozoic, Mesozoic and Tertiary sedimentary rocks
with some volcanic rocks (figure 4). In the central mountains, modem and
Quaternary sediment are discontinuous with streams flowing on bedrock surfaces in
areas. A substantial thickness (50-300 feet or greater), of unconsolidated sand, gravel,
cobbles, boulders, silt, and clay can occur in major river valleys. Sediment size and
sorting is variable. River channel and terrace sands-gravels can be interbedded with
alluvial fan, glacial outwash, landslide, and debris fan deposits.
IRON T RANGE
i:
i
ii I*
tH|
H I
H l!
I
I ll
I
HU
Mil
I LL
T Tertiary, lower-T. upper-Hi [ J"R Jurassic and Iriassic
volco-.-c-Tv ~~'
m Creiacecus
M: Mississippian lo Cambrian
; PIP Permian nnrl Pennsylvanian j~p j Precambnan
Figure 4 Geologic cross section through the Southern Rocky Mountains (Topper,
2003).
17


2.3-5 High Plains in Eastern Colorado
The High Plains in Eastern Colorado are characterized by great thicknesses (up to 400
ft) of unconsolidated to semi consolidated sands, gravels, silts and clays that represent
alluvial, valley-fill, dune sand, and loess (wind blown silt) deposits. Eastern
Colorado has the greatest thickness of unconsolidated deposits on the Great Plains.
These Quaternary-Recent aged sediments overlie the Miocene-aged Ogallala
Formation. The Ogallala Formation gravel and sands are often partially cemented by
calcite and have good bearing capacity for foundations if it not buried too deeply.
For practical purposes, the Quaternary sands, gravels, silts, and clays are largely
indistinguishable in age in the subsurface. The superimposed cycles of erosion and
deposition can produce rapid changes in density, gradation, and soil type Table 3
lists the stratigraphic layers as they occur in nature, with the youngest layers at the
surface and the oldest at the bottom. High variability in the subsurface profile can
occur on a site.
2.4 Rock Strength of Bearing Stratum
Unconfined compressive strength is widely used in the determination of rock mass
strength behavior. On most pile sites, subsurface exploration consisted of Standard
Penetration Test (SPT) sampling using a split spoon or California sample barrel for
the recovery of drive samples. Coring was used on only a few sites. Strength testing
was limited to unconfined compression tests. However, unconfined compressive tests
are not routinely performed on clay shales and sandstone along the Front Range.
18


Table 3 General stratigraphy of sediments in Eastern Colorado (Topper, 2003).
Holocene (0-10,000 yr) River valley deposits 0- 60 ft. Sand, gravel, silt, and clay deposits along modem rivers
Quaternary (10,000 2 million yr) Eolian Dune sand 0-300 ft Loess 0-250 ft. Fine to medium sand with small amounts of silt and clay Silt with lesser amounts of sand and clay
Alluvial deposits 0-500 ft. Gravel, sand, silt and clay with local caliche beds
Tertiary (5-7 million yr) Ogallala formation Sand, gravel, silt and clay, unconsolidated with some caliche beds
Typically, empirical relationships between SPT blow count and rock strength are used
for drilled shaft design and for estimating rock penetration length for driven H-piles
(Chen, 1999). ONeill et al. (1996), as part of a Federal Highway Administration
Research program to develop guidelines for the design of drilled shaft foundations,
defined intermediate geomaterials as cohesive, hard soils and weak rocks with an
unconfined compressive strength between 10,000 and 100,000 psf or cohesionless
materials with standard penetration test blows N6o greater than 50. Three categories
of intermediate geomaterials were defined for foundation design:
1. Argillaceous geomaterials: heavily overconsolidated clays, clay shales,
saprolites (residual soil from intensely weathered igneous-metamorphic rock),
and mudstones that are prone to borehole smearing when drilled. Category 1
materials have a propensity to rapidly slake and soften when exposed to water
or remolded during drilling.
19


2. Calcareous rocks: limestone, calcareous or siliceous shales-mudstones-
siltstones and argillaceous geomaterials that are not prone to borehole
smearing when drilled. Category 2 materials are generally insensitive to
exposure to water but may degrade with long term exposure to the atmosphere.
3. Very dense granular geomaterials: residual, completely decomposed
granular rock material, weakly-cemented sandstones and granular glacial tills
with SPT N values between 50 and 100 blows. Category 3 materials are
generally insensitive to exposure to water but may degrade with long term
exposure to the atmosphere.
2.4-1 Range of Rock Strength in the Front Range
Rock strength in samples from the Pierre Shale, Denver, Laramie, Arapahoe, and
Dawson Formations along the Front Range is typically evaluated by means of the
unconfined compression test on core and California sampler-liner drive samples from
Standard Penetration Test (SPT) tests. The California sample barrel recovers 2 inch
diameter samples compared to the 1 and 5/8 inch diameter samples using the standard
split spoon sampler. Sample disturbance during SPT driving, may cause unconfined
compression tests on SPT drive samples to be conservative compared to tests on core
samples. Due to the high cost, time, and uncertain results of coring in weak, water
sensitive rocks, empirical methods relating SPT blow counts to rock unconfined
compressive strength are widely used in geotechnical analyses along the Front Range.
20


Unconfined compressive strength tests on over 100 clay shale samples from the
Denver and Arapahoe Formations showed a range from 2300 psf to 36,200 psf
(Cesare et al., 2002). Data from the Colorado Department of Transportation (Abu-
Hejleh et al., 2003) on core samples of calcite-cemented shales and sandstones in the
Denver Formation obtained near Broadway Boulevard and the S. Platte River in
Denver, showed unconfmed compressive strengths ranging from 85,000 psf to
312,000 psf. Unpublished data from the Colorado Department of Transportation on
strength testing of calcite cemented Pierre Shale core samples in Trinidad, Colorado
had a strength range from 110,000 psf to 384,000 psf. Comparing the strength range
from 2000 psf (14 psi) to 400,000 psf (2780 psi) for the Tertiary and Cretaceous age
rocks along the Front Range to the rock strength chart from the International Society
of Rock Mechanics (table 4) indicates that these rocks fall within the categories of
very weak rock and weak rock. Thin lenses of more highly-cemented rock (typically
calcite cemented siltstones and fine-grained sandstones) occur sporadically. Cores of
this material can be fractured with a single blow of a geological hammer and likely
fall into the medium weak rock category. The geotechnical reports examined in this
investigation contained few strength measurements as the designers relied on SPT
correlations and experience to estimate probable pile depth. The use of site-specific
pile driving blow count correlations with the nominal pile capacity measured using
the Pile Driving Analyzer (PDA) eliminates uncertainty in the empirical strength
relationships derived from analyses of the boring logs.
21


Table 4 Classification of rock material strengths, International Society of Rock
Mechanics criteria (Wyllie, 1999).
Grade Description Field identification Approximate range of compressive strength
MPa (p.s.ii
Rh Extremely strong rock Specimen can only Iv chipped with geological hammer >250 f>36 000)
R5 Very strong rock Specimen requires many blows oi geological hammer to fracture ir 100-250 (15 000-36 000)
R4 Strong rock Specimen reqtiires more than one blow with a geological hammer to fracture it. 50-100 T 000-15 000)
R5 Medium weak ri >ck Cannot be scraped or peeled with a pocket knife; specimen can be fractured with single firm blow of geological hammer 25-50 (3 500-7 000)
R2 Weak rock Can be peeled with a pocket knife; shallow indentations made by firm blow with point of geological hammer 5-25 (725-3 500)
R] Very weak rock Crumbles under firm blows with point of geological hammer; can be peeled by a pocket knife 1 -5 (150-725;
Rii Extremely weak Indented bv thumbnail 0.25-1 (35-150)
rock
Exploration boring data available from the pile sites contain sample descriptions,
index property tests, SPT N values, graphical logs and infrequent, unconfined
compressive strength values from California liner samples or cores. In this report,
argillaceous rocks were classified into two broad categories of clay shale and
cemented shale based on sample descriptions and SPT N blows. Most argillaceous
samples are estimated to fall within the range of intermediate (IGM) geomaterials
(unconfined compressive strength between 10,000 and 100,000 psf) as defined by
ONeill et al. (1996). Some cemented sandstones and shales have a higher unconfined
22


compressive strength shown through sample testing or estimated from sample
descriptions and very high SPT blow counts.
2.5 General Observation of Rock Profiles in the Front Range, Colorado and H-Pile
Capacity
The required pile resistance by the bearing stratum (geotechnical resistance) for
design in the LRJFD method is calculated as the sum of the factored dead and live
loads divided by the resistance factor. The maximum factored pile load is less than
(0.33) (Fy) (section area) per AASHTO (2007) recommendations. For grade 50 steel
H-piles 12x74 and 12x84 with a limiting maximum load, the required geotechnical
resistance or nominal pile capacity for axial capacity, is 514 kips and 580 kips
respectively, using a resistance factor of 0.7. From review of the boring log profiles
at the pile data sites and known rock profiles encompassing the study area, eight
typical rock profiles are identified which present a range of bearing strata conditions
present along the Front Range.
Type 1 Very thick section of weathered or partially-softened clay shale:
Exploration borings show a 30 to 50 foot section of firm to medium hard (SPT20/12-
49/12) to slightly hard (SPT50/12 50/9) clay shale underlying overburden soil
(figure 5). The clay shale section may show intervals of increasing and/or decreasing
blow counts with depth due to erratic variation in the intensity of weathering. Spatial
variability of rock SPT blows over the structure footprint can be high due to
differences in the degree of rock weathering, the presence of sandstone or siltstone
23


S528
Pile #1
BORING 2
Elevation = 5528'
LEGEND
____55ir>
54 6C
545*
_ f.4 C>C
5445
_ 5*1*10
o
Pipe Pile
(24" 0.5)
58.5 ft

Siirvi
-12ft
foV.
Ho1/!
twJ
KV12
to 7
b?-
22 1..
71?
Clav
'2 n
Jks, Sh.tki
-fMft
5/12
4 DM 2
57/12
72/12
a Sand to Gravelly Sand loose
to medium dense, most to wet.
a

Sandy Clay to Silty Clay -
medum stiff, most.
Clay Shale medium
hard to hard, most.
PILE #1 INFORMATION:
- Location : Pier #3
- Pile Type: Pipe (024", 0.5" thick)
- Open End Pipe Pile 58.5 ft into ground
- Plug Drilled Out
HAMMER INFORMATION:
-Model: APE D30-32
- Hammer Stroke: 7.5'-8.5'
- 2" /10 blows count
- Damping Jc: 0.3
- Time of Restrike: 19 hours
MEASUREMENT:
- Case Method: 347.5 tons
- Max Ddving Stress: 21.0 ksi
- Measured Hammer Energy; 16.8 k-ft
- Energy Transfer Ratio; 24,0
HKO 0J62-G?/ UNIVERSITY OF COLORADO AT CENVEK US 36 AT BOX Fi DFR CRFFK
Mft-BK DEPARTMENT Or CIVIL ENGINEERING LOGS OF EXPLORATORY BORINGS
Figure 5 Boring log profile of weathered and partially-softened clay shale gradational
to hard clay shale.
24


lenses which can produce high blows with little cementation, or the occurrence of
water bearing fractures which locally soften the clay shale. Pile penetration length in
bedrock (excluding overburden resistance) is estimated to be about 35 to 40 feet for
H12x74 and 41 to 46 feet for H12x84 to reach the 514 kip nominal capacity (H12x74)
and 580 kip nominal capacity (HI2x84) for maximum pile loads assuming short pile
setup time.
Type 2A -Weathered or softened clay shale section gradational to hard to very hard
clay shale or shale: Exploration borings show a 5 to 20 foot profile of medium hard
(SPT20/12-49/12) to slightly hard (SPT50/12 50/9) clay shale, underlying
overburden soil, that grades into hard (SPT50/8 50/6) and, or very hard (SPT50/5-
50/4) clay shale or shale (figure 6). This profile occurs frequently along the Front
Range in the Laramie, Denver, Arapahoe and Pierre Shale Formations. The gradation
to harder rock can be gradual or fairly abrupt within a 5 to 7 foot interval. SPT blows
in the hard to very hard clay shale can show a generally uniform count or increase
with depth. Spatial variability of rock SPT blows over the structure footprint can be
low, or vary. Localized erosion or deeper weathering can cause the thickness of the
weathered clay shale interval to change between borings. Slight differences in
cementation and lithification also contribute to variation among borings. The
thickness of the weaker clay shale interval is a major control on pile length in rock. In
addition to penetration length in the weaker clay shale, pile penetration length in the
hard to very hard clay shale is estimated in the 6 to 8 foot range to reach the 514 kip
nominal capacity (HI2x74) and 580 kip nominal capacity (HI2x84) for maximum
25


___ 5020
LEGEND
____ i>0*0
O
O

o
LU
LU

_ 49B5
_ 4985'
4'J76
49/0
4965
4956
4950
4'Mf'
Pile #1
M Pile
(12x74)
56.0 ft
BORING S-1
Elevation = 5005'
esay
Fill day, medium stiff, moist.
pH Sandy Clay medium stiff to
[zj stiff, moist.
Clay Shale Bedrock hard
to very hard, weathered at,
contact, quickly becomng
hard, moist.
Y,
r /
PILE #1 INFORMATION:
- Location : Abutment #1
-Pile Type: H Pile (12 x 74)
- Non-Rein forced Pile Tip
56.0 ft Into ground
HAMMER INFORMATION:
- Model: APE D30-32
- Hammer Stroke: 7.0'-8.0'
- 1" /10 blows count
- Damping Jc: 0.5
- Time of Restrike: 4 flours
MEASUREMENT:
- Case Method: 299.0 Ions
- Max Driving Stress: 29.4 ksi
- Measured Hammer Energy: 29.4 k-ft
- Energy Transfer Ratio: 42.4
NH 28/5-1 *4 UNIVERSITY OF COLORADO AT DENVER IJS 287/BFRTHOUD BYPASS
C-16-BO DEPARTMENT Of CIVIL ENGINEERING LOGS OF EXPLORATORY BORINGS
Figure 6 Boring log profile of weathered or softened clay shale section gradational to
very hard clay shale or shale.
26


pile loads assuming short pile setup time. Higher pile capacities are developed in the
hard to very hard clay shale with short increases in penetration length.
Type 2B Weathered clay shale section gradational to extremely hard cemented
shale: Exploration borings show a 5 to 20 foot profile of medium hard (SPT30/12-
49/12) to slightly hard (SPT50/12 50/9) clay shale, underlying soil overburden, that
grades into hard (SPT50/8 50/6) to very hard (SPT50/5-50/4) to extremely hard
(SPT50/3-50/0) partially-cemented, shale (figure 7). This section profile most
frequently occurs in the Pierre Shale where partially to slightly weathered shale
grades into unweathered shale that is cemented by calcite. Blows in the hard to very
hard clay shale/shale may show a uniform count or increase with depth. SPT blows
tend to rapidly increase over a short interval (5 to 7 feet), approaching the extremely
hard cemented shale. Spatial variability of rock SPT blows over the structure
footprint can be low, or vary. Localized erosion or deeper weathering can change the
thickness of the weathered clay shale interval between borings. Slight differences in
cementation and lithification also contribute to variation among borings. In addition
to the penetration length in any weaker clay shale that may be present, pile
penetration length in the hard to very hard clay shale/shale is estimated in the 6 to 8
foot range to reach the 514 kip nominal capacity (HI2x74) and 580 kip nominal
capacity (HI2x84) for maximum pile loads assuming short pile setup time. In the
very hard to extremely hard shale, pile capacity will rapidly increase with probable
increases of 100 kips per foot of penetration.
27



BORING FB103
Elevation = 4828ft
LEGEND
mo
<
>
UJ
Pile #1


Clay
7
12;-2
50/ U
Stale. weathered
M
H Pile
(14 x 89)
24.0 ft
v.Mi!
5D;o
50/0
Ld

Clay sandy very soft to stiff, slightly moist
to very moist.
Sand fine to medium grained, wet.
Shale, weathered hard to very hard,
moist to slightly moist.
||g Shale cemented, very hard to extremely
hard, moist to slightly moist.
PILE #1 INFORMATION:
- Location: Pier #2
- Pile Type: H Pile (14 x 89)
- Reinforced Pile Tip 24,0 ft into ground
HAMMER INFORMATION: ]
- ModehDelmag D30-32 ]
- Hammer Stroke: 7.5-8.5'
- 2"/10 blows count
- Damping Jc: 0.3
- Time of Restrlke: 0.5 hour
MEASUREMENT: j
- Case Method: 386.3 tons i
- Max Driving Stress: 34.8 ksi !
- Measured Hammer Energy; 23.7 k-ft }
- Energy Transfer Ratio: 33.8 j
IM 0?.V-3J0
K-18-r B
UNIVERSITY OF COLORADO AT DENVER
DEPARTMENT OF CIVIL ENGINEERING
FAGI FRIDGF R! VD
LOGS OF EXPLORATORY BORINGS
Figure 7 Boring log profile of weathered clay shale section gradational to extremely
hard cemented shale.
28


Type 3 Very thick section of hard to very hard with thin weathered interval:
Exploration borings show a 20 to 40 foot section of hard (SPT50/8 50/6) and, or
very hard (SPT50/5-50/4) clay shale underlying the overburden soil (figure 8). A thin
weathered zone may occur at top or be absent. This profile occurs frequently along
the Front Range in the Laramie, Denver, Arapahoe and Pierre Shale Formations
where recent erosion along drainages has removed most weathered/sofitened clay
shale. Blows in the hard to very hard clay shale may show a uniform count or
increase with depth. Spatial variability of rock SPT blows over the structure footprint
is generally low with possible differences due to slight variations in cementation and
lithification, the presence of partially cemented sandstone lenses or clay shale
softening near water bearing fractures (lower blows). Pile penetration length in
bedrock is estimated in the 7 to 12 foot range to reach the 514 kip nominal capacity
(HI2x74) and 580 kip nominal capacity (HI2x84) for maximum pile loads assuming
short pile setup time.
Type 4 Very thick section of extremely hard, partially to moderately cemented
shale: Exploration borings show a 20 to 40 foot section of extremely hard shale
(SPT 50/3-50/0) underlying the overburden soil (figure 9). A thin weathered zone
may occur at top. The shale is partially to moderately-cemented. Most frequent
occurrence is in the Pierre Shale where recent erosion along drainages has removed
most weathered/softened rock leaving a section of extremely hard calcareous shale.
29


BORING S-8
Pile Elevation = 5040' (after fill placement)
STU C-20-007
UNIVERSITY OF COI ORADO AT [jrNVI' R
LEGEND
J
Fill silty to sandy clay and clayey
sand (CL-SC). medium stiff to medium
dense, trace gravel, moist.
Clay (CL) medium to very stiff
sandy, silty, moist to wet.
QSand (SW/SP) very loose to very
dense, fine to coarse grain, trace
gravel to very gravelly, moist to wet.
Clay Shale hard to very hard,
scattered siltstone lenses,
low to high plasticity, moist.
PILE #1 INFORMATION:
- Location : Abutment #2
-Pile Type: H Pile (12x84)
- Reinforced Pile Tip 50.5 ft into ground
HAMMER INFORMATION:
- Model: Ape D30-32
- Hammer Stroke: 8.0-9.0
- 3 j /10 blows count
- Damping Jc: 0.7
- Time of Restrlke: 18 hours
MEASUREMENT:
- Case Method: 286 tons
- Max Driving Stress: 44.3 ksl
- Measured Hammer Energy: 41,2 k-ft
- Energy Transfer Ratio: 58.9
120 AVE @ S PLATTE RIVER
ADA

UcPARMbNT OF CIVIL ENGINEERING
LOGS OF EXPLORATORY BORINGS
Figure 8 Boring log profile of very thick section of hard to very hard clay shale.
30


LEGEND
b0'J6 Pile #1
t-
<
>
LU
. 09/0
H Pile
(12x74)
25.0 ft
BORING
Elevation = 6007'
Cl-/Hy Sand
Gravel
-1 /ft -
-18ft..0...B85i
h*l. 37'1i!
Sand,
Gravel
_j I f>0:4
Pierre Shole -
Pp Clayey Sand and Gravel with lenses
t/j of sandy clay, non to medium
plastic, line grained to gravel, moist.
Sand and Gravel clayey to silty,
H&l fine grained to gravel, with occasional
cobbles, low to non plastic, medium
dense to dense, moist to wet.
gg Pierre Shale slightly lo moderately
cemented, fine grained, low to medium
plasticity, very hard to extremely hard,
slightly moist.
PILE #1 INFORMATION:
- Location : Abutment # 1
- Pile Type: FI Pile (12 x 74)
- Reinforced Pile Tip 25.0 ft into ground
HAMMER INFORMATION:
- Model: APE D30-32
- Hammer Stroke: 8.0-9.0'
- 1" 710 blows count
- Damping Jc: 0.9
- Time of Rcstrike: 1.5 hours
MEASUREMENT:
- Case Method: 367.0 tons
- Max Driving Stress: 33.9 ksi
- Measured Hammer Energy: 28.2 k-ft
- Energy Transfer Ratio: 40.3
siAomA-rca
p-- 8-ax
UNIVERSITY OF COLORADO AT DENVER
DEPARTMENT OT CIVIL ENGINEERING
l 25/TRINIDAD
L OGS OF EXPLORATORY BORINGS
Figure 9 Boring log profile of extremely hard, partially to moderately cemented shale.
31


Spatial variability of rock SPT blows over the structure footprint is generally low.
Pile penetration length (excluding overburden resistance) in the extremely hard shale
is estimated in the 3 to 5 foot range to reach the 514 kip nominal capacity (HI2x74)
and 580 kip nominal capacity (HI2x84) for maximum pile loads assuming short pile
setup time. A 3 foot minimum penetration length is typical although deeper
penetration may be required to provide adequate resistance for lateral loads. Low rock
quality designation values (RQD) due to fracturing, can cause increased pile length.
Type 5 A Very thick section of uncemented sandstone: Exploration borings show a
10 to 50 foot section of uncemented to weakly cemented sandstone with blow counts
(corrected for overburden) in the range of dense (SPT 30/12-49/12) and very dense
(SPT50/12 -50/3) sand (Figure 10). Most frequent occurrence is in the Dawson
Formation although weakly cemented sandstones may occur in the Laramie, Denver,
and Arapahoe Formations. The sandstone can contain lenses of clay shale and
siltstone and grade into partially cemented sand Blows in the sandstones may show a
uniform count or increase with depth. Spatial variability of rock SPT blows over the
structure footprint can be low, or vary due to differences in gradation characteristics
or minor differences in sand cementation between borings. In many areas, the
Dawson Formation has shallow overburden. Thus, effective stress is low which
causes low side friction. Most capacity is end bearing which is strongly dependent on
the friction angle with the critical depth maximum capacity proposed by Meyerhof
(1976). Deeper penetration length may not show a high rate of capacity increase.
32


ELEVATION (feet)
BORING
Elevation = 7000'
7005
___ 7000
__6y%
___ 6900
____ 698r
69BH
___ 6976
Pile #1
M
H Pile
(12x74)
15 ft
Sand
RKS
_ 0370
___ 0305
LEGEND
band slightly silty, occasional clay lenses,
loose to medium dense, moist to wet.
Sandstone occasional slltstone,
clay shale lenses, uncemented to
slightly cemented, hard to very hard,
moist to wet.
PILE #1 INFORMATION:
- Location : Abutment # 2
- Pile Type: H Pile (12 x 74)
- Reinforced Pile Tip 15 ft into ground
HAMMER INFORMATION:
- Model: DELMAG D19-42
- Hammer Stroke: 6.5'-7.5'
- 1.25 /10 blows count
- Damping Jc: 0.3
- Time of Restrlke: 1 hour
MEASUREMENT:
- Case Method: 269,0 tons
- Max Driving Stress: 28.4 ksi
- Measured Hammer Energy: 13.0 k-ft
- Energy Transfer Ratio: 30.4
i
!M r:?h2-34/ UNIVERSITY OF COLORADO AT DENVER 1 25 at MONUMENT INTERCHANGE
1-17-DA DEPARTMENT OT CIVIL ENGINEERING LOGS OF EXPLORATORY BORINGS
Figure 10 Boring log profile of thick section of uncemented sandstone.
33


Limited data from piles in uncemented sandstone indicate that SPT blows at the pile
base should be 50/3 or greater to produce pile nominal capacities above 500 kips for
an H12x74 penetration length of 10 feet or less. Profiles with SPT blows in the 50/9
to 50/5 range had nominal capacities from 400 to 470 kips.
Type 5B Very hard, cemented sandstone/siltstone lenses in a profile: Exploration
borings in the Laramie, Denver, Arapahoe and Pierre Shale Formations may
encounter lenses 1 to 3 feet thick of moderately to highly cemented sandstone or
siltstone with blow counts generally in the range of SPT 50/3-50/0. The hard
sandstone/siltstone lenses may not be shown on the exploration logs. Spatial
variability of cemented lenses can be high. In slightly hard and hard clay shale,
cemented lenses 1 to 3 feet thick produce, after partial penetration, intervals with
higher capacity that are too thin to provide resistance to fracturing or shear failure for
high pile loads. In these cases, the lenses should be penetrated and the required
resistance reached in the underlying clay shale. Thicker cemented sandstone/siltstone
lenses can produce adequate resistance subject to site specific analysis.
Type 6 Coal lenses in a profile: Exploration borings may show lenses of varying
thickness (typically 1 to 7 feet in the Denver, Arapahoe and Laramie Formations) of
lignite or sub-bituminous coal. Thicker intervals of closely interbedded coal and clay
shale may be logged as all coal. Some coals lenses can give very high blows (SPT
50/12-50/4). Spatial variability of coal lenses can be high. Estimates of pile capacity
should exclude coal lenses. Piles should not terminate in coal regardless of the PDA
34


measured capacity. Two feet of penetration, past the base of a thick coal lens, into
hard to very hard clay shale or sandstone produces a higher end bearing resistance.
2.6 Discussion of Grade 50 Steel H Piles Bearing in Expansive Clay Shale and Shale
The effect of soil expansion on H piles is poorly documented in the technical
literature and analogies are drawn from analyses used on drilled concrete shafts. As
summarized in Chen (1999), drilled shaft foundations have been widely used in the
Rocky Mountain region since the 1950s to prevent structural damage caused by soil
expansion. The use of driven piles in expansive soils is stated as still under study
with no recommendations for use. Prior to the development and field use of the pile
driving analyzer in the late 1980s, estimation of pile capacity from design formulas
were held in low confidence and ranges of working loads were established by local
codes and usage. For example, an H 14x117 section had a suggested working load of
only 17 to 22 tons for preliminary design estimates in the absence of a load test (Chen,
1999). Greater confidence in the capacity of drilled shafts to bear higher loads and
improvements in the speed of drilled shaft construction contributed to the widespread
use of drilled shafts in expansive soils and rocks along the Front Range.
The Colorado Association of Geotechnical Engineering (CAGE, 1999) published a
commentary (Drilled Pier Design Criteria for Lightly Loaded Structures in the
Denver Metropolitan Area) which summarizes the state of practice for drilled shaft
design in expansive soil. The evaluation of drilled shaft uplift assumes that moisture
variation will occur in a zone below the top of the shaft after the shaft is installed.
35


This zone is defined as the zone of moisture variation. Some engineers do not
consider wetting to occur instantaneously throughout the zone of moisture variation
and define a zone of influence as the zone through which instantaneous wetting and
uplift occurs. Repeated cycles of desiccation and wetting initiate slaking which
causes a fissure system to form in the soil (Botts, 1985). In practice, the zone of
moisture influence is taken as equal to the zone of moisture variation or, to be less
than the zone of moisture variation depending on engineering judgment. Uplift force
acting along the shaft perimeter is calculated as:
U = n D Lw Sp a where: U = shaft uplift force (kips)
D = shaft diameter (ft)
Lw = zone of influence (ft)
Sp swell pressure (ksf)
a = swell pressure coefficient
The swell pressure coefficient is the tangent of the effective angle of pile-soil friction.
The coefficient of friction between the pile and soil is lower than the peak friction
angle and is generally taken to equal a residual value (ONeill, 1980). Chen (1999)
suggests a value of 0.15 for expansive soils with concrete shafts in the Rocky
Mountain region. The coefficient of friction is approximately 50 percent lower for
smooth steel piles in sand compared to concrete piles in sand (McCarthy, 1993).
Assuming a similar reduction for the residual friction angle for smooth steel piles in
cohesive soils produces lower uplift force per unit pile surface area.
36


For an H 12x84 pile, the full perimeter surface area is approximately six ft2 per foot
of pile length. The uplift force (U) on the H 12x84 pile with seven feet of penetration
in a zone of influence with a swelling pressure of 10,000 psf is calculated as:
U = (length = 7 ft) x (perimeter area per unit length = 6 ft) x
(swelling pressure = 10,000 psf) x
(swell pressure coefficient = 0.075)
U = 31.5 kips
Uplift forces of this magnitude can be resisted in many structure designs by dead
loads in addition to uplift resistance in overburden and any resistance due to
embedment beyond the zone of swelling influence.
On sites with very shallow bedrock, the use of driven piles is limited by minimum
penetration requirements for lateral loading and the need to extend the pile beyond
the surface zone of wetting and desiccation that can cause the soil to pull away from
the pile surface. Determination of the length of the zone of moisture influence is one
the most important design parameters and subject to considerable judgment. For a
typical soil profile in the Rocky Mountain Front Range is commonly taken to be in
the range of 10 to 15 feet. Local, site specific drainage and moisture conditions can
affect estimates. Special geologic conditions such as the dipping bedrock district,
Jefferson County, Colorado, produce a greater depth of moisture influence in design
codes reflecting the potential for deep-seated heave. Soil profiles that show no
37


groundwater are the most straightforward in which to evaluate uplift force due to soil
expansion. Perched water tables, whether natural or manmade, are common above
clay shale bedrock along the Front Range. Water content of clay shale is higher
below the perched water table and typically decreases with depth with a concurrent
increase in swelling potential. Chen (1999) lists perched water tables as the most
potentially dangerous situation in drilled shaft performance. Subsequent to auguring
through a perched water table into clay shale and placement of concrete in the hole,
concern exists that water will percolate or wick down the sides of the shaft due to
voids in the concrete or through debris along the hole side. Additional mobile water
in clay shale intervals can occur in fractures or sandstone lenses with or without the
presence of a perched water table. No uniform design guidelines exist on the depth of
the zone of moisture influence for perched water tables. Some engineers consider the
zone of moisture influence to extend a number of feet or shaft diameters below the
top of the clay shale or to extend to the total length of the shaft including the base.
Thus, in the most conservative approach, the zone of moisture influence and soil
expansion is equal to the length of the drilled shaft in clay shale which requires that
all uplift resistance be provided by dead loads.
Perched water table conditions are present at 95 percent of the sites in this study in
which H piles bear in clay shale or shale. A large majority of the structures in this
study have H piles that are embedded in potentially expansive clay shale or shale
based on water content and plasticity index. No instances of distress due to soil
heaving are documented for any of these structures. Additionally, no settlement
38


problems have occurred indicating that the clay shale and shale did not undergo
significant softening leading to loss of shear strength. H piles driven in clay shale
could have lower potential for extensive water infiltration along the clay shale-pile
interface than drilled concrete shafts. Driven H piles in clay shale are low
displacement and do not significantly change the at rest soil pressure at the soil pile
interface. In drilled shaft construction, stress release caused by auguring an open hole,
can decrease the soil pressure coefficient depending on the actual construction
conditions (Coduto, 2001). Water-bearing fractures or sandstone lenses have a
smaller surface area exposure to the pile face and are potentially, more readily sealed
off by clay smearing along the pile. If protective pile tips are not used, only very
small gaps could form along the pile flange and web interfaces. Reinforcing, cast
steel pile tips were used on 95 percent of the H piles in this study. The pile tips are
flush with the outside flange and have a lip that extends slightly beyond the pile web
area, creating a potential gap with the soil during driving. Pile driving is a dynamic
process which mobilizes viscous behavior in a ductile soil as the short-duration,
intense stress wave propagates down the pile and interacts with the soil. The
combination of the stress wave and lateral confining soil pressure could cause the
clay shale to deform and fill gaps along the pile interface. Ductile clay shale or shale
may also be deformed and dragged down, along the pile shaft during driving.
Excavation of a test pile driven in clay shale would provide definite evidence of
conditions along the shaft-soil interface. H piles avoid construction issues such as:
using casing in flowing wet sands, potential construction defects related to tremie
39


pipe placement of concrete in water-filled holes, and mud debris or softened clay
shale along the side of wet, augered holes. Long term monitoring of test piles driven
into expansive clay shale is needed to better quantity performance and design
guidelines for H piles in expansive soil.
40


3. Piles Driven into Clay Shale. Shale, or Sandstone
3.1 Pile Design Loads and Design Resistance
Factored design loads for H-piles and pipe piles in the study range from 133 kips to
507 kips. Most of the piles are utilized in bridge abutments with a minority for walls
or bridge piers. Seventy-eight percent of the factored design loads are 350 kips or less
reflecting the H 12x74 section area capacity of 360 kips (figure 11). Higher design
loads were for piles with larger section areas including H 12x84 and H 14x89. The H
12x74 grade 50 steel pile is the most frequently used pile in bridge abutments.
H-Piles, Pipe Piles Clay Shale, Shale, Sandstone
Factored Design Load kips
Figure 11 Distribution of factored design loads for H-piles and pipe piles in clay shale,
shale, and sandstone.
41


A review of the project worksheets from all sites showed that most designs used a
resistance factor of 0.7 in the LRFD method to calculate the minimum required
resistance from the factored load. A few sites used a different factor with a range
from 0.6 to 0.8. In these cases, the minimum required resistance was recalculated
using a resistance factor of 0.7 to compare all sites on a consistent basis. The
required geotechnical resistance for the loads in figure 11 ranges from 197 kips to 724
kips (figure 12). At one site, the designer calculated the factored load for a H 12x74
pile using a procedure that differed from the rest of the database, maximum factored
pile load is less than (0.33) (Fy) (section area), resulting in a very high factored load
of 507 kips for a FI 12x74 pile. Eighty-five percent of the required geotechnical
resistance by the bearing strata is in the 375 to 550 kip range (figure 13).
H-Piles, Pipe Piles Clay Shale, Shale, Sandstone
d>
O
s I
E -S2
5 to
o
0) Q:
II
T3 '
d) (D
i= O
3 C
cr <3
CC to
d>
CC
Figure 12 Range of factored design load and required geotechnical resistance for a
resistance factor of 0.7; (*) is from a site with differing load calculations.
42


H-Piles, Pipe Piles Clay Shale, Shale, Sandstone
Figure 13 Distribution of required nominal geotechnical capacity for H-piles, pipe
piles in clay shale, shale, and sandstone.
3.2 Provided Nominal Capacity Measured by the PDA
Comparison of the provided nominal pile resistance measured by the PDA (pile
driving analyzer) with the required factored pile resistance shows that the provided
nominal pile capacity exceeds the minimum required capacity by 400 to 500 kips at
fourteen sites (figure 14). These measurements indicate that the rock strata along the
Front Range can potentially develop the capacity to support higher pile loads. It is
important to note that most of the CDOT PDA measurements were performed at the
beginning of the project to establish pile driving criteria for the contractor in terms of
blows per inch and hammer stroke for a particular site and hammer. Thus, the
subsequent production piles may have had a lower nominal capacity closer to the
43


required minimum capacity. The higher capacity test piles do provide valuable data
on the nominal capacity of a boring profile.
H-Piles, Pipe Piles Clay Shale,Shale.Sandstone
1400
1200 -
1000 -
800
600 -
400 -
200
0
0 200 400 600 800 1000 1200 1400
Required Nominal Capacity kips (Factor 0.7) j
Figure 14 Comparison between required nominal pile capacity and provided
nominal pile capacity as measured by the PDA. The dashed line represents the
minimum required nominal capacity for a specific factored load.
3.3 Pile Setup Time
The PDA measured nominal pile capacity plot is not normalized with respect to pile
setup time. Setup time, defined as the time increment between the end of driving and
the beginning of pile restrike, ranges from 0.3 to 288 hours for the data set (figure 15).
When saturated cohesive soils are compressed and disturbed due to pile driving,
excess pore pressures develop. The excess pore pressure causes a reduction in the
effective stresses acting on the pile resulting in a lower pile capacity during driving
44


and for a period of time after driving (Rausche et al., 1996). With the dissipation of
pore pressure after pile driving, the soil reconsolidates and increases in shear strength.
This increase in soil shear strength results in an increase in static pile capacity and is
termed soil set up (Hannigan et al., 1998). Within practical limits, the use of longer
setup times can achieve higher measured pile capacity in argillaceous strata.
H-Piles, Pipe Piles Clay Shale, Shale, Sandstone
Pile Setup Time hours
Figure 15 Distribution of setup times at the pile data sites. The horizontal scale
(hours) gaps after 24 hours to 288 hours with no intervening data points.
The gain in axial capacity with increasing setup time is well documented in normally
consolidated clays and in silty-clayey sands Seed & Reese (1955), Tomlinson (1980).
Soil/pile set-up in cohesionless soil is due to: (a) chemical effects which may cause
45


the sand particles to bond to the pile surface, (b) soil ageing effects resulting in an
increase in shear strength and stiffness with time, and (c) gain in radial effective
stress due to creep effects or relaxation on the established circumferential arching
around the pile shaft during installation (Chow et ah, 1998). Pile capacity increase
due to setup effects in the shallow bedrock strata along the Front Range has been
observed at many sites by the Colorado Department of Transportation with PDA
testing (Alan Hotchkiss, CDOT, personal communication).
The highest measured pile capacity in clay shale, 1286 kips, was from a 24 inch pipe
pile at US Highway 36/Box Elder Creek in Adams County. The 24 inch pipe pile
originally had an end plate but could not penetrate a sandy gravel layer with the
delivered hammer. After removal of the end plate, the pile was driven as an open
pipe to the required penetration depth. Two, open-end 24 inch pipe piles driven into
medium hard to hard, moist clay shale (Denver Formation) had setup times of 19
hours and 288 hours. The clay shale plugs in the piles were drilled out prior to PDA
testing. Thus, end bearing capacity was limited to the pile section area without the
soil plug and pile capacity was essentially developed as side resistance. The pile with
19 hours setup had a PDA measured nominal capacity of 695 kips. The pile with 288
hours setup had a nominal capacity of 1286 kips. The piles were driven for adjacent
abutment and bride pier and penetrated a very similar geologic section (figures 16 and
17). The 695 kips capacity pile had an embedment length of 18 feet into clay shale
while the 1286 kips capacity pile had an embedment length of 16.5 feet into clay
shale. Setup time is the significant difference between the two piles. The Box Elder
46


* fi?2*
_ 5525
Z Ml 5
551C
549b
0)
3
o
-
<
>
LU
_J
UJ
54fc.
r.4fio
_ 54/5
- . 5465
--- 5460
____nan-'
f.4f?n
5445
___ 5440
- 5405
LEGEND
Sand to Gravelly Sand loose
to medium dense, most to wet.
Sandy Clay to Silty Clay -
medum stiff, most.
Clay Shale medium
hard to hard most.
PILE #1 INFORMATION:
- Location : Pier #3
- Pile Type: Pipe (024, 0.5" thick)
- Open End Pipe Pile 58.5 ft into ground
- Plug Drilled Out
HAMMER INFORMATION:
- Model: APE D30-32
- Hammer Stroke: 7.5'-8.5'
-2" HO blows count
- Damping Jc: 0.3
- Time of Rcstrike: 19 hours
MEASUREMENT:
- Case Method: 347.5 tons
- Max Driving Stress: 21,0 ksi
- Measured Hammer Energy: 16.8 k-ft
- Energy Transfer Ratio: 24.0
BRO (ISKMKV
UNIVERSITY OF COLORADO AT DFNVER
DEPARTMENT OF CIVIL ENGINEERING
US 36 AT BOX FI DFR CREFK
LOGS OF EXPLORATORY BORINGS
Figure 16 Boring log profile of 24 inch open-end pipe pile with 695 kips nominal
capacity.
47


BORING 4
Elevation = 5536'
LEGEND

N2i
Fill gravelly sand, clayey sand.
___Pile #1
___ 5525

___ 6495
--- 5490
~ 5485
___ 5480
--- 5475
_ 54 70
5465
I 5460
BSand to Gravelly Sand loose to
medum dense, most to wet.
Sandy Clay to Silty Clay -
I''. 0 medum stiff, very most.
Clay Shale Bedrock medum hard to
hard, most.
PILE ft 1 INFORMATION:
- Location : Abutment #7
- Pile Type: Pipe (024", 0.5" thick)
- Open End Pipe Pile 59.3 ft Into ground
- Plug Drilled Out
HAMMER INFORMATION:
- Model: APE D30-32
- Hammer Stroke: 7.5-8.5
- 710 blows count
- Damping Jc: 0.3
- Time of Rsstrike: 12 days
MEASUREMENT:
- Case Method: 643 tons
- Max Driving Stress: 34.6 ksi
- Measured Hammer Energy: 35.8 k-ft
- Energy Transfer Ratio: 51.1
5-155
BRO 6362-02/ UNIVERSITY OF COLORADO AT DENVER US 36 AT BOX Ft DFR CRFFK
r-in-BK DEPARTMENT OT CIVIL ENGINEERING LOGS OF EXPLORATORY BORINGS
Figure 17 Boring log profile of 24 inch open-end pipe pile with 1296 kips nominal
capacity.
48


Creek pile capacity measurements are consistent with time related strength gains
along the pile shaft. Determination of time dependent setup rate and magnitude is
based on PDA measurements from restriking or long term load tests over an extended
time. There is probably no universal setup factor for the rocks along the Front Range.
Differences in plasticity, moisture content, rock fabric, and extent of cementation
likely contribute to variations in setup.
An opposite phenomenon called pile relaxation has been documented (Fellenius et ah,
1989), in which the load carrying capacity of the pile decreases with time after
installation requiring deeper driving to reach the initial capacity. Pile relaxation is not
common, but can be occur at certain sites in dense fine sand, inorganic dense silt, or
in certain shales. In these cases, the driving process is believed to cause to cause the
dense soil to dilate near the pile toe to dilate, generating negative pore pressures. The
negative pore pressures temporarily increase the effective stresses acting on the pile,
resulting in temporarily higher soil strength and driving resistance. When these pore
pressures dissipate, the effective stresses decrease lowering the pile capacity
(Hannigan et ah, 1998).
Pile relaxation in rock was first investigated in Paleozoic-age cemented shales in
Ohio, Pennsylvania, and southern Ontario. In an 8 year study involving hundreds of
driven piles, dynamic piles testing, and loads test in southern Ontario and the
northeastern United States, Thompson and Thompson (1985) concluded that pile
relaxation did not occur in most geotechnical conditions. Pile relaxation was
49


documented by dynamic and static testing to occur in H-piles and in closed-end pipe
piles driven into shale interbedded with limestone. The degree of relaxation was
significantly higher for pipe piles than H piles. Thompson and Thompson (1985)
hypothesized that the piles drive through the bedrock until sufficient resistance is
obtained from end bearing and side friction in rock. The shale and interbedded
limestone have high locked-in lateral stress due to erosion of thousands of feet of
overburden. The high lateral stress will then relax into the disturbed zones caused by
the shearing and displacement of the rock. H-piles will tend to slice through the
bedrock. The closed end pipe piles displace more rock during driving, creating more
disturbance in the rock structure. Consequently, there would be a larger relaxation of
the high lateral stresses and reduction in the frictional capacity in closed-end pipe
piles as opposed to H-piles. Pile relaxation has not been observed in the bedrock
strata along the Front Range by the Colorado Department of Transportation at the
sites in this investigation.
3.4 Maximum Driving Stresses in Piles Measured by PDA
AASHTO standard specification limit the maximum driving stress in steel H-piles
and pipe piles to 90 percent of the steel yield strength. For grade 50 steel, the
maximum allowable driving stress is 45 ksi. Dynamic stresses during pile driving are
calculated by the Pile Driving Analyzer (PDA). The maximum compressive stress in
all piles in the investigation, measured by the PDA during stress wave propagation
along piles, ranges from 21.5 ksi to 44.3 ksi. The maximum driving stress measured
50


by the PDA and the nominal pile capacity show broad correlations with the increase
in hammer energy transferred to the pile. Variation in the correlations reflects the use
of a variety of hammers with a wide range of energy ratings and energy transfer ratios,
a range of pile section areas for different piles included in the database and instrument
errors (figures 18 and 19). Additionally, different soil section profiles affect the
distribution of soil-pile interface resistance and energy damping values during driving.
This can also be a contributing factor to nominal pile resistance. Superimposed on
the plot of transferred hammer energy and nominal capacity (figure 19) is a trend line
derived from CDOT standard specifications for the minimum-rated hammer energy
for a range of H pile sections. The trend line is based on a hammer energy transfer
ratio of 30% to the pile (see section 3.5) and the nominal capacity required for pile
sections with the maximum load controlled by the section area for Grade 50 steel.
The trend line closely follows the lower band of the data range indicating that the
CDOT minimum-rated hammer energy requirements are reasonable for the probable
range of transferred energy in hammers. At sites where lenses of cemented
siltstone/sandstone have to be penetrated, a higher energy-rated hammer may be
required for reasonable driving rates.
The highest pile stress of 44.3 ksi was measured in a 12x84 H-pile with a capacity of
586 kips and the high hammer energy of 41 kip-ft (figure 18). Within the range of
measured ultimate H-pile capacity, maximum pile compressive stress did not exceed
44 ksi over a wide range of pile capacities in different geologic profiles. Excluding
the one data point previously discussed, pile capacities up to 900 kip had PDA
51


H-Piles, Pipe Piles Clay Shale, Shale, Sandstone
' 1600 < Q 1400
CL l4UU c 1onn - 24 in Pipe a H14x89 a H 12x84 xH 12x74 + H 10x57
o 1000 ~ if) o .9- 800 nj ^ n 600 o Ann A ...
X

X x
c 'F onn - + i
o z o
0 10 20 30 40 50
Maximum Driving Stress from PDA ksi
Figure 18 Correlation between maximum pile stress and nominal pile capacity as
measured by the PDA.
Nominal Capacity from PDA kips
Figure 19 Correlation between transferred hammer energy and nominal pile
capacity as measured by the PDA with superimposed trend line of CDOT minimum
hammer energy specification at 30% hammer energy transfer ratio.
52


measured compressive stresses below 42 ksi for HI2x74 piles. The 900 kip capacity
greatly exceeds the nominal capacity required for HI2x74 piles with the factored
loads in the bridge structures. The pile driving stress does not appear to be a limiting
factor to utilizing higher pile loads unless a very hard cemented rock layer has to be
penetrated to reach a minimum embedment length. For a given pile section area, the
transferred hammer energy is the greatest, but not the sole, controlling factor over pile
driving stress. The driving stress measured by PDA shows a general trend of
increasing stress with higher transferred energy (figure 20). A maximum transferred
energy of 40 kip-ft correlates with a safe compressive stress of less than 45 ksi in H
12x74 and H 12x84 piles.
H-Piles, Pipe Piles Clay Shale, Shale, Sandstone
E
P
CO
CO
CD
W
O)
C i
> <
E
E
- 24 in pipe
14x89 H
12x84 H
x12x74 H
+10x57 H
Hammer Energy from PDA kip-ft
Figure 20 Correlation between transferred hammer energy and pile compressive
stress as measured by the PDA.
53


Although the transferred hammer energy to the pile head and the pile section area are
the principal controls of compressive stresses developed during driving, different soil
section profiles affect the distribution of soil-pile interface resistance and energy
damping values during driving which can affect pile stress. This can also be a
contributing factor to the nominal pile resistance. The effect of the distribution of
soil-pile interface resistance and energy damping values is discussed using
GRLWEAP (wave equation) to model pile driving stress in a hypothetical example.
Consider a section profile consisting of 20 feet of medium dense sand with a friction
angle of 34 degrees overlying 20 feet of bed rock. An H 12x74 grade 50 steel pile is
driven through the overburden sand 15 feet into the bedrock with a Delmag D30-32
hammer operating at 75 percent of rated efficiency. Two potential models of pile
resistance are modeled using the wave equation analysis program GRLWEAP. Each
pile has a resistance of 420 kips of which 43 kips is developed in the sand layer as
side resistance and 377 kips is developed in the bedrock as a combination of side and
end bearing resistance in varying proportion.. In model one, 80 percent of the bedrock
resistance is side resistance (shaft) with 20 percent as end bearing. In model two, 20
percent of the bedrock resistance is side resistance (shaft) with 80 percent as end
bearing. Wave equation depth plots of pile capacity, blow counts, pile stresses,
hammer stroke, and energy transferred to the pile head (ENTHRU) are shown in
figures 21, 22. Maximum compressive stress in both piles at a capacity of 420 kips is
similar. The pile with the higher percentage of side resistance in bedrock (Model 1)
has a slightly higher calculated maximum compressive stress of 34 ksi verses 33 ksi
54


Depth (ft)
CO Dept of Transp Univ of Colorado
Jul 19 2010
: 07/19/2010:
------ Ult. Capacity (kips)
0 100 200 300 400
451
50 i
0 10 20 30 40
------- Blow Count (blows/ft)
Gain/Loss 3 at Shaft and TcxGRLWEAP(Tl\/l) Version 2005
-------- Comp. Stress (ksi)
0 10 20 30 40
; |
5 i !
10 |
15 i \ ;
\
20 j........................ ;
251...................> i
30
35
40
45 .......!.... ..........I.....
i ;
; : ; |
50 1 !
0 10 20 30 40
------- Tension (ksi)
ENTHRU (kips-ft)
0.0 20.0 40.0 60.0 80.0
Stroke (ft)
Figure 21 Wave equation analysis of H 12x74 pile driven through 20 feet of sand into
20 feet of bedrock. Model 1: resistance in bedrock is 80 percent side resistance (shaft)
and 20 percent end bearing.


CO Dept of Transp Univ of Colorado
Jul 19 2010
Gain/Loss 3 at Shaft and TckGRLWEAP(7M) Version 2005
: 07/19/2010:
------- Ult. Capacity (kips)
0 200 400 600 800
| |
i
5 S' |.....j -
Sand
45 i
50
0 10 20 30 40
----- Blow Count (blows/ft)
-------- Comp. Stress (ksi)
0 10 20 30 40
5...............! ' !--
10
15
\
201 -..................!'
25| ; | i
301 ..........;.....
35 | .........I.....f
40
i .......i... ;
10 20 30
- Tension (ksi)
ENTHRU (kips-ft)
0 20 40 60 80
501 - i
40 0 4 8 12 16
------ Stroke (ft)
45
50'
Figure 22 Wave equation analysis of H 12x74 pile driven through 20 feet of sand into
20 feet of bedrock. Model 2: resistance in bedrock is 20 percent side resistance (shaft)
and 80 percent end bearing.
56


for the pile (Model 2) with the greater percentage of end bearing resistance in bedrock.
However, for the case of higher side friction, pile compressive stress can be seen to
increase progressively with depth. For a pile that develops high end bearing capacity
in a stronger layer, compressive stress increases rapidly as the layer is encountered. In
this situation, careful PDA is necessary to prevent pile damage due to overstressing.
3.5 Hammer Energy Transfer Ratio
Only a portion of the rated hammer energy is delivered to the pile head. The energy
transfer ratio, defined as the ratio between the energy transferred to the pile head
measured by PDA and the rated hammer energy, ranges from 18 to 55.6 percent. The
energy transfer ratio is most frequently between 30 and 40 percent for hammers
frequently used in Colorado (figure 23).
V)
0)
iE
4
0
1
a)
n
E
3
15 20 25 30 35 40 45 50 55 60 65
Energy Transfer Ratio %
Figure 23 Distribution of hammer energy transfer ratio for all H-piles and pipe piles.
57


4. DRIVEN Analysis of Piles in Clay Shale. Shale. Sandstone
The calculation of pile capacity is a based partially on the theoretical concepts from
soil and rock mechanics but mainly on empirical methods based on experience
(Tomlinson, 1994). The general procedure is to apply simple empirical factors to the
strength, density and compressibility properties of the undisturbed soil and rock.
DRIVEN is a program developed through the Federal Highway Administration for
axial capacity design of driven piles for deep foundations. Pile capacity was estimated
with DRIVEN for end of drive conditions at the pile sites in the database. The output
from the DRIVEN program can be directly fed into the GRLWEAP (wave equation)
program for a pre-driving analysis of pile performance during pile driving. In general
the ultimate vertical load resistance of a pile, Ruit (or Rn-nominal resistance) from a
soil mechanics approach, is composed of two parts: pile tip resistance and side (or
shaft) resistance given below:
Ruit Rp + Rs
where: pile tip resistance Rp = qpAp,
pile side resistance Rs = Z qSi Az, a,
qp = unit tip resistance
qs = unit side resistance, which is constant along segment Azj of the pile
a = perimeter of the pile shaft, Ap = area of the tip of the pile
58


H piles and pipe piles without endplates are low displacement piles of relatively small
cross-sectional areas (figure 24). Less compaction and soil disturbance develops
during driving of H piles compared to closed-end piles.
Figure 24 Low displacement piles that can be driven into weak rock (Azizi, 2000).
4,1 DRIVEN Analysis of Piles in Clay Shale, Shale
Analysis of pile capacity in clay shale and shale intervals initially followed the design
procedures for piles in cohesive soils. The ultimate unit tip resistance of piles in
saturated clay from consideration of the general bearing capacity equation for axial
capacity may be taken as:
qP = 9 Su
where:
Su = average undrained shear strength in the range from 2B to
3.5B below the pile tip and B is the diameter of the pile.
59


Unit side resistance is expressed as a function of undrained shear strength Su, with
consideration of both the pile type and the embedded pile length. The a method
(Tomlinson, 1980), based on total stress analysis, is used to relate the side friction
resistance between the pile shaft and clay soil to the undrained shear strength of the
clay, Su. The adhesion factor a, is not a soil property, but an empirical factor to relate
undrained shear strength to unit side resistance for a pile in clay and clay shale. For drilled
shaft and pile foundations, the adhesion factor varies with the pile material, soil
characteristics, and construction practices. The ultimate unit side resistance may be
taken as:
CJs OtSu
where:
a = adhesion factor
Su = average undrained shear strength of the soil in the segment of interest.
The adhesion factor can be misleading in implying that side resistance is due to an
effect of gluing the pile to the soil. Side resistance is more accurately described as a
sliding friction model (Conduto, 2001) using an effective stress analysis taken as:
fs = K0 g'z (K/Ko) (fr/f)
where:
fs = unit side friction resistance
Ko = at rest lateral earth pressure coefficient before pile installation
K = at rest lateral earth pressure coefficient after pile installation
a'z = effective vertical stress
60


(j)f= soil-foundation interface friction angle
())' = effective friction angle of the soil along the pile
Due to the practical difficultly in evaluating all of the parameters for an effective
stress analysis, the alpha method is commonly used to evaluate side friction.
4.2 Selection of Input Parameters for DRIVEN Analysis
The program DRIVEN requires the following soil input parameters to estimate pile
capacity in cohesive soil at end of drive conditions: undrained shear strength,
adhesion coefficient, and percent strength loss during driving. Along the Colorado
Front Range, deep foundation design methods typically use SPT N values to establish
empirical relationships to rock strength. Unconfmed compressive strength tests are, at
times, performed on California liner samples and rarely on cores due to the cost and
difficulty in coring weak rocks. For equivalent zones of sampling, core samples
frequently have a higher unconfined compressive strength than SPT drive samples
due to sample disturbance. At most data sites in this study, unconfined compressive
strength data was absent and SPT N values were the only indicator or rock strength.
In the DRIVEN analyses, the unconfmed compressive strength of clay shale and shale
was estimated from SPT data using the relationship 0.27 N (ONeill et al., 1996) for
medium hard (30-50 blows for 12 inch penetration) and hard clay shale (50/12 to
50/5), and 0.24 N for very hard clay shale and partially cemented shale (higher than
50/5). Comparison of the unconfined compressive strength of core samples from
61


extremely hard, partially cemented Pierre Shale from Trinidad Colorado to blow
counts from partial penetration SPT tests indicated the use of the 0.24 factor in harder
shale. Blow counts were corrected for hammer energy using a coefficient of 1.5 for
auto hammer samples, i.e. the value of auto hammer blow counts times 1.5 are to be
used in the computation.
An adhesion factor of 1.0 for normally consolidated moist clay is commonly used to
evaluate side resistance in piles (Conduto, 2001). Numerous studies involving load
tests of piles are in general agreement of the 1.0 factor for normally consolidated clay
defined as clay having an unconfined compressive strength less than 1000 psf with a
soil strength ratio, undrained shear strength divided by the present day effective
vertical stress, less than 0.35 (Semple and Rigden, 1984). After driving through
moist normally consolidated clay, the dissipation of excess pore pressures is thought
to occur in conjunction with reconsolidation and aging of the soil structure to reflect
the original strength of the clay in contact with the pile shaft. The adhesion factor
both for clay and overconsolidated clay with an unconfined compressive strength
greater than 1000 psf shows a general trend of decreasing value with increasing
undrained shear strength (Tomlinson, 1980, 2004). In a study of pile capacity
measured for pipe piles in offshore structures that was sponsored by The American
Petroleum Institute, Semple and Rigden, (1984) recommend an adhesion factor of 0.5
for steel pipe piles in overconsolidated clay (figure 25).
62


Figure 25 Correlation between clay undrained shear strength and friction (adhesion)
factor in steel pipe piles (Semple and Rigden, 1984).
ONeill et al. (1996) present data from load tests on drilled concrete shafts in
intermediate geomaterials and weak rock which show a range in the adhesion factor
from less than 0.1 to 1 (figure 26). They attribute the wide range in the value of the
adhesion coefficient as a major contributing factor in the low correlation between
estimated and measured side resistance in drilled shafts. Although drilled concrete
shafts are not strictly analogous with driven steel piles, the study does show a similar
trend of lower adhesion factors in higher strength clays. Adhesion factors in weak
rock including shale, mudstone, limestone, and sandstone display a wide range in
value.
63


Sy(CIUC)/pa qy/2pa
Figure 26 Variation in adhesion factor based on geomaterials strength (ONeill et al.,
1996).
The lower adhesion factor for overconsolidated clay is attributed to; shearing during
pile driving which exceeds the peak strength and approaches a lower residual strength
value, the presence of fissures which lower soil strength against the pile, and greater
stiffness which may lower the ability of the clay to reconsolidate around the pile
filling any gaps that may form during driving. Cores and California liner samples of
clay shale along the Front Range predominantly show a massive rock texture with a
lack of close-spaced Assuring. Planar fractures of tectonic origin occur where strata
drape over faults or form in response to broad crustal movements. A blocky texture,
indicative of weathering or slaking, appears infrequently in subsurface samples.
Closely spaced Assuring mostly occurs in shallow bedrock within the zone of
64


seasonal moisture variation and weathering. The magnitude of the adhesion factor at
time of measurement can also vary with the effect of the setup factor.
For example, consider a pile driven into a soil that experiences strength loss during
driving with subsequent strength gain (pile setup). If the pile is tested shortly after
driving, the unit side resistance divided by the undrained shear strength yields an
adhesion factor for that time from the end of drive. If the pile is tested, say 1 month
after driving, a load test would give a greater side resistance and higher corresponding
adhesion factor. Thus for a steel pile driven in cohesive soil or rock with a significant
setup effect, the adhesion factor will increase with time. The maximum adhesion
factor is measured after pile setup is largely complete.
DRIVEN has the option of specifying a percentage strength loss during driving and
an adhesion value. The adhesion value can be a user-defined percentage of the
undrained shear strength corresponding to an adhesion factor. Using the percentage
strength loss, DRIVEN calculates ultimate (nominal) static pile capacity at restrike.
The program also generates the soil input file required for a driveability study in the
GRLWEAP wave equation program. The use of high values for driving strength loss
and setup factors require reasonable certainty of driving strength loss and can produce
non-conservative estimates of pile capacity at restrike.
DRIVEN static capacity estimation of pile capacity for the end of drive condition
with zero setup time used the following parameters: adhesion factor of 0.70 and 0.50
for clay shale and shale, adhesion factor of 1.0 for moist normally consolidated clay,
65


adhesion factor of 0.50 for overconsolidated dry clay, 50 percent driving strength loss
for normally consolidated apd overconsolidated clay and 50 percent driving strength
loss for clay shale and shale. The 50 percent driving strength loss for clay shale and
shale does not imply that these materials experience ultimate strength gain similar to
that expected for normally consolidated clay. Thus, for an adhesion factor of 0.5, the
unit shaft resistance calculated by DRIVEN is the product of: (0.5 strength loss) (0.5
adhesion factor) (undrained shear strength). No strength gain due to setup was
incorporated into the DRIVEN analysis due to a high uncertainty on setup rates.
ONeill (1983) presents data which shows that, for a single pile in clay, forty percent
of the excess pore pressure generated by driving dissipates in 24 hours, but the
literatures show a range of dissipation rates. Limited evidence suggests that strength
loss during driving and subsequent setup in a cohesive soil took place in clayey soils
with the water content greater a value of, say, eight percent. Clay or clay shale with
low water content may not experience as much strength loss/gain during driving. In
computing pile capacity, resistance contribution from sand and clay overburden was
incorporated. No strength loss or setup was assigned to sand overburden. In addition
to the soil input parameters, DRIVEN also requires selection of the pile shaft surface
area for side friction and base area for end bearing resistance. For H piles, the shaft
surface area was specified as: 1) the total pile perimeter including the flange and web
area, 2) the flange perimeter equal to only the flange area, or 3) the box perimeter
equal to a box encompassing the four sides. Base bearing area was specified as the:
1) pile box area, or 2) tip area. The tip area is equal to either the section area for piles
66


without protective tips or the section area increased by 15 percent for piles with
protective tips welded on.
4.3 DRIVEN Capacity Estimates for H Piles in Clay Shale, Shale
Four models of shaft resistance (side) and end bearing resistance using adhesion
factors of 0.50 and 0.70 were considered. The models are designated in terms of
(side)/(end resistance and include: ( 1) box perimeter/box area, 2) flange
perimeter/box area, 3) total perimeter/tip area, and 4) flange perimeter/tip area.
Results of the analysis are summarized in table 5.
Table 5 Summary of DRIVEN axial capacity analysis of four H pile resistance
models compared to measured PDA nominal pile capacity.
Model Correlation Coefficient Mean Difference from PDA /Range Conservative % of analysis degree
Flange Perimeter/Box Area a = 0.70 0.75 -162 kips (+79 to-499) 85%- High/Moderate
Flange Perimeter/Box Area a = 0.50 0.72 -202 kips (+74 to -543) 91 %-High/Moderate
Flange Perimeter/Tip Area a = 0.70 0.82 -359 kips (-93 to -712) 100% -Very High
Flange Perimeter/Tip Area a = 0.50 0.79 -390 kips (-98 to -753) 100% -Very High
Box Perimeter/Box Area a = 0.70 0.82 -8 kips (+242 to -322) 47%-Moderate/N on
Box Perimeter/Box Area a = 0.50 0.80 -73 kips (+133 to-411) 74%-Moderate/Non
Pile Total Perimeter/Tip Area a = 0.70 0.77 -60 kips (+164 to-439) 74%-Moderate/Non
Pile Total Perimeter/Tip Area a = 0.50 0.77 -158 kips (+5 to -511) 91%-Moderate
67


The pile flange perimeter area/tip area is the lowest capacity pile model considered.
Analyses for both an adhesion factor of 0.70 and 0.50 yield an overly conservative
estimate of pile capacity compared to the PDA nominal values (figure 27). The mean
difference between the DRIVEN estimate and the PDA values are -359 kips (a = 0.70)
and -390 kips (a = 0.50) with a range up to -753 kips. The pile flange perimeter
area/tip area model is overly conservative and not recommended. The pile flange
perimeter area/box area model presents higher resistance. The model assumes that
sufficient frictional resistance is developed in the pile web area to mobilize an end
bearing resistance upon loading greater than that provided by the pile section area.
Analysis for both an adhesion factor of 0.70 and 0.50 yields a generally conservative
estimate of pile capacity compared to the PDA nominal values (figure 28). The mean
difference between the DRIVEN estimate and the PDA values are -162 kips (a = 0.70)
and -202 kips (a = 0.50) with a range from +74 to -753 kips. The pile flange
perimeter area/box area model could be used in DRIVEN for initial estimates of pile
length, but very conservative estimates are probable. Use of the box perimeter area of
four sides for shaft resistance in conjunction with the box area for end bearing
resistance produces a less conservative estimate of pile length and capacity estimate
(figure 29). The mean difference between the DRIVEN estimate and the PDA values
are -8 kips (a = 0.70) and -73 kips (a = 0.50) with a range from +242 to -411 kips. An
adhesion factor of 0.70 in the DRIVEN analysis produces a closer match to the PDA
capacity, but is somewhat non-conservative as setup effects are not considered. An
adhesion factor of 0.50 is recommended for the box perimeter/box area model.
68


H Piles Clay Shale, Shale Dominant Profile
DRIVEN Estimated Capacity (kips) (pile flange perimeter, tip area model)
(adhesion factor = 0.70)
H Piles Clay Shale, Shale Dominant Profile
DRIVEN Estimated Capacity (kips) (pile flange perimeter, tip area model)
(adhesion factor = 0.50)
Figure 27 Nominal pile capacity (PDA) verses DRIVEN estimated capacity (EOD)
for total perimeter/ tip area model, adhesion factor equal 0.70 (upper), 0.50 (lower).
69


H Piles Clay Shale, Shale Dominant Profile
DRIVEN Estimated Capacity (kips) (pile flange perimeter, box area model)
(adhesion factor = 0.70)
H Piles Clay Shale, Shale Dominant Profile
DRIVEN Estimated Capacity (kips) (pile flange perimeter, box area model)
(adhesion factor = 0.50)
Figure 28 Nominal pile capacity (PDA) verses DRIVEN estimated capacity (EOD)
for flange perimeter/box area model, adhesion factor equal 0.70 (upper), 0.50 (lower).
70


H Piles Clay Shale,Shale Dominant Profile
DRIVEN Estimated Capacity (kips) (pile box perimeter, box area model)
(adhesion factor = 0.70)
H Piles Clay Shale, Shale Dominant Profile
1
DRIVEN Estimated Capacity (kips) (pile box perimeter, box area model)
(adhesion factor = 0.50)
Figure 29 Nominal pile capacity (PDA) verses DRIVEN estimated capacity (EOD)
for box perimeter, box area model/ adhesion factor equal 0.70 (upper), 0.50 (lower).
71


The final model considers shaft resistance developed along the total perimeter area
with toe resistance limited to the tip area. The total perimeter model is generally not
used for H piles in cohesive soil (Hannigan and others, 1998) but was considered in
DRIVEN to evaluate any empirical relationship to PDA nominal capacity. Analyses
for both an adhesion factor of 0.70 and 0.50 yield a generally conservative estimate of
pile capacity compared to the PDA nominal values (figure 30). The mean difference
between the DRIVEN estimate and the PDA values are -60 kips (a = 0.70) and -158
kips (a = 0.50) with a range from +164 to -511 kips. An adhesion factor of 0.70 in
the DRIVEN analysis produces a closer match to the PDA capacity, but is more non-
conservative as setup effects are not considered. The total perimeter/tip area model
produces more high magnitude non-conservative estimates of pile capacity than does
the box perimeter/box area model.
PDA traces from the data sites typically indicate a significant percentage of end-
bearing resistance for H piles driven into clay shale (Alan Hotchkiss, CDOT). A
combined resistance due to the soil-steel interface friction and adhesion within the
pile web is activated when the pile is struck. With each hammer blow, there is a
shear failure at the soil-pile interface as the pile advances. Within the small time
increment of the PDA measurement, this interface resistance will have an effect on
the dynamic record similar to the effect on the record from an H/pipe pile with an end
plate (Frank Rausche, GRL). The box perimeter/box area or flange perimeter/box
area (more conservative) models are recommended for preliminary estimates of pile
length and capacity using DRIVEN with an adhesion coefficient of 0.50.
72


H Piles Clay Shale, Shale Dominant Profile
DRIVEN Estimated Capacity (kips) (pile total perimeter, tip area model)
(adhesion factor = 0.70)
L
1200
g. 1000
is:
<
£ 800
I
ro 600
<3
Q)
E 400
To
c
| 200
H Piles Clay Shale, Shale Dominant Profile
.. */**,<*'
i-r -
V V-v,rLr

... ~~~ V ^ \ r; t Ar ^ -.
^ ; ,

200
400
600
800
1000
1200
DRIVEN Estimated Capacity (kips) (pile total perimeter, tip area model)
(adhesion factor = 0.50)
Figure 30 Nominal pile capacity (PDA) verses DRIVEN estimated capacity (EOD)
for total perimeter/ tip area model, adhesion factor equal 0.70 (upper), 0.50 (lower).
73


4.3-1 Effects of Pile Setup Times and SPT Blow Count on DRIVEN Analysis
Pile setup time was assigned into three categories: 1 hour and less, greater than 1 to
10 hours, and greater than 10 hours. The general effect of increasing setup time is
suggested by a trend for piles with longer setup time to have significantly higher
capacity than the DRIVEN analysis for end of drive conditions (figure 31) with the
flange perimeter/box area and box perimeter/box area models. Setup time and
magnitude is likely not uniform for clay shales and shale along the Front Range.
Variation in moisture content, plasticity, rock fabric and degree of cementation likely
contributes to differences in setup effects. Long term restrike tests in different rock
types with PDA monitoring are needed for application of setup effect in pile design.
The energy corrected SPT blow count most characteristic of the pile penetration
length was determined from the boring logs and placed into categories of 100 or less,
greater than 100 to 200, and greater than 200. DRIVEN analysis of H piles with SPT
greater than 200 shows the widest range in deviation from the PDA measurement for
the box perimeter/ box area model (figure 32). Deviations range from moderately
non-conservative to highly conservative. SPT blows above 200 were derived from
partial tests less than 12 inches. Estimates of unconfined compressive strength from
SPT blows are probably more inaccurate in these shales. More highly cemented beds,
not detected by exploration sampling, could occur and increase pile capacity.
Fracturing that produces lower Rock Quality Designation (RQD) values can lower
capacity. DRIVEN analysis using the flange perimeter/box area model produces a
slightly conservative capacity estimate in partially cemented shale.
74


H Piles Clay Shale, Shale Dominant Profile
1200
a 1000
g
0_
(0
o
800
600
400
200 -



;%41 ,,
a \.s:

Setup Time 0-1 hour
Setup Time 1-10 hours
a Setup "Time 10 hours +
200
400
600
800
1000
1200
DRIVEN Estimated Capacity (kips) (pile box perimeter, box area model)
(adhesion factor = 0.50)
H Piles Clay Shale, Shale Dominant Profile
DRIVEN Estimated Capacity (kips) (pile flange perimeter, box area model)
(adhesion factor = 0.50)
Setup Time 0 -1 hour
Setup Time 1-10 hours i
a Setup Time 10 hours + j
Figure 31 Nominal pile capacity (PDA) verses DRIVEN estimated capacity (EOD)
for box perimeter/ box area model, (upper) and for flange perimeter/box area model
(lower) with setup time from end of initial drive for PDA measurement.
75


H Piles Clay Shale, Shale Dominant Profile
! SPT less than 100 i
SPT 100-200
a SPT greater than 200
DRIVEN Estimated Capacity (kips) (pile box perimeter, box area model)
(adhesion factor = 0.50)
H Piles Clay Shale, Shale Dominant Profile
1200
1000
<
£ 800
a 600
CO
O
Q)
K 400
200

. |;§;7:P;;

* v4'
; £\ ~ v. : y* '/'C ..
y'
SPT less than 100
SPT 100-200
a SPT greater than 200
200
400
600
800
1000
1200
DRIVEN Estimated Capacity (kips) (pile flange perimeter, box area model)
(adhesion factor = 0.50)
Figure 32 Nominal pile capacity (PDA) verses DRIVEN estimated capacity (EOD)
for box perimeter/ box area model, (upper) and for flange perimeter/ box area model
(lower) with energy corrected SPT blows counts most characteristic of the profile.
76


Four sites in very hard Pierre Shale that have the greatest difference between
DRIVEN capacity and pile capacity measured by the PDA are listed in Table 6.
DRIVEN underestimated capacity at 2 sites and overestimated capacity at 2 sites
using the box perimeter/box area model. Setup times are low at the sites.
Table 6 Pile capacity in very hard Pierre Shale for DRIVEN (adhesion factor) and
PDA.
Site Pile Capacity DRIVEN kips Capacity PDA kips
Steel Hollow, Pueblo Co. 12x74 515 (0.50) 926 (0.5 hr setup)
Porter Draw, Pueblo Co. 12x74 655 (0.50) 522 (0.5 hr setup)
Scroggs Arroyo, Pueblo Co. 12x74 605 (0.50) 484 (0.5 hr setup)
125 @ Trinidad 12x74 661 (0.50) 796 (1.5 hr setup)
DRIVEN analyses gave lower capacities than those from PDA measurements for the
two piles at Steel Hollow and I25@Trinidad. At Porter Draw and Scroggs Arroyo,
the observations are just the opposite. The Pierre Shale at Steel Hollow had SPT blow
count of 50/4 and blow count of 150/3 at 125 @ Trinidad. The Pierre Shale at
Trinidad was partially cemented. In addition to shearing and remolding of the shale
to a state of lower strength at the soil pile interface, an increase in pore water pressure
that changes the effective stress at the pile-soil interface can also contribute to
strength loss. Water content of the shale was low, 7 to 9 percent at Steel Hollow and
4 to 6 percent at Trinidad. In these two cases, however, because of the lower water
contents, the pore water pressure effect on the strength loss was expected to be lower.
This might explain the lower capacity values from DRIVEN analyses. However,
DRIVEN analysis from a site in Trinidad at SH 12@I25 using the SPT based strength
77


method produced a slightly conservative capacity (695 kips) to the PDA nominal
capacity (734 kips) in Pierre Shale. The effect of shale moisture content on Front
Range clay shales and shales is uncertain. As discussed previously, the occurrence of
stronger cemented beds or lower reliability of SPT based strength estimates in
partially cemented shales could contribute to under estimating unconfmed
compressive strength at these sites.
The Pierre Shale at Porter Draw and Scroggs Arroyo had SPT blows of 50/4 to 50/3
(figure 33). CDOT performed the geotechnical borings at both sites as well as at
Steel Hollow. The Pierre Shale was cored at Scroggs Arroyo through the depth of pile
penetration. The RQD was in the 50 to 60 percent range for both abutments. ONeill
and Reese (1999) presented a table of rock joint-effect factors for drilled shafts,
which lower capacity, related to RQD for cohesive intermediate geomaterials (table
7). Similar effects, perhaps not the same magnitude, are reasonable for H piles in
fractured rock.
Table 7 Joint-effect factor for drilled shafts in cohesive intermediate geomaterials.
RQD (percent) Joint-Effect Factor
Closed Joints Open or Gouge-Filled Joints
100 1.00 0.85
70 0.85 0.55
50 0.60 0.55
30 0.50 0.50
20 0.45 0.45
78


ELEVATION (feel)
4f*00
LEGEND
--- J695
BONING H2 Sandy Clay stiff, moist.
Elevation =4892
_ 489C
- Piie#1
IL- 4835 If
4&8C
Z 46^ |
Z_ 4870
~ 48**: ;
L i i
- I Pile
- (12x74)
I_ uw-1' 30ft
jtg^j Gravelly Sand loose,
moist to wet.
Pierre Shale partially cemented,
very hard, slightly moist, moist.
PILE #1 INFORMATION:
- Location : Abutment ft2
- Pile Type; H Pile (12 x 74)
- Rel'Tomed Pile Tip 30.0 ft Into qround
HAMMER INFORMATION:
- Model; Dclmay D30-32
- Hammer Stroke: 7,5'-8.5'
- 1j" /10 blows count
- Damping Jc; 0,7
- Time of Restrke: 0,5 hour
MEASUREMENT:
- Case Method: 261 tons
- Max Driving Stress: 32 9 ksl
- Measured Hammer Energy; 26,1 k-tt
- Energy Transfer Ratio: 37.2
____ 4640
BK *.;>:/-1 r>? UMIV£-iSI!v OF CCLCKADO A! UfcMVtrK PORTFR DRAW rUFRl O COUNTY
K-18~OfJ UUAKlf'/zNl '.IF CIVIL bNONhbklNG LOGS or EXPLORATORY BORINGS
Figure 33 Boring log profile for abutment #2, structure K-18-GQ with test pile.
79


Reducing the estimated shale strength by a factor of 0.70 to account for RQD yields a
DRIVEN pile capacity estimation of 424 kips for Scroggs Arroyo. No coring was
performed at Porter Draw to verify a similar occurrence. Using the same strength
reduction yielded a DRIVEN pile capacity of 474 kips; conservative to the PDA
capacity of 522 kips.
Capacity derived from CAPWAP analysis differed significantly from the pile
capacity measured by the PDA with the Case method for a pile bearing in partially
cemented sandstone (Denver Formation) from 120th Ave at the Platte River, structure
ADA 120-09.5W308 (figure 34). This site had two pile tests on the same abutment
with rock penetration into very hard clay shale (SPT 50/5) and slightly-cemented
sandstone (SPT 50/2). Boring logs adjacent to the abutment indicate that the high
SPT blow count sandstone is present below the pile depth. The PDA data indicates
that little resistance was gained with 20 additional feet of sandstone penetration with
a strength gain of about 10 kips per foot (table 8). The DRIVEN estimate of the end
of drive capaciiv for Pile 1 was 537 kips and 1152 kips for Pile 2. The PDA nominal
capacity of Pile 1 is 848 kips, 311 kips higher than the DRIVEN estimate. A setup
time of 17 hours at testing likely contributed to increased pile capacity. Additionally,
the presence of partially-cemented siltstone lenses (noted on the boring log) may
cause higher capacity in Pile 1, especially for end bearing resistance. A CAPWAP
analysis of Pile 2 had a good signal matching quality and showed a capacity of 1480
kips (Hien Nghiem, personal communication).
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Table 8 Pile tests at abutment 1, structure ADA 120-09.5W308.
Test Pile Overburden Rock Penetration Capacity in Kips PDA CAPWAP DRIVEN
Pile 1 12x84 Sand 24 ft 11.5 ft CS 848 (17 hr) 608 537
Pile 2 12x84 Sand 24 ft 11.5 ft CS, 20ft SS 1068 (19 hr) 1480 1152
Frank Rausche of GRL interpreted the discrepancies in capacities, upon reviewing the
data, as potentially caused by rebound-induced unloading in the upper portion of the
longer Pile 2 during driving before the pile toe advanced. The simplified analysis
method (Case Method) does not see all of the resistance at the same time. The vertical
resistance distribution has an influence as more friction in the upper pile portion
causes a greater unloading effect. Other possibilities for the discrepancies include the
error in measurements, CAPWAP analysis, or Case Damping Factor. The majority of
H-piles in the database have resistance concentrated in the bottom 7 to 15 feet due to
limited rock penetration lengths. Thus, pile unloading problems are atypical in
relatively short bedrock penetration lengths in Front Range rocks.
The empirical model of pile resistance implemented with DRIVEN for clay shale and
shale uses an average adhesion coefficient (a) with soil strength controlling resistance.
This is an oversimplification of the actual conditions at the pile-soil interface (Bond
and Jardine, 1991). The adhesion coefficient likely varies with depth along the pile
shaft as greater displacements along the upper portion of the pile, deforms and molds
the soil to a lower, residual friction state. Also, the adhesion coefficient along the pile
81