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NATIONAL
NCHRP REPORT 697
COOPERATIVE
HIGHWAY
RESEARCH
PROGRAM
Design Guidelines for Increasing
the Lateral Resistance of
Highway-Bridge Pile Foundations
by Improving Weak Soils
OCR for page R2
TRANSPORTATION RESEARCH BOARD 2011 EXECUTIVE COMMITTEE*
OFFICERS
CHAIR: Neil J. Pedersen, Administrator, Maryland State Highway Administration, Baltimore
VICE CHAIR: Sandra Rosenbloom, Professor of Planning, University of Arizona, Tucson
EXECUTIVE DIRECTOR: Robert E. Skinner, Jr., Transportation Research Board
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*Membership as of June 2011.
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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM
NCHRP REPORT 697
Design Guidelines for Increasing
the Lateral Resistance of
Highway-Bridge Pile Foundations
by Improving Weak Soils
Kyle Rollins
BRIGHAM YOUNG UNIVERSITY
Provo, UT
Dan Brown
DAN BROWN & ASSOCIATES
Sequatchie, TN
Subscriber Categories
Bridges and Other Structures · Design · Geotechnology
Research sponsored by the American Association of State Highway and Transportation Officials
in cooperation with the Federal Highway Administration
TRANSPORTATION RESEARCH BOARD
WASHINGTON, D.C.
2011
www.TRB.org
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NATIONAL COOPERATIVE HIGHWAY NCHRP REPORT 697
RESEARCH PROGRAM
Systematic, well-designed research provides the most effective Project 24-30
approach to the solution of many problems facing highway ISSN 0077-5614
administrators and engineers. Often, highway problems are of local ISBN 978-0-309-21341-7
interest and can best be studied by highway departments individually Library of Congress Control Number 2011934448
or in cooperation with their state universities and others. However, the © 2011 National Academy of Sciences. All rights reserved.
accelerating growth of highway transportation develops increasingly
complex problems of wide interest to highway authorities. These
problems are best studied through a coordinated program of COPYRIGHT INFORMATION
cooperative research.
Authors herein are responsible for the authenticity of their materials and for obtaining
In recognition of these needs, the highway administrators of the written permissions from publishers or persons who own the copyright to any previously
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initiated in 1962 an objective national highway research program Cooperative Research Programs (CRP) grants permission to reproduce material in this
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understanding that none of the material will be used to imply TRB, AASHTO, FAA, FHWA,
a continuing basis by funds from participating member states of the
FMCSA, FTA, or Transit Development Corporation endorsement of a particular product,
Association and it receives the full cooperation and support of the method, or practice. It is expected that those reproducing the material in this document for
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COOPERATIVE RESEARCH PROGRAMS
CRP STAFF FOR NCHRP REPORT 697
Christopher W. Jenks, Director, Cooperative Research Programs
Crawford F. Jencks, Deputy Director, Cooperative Research Programs
Andrew C. Lemer, Senior Program Officer
Sheila A. Moore, Senior Program Assistant
Eileen P. Delaney, Director of Publications
Hilary Freer, Senior Editor
NCHRP PROJECT 24-30 PANEL
Field of Soils and Geology--Area of Mechanics and Foundations
Jon E. Bischoff, Utah DOT, Salt Lake City, UT (Chair)
Mark DeSalvatore, California DOT, Sacramento, CA
Manoj B. Chopra, University of Central Florida, Orlando, FL
Nicholas E. Harman, South Carolina DOT, Columbia, SC
Michael G. Katona, Washington State University (Retired), Gig Harbor, WA
Daehyeon Kim, Chosun University, Gwangju, Korea
Lianyang Zhang, University of Arizona, Tucson, AZ
Silas Nichols, FHWA Liaison
G. P. Jayaprakash, TRB Liaison
AUTHOR ACKNOWLEDGMENTS
The research reported herein was performed under NCHRP Project 24-30 by the Department of Civil
and Environmental Engineering at Brigham Young University (BYU) in Provo, Utah. Kyle M. Rollins,
Ph.D., professor of civil and environmental engineering, was the project director and principal investiga-
tor. Dan Brown, Ph.D., P.E., principal engineer at Dan Brown & Associates in Sequatchie, Tennessee, was
co-principal investigator. The other authors of this report are Hubert Law, Ph.D., P.E., and Dr. Zhao (Joe)
Chang, Ph.D., of Earth Mechanics Inc. of Fountain Valley, California. Matthew Adsero, Mark Herbst,
Nathan Lemme, and Dustin Miner performed the field load testing reported in this study under the super-
vision of Dr. Rollins of BYU with the assistance of David Anderson, chief technician for the Civil & Envi-
ronmental Engineering Department at BYU.
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FOREWORD
By Andrew C. Lemer
Staff Officer
Transportation Research Board
NCHRP Report 697: Design Guidelines for Increasing the Lateral Resistance of Highway-
Bridge Pile Foundations by Improving Weak Soils presents design guidance for strengthen-
ing of soils to resist lateral forces on bridge pile foundations. Lateral loads may be produced
by wave action, wind, seismic events, ship impact, or traffic. Strengthening of soil sur-
rounding the upper portions of piles and pile groups--for example by compaction,
replacement of native soil with granular material, or mixing of cement with soil--may be
more cost-effective than driving additional piles and extending pile caps as ways to increase
the bridge foundation's capacity to resist lateral forces associated with these loads. This
report presents computational methods for assessing soil-strengthening options using
finite-element analysis of single piles and pile groups and a simplified approach employ-
ing commercially available software. The analysis methodology and design guidelines will
be helpful to designers responsible for bridge foundations likely to be exposed to signifi-
cant lateral loads.
Lateral resistance of pile foundations typically is controlled by the stiffness and strength
of the materials in the vicinity of the pile cap and surrounding the upper portion of the piles.
When these materials are weak in comparison to the lateral loads that may be placed on the
foundation, the foundation's design may be controlled by these lateral loads. A larger num-
ber of piles or larger diameter piles and larger caps may be required and construction costs
will be increased.
Previous studies have shown that improving the strength of the weak materials may sig-
nificantly increase pile lateral resistance. Improvements to be considered typically include
removal and replacement of the in-situ materials, in-situ densification, grouting, or soil mix-
ing using more granular materials or a binder such as Portland cement. Soil improvement
extending a relatively limited distance around the piles and below the pile cap may be a cost-
effective method for meeting foundation design requirements.
Bridge foundation engineers have been hampered by a lack of verified design guidelines
for estimating the increase in pile lateral resistance to be gained from soil improvement. The
objective of NCHRP Project 24-30 was to develop such design guidelines.
A team led by Brigham Young University first reviewed recent practice, test data, exist-
ing specifications, and research findings from both foreign and domestic sources concern-
ing the use of soil improvement techniques to increase the lateral resistance of piles. From
this review, the research team developed a descriptive cataloging of soil improvement tech-
niques to be addressed by the design guidelines. The catalog included likely applicability of
each technique to specific weak soil types, such as soft cohesive soils, loose granular soils, or
organic materials.
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The team then described analytical methods that may be used to estimate the increased
lateral resistance achievable through soil improvement around single piles and pile groups.
A set of prototypical foundation designs was developed for testing to calibrate and verify
analysis estimates. These designs were then field tested in weak soils near Interstate 15 in
Salt Lake City, Utah. This report describes the experimental design and field testing.
The research team used finite-element methods and field-test results to perform a com-
prehensive parametric analysis to quantify the effect of soil improvement on the lateral
resistance of piles in bridge foundations. Through this analysis, the researchers developed
design guidelines and found that simplified computational methods employing widely used,
commercially available software generally will provide acceptably accurate results for
highway-bridge design.
The guidelines and analysis methods presented in this report may be useful to bridge foun-
dation designers facing the problem of ensuring that foundations will perform acceptably
under lateral loads produced by wave action, wind, seismic events, ship impact, or traffic.
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CONTENTS
1 Summary
3 Chapter 1 Introduction
5 Chapter 2 Available Ground Improvement Case Histories
and Approaches
14 Chapter 3 Field Load Testing
14 3.1 Test Site Location
14 3.2 Geotechnical Site Characterization
15 3.3 Single Pile Test in Untreated Soil
23 3.4 Pile Group Properties
23 3.5 Pile Group Testing Procedure
25 3.6 Pile Group Tests in Untreated Clay
32 3.7 Pile Group Load Tests Involving Jet Grouting
36 3.8 Pile Group Load Tests Involving Soil Mixing
37 3.9 Pile Group Load Tests Involving Flowable Fill
39 3.10 Pile Group Load Tests Involving Excavation and Replacement
48 3.11 Summary of Increased Resistance from Soil Improvement Methods
and Cost Considerations
51 Chapter 4 Finite Element Modeling of Single Pile Load Test
54 Chapter 5 Finite Element Modeling of Pile Group Load Tests
54 5.1 Pile Group FEM Mesh Design
56 5.2 FEM Model for Pile Group Model in Virgin Clay
56 5.3 Pile Group Model in Virgin Clay with Excavation
57 5.4 FEM Model of Pile Group with Mass Mixing
57 5.5 Pile Group Model with Jet Grouting
61 Chapter 6 Parametric Studies
61 6.1 Mass Mix Depth Effect (Beside the Cap) on Lateral Resistance
61 6.2 Mass Mix Depth Effect (Below the Cap) on Lateral Resistance
65 6.3 Mass Mix Length Effect (Beside the Cap) on Lateral Resistance
66 6.4 Jet Grout Depth Effect (Beside the Cap) on Lateral Resistance
68 6.5 Jet Grout Depth Effect (Below the Cap) on Soil Improvement
68 6.6 Jet Grout Length Effect (Beside the Cap) on Soil Improvement
71 6.7 Material Strength Effect on Lateral Pile Group Resistance
72 6.8 Conclusions Based on Parametric Studies
76 Chapter 7 Development of Simplified Model
76 7.1 Calibration GROUP Analysis Model
76 7.2 Comparison with Results from Tests in Virgin Soil
79 7.3 Comparison with Results from Tests Involving Mass Mixing
79 7.4 Development of Simplified Method
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85 7.5 Evaluation for Jet Grouting Cases
89 7.6 Design Recommendations
96 Chapter 8 Conclusions
97 References
99 Appendix A Schematic Drawings Showing the Layout
of the 16 Lateral Pile Group Tests
Note: Many of the photographs, figures, and tables in this report have been converted from color to grayscale
for printing. The electronic version of the report (posted on the Web at www.trb.org) retains the color versions.
