Investigation of Drilled Shafts under Axial, Lateral, and Torsional Loading

414 Pages·2017·12.22 MB·English

AN ABSTRACT OF THE DISSERTATION OF
Qiang Li for the degree of Doctor of Philosophy in Civil Engineering presented on
November 21, 2017.
Title: Investigation of Drilled Shafts under Axial, Lateral, and Torsional Loading
Abstract approved:
______________________________________________________
Armin W. Stuedlein
Drilled shaft foundations provide significant geotechnical resistance for support of
structures, such as highway bridges, traffic sign, and signal pole structures, and are used
widely to meet their structural foundation requirements. The amount of steel reinforcement
in drilled shaft foundations has increased over the past several decades to account for
anticipated seismic hazards. Increased reinforcement may lead to increased possibilities of
anomalies within shafts due to the increased difficulty for concrete to flow through reduced
clearance between the reinforcement. High-strength steel reinforcement and permanent
steel casing may be used to mitigate the concreting concern. However, the comparison of
axial and lateral load transfer between drilled shafts with and without permanent steel
casing and high-strength reinforcement has not been previously investigated, raising
questions regarding the suitability of existing analytical approaches for the evaluation of
axial and lateral load transfer. In addition to axial and lateral loading, deep foundations
may need to resist torsional loads, resulting from wind loading on traffic sign and signal
pole structures, or seismic loading on curved or skewed bridges. However, the
understanding of the actual resistance to torsion provided by deep foundation elements is
not well established. The design methods for deep foundations in torsion at the ultimate
limit states need to be evaluated and their accuracy needs to be quantified with loading test
data. Furthermore, the accuracy of existing load transfer-based torsion-rotation methods to
predict the full-scale, in-service rotation performance that considers state-dependence of
the soil needs to be quantified.
Two uncased instrumented drilled shafts were constructed and used to evaluate the
torsional capacity and load transfer at full-scale. The quasi-static monotonic and cyclic
torsional loading tests were conducted. Based on the results of the torsional loading tests,
design methods to predict ultimate resistance were proposed. To facilitate the serviceability
and ultimate limit state design of geometrically-variable deep foundations constructed in
multi-layered soils, a torsional load transfer method was presented using a finite difference
model (FDM) framework. Simplified state-dependent spring models, relating the unit
torsional resistance to the magnitude of relative displacement, were developed in
consideration of soil-structure interface shear test results. Parametric studies illustrated the
significant effect of nonlinear soil responses and nonlinear structural response on the
torsional behavior of deep foundations.
The axial and lateral load transfer of drilled shaft foundations were studied using four
instrumented drilled shafts at full-scale: two uncased and two cased drilled shafts,
reinforced with either mild or high strength steel reinforcement. Based on the results of
axial loading tests, selected axial load transfer models were evaluated and modified to
produce region-specific axial load transfer models to aid the design of drilled shaft bridge
foundations for similar soils in the Willamette Valley. The effects of permanent casing on
axial load transfer were summarized to provide an up-to-date reference on the reductions
expected based on construction sequencing and installation methods. The lateral responses
of the test drilled shaft foundations indicated that the high-strength reinforcement could be
used without detriment to the lateral performance of drilled shafts; and the cased shafts
responded in a more resilient manner than uncased shafts at the same nominal diameter
due to their significantly greater flexural rigidity. Based on the empirical soil reaction-
displacement (p-y) curves, a region-specific p-y curve model was proposed with
recommendations to account for pseudo-scale effects due to the increasing contribution of
shaft resistance to lateral resistance with increased diameter.
©Copyright by Qiang Li
November 21, 2017
All Rights Reserved
INVESTIGATION OF DRILLED SHAFTS UNDER AXIAL, LATERAL, AND
TORSIONAL LOADING

by
Qiang Li

A DISSERTATION

Submitted to

Oregon State University

in partial fulfillment of
the requirements for the
degree of

Doctor of Philosophy

Presented November 21, 2017
Commencement June 2018
Doctor of Philosophy dissertation of Qiang Li presented on November 21, 2017

APPROVED:

Major Professor, representing Civil Engineering

Head of the School of Civil and Construction Engineering

Dean of the Graduate School

I understand that my dissertation will become part of the permanent collection of Oregon
State University libraries. My signature below authorizes release of my dissertation to
any reader upon request.

Qiang Li, Author
ACKNOWLEDGEMENTS

I wish to acknowledge the many agencies, firms, and individuals who have contributed
to this research effort. First and foremost, I would like to thank God for giving me the
wisdom and the perseverance to complete this research. I would like to express my
gratitude to my advisor, Dr. Armin Stuedlein, who has been a friend and mentor, for
offering support and direction on this research. I would also like to express my sincere
appreciation to the members of my research committee, including Dr. Andre Barbosa, Dr.
Ben Leshchinsky, Dr. Brian Fronk, and Dr. T. Matthew Evans, for the thoughtful
comments and guidance in this research.
I want to thank my family, including my father and mother, Yuanlu Li and Donghua
Niu, my father- and mother-in-law, Yujie Yang and Jianrong Chai, for their full support
and endless encouragement during this process. I would like to specifically acknowledge
my wife Ting Yang, for her love, patience, and support on my research, for listening to my
concerns and offering guidance, and for taking care of the whole family.
This research was funded by Grant SPR 304-701 and SPR 765 through the Oregon
Department of Transportation and Grant DTRT13-G-UTC4O and DTRT12-UTC10
through the Pacific Northwest Transportation Consortium (PacTrans). PLI Systems, Inc.,
of Hillsboro, Oregon, donated materials, equipment and labor to construct the test shafts
for the full-scale torsional loading tests. For the full-scale axial and lateral loading tests,
the West Coast Chapter (WCC) of the ADSC contributed funds to help offset material costs
associated with the construction of the test shafts, with critical coordination efforts and
guidance provided by John Starcevich (Malcolm Drilling, Inc.), Becky Patterson (WCC
ADSC), and Rick Walsh (Hayward Baker, Inc.). Malcolm Drilling, Inc. constructed the
test shafts for axial and lateral loading tests; Pacific Foundation, Inc. installed the reaction
piles for axial loading tests; and Ralph’s Concrete donated the concrete pumping services.
The Grade 80 solid and hollow steel reinforcement bars were donated by ConTech Systems,
whereas the Grade 60 steel reinforcement bars and all cage fabrication was donated by PJ’s
Rebar. The permanent steel casing was donated by Skyline Steel, and the Grade 150 steel
reinforcement bars for the reaction anchors were contributed by Williams Form, Inc.
Spacers and bar boots were provided by Foundation Technologies. Crosshole sonic logging
service was donated by GEI Consultants; and Thermal Integrity Profiling Thermal Wires®
and logging services were provided by Pile Dynamics, Inc. I would also like to thank James
Batti for his help with the setup of the data acquisition system used in the loading tests.
Helpful assistance with the test setup and execution was provided by Andrew Strahler,
David Bailey, Eric North, Jeff Gent, John Martin, Robert Leaf, Tygh Gianella, Xiaomin
(Jacky) Chen, and Youssef Bougataya. Without the support of all of these individuals,
firms, and organizations, this research would not have been completed.
TABLE OF CONTENTS

Page

  INTRODUCTION ........................................................................................................1 
Statement of Problem............................................................................................1 
Purpose and Scope ................................................................................................2 
Organization of this Document .............................................................................3 
References .............................................................................................................5 
  LITERATURE REVIEW .............................................................................................6 
An Introduction to Drilled Shaft Foundations ......................................................6 
Studies of Drilled Shafts with Steel Casing ..........................................................7 
2.2.1 Impact of Permanent Steel Casing on Axial Capacity of Drilled Shafts .....7 
2.2.2 Impact of Permanent Steel Casing on Lateral Capacity of Drilled Shafts .11 
2.2.3 Design Methods for Concrete Filled Steel Tubes (CFTs) .........................11 
Related Studies on High-Strength Reinforcement ..............................................16 
Torsional Loading Tests Reported in the Literature ...........................................17 
2.4.1 Torsional Loading Tests on Small-Size Model Piles and Drilled Shafts ..18 
2.4.2 Torsional Loading Tests on Centrifuge Model Piles and Shafts ...............24 
2.4.3 Torsion Tests on Full-scale Driven Piles and Drilled Shafts .....................31 
Design Methods for Drilled Shafts .....................................................................40 
2.5.1 Design Methods for Axially Loaded Shafts ..............................................40 
2.5.2 Design Methods for Laterally Loaded Piles ..............................................44 
2.5.3 Design Methods for Torsionally Loaded Piles ..........................................45 
Summary .............................................................................................................48 
References ...........................................................................................................50 
  RESEARCH OBJECTIVES AND PROGRAM .........................................................58 
Research Objectives ............................................................................................58 
Research Program ...............................................................................................59 
  SUBSURFACE CONDITIONS AT THE TEST SITE ...............................................61 
Overview .............................................................................................................61 
General Site at the GEFRS .................................................................................62 
Site Specific Geotechnical Exploration for Torsional Loading Test ..................66
TABLE OF CONTENTS (Continued)

Page

Site Specific Geotechnical Exploration for Axial and Lateral Loading Tests ....69 
References ...........................................................................................................74 
  TORSIONAL LOAD TRANSFER OF DRILLED SHAFT FOUNDATIONS ..........75 
Abstract ...............................................................................................................76 
Introduction .........................................................................................................76 
Experimental Program ........................................................................................79 
5.3.1 Subsurface Conditions ...............................................................................79 
5.3.2 Construction and Experimental Details of the Test Shafts ........................79 
5.3.3 Instrumentation and Interpretation of Torsional Load Transfer ................80 
Loading Test Results and Discussion .................................................................82 
5.4.1 Quasi-Static Loading of the Test Shafts ....................................................83 
5.4.2 Cyclic Loading of the Test Shafts..............................................................95 
Assessment of Torsional Resistance of Drilled Shafts .......................................98 
5.5.1 Recommended Design Methodologies ......................................................98 
5.5.2 Assessment of Total Torsional Resistance ..............................................102 
5.5.3 Assessment of Unit Torsional Shaft Resistance ......................................106 
Summary and Conclusions ...............................................................................108 
Acknowledgements ...........................................................................................111 
References .........................................................................................................111 
  SIMULATION OF TORSIONALLY-LOADED DEEP FOUNDATIONS
CONSIDERING STATE-DEPENDENT LOAD TRANSFER ................................115 
Abstract .............................................................................................................116 
Introduction .......................................................................................................116 
Finite Difference Model....................................................................................119 
6.3.1 Assumptions and Governing Differential Equations ...............................119 
6.3.2 Solution of Governing Differential Equations .........................................123 
Proposed Torsional Load Transfer Curves for Granular Soils .........................125 
6.4.1 Relevant Soil-Interface Mechanics ..........................................................125 
6.4.2 Displacement-Hardening Model ..............................................................128