Preloading effects on dynamic sand behavior by resonant column tests [Elektronische Ressource] / vorgelegt von Lidong Bai

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Informations

• Publié par: technische_universitat_berlin
• Publié le: 01 janvier 2010
• Nombre de lectures: 14
• Langue: English
• Poids de l'ouvrage: 9 Mo

Extrait

Preloading Effects on Dynamic Sand Behavior by
Resonant Column Tests

vorgelegt von
Master of Science
Lidong Bai
aus Guizhou, China

von der Fakultät VI - Planen Bauen Umwelt
der Technischen Universität Berlin
zur Erlangung des akademischen Grades

Doktor der Ingenieurwissenschaften
(Dr.-Ing.)

genehmigte Dissertation
Promotionsausschuss:
Vorsitzender: Prof. Dr.-Ing. Y. Petryna
Berichter: Prof. S. Savidis Dr.-Ing. C. Vrettos

Tag der wissenschaftlichen Aussprache: 13. Dezember 2010

Berlin 2011
D83


To



My Wife, Wei Wei
for her support and understanding

My father, Zuoguang Bai
for his encouragement

My mother, Jianv Jia
for her endurance and love

My brothers, Liling Bai and Hai Bai
for their support, understanding and looking after parents


ACKNOWLEDGMENTS


I would like to thank my supervisor, Professor Dr.-Ing. Stavros A. Savidis, the dean
of Faculty VI of Technical University of Berlin (TU Berlin), for his guidance, training,
patience, and friendship, his research and work attitude greatly impresses me. I owe
him my deepest respect and appreciation. I also would like to thank Dr.-Ing. Frank
Rackwitz for his assistance, comments, friendship, and arranging a lot of work for my
testing in the laboratory. Special appreciation is given to my second supervisor,
Professor Dr.-Ing. Christos Vrettos from Technical University of Kaiserslautern for
his constructive suggestions to improve this thesis, sincere acknowledgments also are
extended to Professor Y. Petryna, the chairman of the academic degree commission
for his encouragement. I am also greatly indebted to Professor Wei Xiang of China
University of Geosciences (Wuhan) for his encouragement during my study at TU
Berlin.

The financial support of my study abroad was provided by China Scholarship Council
(CSC) and TU Berlin which is gratefully acknowledged.

Special words of appreciation go to laboratory technicians Mr. Harald Lorenz, Mr.
Harald Podeswa, Mr. Boguslav Grzedzinski for their assistance in instrument
modification and some additional tests. Great appreciation also goes to Mr. Jerry
Sutton from GDS Instruments Limited for his valuable suggestions to install the
testing system. I also thank diplom students Ms. Asja Kühn, Ms. Juliane Stopper, and
Mr. Viet Hung Le for their assistance in the laboratory at the beginning of my study at
TU Berlin. Many thanks are extended to Mr. Dipl.-Ing. Winfried Schepers and Mr.
Dipl.-Ing. Ralf Glasenapp, Mr. Dipl.-Ing. Ercan Tasan, and other colleagues and
friends for their support and good times.

Special thanks are extended to the staffs of Education Section of China Embassy in
Germany, particularly to Minister-counselor Dr. Feng Jiang and his wife for their
great help, solicitude, friendship and encouragement.

Finally, I extend my deepest gratitude to my father, Zuoguang Bai, my mother, Jianv
Jia, my younger brothers, Liling Bai and Hai Bai and their wifes, for their love,
constant encouragement and belief in me. My endless words of gratitude go to my
beloved wife Wei Wei for her support, understanding, and sacrifice; without her I can
not make my doctoral dream come true.
1
ABSTRACT

Dynamic behavior of Berlin sand and the preloading effects on shear modulus and
damping properties of sand were investigated by resonant column tests in this study,
in addition, a new reliable calibration method for the Stokoe resonant column
apparatus is also presented. The influences of confining pressure, void ratio, water
content, sampling method, stress history, confinement duration and others on dynamic
properties of Berlin sand were examined by resonant column tests. An empirical
equation was proposed to predict the small-strain shear modulus, and two em
models were proposed to simulate the nonlinear modulus and damping properties of
Berlin sand, a brief comparison of small-strain shear modulus by resonant column and
bender element tests is addressed as well.

In this study, the author initially introduced the preloading concept to investigate
vibration history effects on dynamic sand behavior, which is quite different from the
prestraining concept conventionally employed in previous investigations. For the
preloading concept, the previous vibration applied to specimen is employed by the
non-resonant vibration mode of stress-controlled shear by resonant column apparatus.
With this concept the number of loading cycles can be enlarged to a range from one to
any desired number. By contrast the prestraining concept cannot investigate low
number of cycles due to the necessary several hundreds of cycles to determine the
resonant frequency. In addition, the use of the preloading concept can also ensure
constant preloading stress during the previbration is applied to the tested specimen at
the same vibration frequency and input drive voltage. The prestraining concept may
introduce less precision of the calculation of prestraining amplitude if the set vibration
frequency and input drive voltage are not adjusted during previbration. That is due to
variation of the resonant vibration frequency and other parameters, if the stiffness of
tested specimen varies with number of cycles, and therefore the set vibration
frequency is not the resonant frequency of the vibration system any more.

The effects of many factors which may influence the preloading effects on the
dynamic behavior of sand were fully explored in this study. One of the most important
findings is that the shear modulus or stiffness of sand decreases with number of cycles
if it does not exceed a threshold number and increases when the number of cycles
exceeds this threshold. A theoretical interpretation of the reduction of stiffness of sand
subjected to preloading was proposed herein.

Key Words: Berlin sand, shear modulus, damping ratio, resonant column test, number
of cycles, preloading frequency, unloading, reloading, water content
II


LISTS OF CONTENTS



CHAPTER 1 INTRODUCTION ...................................................................................1
1.1 Background......................................................................................................1
1.2 Objectives ........................................................................................................2
1.3 Organization.....................................................................................................3

CHAPTER 2 LITERATURE REVIEW.........................................................................4
2.1 Introduction4
2.2 Factors Influence Small-strain Shear Modulus................................................8
2.2.1 Void Ratio .............................................................................................8
2.2.2 Confining Pressure................................................................................9
2.2.3 Stress Ratio .........................................................................................12
2.2.4 Grain Characteristics...........................................................................16
2.2.5 Degree of Saturation17
2.2.6 Frequency of Loading.........................................................................18
2.2.7 Duration of Confinement ....................................................................19
2.2.8 Prestraining21
2.3 Factors Influence Nonlinear Dynamic Soil Properties ..................................24
2.3.1 Confining Pressure..............................................................................24
2.3.2 Frequency of Loading26
2.3.3 Stress Ratio .........................................................................................27
2.3.4 Number of loading cycles ...................................................................28
2.3.5 Prestraining30
2.4 Summary........................................................................................................33

CHAPTER 3 TESTING EQUIPMENT AND CALIBRATION..................................34
3.1 Introduction....................................................................................................34
3.2 Detail of Resonant Column Apparatus ..........................................................35
3.2.1 Procedure of Resonant Column Test...................................................36
3.2.2 Drive system .......................................................................................37
3.2.3 Rotation Monitoring............................................................................38
3.2.4 Confining Chamber and Cell Pressure................................................39
3.3 Resonant Column Test ...................................................................................40
3.3.1 Shear Modulus ....................................................................................40
III
3.3.2 Damping Ratio....................................................................................42
3.3.3 Shearing Strain44
3.4 Torsional Shear Test.....................................................