Basic Geotechnical Earthquake Engineering

PREFACE

Earthquake resistant geotechnical construction has become an important design aspect recently. This book BASIC GEOTECHNICAL EARTHQUAKE ENGINEERING is intended to be used as textbook for the beginners of the geotechnical earthquake engineering curriculum.

Civil engineering undergraduate students as well as first year postgraduate students, who have taken basic undergraduate course on soil mechanics and foundation engineering, will find subject matter of the textbook familiar and interesting.

Emphasis has been given to the basics of geotechnical earthquake engineering as well as to the basics of earthquake resistant geotechnical construction in the text book. At the end of each chapter home work problems have been given for practice. At appropriate places, solved numerical problems and exercise numerical problems have also been given to make the subject matter clear. Subject matter of the textbook can be covered in a course of one semester which is about of 4 to 4.5 months duration. List of references given at the end of book enlists references which have been used to prepare this basic book on geotechnical earthquake engineering. Although the book is on geotechnical earthquake engineering, the last chapter of book is on earthquake resistant design of buildings, considering its significance in the context of earthquake resistant construction.

The ultimate judges of the book will be students, who will use the book to understand the basic concepts of geotechnical earthquake engineering.

Suggestions to improve the usefulness of the book will be gratefully received.

INTRODUCTION TO GEOTECHNICAL EARTHQUAKE ENGINEERING

1.1 INTRODUCTION

The effect of earthquake on people and their environment as well as methods of reducing these effects is studied in earthquake engineering. It is a new discipline, with most of the developments in the past 30 to 40 years. Most earthquake engineers have structural or geotechnical engineering background. This book covers geotechnical aspects of earthquake engineering.

Geotechnical earthquake engineering is an area within geotechnical engineering. It deals with the design and construction of projects in order to resist the effect of earthquakes.

Geotechnical earthquake engineering requires an understanding of geology, seismology and earthquake engineering. Furthermore, practice of geotechnical earthquake engineering also requires consideration of social, economic and political factors. In seismology, internal behavior of the earth as well as nature of seismic waves generated by earthquake is studied.

In geology, geologic data and principles are applied so that geologic factors affecting the planning, design, construction and maintenance of civil engineering works are properly recognized and utilized. Primary responsibility of geologist is to determine the location of fault, investigate the fault in terms of either active or passive, as well as evaluate historical records of earthquakes and their impact on site. These studies help to define design earthquake parameters. The important design earthquake parameters are peak ground accleration and magnitude of anticipated earthquake.

The very first step in geotechnical earthquake engineering is to determine the dynamic loading from the anticipated earthquake. The anticipated earthquake is also called design earthquake. For this purpose, following activities needs to be performed by geotechnical earthquake engineer:

2 Basic Geotechnical Earthquake Engineering

• Investigation for the possibility of liquefaction at the site. Liquefaction causes complete loss of soil shear strength, causing bearing capacity failure, excessive settlement or slope movement. Consequently, this investigation is necessary.
• Calculation of settlement of structure caused by anticipated earthquake.
• Checking the bearing capacity and allowable soil bearing pressures, to make sure that foundation does not suffer a bearing capacity failure during the design earthquake.
• Investigation for slope stability due to additional forces imposed due to design earthquake. Lateral deformation of slope also needs to be studied due to anticipated earthquake.
• Effect of earthquake on the stability of retaining walls.
• Analyze other possible earthquake effects, such as surface faulting and resonance of the structure.
• Development of site improvement techniques to mitigate the effect of anticipated earthquake. These include Ground stabilization and ground water control.
• Determination of the type of foundation (shallow or deep), best suited for resisting the effect of design earthquake.
• To assist the structural engineer by investigating the effect of ground movement due to seismic forces on the structure.

1.2 EARTHQUAKE RECORDS

Fig. 1.1 Earthquake records (Courtesy: http://www.stvincet.ac.uk)

Accurate records of earthquake magnitudes have been kept only for some 100 years since the invention of the seismograph in the 1850s. Recent records of casualties are likely to be more reliable than those of earlier times. There are estimated to be some 500,000 seismic events each year. Out of these, about 100,000 can be felt and about 1,000 cause some form of damage. Some of the typical earthquake records have been shown in Fig. 1.1.

Contents

Preface (v)

1.INTRODUCTION TO GEOTECHNICAL EARTHQUAKE ENGINEERING

1.1 Introduction 1
1.2 Earthquake Records 2
1.3 Earthquake Records of India 4

2.EARTHQUAKES

2.1 Plate Tectonics, The Cause of Earthquakes 9
2.2 Seismic Waves 15
2.3 Faults 17
2.4 Earthquake Magnitude and Intensity 22
2.5 Seismograph 26

3.SEISMIC HAZARDS IN INDIA

3.1 Introduction 30
3.2 Earthquake Hazards in India 31
3.3 Earthquake Hazards in the North Eastern Region 32
3.4 Frequency of Earthquake 34
3.5 Earthquake Prediction 34
3.6 Earthquake Hazard zonation, Risk Evaluation and Mitigation 35
3.7 Earthquake Resistant Structures 36
3.8 Awareness Campaign 36

4.DYNAMIC SOIL PROPERTIES

4.1 Introduction 38
4.2 Soil Properties for Dynamic Loading 38
4.3 Types of Soils 39
4.4 Measuring Dynamic Soil Properties

5.SITE SEISMICITY, SEISMIC SOIL RESPONSE AND DESIGN EARTHQUAKE

5.1 Site Seismicity 46
5.2 Seismic Soil Response 48
5.3 Design Earthquake 50

6.LIQUEFACTION

6.1 Introduction 57
6.2 Factors Governing Liquefaction in the Field 64
6.3 Liquefaction Analysis 67
6.4 Antiliquefaction Measures 72

7.EARTHQUAKE RESISTANT DESIGN FOR SHALLOW FOUNDATION

7.1 Introduction 76
7.2 Bearing Capacity Analysis for Liquefied Soil 77
7.4 Bearing Capacity Analysis for Cohesive Soil Weakened by Earthquake 83

8.EARTHQUAKE RESISTANT DESIGN OF DEEP FOUNDATION

8.1 Introduction 87
8.2 Design Criteria 88

9.SLOPE STABILITY ANALYSES FOR EARTHQUAKES

9.1 Introduction 90
9.2 Inertia Slope Stability – Pseudostatic Method 91
9.3 Intertia Slope Stability – Network Method 94
9.4 Weakening Slope Stability – Flow Slides 96

10.RETAINING WALL ANALYSES FOR EARTHQUES

10.1 Introduction 102
10.2 Pseudostatic Method 103
10.3 Retaining Wall Analysis for Liquefied Soil 106
10.4 Retaining Wall Analysis for Weakened Soil 108
10.5 Restrained Retaining Walls 108
10.6 Temporary Retaining Walls

11.EARTHQUAKE RESISTANT DESIGN OF BUILDINGS

11.1 Introduction 115
11.2 Earthquake Resisting Performance Expectation 116
11.3 Key Material Parameters for Effective Earthquake Resistant Design 117
11.4 Earthquake Design Level Ground Motion 118
11.5 Derivation of Ductile Design Response Spectra 121
11.6 Analysis and Earthquake Resistant Design Principles 122
11.7 Earthquake Resistant Structural Systems 126
11.8 The Importance and Implications of Structural Regularity 127
11.9 Methods of Analysis 129
References 132
Index