Back Analysis in Rock Engineering

Shunsuke Sakurai

• Éditeur: CRC Press
• Année: 2017
• ISBN:
  9781315349541
• Édition: 1
• Sujet: Technologie et ingénierie
• Sous-sujet: Ingénierie civile

This book provides practicing engineers working in the field of design, construction and monitoring of rock structures such as tunnels and slopes with technical information on how to design, how to excavate and how to monitor the structures during their construction. Based on the long-term engineering experiences of the author, field measurements together with back analyses are presented as the most powerful tools in rock engineering practice. One of the purposes of field measurements is to assess the stability of the rock structures during their construction. However, field measurement results are only numbers unless they are quantitatively interpreted, a process in which back analyses play an important role.

The author has developed both the concepts of "critical strain" and of the "anisotropic parameter" of rocks, which can make it possible not only to assess the stability of the structures during their construction, but also to verify the validity of design parameters by the back analysis of field measurement results during the constructions. Based on the back analysis results, the design parameters used at a design stage could be modified if necessary. This procedure is called an "Observational method", a concept that is entirely different from that of other structures such as bridges and buildings. It is noted that in general, technical books written for practicing engineers mainly focus on empirical approaches which are based on engineers' experiences. In this book, however, no empirical approaches will be described, instead, all the approaches are based on simple rock mechanics theory. This book is the first to describe an observational method in rock engineering practice, which implies that the potential readers of this book must be practicing engineers working on rock engineering projects.

Table of Contents

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Acknowledgments

About the Author

1 Introduction

1.1 Aims and Scope

1.2 Field measurements and back analyses

2 Back analysis and forward analysis

2.1 What is back analysis?

2.2 Difference between back analysis and forward analysis

2.3 Back analysis procedures

2.3.1 Introduction

2.3.2 Inverse approach

2.3.3 Direct approach

2.3.4 Probabilistic approach

2.3.5 Fuzzy systems, Artificial Intelligence (AI), Neural network, etc.

2.4 Brief review of back analysis

3 Modelling of rock masses in back analysis

3.1 Modelling of rock masses

3.2 Back analysis and modelling

3.3 Difference between parameter identification and back analysis

4 Observational method

4.1 What is observational method?

4.2 Design parameters for different types of structures

4.3 Difference Between Stress-Based Approach and Strain-Based Approach

4.4 Strain-based approach for assessing the stability of tunnels

4.5 Displacement measurements in observational method

4.6 Back analysis in observational method

4.7 Flowchart of observational methods

4.8 Hazard warning levels

4.8.1 Introduction

4.8.2 Numerical analysis methods

4.8.3 Critical strain methods

5 Critical strains of rocks and soils

5.1 Definition of critical strain of geomaterials

5.2 Scale effect of critical strains

5.3 Simple approach for assessing tunnel stability

5.4 Hazard warning level for assessing crown settlements and convergence

5.5 Uniaxial compressive strength and young’s modulus of rock masses

6 Environmental effects on critical strain of rocks

6.1 Critical strain in triaxial condition

6.2 Effects of confining pressure

6.3 Effects of moisture content

6.4 Effects of temperature

7 General approach for assessing tunnel stability

7.1 Critical shear strain of geomaterials

7.2 Hazard warning levels in terms of maximum shear strain

7.3 How to determine the maximum shear strain distribution around a tunnel

8 Back analyses used in tunnel engineering practice

8.1 Introduction

8.2 Mathematical formulation of the proposed back analyses

8.2.1 Introduction

8.2.2 Assumption of mechanical model

8.2.3 Mathematical formulation

8.3 Case study I (Washuzan Tunnels)

8.3.1 Exploration tunnel (work tunnel)

8.3.1.1 Introduction

8.3.1.2 Displacement measurements and back analyses

8.3.1.3 Design analysis of the main tunnels

8.3.2 Excavation of the main tunnels

8.3.2.1 Brief description with respect to the tunnels and instrumentation

8.3.2.2 Back analysis of measured displacements

8.3.2.3 Assessment of the stability of tunnels

8.4 Case study II (two-lane road tunnel in shallow depth)

8.4.1 Introduction

8.4.2 Brief description of the tunnel

8.4.3 Field measurements

8.4.3.1 Convergence measurements

8.4.3.2 Multi-rod extensometer and sliding micrometer measurements

8.4.4 Back analysis of measured displacements

8.4.5 Assessment of the stability of tunnels

9 Universal back analysis method

9.1 Introduction

9.2 Mathematical formulation considering non-elastic strain

9.3 Case Study (Tunnel Excavated in Shallow Depth)

9.3.1 Tunnel configuration and instruments

9.3.2 Back analyses

9.3.3 Supporting mechanism of rock bolts, shotcrete and steel ribs

9.4 Modelling of support structures

9.4.1 Modelling of rock bolts

9.4.2 Modelling of shotcrete and steel ribs

10 Initial stress of rock masses determined by boundary element method

10.1 Introduction

10.2 Three-dimensional back analysis method

10.2.1 Mathematical formulation of the method

10.2.2 Computational stability

10.3 Case Study

11 Back analysis for the plastic zone occurring around underground openings

11.1 Introduction

11.2 Assumptions

11.3 Fundamental equations

11.3.1 Maximum shear strain on the elasto-plastic boundary

11.3.2 Relationship between real and equivalent Young’s modulus

11.4 The method for determining the elasto-plastic boundary

11.5 Computer simulation

11.5.1 Procedure

11.5.2 An example problem and simulation results

12 Back analysis considering anisotropy of rocks

12.1 Introduction

12.2 Constitutive equations

12.3 Different modes of deformation

12.3.1 Spalling of joints

12.3.2 Sliding along joints

12.3.3 Plastic flow

12.4 Computer simulations

12.4.1 Spalling of joints

12.4.2 Plastic flow

12.5 Case study (underground hydropower plant)

13 Laboratory experiments

13.1 Absolute triaxial tests (true triaxial tests)

13.2 Conventional triaxial compression tests

13.3 Simple shear tests

14 Constitutive equations for use in back analyses

14.1 Fundamental theory of constitutive equations for geomaterials

14.2 Failure criteria

14.2.1 Mohr?Coulomb failure criterion

14.2.2 Von Mises yield criterion

14.2.3 Nadai’s failure criterion and Drucker–Prager failure criterion

14.3 Anisotropic parameter and anisotropi...