Rock Engineering RiskBy John A. Hudson

Table of Contents

Preface
Acknowledgements: International Society for Rock Mechanics
About the authors

1 Introduction and background
1.1 The previous book “Rock Engineering Design” and this book “Rock Engineering Risk”
1.2 Rock engineering risk
1.3 Governing flowchart for the book
1.4 Structure and content of the book
1.5 Chapter summary

2 Uncertainty and risk
2.1 Introduction
2.2 Approaches to risk management
2.3 Epistemic and aleatory uncertainties
2.3.1 Explanation of the terms ‘epistemic’ and ‘aleatory’
2.3.2 Procedures for dealing with epistemic/aleatory uncertainties and Eurocode
2.4 Chapter summary

3 Rock Engineering Systems (RES), auditing and Protocol Sheets
3.1 Introduction to the systems approach and auditing concepts
3.2 Reducing epistemic uncertainty using the rock engineering systems approach
3.3 A review and explanation of the Rock Engineering Systems (RES) methodology
3.3.1 The interaction matrix
3.3.2 Coding the interaction matrix, and the Cause–Effect plot
3.3.3 Mechanism pathways
3.3.4 Step-by-step evolution of the interaction matrix
3.4 Examples of Rock Engineering Systems (RES) applied to rock mechanics and rock engineering design
3.4.1 Natural and artificial surface rock slopes
3.4.1.1 Surface blasting
3.4.1.2 Natural slopes
3.4.1.3 Instability of artificial rock slopes
3.4.2 Underground rock engineering
3.4.2.1 Underground blasting
3.4.2.2 Tunnel Boring Machines (TBMs)
3.4.2.3 Tunnel stability
3.4.3 Underground radioactive waste disposal
3.4.4 Use of the RES interaction matrix in other subject areas
3.5 Further development of the RES methodology
3.6 Auditing and Protocol Sheets
3.6.1 ‘Soft’, ‘semi-hard’ and ‘hard’ technical audits and the audit evaluation
3.7 Chapter summary

4 Rock fractures and in situ rock stress
4.1 Introduction
4.2 Rock fractures
4.2.1 The spectrum of brittle and ductile rock deformation
4.2.2 Multiple deformational sequences
4.2.3 The risks associated with different types of rock mass
4.3 In situ rock stress
4.3.1 The stress state in a rock mass
4.3.1.1 In situ rock stress scales
4.3.2 Stress perturbation factors
4.3.2.1 Rock inhomogeneity
4.3.2.2 Rock anisotropy
4.3.2.3 Rock fractures
4.3.2.4 The influence of a free surface
4.3.3 Evidence of in situ stress variability
4.3.3.1 Stress vs. depth compilations
4.3.3.2 The ways ahead for improving the understanding of rock stress variability
4.3.4 A case study of modelling in situ rock stress at the Olkiluoto site, western Finland
4.4 Chapter summary

5 Radioactive waste disposal: overcoming complexity and reducing risk
5.1 The disposal objective
5.1.1 An example of radioactive waste repository statistics
5.2 Features, Events and Processes
5.3 Thermo-Hydro-Mechanical (THM+) processes
5.3.1 The THM+ issues in context
5.3.2 The excavation, operational and post-closure stages
5.3.2.1 The excavation stage
5.3.2.2 Operational stage
5.3.2.3 Post-closure stage
5.3.2.4 Heterogeneity and multiple stage data needs
5.3.2.5 Modelling phases and scaling
5.3.3 The use of numerical computer codes
5.3.3.1 The nature of numerical codes
5.3.3.2 Uncoupled and coupled codes
5.3.3.3 Technical auditing of numerical codes
5.3.3.4 Capturing the essence of the problem
5.3.3.5 The overall Technical Auditing (TA) procedure and risk
5.3.3.6 Validation
5.3.3.7 The future of numerical codes
5.4 The DECOVALEX programme
5.4.1 The development of the DECOVALEX programme
5.4.2 Research work in the current DECOVALEX phase: D-2015
5.4.2.1 Task A: The Sealex in situ experiment, Tournemire site, France
5.4.2.2 Task B1: The HE-E in situ heater test, Mont Terri Underground Research Laboratory, Switzerland
5.4.2.3 Task B2: The EBS experiment at Horonobe, Japan
5.4.2.4 Task C1: THMC modelling of rock fractures
5.4.2.5 Task C2: Modelling water flow into the Bedrichov Tunnel, Czech Republic
5.5 Underground Research Laboratories (URLs)
5.5.1 The purpose of URLs
5.5.2 The Swedish Äspö URL
5.6 Chapter summary

6 Risks associated with long deep tunnels
6.1 Introduction
6.1.1 Development of long deep tunnels
6.1.2 Flowchart to develop risk management for long, deep tunnels
6.2 Epistemic uncertainty analysis of design and construction for long deep tunnels
6.2.1 Geological settings
6.2.1.1 Geological factors relating to rockbursts in deep tunnels
6.2.1.2 Geological conditions exhibiting squeezing or large deformation behaviour
6.2.2 Rock stress
6.2.3 Hydrogeology
6.2.4 Properties of the rock mass
6.2.5 Project location
6.2.6 Excavation and support methods
6.3 Aleatory uncertainty analysis of design and construction for long deep tunnels
6.3.1 Detailed geology variations
6.3.2 Rock stress variations
6.3.3 Local water variations
6.3.4 Mechanical behaviour of the rock mass after excavation and in the long term
6.4 Methods to assess and mitigate risk for long deep tunnels
6.4.1 Rockbursts
6.4.1.1 Rockburst risk assessment
6.4.1.2 Risk mitigation concepts in rockburst prone tunnels
6.4.1.3 New approaches and optimisation of the risk-reduced construction procedures
6.4.2 Water inrush
6.4.2.1 Procedures for water inflow assessment
6.4.2.2 Assessment of water inrush potential
6.4.2.3 Assessment of tunnel water inflow
6.4.2.4 Treatment technologies for tunnel water inrush
6.4.3 Large deformations of weak rock in deep tunnels
6.4.3.1 Large deformation assessment
6.4.3.2 Treatment technologies for large deformations
6.4.4 Long term stability
6.4.4.1 Long term stability assessment in deep tunnels
6.4.4.2 Treatment technologies to ensure long term stability in deep and long tunnels
6.5 Illustrative example: Assessment and mitigation of risk for deep tunnels at the Jinping II Hydropower Station, China
6.5.1 Epistemic uncertainty analysis of headrace long deep tunnels
6.5.1.1 Geological setting
6.5.1.2 Rock stress
6.5.1.3 Hydrology
6.5.1.4 Properties of the rock mass
6.5.1.5 Specific project location
6.5.1.6 Excavation and support method
6.5.1.7 Water inrush
6.5.1.8 Rockbursts
6.5.1.9 Large deformations
6.5.1.10 Long term stability
6.5.2 Aleatory uncertainty analysis of the headrace tunnels
6.5.2.1 Geological variations at different chainage intervals
6.5.2.2 Rock stress variations affecting the threedimensional stress field
6.5.2.3 Local water variations based on prediction in advance
6.5.2.4 Mechanical behaviour of the rock mass after excavation and in the long term
6.5.3 Assessment and mitigation of local risk during the construction of the headrace tunnels
6.5.3.1 Water inrush
6.5.3.2 Rockburst: monitoring, in situ tests, warning and mitigation
6.5.3.3 Large deformation: monitoring and treatment
6.5.3.4 Long term stability
6.6 Chapter summary

7 Risks associated with hydropower cavern groups
7.1 Introduction
7.1.1 Development of large hydropower cavern groups
7.1.2 Current status of design and risk management for large rock caverns
7.1.3 Why is a new method of risk management required?
7.1.4 Outline flowchart for risk management for large hydropower cavern groups
7.1.5 Initial and final risk management for assessing and mitigating the risks for a large hydropower cavern group
7.2 Database of 60 large hydropower cavern groups in China
7.2.1 Principles for establishing a database
7.2.2 Content of the database
7.2.3 Statistical analysis of key issues
7.2.3.1 Lithological character and rock mass quality
7.2.3.2 Structure and strength of the rock mass
7.2.3.3 Stress conditions
7.2.3.4 Arrangement of cavern group by size
7.2.3.5 Excavation scheme and parameters
7.2.3.6 Support parameters
7.2.3.7 Monitoring
7.2.3.8 Rockbolt stresses
7.2.3.9 Stress in cable anchors
7.2.3.10 Relaxation depth of the surrounding rock
7.2.3.11 Fractures in the surrounding rock mass
7.2.3.12 Typical failure modes
7.2.3.13 Effect of loss of cable anchors and rockbolts
7.2.3.14 Measures used to reduce local risks
7.3 Epistemic uncertainty analysis
7.3.1 Geological setting
7.3.2 In situ rock stress
7.3.3 Hydrogeology
7.3.4 Properties of the rock mass
7.3.5 Specific project location
7.3.6 Excavation and support method
7.4 Aleatory uncertainty analysis
7.4.1 Detailed geology variations
7.4.2 Rock stress variations
7.4.3 Local water variations
7.4.4 Mechanical behaviour of the rock mass after excavation and in the long term
7.5 Risk assessment method for a large hydropower cavern group
7.5.1 Principles
7.5.2 Method for assessment and mitigation of overall risk for a large hydropower cavern group before construction
7.5.2.1 Method to determine the membership degree of the assessment index
7.5.2.2 Weight vector determining method
7.5.2.3 Determining the overall risk frequency
7.5.2.4 Determining overall risk consequence
7.5.2.5 Overall risk control analysis
7.5.3 Method for assessment and mitigation of local risk for a large hydropower cavern group before construction
7.5.3.1 Large deformation local risk assessment model before construction
7.5.3.2 Index membership degree determining method
7.5.4 Method for assessment and mitigation of local risk for a large hydropower cavern group during construction
7.6 Illustrative example: Assessment and mitigation of risk for the underground powerhouse at Jinping II Hydropower Station, China
7.6.1 Epistemic uncertainty analysis
7.6.1.1 Geological setting
7.6.1.2 Rock stress
7.6.1.3 Hydrology
7.6.1.4 Specific project location
7.6.1.5 Excavation and support method
7.6.2 Assessment and mitigation of overall risk before construction
7.6.2.1 Assessment
7.6.2.2 Risk mitigation measures
7.6.3 Assessment and mitigation of local risk before the construction
7.6.3.1 Assessment
7.6.3.2 Risk mitigation measures
7.6.4 Aleatory uncertainty analysis
7.6.4.1 Estimation of geological conditions at different layers
7.6.4.2 Estimation of three dimensional stress field
7.6.4.3 Local water variations
7.6.4.4 Mechanical behaviour of the rock mass after excavation and in the long term
7.6.5 Assessment and mitigation of local risk during construction
7.6.5.1 Construction of the main powerhouse layer I
7.6.5.2 Construction of main powerhouse layer II and transformer chamber layer I
7.6.5.3 Construction of main powerhouse layer III and transformer chamber layer II
7.6.5.4 Construction of main powerhouse layer IV and transformer chamber layer III
7.6.5.5 Construction of layer V of the main powerhouse
7.6.5.6 Construction of layers VI, VIII and IX of the main powerhouse
7.6.5.7 Construction of layer VII of the main powerhouse
7.6.5.8 Construction of different types of tunnel
7.6.5.9 Overall evaluation of the complete construction and final design
7.6.6 Important points
7.6.6.1 Optimisation of bench height of layers II and III, and the excavation procedure for layers IV–IX
7.6.6.2 More than ten local warnings and reinforcement improved the main powerhouse and transformer chamber
7.6.6.3 Support reinforcement for different types of tunnel
7.6.6.4 Overall evaluation of the complete construction process and final design
7.7 Chapter summary

8 Concluding remarks

Appendix A: Cavern risk events during construction

Appendix B: The Chinese ‘Basic Quality’ (BQ) system for rock mass classification
B1 Introduction
B2 Terminology and symbols
B2.1 Terminology
B2.2 Symbols
B3 Classification parameters for the rock mass basic quality
B3.1 Classification parameters and the method of their determination
B3.2 Qualitative classification of rock mass solidity
B3.3 Qualitative classification of rock mass integrity
B3.4 Determination and classification of quantitative indices
B4 Classification of rock mass basic quality
B4.1 Determination of the rock mass basic quality class
B4.2 Qualitative characteristics of the basic quality and the basic quality index
B5 Engineering classification for a rock mass
B5.1 General rules
B5.2 Engineering rock mass classification
B6 Establishing the KV and Jv indices
B6.1 The KV index
B6.2 The Jv index
B7 Preliminary assessment of the rock stress field
B8 Physical and mechanical parameters of the rock mass and discontinuities
B8.1 Rock mass parameters
B8.2 Discontinuity parameters
B9 Corrected value of the rock mass basic quality index
B10 Stand-up time for an underground rock mass
B11 Acknowledgements