Page 9 - Engineering Rock Mass Classification_ Tunnelling, Foundations and Landslides

viii Contents

6. Rock Mass Rating 45

Introduction 45
Collection of Field Data 45
Estimation of RMR 50
Applications of RMR 52
Precautions 55
Rock Mass Excavability Index for TBM 58
Tunnel Alignment 60

7. Tunneling Hazards 63

Introduction 63
Tunneling Conditions 65
Empirical Approach for Predicting Ground Conditions 74
Theoretical/Analytical Approach 78
Effect of Thickness of Weak Band on Squeezing Ground Condition 80
Sudden Flooding of Tunnels 80
Chimney Formation 80
Environmental Hazards due to Toxic or Explosive Gases
83
and Geothermal Gradient 83
Concluding Remarks

8. Rock Mass Quality Q-System 85

The Q-System 85
Joint Orientation and the Q-System 93
Updating the Q-System 93
Collection of Field Data 93
Classification of the Rock Mass 94
Estimation of Support Pressure 96
Estimation of Deformation or Closure 101
Unsupported Span 102
Design of Supports 103
New Austrian Tunneling Method 104
Norwegian Method of Tunneling 106
Rock Mass Characterization 106
Drainage Measures 112
Experiences in Poor Rock Conditions 113
Concluding Remarks 113

9. Rock Mass Number 119

Introduction 119
Interrelation Between Q and RMR 120
Prediction of Ground Conditions 123
Prediction of Support Pressure 123
Effect of Tunnel Size on Support Pressure 123
Correlations for Estimating Tunnel Closure 126