Static Effects and Aspects of Feasibility and Design of Drainages in Tunnelling (eBook)

Static effects and aspects of feasibility and design of drainages in tunnelling 1
Imprint 3
Foreword 4
Vorwort 6
Acknowledgments 8
Abstract 10
Kurzfassung 12
Table of contents 14
1. Introduction 18
1.1 Problem statement 18
1.2 State of research 18
1.2.1 Face stability 18
1.2.2 Grouting body 19
1.3 Research objectives 20
1.3.1 Methods 20
1.3.2 Limitations of scope 20
1.4 Structure of the thesis 21
1.4.1 Face stability 21
1.4.2 Grouting body 23
1.5 Publications 23
2. An investigation into efficient drainage layouts for the stabilisation of tunnel faces in homogeneous ground 24
2.1 Introduction 24
2.2 Computational model 25
2.2.1 Seepage flow analyses 26
2.2.2 Support pressure 26
2.2.2.1 Mechanism 27
2.2.2.2 Limit equilibrium 27
2.2.2.3 Seepage forces 27
2.2.2.4 Silo pressure 28
2.2.2.5 Support pressure 30
2.2.2.6 Dimensional analysis of the hydraulic head field 31
2.3 Comparative analyses 32
2.3.1 Introduction 32
2.3.2 Reference cases 33
2.3.3 Drainage via boreholes from the tunnel face or niches 34
2.3.3.1 Number of drainage boreholes 34
2.3.3.2 Location of drainage boreholes 36
2.3.3.3 Length of drainage boreholes 38
2.3.3.4 Radial distance of drainage boreholes 42
2.3.4 Drainage action of a pilot tunnel 42
2.3.5 Drainage action of the first tube of a twin tunnel 44
2.3.6 Effect of drainage curtains from a pilot tunnel 45
2.4 Design equation 48
2.4.1 Development of the design equation 48
2.4.1.1 Reduction in the number of parameters in the case of T > 5D
2.4.1.2 Linearization 53
2.4.2 Applicability limits of the design nomograms 58
2.4.2.1 Error of the nomograms 60
2.4.3 Use of the nomograms 61
2.5 Application examples 66
2.5.1 Albula tunnel 66
2.5.2 Lake Mead Intake No. 3 Tunnel 69
2.6 Conclusions 71
3. Effectiveness of drainage measures for tunnel face stability in ground of non-uniform permeability 72
3.1 Introduction 72
3.2 Tunnelling close to the horizontal interface of aquitard and aquifer 75
3.3 A single, horizontal aquifer or aquitard symmetric to the tunnel axis 78
3.4 A single horizontal layer of variable elevation and thickness 80
3.4.1 Support pressure and hydraulic head field 80
3.4.1.1 Layer at the tunnel roof 83
3.4.1.2 Layer just above the tunnel roof 84
3.4.2 Optimizing the drainage borehole layout 85
3.4.3 Application example 86
3.5 Thinly interbedded horizontal aquifers and aquitards 87
3.5.1 Homogenisation to an equivalent anisotropic model 87
3.5.2 Maximum layer thickness 87
3.5.3 Effect of permeability anisotropy 88
3.5.3.1 Without advance drainage measure 88
3.5.3.2 With advance drainage boreholes 89
3.6 Tunnelling close to the vertical interface of an aquitard or an aquifer 90
3.7 Encountering a vertical fault zone 93
3.8 Entering a single vertical zone 94
3.8.1 Hydraulic head field 94
3.8.1.1 Without advance drainage measures 94
3.8.1.2 With advance drainage boreholes 94
3.8.2 Support pressure 96
3.8.2.1 Unstable or stable neighbouring rock 96
3.8.2.1.1 Unstable neighbouring rock 96
3.8.2.1.2 Stable neighbouring rock 97
3.8.2.2 Parametric study 97
3.8.2.2.1 Without drainage measure 98
3.8.2.2.2 With advance drainage boreholes 98
3.8.3 Application example 99
3.9 Thinly interbedded vertical aquifers and aquitards 101
3.9.1 Homogenisation to an equivalent anisotropic model 101
3.9.2 Maximum layer thickness 101
3.9.3 Effect of permeability anisotropy 102
3.9.3.1 Without advance drainage measure 103
3.9.3.2 With advance drainage boreholes 103
3.10 Conclusions 104
4. Effects of the hydraulic capacity of drainage boreholes on tunnel face stability 106
4.1 Introduction 106
4.2 Flow capacity of the drainage boreholes 107
4.2.1 Introduction 107
4.2.2 Equivalent permeability 108
4.2.2.1 Borehole with pressurized pipe flow 108
4.2.2.2 Borehole with open-channel flow 110
4.2.2.3 Transverse permeability 112
4.2.3 Ground-single drainage borehole interaction 113
4.2.3.1 FE simulation 113
4.2.3.1.1 Computational model 113
4.2.3.1.2 Model behaviour 115
4.2.3.1.3 Simplification for open-channel flow 115
4.2.3.1.4 Characteristic results 116
4.2.3.2 Analytical treatment and FE validation 119
4.2.3.2.1 Governing equations 119
4.2.3.2.2 Approximate solution 121
4.2.3.2.3 Computational results and validation of the FE-solution 122
4.2.4 Face stability 125
4.2.4.1 Computational model 125
4.2.4.2 Characteristic results 125
4.2.4.3 Applicability of nomograms 128
4.2.4.3.1 Radial inflow from the ground into several boreholes 128
4.2.4.3.2 Criterion of admissible maximum hydraulic gradient 129
4.2.4.3.3 Admissible ground permeability 130
4.3 Borehole casings 132
4.3.1 Computational model 132
4.3.2 A single cased drainage borehole 133
4.3.3 Face stability 133
4.4 Conclusions 135
5. Other operational and environmental factors limiting the effectiveness of advance drainage measures for face stability 136
5.1 Introduction 136
5.2 Time dependency 137
5.2.1 Problem 137
5.2.2 Computational model 137
5.2.3 Characteristics of time-dependent behaviour 139
5.2.4 Effect of axial drainage arrangements 141
5.2.4.1 Degree of pore pressure relief 141
5.2.4.2 Lead time for face stability 142
5.2.4.3 Application example 143
5.3 Groundwater drawdown 144
5.3.1 Problem 144
5.3.2 Computational model 144
5.3.3 Borderline cases 145
5.3.4 Effect of distinct drainage boreholes 145
5.4 Settlements 147
5.4.1 Problem and approach 147
5.4.2 Effect of drainage boreholes 148
5.4.2.1 Comparison to no drawdown of groundwater table 148
5.4.3 Comparison to FE-model 149
5.5 Water discharge 149
5.5.1 Problem 149
5.5.2 Effect of drainage boreholes 150
5.5.2.1 Comparison to no drawdown of groundwater table 150
5.6 Conclusions 151
6. On the stabilizing effect of drainage on tunnel support in grouted fault zones 152
6.1 Introduction 152
6.2 Modelling ideal drainage 153
6.2.1 Static system, initial and boundary conditions 153
6.2.2 Material properties 154
6.2.3 Solution method and dimensioning criterion 155
6.3 Equations of ideal drainage 156
6.3.1 Sequence of drainage and grouting 156
6.3.1.1 Previous investigations: drainage after grouting (l = b) 156
6.3.1.2 New investigations: drainage in advance of grouting (l ? b) 157
6.3.1.3 Water inflow 158
6.3.2 Extent of the radius of drainage 158
6.3.2.1 Case I (a ? ? < l)
6.3.2.2 Case II (l ? ? ? b) 162
6.3.2.3 Outer plastification 164
6.3.2.4 Water inflow 164
6.4 Effect of ideal drainage of the grouting body 165
6.4.1 Ideal drainage after grouting 165
6.4.1.1 Characteristic line 165
6.4.1.2 Radius of drainage and plastification 166
6.4.1.3 Required strength of grouting body 167
6.4.1.4 Parametric study 167
6.4.1.5 Water inflow 169
6.4.2 Ideal drainage in advance of grouting 170
6.4.2.1 Characteristic line 170
6.4.2.2 Dimensioning aids 171
6.4.3 Assumption of stiff grouting body 171
6.5 Modelling specific drainage borehole arrangements 172
6.5.1 Problem and approach 172
6.5.2 Arrangement of drainage boreholes 172
6.5.3 Computational model 173
6.5.3.1 Computational steps: drainage in advance of grouting 174
6.5.3.2 Computational steps: drainage after grouting 174
6.5.4 Validation 176
6.6 Effect of drainage borehole arrangements drilled after grouting 179
6.6.1 Drainage slits (2D-model) 179
6.6.1.1 Number of drainage slits 179
6.6.1.2 Plastic zones 179
6.6.1.3 Required lining support pressure 180
6.6.1.4 Inflow 182
6.6.2 Drainage boreholes (3D-model) 182
6.6.2.1 Axial borehole distance 182
6.6.2.2 Required lining support pressure 183
6.6.2.3 Comparison of characteristic lines 183
6.6.2.4 Inflow 185
6.7 Effect of drainage borehole arrangements drilled in advance of grouting 186
6.7.1 Layout A: circular borehole arrangements 186
6.7.1.1 Number of drainage boreholes 186
6.7.1.2 Circle line of drainage boreholes 188
6.7.1.3 Required lining support pressure 189
6.7.2 Layout B: lateral borehole arrangements 191
6.7.2.1 Effect of Layout B compared to Layout A 191
6.7.2.2 Required lining support pressure 192
6.7.3 Application example 192
6.7.4 Effect of fault zone of limited extent 195
6.7.4.1 Host rock and fault zone of uniform permeability 196
6.7.4.2 Host rock and fault zone of different permeability 197
6.8 Conclusions 199
6.8.1 Analytical solution of ideal drainage 199
6.8.1.1 Drainage after grouting 199
6.8.1.2 Drainage in advance of grouting 200
6.8.2 Specific drainage borehole arrangements 200
6.8.2.1 Drainage borehole arrangements drilled after grouting 200
6.8.2.2 Drainage borehole arrangements drilled in advance of grouting 200
7. Conclusions and outlook 202
Appendix A. Publications from the present thesis 206
Appendix B. Matlab-code drainage in advance of grouting 208
Appendix C. Matlab-code drainage after grouting I 210
Appendix D. Matlab-code drainage after grouting II 214
Notation 216
References 222