Field measurements above twin tunnels in London Clay

234 Pages·2008·12.82 MB·English

page vi
Table of contents
Volume I
Abstract.........................................................
Acknowledgements..................................................v
Tableof contents .................................................. Vii
Listof Tables .................................................... Xii
Listof Figures .................................................... Xiii
Symbolslist .................................................... XXiX
1 Introduction

1.1 General background ....................................... 1

1.2 Soft ground tunnelling ..................................... 2

1.3 The Jubilee Line Extension Project ............................. 3

1.4 Research description and aims ................................ 4

1.5 Organisation of the thesis ................................... 5
2 Assessing potential ground response to bored tunnelling

2.1 Changes around a constructed tunnel ............................ 8

2.2 Tunnel stability .......................................... 10
2.2.1 Undrained stability ................................. 10

2.2.2 Drained stability ................................... 11
2.3 Numerical modelling of ground response ......................... 11
2.4 Empirical methods for predicting surface displacements .............. 13
2.4.1 Vertical displacements ............................... 13
2.4.2 Horizontal displacements ............................. 15
2.4.3 Ground slopes, curvatures and strains .................... 16
2.4.4 Estimation of from crown displacements .............. 16
Wm
2.4.5 Estimation of Wm from ground loss .................... 17
2.4.6 Tmugji width parameter i. and trough length parameter i, ...... 19
2.4.7 Time-dependent displacements ......................... 21
2.4.8 Multiple tunnels ................................... 24
2.5 Empirical methods for predicting subsurface displacements ............ 24
2.5.1 Idealised framework for movements around a tunnel .......... 24
2.5.2 Subsurface vertical displacement profiles .................. 25
2.5.3 Horizontal displacements ............................. 27

2.6 Empirical methods for predicting pore pressure and total stress changes 27
2.7 Tunnel performance ....................................... 30
2.8 Potential damage to structures ................................ 31

2.9 Summaiy .............................................. 33
page vii
3 Project site investigation
3.1 Geology of the London Basin ................................ 35
3.2 Geotechnical characteristics of the site .......................... 36
3.2.1 Made Ground or fill .......... 36
3.2.2 Alluvium .................. 36
3.2.3 Terrace Gravels ............. 36
3.2.4 London Clay ............... 36
3.3 Hydrogeology of the site .............. 41
4 Instrumentation and monitoring details
4.1 Measurement uncertainly and sources of error ..................... 43
4.2 Surface monitoring points ................................... 45
4.3 3-dimensional displacements measured using total station surveying ...... 45
4.3.1 Total station measurements: uncertainty and sources of error 47
4.3.2 Processing of the total station measurements ............... 48
4.4 Vertical displacements measured using precision levelling ............. 49
4.4.1 Levelling: uncertainly and sources of error ................. 49
4.4.2 Processing of levelling measurements .................... 50
4.5 Transverse horizontal displacements measured using a micrometer stick 50
4.5.1 Micrometer stick measurements: uncertainty and sources of
error..........................................51
4.5.2 Processing micrometer stick measurements .................51
4.6 Longitudinal horizontal displacements measured using a collimation tool ... 52
4.6.1 Collimation tool measurements: uncertainly and sources of
error.......................................... 53
4.6.2 Processing of collimation tool measurements ............... 54
4.7 Subsurface displacement monitoring ............................ 54
4.8 Subsurface vertical displacement measurements using rod extensometers 55
4.8.1 Rod extensometer: uncertainty and sources of error ........... 56
4.8.2 Processing rod extensometer measurements ................ 56
4.9 Horizontal displacement measurements using electrolevel inclinometers 57
4.9.1 Electrolevel inclinometer measurements: uncertainly and
sourcesof error .................................. 58
4.9.2 Processing electrolevel inclinometer measurements ........... 59
4.10 Piezometric and stress change monitoring ....................... 60
4.11 Total stress and piezometric measurements using pneumatic
piezometers and push-in spade cells with integrated piezometers ...... 60
4.11.1 Spade cell and piezometer measurements: uncertainty and
sourcesof error .................................. 61
4.11.2 Processing of total stress and piezometer measurements ....... 62
5 St. James's Park instrumented site and JLE project works
5.1 Introduction ........................................ 63
5.2 Site layout, instrumentation plan and tunnel positions 63
insuumentauou iayuui....................................... 64
5.4 Monitoring goals ......................................... 64
5.5 Shield and lining details .................................... 65
5.6 In-tunnel monitoring ....................................... 66
5.7 Tunnel progress and monitoring periods ......................... 67
5.8 Observations during tunnel excavation .......................... 67
5.8.1 Period 2 (westbound drive) ........................... 67
page viii
5.8.2 Period 4 (eastbound drive) . 67
5.8.3 Other information ..................................68
5.9 Discussions .............................................68
6 Monitoring results from St. James's Park
6.1 Surface monitoring for Period I ............................... 70
6.1.1 Vertical displacements for precision levelling ............... 70
6.1.2 Transverse horizontal ground strains and displacements by
micrometerstick ................................. 70
6.1.3 Parallel horizontal displacements by collimation tool .......... 71
6.1.4 3-dimensional displacements by total station ................ 71
6.1.5 Assessment of surface displacement monitoring ............. 74
6.2 Surface monitoring in Period 2 ............................... 75
6.2.1 Vertical displacements for precision levelling .............. 75
6.2.2 Transverse horizontal ground strains and displacements by
micrometerstick ................................. 76
6.2.3 Parallel horizontal displacements by collimator tool .......... 76
6.2.4 3-dimensional displacements by total station ................ 77
6.2.5 Comparison of Period 2 measurements ................... 78
6.3 Surface monitoring for Period 3 ............................... 78
6.3.1 Vertical displacements for precision levelling .............. 79
6.3.2 Transverse horizontal ground strains and displacements by
micrometerstick ................................. 79
6.3.3 3-dimensional displacements by total station ................ 80
6.3.4 Comparison of Period 3 measurements ................... 81
6.4 Surface monitoring for Period 4 ............................... 82
6.4.1 Vertical displacements for precision levelling .............. 82
6.4.2 Transverse horizontal ground strains and displacements by
micrometerstick ................................. 83
6.4.3 Parallel horizontal displacements by collimator tool .......... 84
6.4.4 3-dimensional displacements by total station ................ 84
6.4.5 Comparison of Period 4 surface measurements .............. 87
6.5 Surface monitoring for Period 5 ............................... 87
6.5.1 Vertical displacements for precision levelling ............... 87
6.5.2 Transverse horizontal ground strains and displacements by
micrometerstick ................................. 88
6.5.3 3-dimensional displacements using total station .............. 88
6.5.4 Comparison of Period 5 surface measurements .............. 90
6.6 Subsurface displacement monitoring results in Period 1 ............... 90
6.6.1 Rod extensometers ................................. 90
6.6.2 Electrolevel inclinometers ............................ 91
6.7 Subsurface displacement monitoring for Period 2 ................... 92
6.7.1 Rod extensometers ................................. 92
6.7.2 Electrolevel inclinometers ............................ 93
6.8 Subsurface displacement monitoring in Period 3 .................... 94
6.8.1 Rod extensometers ................................. 95
6.8.2 Electrolevel inclinometers ............................ 96
6.9 Subsurface displacement monitoring for Period 4 ................... 96
6.9.1 Rod extensometers ................................. 96
6.9.2 Electrolevel inclinometers ............................ 97
6.10 Subsurface displacement monitoring in Period 5 ................... 99
page ix
6.10.1 Rod extensometers . 99
6.10.2 Electrolevel inclinometers ...........................100
6.11 Pore pressure and total stress measurements in Period 1 ..............100
6.11.1 Piezometers .....................................100
6.11.2 Spade cells with integrated piezometers ..................101
6.12 Pore pressure and total stress measurements in Period 2 ..............101
6.12.1 Piezometers .....................................101
6.12.2 Spade cells with integrated piezometers ..................102
6.13 Pore pressure and total stress measurements in Period 3 ..............103
6.13.1 Piezometers .....................................103
6.13.2 Spade cells with integrated piezometers ..................103
6.14 Pore pressure and total stress measurements in Period 4 ..............104
6.14.1 Piezometers .....................................104
6.14.2 Spade cells with integrated piezometers ..................104
6.15 Pore pressure and total stress measurements during Period 5 ..........105
6.15.1 Piezometers .....................................105
6.15.2 Spade cells with integrated piezometers ..................105
6.16 In-tunnel measurements ....................................106
6.16.1 Measured diametric changes in tunnel linings ..............106
6.16.2 Lining loads in eastbound tunnel .......................106
7 Data Analysis
7.1 Displacement development and characterisation above both tunnels .......109
7.1.1 Surface settlement, horizontal movement and vectors of
displacement....................................109
7.1.2 Subsurface settlement profiles .........................114
7.1.3 Discussions on surface and subsurface displacement patterns .... 115
7.1.4 Near-tunnel displacements ............................116
7.2 General ground response around both tunnels ......................119
7.2.1 Data coverage ....................................119
7.2.2 Westbound tunnel - parallel profile ......................121
7.2.3 Westbound tunnel - transverse profile ....................122
7.2.4 Eastbound tunnel - parallel profile ......................124
7.2.5 Eastbound tunnel - transverse profile .....................125
7.2.6 Comments on the mechanics of ground response around both
tunnels........................................126
7.3 Total and effective stress and pore pressure changes around eastbound
drive...............................................127
7.4 Time-dependent displacements and tunnel lining response .............131
7.4.1 General response across St. James's Park ..................132
7.4.2 Soil response after westbound tunnel construction ............133
7.4.3 Soil response after eastbound tunnel construction ............134
7.4.4 Tunnel lining performance in relation to soil response ........136
page x
8 Conclusions
8.1 Conclusions and lessons learned from instrumentation and monitoring of
tunnelling-induced displacements ............................141
8.2 Conclusions relating generally to tunnelling in London Clay ...........145
8.3 Conclusions relating to characterisation of construction displacements
abovetunnels in London Clay ..............................148
8.4 Conclusions relating to characterisation of long-term displacements
abovetunnels in London Clay .............................. 150
8.5 Further work ...........................................151
Appendices
Appendix A London Clay: investigations into fabric, structure and variability ......167
Appendix B Details of local coordinate system for total station measurements, and
stability of reference points during monitoring ...................173
Appendix C Temperature calibration testing for micrometer bar ...............179
Appendix D Borehole mapping using inclinometer torpedo and temporary inclinometer
tubing..............................................183
Appendix E Schedules of borehole drilling, instrumentation coordinates, orientations,
gauge lengths, calibrations, and zero readings ...................187
Appendix F Scheduleof Surveys .....................................189
Appendix G Subsurface horizontal displacements in the empirical framework ......191
Appendix H The form of construction and long-term transverse displacement profiles
observedat St. James's Park ...............................195
Appendix I Observations relating to long-term tunnel lining performance ........201
-P.ferencv,-
Volume 2
Tables for chapters and appendices
Figures for chapters and appendices
page xi
List of tables
Table 2.1 Comparison of slope, curvature and horizontal strains for idealised
Gaussian displacement profiles (after Lake et al, 1992) .............207
Table 2.2 General influence on choosing parameters for ground displacement
prediction which are larger than the measured values during tunnel
construction..........................................207
Table 3.1 Simplified summary of geological strata found in the London Basin
(after Sumbler, 1996) ....................................208
Table 3.2 Geotechnical parameters suggested for Alluvium .................208
Table 3.3 Geotechnical parameters suggested for Terrace Gravels .............209
Table 3.4 Geotechnical parameters suggested for London Clay ...............209
Table 4.1 Summary of the resolutions and accuracies for the monitoring
systems used at St James's Park.............................210
Table 5.1 Ground response periods identified at St. James's Park .............211
Table 6.1 Measurement precision estimated from Period 1 monitoring at St.
James's Park ..........................................212
Table 7.1 Summary of surface settlement profile characteristics at St. James's
Park................................................213
Table 7.2 Summary of subsurface settlement profile characteristics at St.
James's Park ..........................................214
Table 7.3 Effects of changing on maximum displacements, slopes, and
curvatures............................................215
Table 7.4 Comparison of shear stiffhess to undrained strength (GIs) and
percentage unloading (n) for idealised cylinder model .............215
Table Bl Variation of calculated reference point coordinates ................216
Table B2 Variations of calculated height differences and distances between
referencepoints ........................................217
Table B3 Results of distance measurements when assessing tripod mounted
prismperformance, Nov 1995 ..............................218
Table Cl Span length calculated from total station measurements for
micrometerstick calibration ...............................218
Table Dl Maximum borehole deviations from the vertical .................218
Table El Surface monitoring point locations ...........................219
Table E2 Rod extensometer anchor locations ...........................219
Table E3 Electrolevel carriage locations and details .....................220
TableE4 Piezometer locations ....................................222
Table E5 Combined pneumatic total stress/piezometer spade cell locations and
details..............................................222
Table E6 Contractor's surface monitoring point locations ..................223
Table El Drilling summary and comments for subsurface instrumentation
installation...........................................224
Table Fl Precision levelling surveys ................................226
TableF2 Micrometer stick surveys .................................227
TableF3 Extensometer surveys ....................................228
TableF4 Total station surveys ....................................229
TableF5 Collimation tool surveys ..................................230
Table F6 Piezometer and spade cell surveys ...........................231
Table F7 Manual electrolevel inclinometer surveys ......................232
Table Hl Surface settlement profile characteristics of construction settlements
for different methods of determining the trough width parameter ......233
page xii
Table H2 Near surface settlement profile characteristics of long-term
construction settlements for different methods of determining the
troughwidth parameter ...................................234
List of figures
Chapter 1
Figure 1.1 Schematic diagrams of sprayed concrete lining tunnelling system, and
conventionalshields and ThMs..............................235
Figure 1.2 Representation of potential tunnel instability with tunnel advance......236
Figure1.3 JLE project route alignment ...............................236
Figure 1.4 Overall JLE project geology for tunnelling west of Canada Water......237
Chapter 2
Figure 2.1 Idealised stress paths around a tunnel in London Clay at crown and
axislevels............................................239
Figure 2.2 Schematic diagram defining tunnel geometry....................240
Figure 2.3 Influence of heading geometry and depth on tunnel stability..........240
Figure 2.4 Stability ratio limiting criteria for clay soils and modes of behaviour. .. . 241
Figure 2.5 Idealised transverse vertical displacement profile: (a) Gaussian form
and stochastic model of settlement, and (b) normalised forms of
idealised surface displacement, slope and curvature................242
Figure 2.6 Idealised longitudinal vertical displacement profile: (a) Gaussian form
defining the cumulative probability as the area under the curve; (b)
cumulative probability function curve; and (c) its use in
corresponding normalised shapes of surface displacement, slope and
curvature.............................................243
Figure 2.7 Example of measured longitudinal settlement profiles from Green
Park, London..........................................244
Figure 2.8 Idealised 3-dimensional surface settlement trough and tunnel
coordinatesystem.......................................245
Figure 2.9 Normalised profile of transverse horizontal displacements, v, with
tunnelaxis as point sink...................................246
Figure 2.10 Normalised distribution of parallel horizontal displacements, u, with
the centre of the tunnel face as a point sink.....................246
Figure 2.11 Horizontal strain measurements made above the Heathrow Express
trialtunnel............................................247
Figure 2.12 Ratios of surface settlement to crown settlement for tunnels in clays
againstcover to diameter ratios..............................247
Figure 2.13 Idealisation of ground loss (a) 2-dimensional simplification and (b)
arounda tunnelling shield.................................248
Figure 2.14 Stability ratio versus volume loss (a) case history data for clay soils,
and(b) suggested relationships..............................249
Figure 2.15 Variation of load factor with volume loss.......................249
Figure 2.16 Estimating from measured settlements.......................250
Figure 2.17 Variation of trough width parameter, 1r with depth to tunnel axis for
tunnelsin clays.........................................251
Figure 2.18 Long-term settlement development: (a) normalised post-construction
surface settlement troughs above tunnels in soft clays, and (b)
settlement profiles above the Heathrow Express trial tunnel.......... 252
page xiii
Figure 2.19 Comparison of change in trough width parameter between initial and
longer-term settlement profiles in cohesive soils..................253
Figure 2.20 Surface settlement profiles above twin tunnels, Victoria Line,
London..............................................253
Figure 2.21 Twin tunnel interaction from Finite Element Analyses: (a) normalised
surface settlement profiles above a second tunnel, and (b) variation of
eccentricity of maximum settlement with twin tunnel geometry.......254
Figure 2.22 Idealisation of a tunnel heading.............................255
Figure 2.23 Radial deformation associated with unloading of a cavity in a linear-
elastic perfectly-plastic continuum............................255
Figure 2.24 Deformations in front of an advancing tunnel heading in London
Clay................................................256
Figure 2.25 Measured displacements around tunnels in London Clay............257
Figure 2.26 Variation of trough width parameter, i, with depth below the ground
surface...............................................258
Figure 2.27 Maximum displacements for subsurface settlement profiles above
tunnelsin London Clay...................................259
Figure 2.28 Schematic diagram of total stress and pore pressure changes around
an idealised contracting cylinder for undrained conditions...........260
Figure 2.29 Schematic diagram of effective stress and pore pressure changes
around an idealised contracting cylinder for drained and undrained
conditions............................................261
Figure 2.30 Movement, horizontal stress, and pore water pressure time histories
Heathrow Express trial tunnel, type 2 excavation.................262
Figure 2.31 Lining loads observed for a running tunnel in London Clay..........263
Figure 2.32 Building deformation parameters: maximum slope and deflection
(zVL)............................................
ratio 264
Chapter 3
Figure 3.1 Geological map and section of the London Basin.................265
Figure 3.2 Plan of Westminster and St. James's areas showing JLE SI borehole
locationsand major excavations.............................267
Figure 3.3 Geological sections from JLE SI, samples obtained during
instrumentation installation at St. James's Park, and other available
sources..............................................268
Figure 3.4 Atterberg limit test results from different London Clay sites..........269
Figure 3.5 Range of measured undrained shear strengths in London Clay at
selectedsites..........................................269
Figure 3.6 Effective stress failure envelopes determined for London Clay in
triaxial compression for several sites in London..................270
Figure 3.7 Undrained stiffnesses: (a) changes with depth, and (b) variations at
smallstrains...........................................271
Figure 3.8 Measured range of the in-situ earth pressure coefficient in London
Clay................................................272
Figure 3.9 Permeabilities measured in London Clay.......................272
Figure 3.10 Geophysical borehole logs from BH1I5T near Westminster Station.....273
Figure 3.11 Pore water pressure profile near St. James's Park in Westminster,
London..............................................275
page xiv
Chapter 4
Figure 4.1 Surface Monitoring Point (SMP) details........................277
Figure 4.2 Schematic diagram of total station theodolite and representation of
collimationerrors.......................................277
Figure 4.3 Total station surveying targets used at St. James's Park..............278
Figure 4.4 Influence of temperature and relative humidity on distance
measurements using the total station..........................278
Figure 4.5 Schematic drawing of the micrometer stick used for horizontal strain
measurements..........................................279
Figure 4.6 Comparison of idealised horizontal point strain profile and the
idealised average horizontal strains calculated for 2.5m spans.........279
Figure 4.7 Schematic drawing of the collimation tool used to measure horizontal
displacements parallel to the tunnel axes.......................280
Figure 4.8 Collimation survey plan defining collimation tool 'face' convention. . . . 280
Figure 4.9 Schematic drawing of a rod extensometer hole and reference head.....281
Figure 4.10 Extensometer dial gauge: (a) usage with calibration socket and (b)
measurement on rod tip and use of extension piece................282
Figure 4.11 Schematic diagram of electrolevel showing (a) the basic operating
principle and (b) details of the electrolevel carriages used in the
instrumentationtubes.....................................283
Figure 4.12 Determining vertical profiles of horizontal displacements from
discrete measurements of tilt in electrolevel inclinometers...........284
Figure 4.13 Schematic diagrams of (a) a pneumatic piezometer installed in a
borehole and (b) a push-in spade-shaped pressure cell..............285
Chapter 5
Figure 5.1 Planof area near St. James's Park............................287
Figure 5.2 Instrumentation layout at St. James's Park......................288
Figure 5.3 Section showing relative position and depths of subsurface
instrumentation boreholes and tunnels.........................289
Figure 5.4 Locations of subsurface displacement measurement points: (a)
extensometer anchors and (b) electrolevel carriages................290
Figure 5.5 Contractor's surface levelling point locations in St. James's Park......291
Figure 5.6 Shield details for running tunnel drives from waterloo to Green Park. . . 292
Figure 5.7 Details of fixed bead on shield drives through St. James's Park.......293
Figure 5.8 General arrangement of expanded lining showing segment and key
locationsand dimensions..................................294
Figure 5.9 Potential key combinations and positions.......................295
Figure 5.10 Instrumentedring details..................................296
Figure 5.11 A typical vertical displacement response for a surface monitoring
point and the identified response periods.......................297
Chapter 6
Figure 6.1 Key figure defining the sign conventions for 3-dimensional
movements relative to the tunnel centre-lines....................299
Figure 6.2 Precision levelling results, Period 1...........................300
Figure 6.3 Micrometer stick measurement results, Period I..................301
Figure 6.4 Transverse horizontal displacement profiles from micrometer stick
measurements, Period I...................................302
Figure 6.5 Collimation tool measurement results, Period 1...................303
Figure 6.6 Difference from mean value of coordinates calculated from total
page xv