Tunnel Face Stability & New CPT Applications - Geo-Engineering

More documents

Recommendations

Info

34 2. Stability Analysis of the Tunnel Facedzτγ ′BD cotθFigure 2.30: Arching soil column with shear forces on all boundariessilo. Jancsecz [89] on the other hand proposes a column of soil with a width equal to the tunneldiameter D and depth equal to the wedge depth at the top, w(z t ) = D cot θ (see figure 2.30) andshear stresses acting on all four silo boundaries. Using this approach the relaxation length a in(2.52) is found as the quotient of area over circumference of the silo,a = A O =B D cot θ2(D + B tan θ)(2.53)Although this seems to take into account the three-dimensional nature of the soil silo, Huderhas shown that for slurry trenches the two-dimensional schematisation, where 2a is equal tothe largest length of the trench, is in good agreement with field observations. The equivalentapproximation for the face stability model leads toa = B 2(2.54)This leads to three possible ways to estimate the vertical load on the top of the wedge: (a)without soil arching, (b) with two-dimensional arching or (c) with three-dimensional arching.The results of these model implementations will be compared to a number of centrifuge testsreported in literature. For now the possible influence of the wedge width B will be neglectedand it will be assumed that B = D. The relaxation length for the different cases can then besimplified toa = ∞,(2.55a)a = R,(2.55b)1a = R1 + tan θ . (2.55c)The resulting vertical stresses for an example in dry sand (c ′ = 0, ϕ ′ = 35 ◦ , γ = 20kN/m 3 )have been plotted in figure 2.31.Having established the vertical stress on top of the wedge, a further problem arises with thedistribution of vertical stresses along the sides of the wedge and the accompanying horizontalstresses, which contribute to the force T . Again three possible implementations are suggested.The first possibility is to disregard any arching effects when calculating the horizontal stressesat the wedge sides. The second option is to continue the arching stress distribution σ ′ v,a given
2.2. Wedge Stability Model 35200400600σ ′ v,a [kPa]10γ = 20kN/m 3c ′ = 0φ ′ = 35 ◦K = K 0R = 5mθ = 70 ◦2030z [m]cbaFigure 2.31: Vertical stress distribution for different arching implementationsby (2.52) and derive the horizontal stresses from this. A third option would be to choose thestress on the wedge sides in such a manner that it falls between the first two options, for exampleto linearly interpolate the vertical stress between the stress including arching at the top of thewedge, σ ′ v,a (z t), and the vertical stress without arching effects σ ′ v (z b) at the bottom of the wedge,as sketched in figure 2.32 [93].The idea behind this last model is that the soil-arch widens with depth and is caused bydeformations at the top of the tunnel only. That would then result in an increase of the totalstresses below the top of the tunnel, either proportional to γ or to the stress level without archingeffects. Deformation occurs over the entire face and not only at the top of the wedge and assuch this model is not considered very likely. Furthermore, in slurry-filled trenches it has beenobserved that an effective stress reduction occurs within the deforming soil body, but also thatthis body is defined by clear shear bands and that outside these shear bands no stress reductionor even a slight stress increase can be observed. Therefore an intermediate model has not beenimplemented.The combined effects of soil arching and the stress distribution on the wedge sides leadto nine possible implementations, which we will refer to as a 1 , a 2 , etc. As a 1 , a 2 and a 3 arecompletely identical and, as said above, b 3 and c 3 have not been implemented, this leaves fivedifferent possible models. Within each of these models the value of K y is needed to calculateT , and from that E. Two possible values K y = K 0 and K y = K a have been implementedand will be referred to as a 1,0 and a 1,a , etc. The support pressure calculated with each of theseimplementations is compared with the results from the centrifuge tests by Bezuijen [37] andChambon [60] in table 2.4. Here the measured values of s ′ are listed, as well as the ratio of thecalculated value over the measured value.The comparison between centrifuge test results and calculated support pressures does notyield a definite answer which arching model to use. This is partly due to the limited number ofcentrifuge tests and the differences between the tests. The tests reported by Chambon & Cortéhave been performed in dry Fontaineblue sand with a reported ϕ ′ = 35 ◦ . These tests show adifferent behaviour with varying overburden. For the tests with low overburden, C/D ≤ 1, thec 1,0 model yields the best, and safe, prediction of the required support pressure. For the tests
Page 1: Tunnel Face Stability&New CPT Appli
Page 4 and 5: Dit proefschrift is goedgekeurd doo
Page 6 and 7: viAcknowledgementsKolla här, min
Page 8 and 9: viiiAbstractThe tunnel wound on and
Page 10 and 11: xContents3.2.4 Finite Element Model
Page 12 and 13: xiiList of Symbols× ij i = j norma
Page 14: xivList of Symbolsλfirst Lamé con
Page 17 and 18: 1.2. Outline of this Thesis 3suppor
Page 19 and 20: Chapter 2Stability Analysis of the
Page 21 and 22: 2.1. Introduction 7fluidsoilzs Fα
Page 23 and 24: 2.1. Introduction 9Figure 2.3: Unsu
Page 25 and 26: 2.1. Introduction 11q sq sq sααα
Page 27 and 28: φ = 40 ◦φ = 35 ◦2.1. Introduc
Page 29 and 30: 2.1. Introduction 15T 1 T 1E1 E 1G
Page 31 and 32: 2.1. Introduction 17N Deformation<
Page 33 and 34: 2.1. Introduction 19GC45 ◦ + φ/2
Page 35 and 36: 2.1. Introduction 21Figure 2.19: Ce
Page 37 and 38: 2.1. Introduction 23Figure 2.21: In
Page 39 and 40: 2.1. Introduction 25D (m) Soil type
Page 41 and 42: 2.2. Wedge Stability Model 27the su
Page 43 and 44: 2.2. Wedge Stability Model 29xyhz =
Page 45 and 46: 2.2. Wedge Stability Model 31s ′
Page 47: 2.2. Wedge Stability Model 33q 02ad
Page 51 and 52: 2.2. Wedge Stability Model 37with a
Page 53 and 54: 2.2. Wedge Stability Model 39s(z t
Page 55 and 56: 2.2. Wedge Stability Model 41∆p f
Page 57 and 58: 2.2. Wedge Stability Model 43has be
Page 59 and 60: 2.2. Wedge Stability Model 45from t
Page 61 and 62: 2.2. Wedge Stability Model 47γF(t/
Page 63 and 64: 2.2. Wedge Stability Model 49s min
Page 65 and 66: 2.2. Wedge Stability Model 5140∆s
Page 67 and 68: 2.3. Model Sensitivity Analysis 53P
Page 69 and 70: 2.3. Model Sensitivity Analysis 55i
Page 71 and 72: 2.3. Model Sensitivity Analysis 57
Page 77 and 78: 2.3. Model Sensitivity Analysis 63t
Page 79 and 80: 2.3. Model Sensitivity Analysis 65o
Page 81 and 82: 2.4. Comparison with Field Cases 67
Page 85 and 86: Figure 2.57: Overview of soil strat
Page 99 and 100:
2.4. Comparison with Field Cases 85
Page 101 and 102:
Page 103 and 104:
Page 105 and 106:
Page 107 and 108:
Page 109 and 110:
2.5. Further Groundwater Influences
Page 111 and 112:
2.6. Conclusions 97the effective st
Page 113 and 114:
2.6. Conclusions 99has been made th
Page 115 and 116:
Chapter 3Horizontal Cone Penetratio
Page 117 and 118:
3.2. Interpretation of Cone Penetra
Page 119 and 120:
Page 121 and 122:
Page 123 and 124:
3.3. Calibration Chamber Tests on S
Page 125 and 126:
Page 127 and 128:
Page 129 and 130:
Page 131 and 132:
Page 133 and 134:
Page 135 and 136:
Page 137 and 138:
Page 139 and 140:
Page 141 and 142:
Page 143 and 144:
3.4. Scale Model Tests 129Figure 3.
Page 145 and 146:
3.4. Scale Model Tests 1315210Figur
Page 147 and 148:
3.5. Field Tests 133Figure 3.35: Pl
Page 149 and 150:
3.6. Modelling Horizontal Cone Pene
Page 151 and 152:
Page 153 and 154:
Page 155 and 156:
3.7. Conclusions 141W H/V 043Ticino
Page 157 and 158:
Chapter 4High-Speed Piezocone Tests
Page 159 and 160:
4.2. Determination of Liquefaction
Page 161 and 162:
4.2. Determination of Liquefaction
Page 163 and 164:
4.4. Calibration Chamber Tests 149
Page 165 and 166:
4.4. Calibration Chamber Tests 1518
Page 167 and 168:
4.4. Calibration Chamber Tests 153v
Page 169 and 170:
4.4. Calibration Chamber Tests 155-
Page 171 and 172:
4.5. Conclusions and Recommendation
Page 173 and 174:
4.5. Conclusions and Recommendation
Page 175 and 176:
Chapter 5Conclusions and Recommenda
Page 177 and 178:
5. Conclusions and Recommendations
Page 179 and 180:
Bibliography[1] M.Y. Abu-Farsakh, G
Page 181 and 182:
Bibliography 167[30] B. Belter, W.
Page 183 and 184:
Bibliography 169[65] J.K. van Deen.
Page 185 and 186:
Bibliography 171[99] E. Kreyszig. A
Page 187 and 188:
Bibliography 173[133] Committee on
Page 189 and 190:
Bibliography 175[171] F.W.J. van Vl
Page 191 and 192:
Curriculum VitaeWout Broere was bor
Page 193 and 194:
SamenvattingGraaffrontstabiliteit &
Page 195 and 196:
Samenvatting 181spanningen ook in d
Page 197 and 198:
NawoordIn de afgelopen jaren heb ik
Page 199 and 200:
Appendix ABasic Equations of Ground
Page 201 and 202:
A.1. Semi-confined System of Aquife
Page 203 and 204:
A.2. Transient Flow 189withS s the
Page 205 and 206:
....Appendix BBasic Equations of El
Page 207:
B. Basic Equations of Elasticity 19
show all

Tunnel Face Stability & New CPT Applications - Geo-Engineering

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?