Tunnel Face Stability & New CPT Applications - Geo-Engineering

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36 2. Stability Analysis of the Tunnel Faceσ ′ h231zFigure 2.32: Possible horizontal stress distributions along wedge sidesMeas. Calculated s ′ divided by Measured s ′ a BestTest b s ′ (kPa) a ,0 a ,a b 1,0 b 1,a b 2,0 b 2,a c 1,0 c 1,a c 2,0 c 2,a ResultCS0.5/5 3.6 3.65 4.45 3.26 4.20 3.76 4.42 2.54 3.70 3.73 4.31 c 1,0CS0.5/5 3.3 4.00 4.88 3.58 4.61 4.12 4.85 2.79 4.06 4.09 4.73 c 1,0CS1/5 3.5 5.52 6.85 4.08 5.81 5.14 6.33 1.97 4.19 4.48 5.52 c 1,0CS1/5 3.0 6.41 7.95 4.73 6.74 5.97 7.35 2.28 4.87 5.20 6.41 c 1,0CS1/5 3.3 5.79 7.18 4.27 6.09 5.39 6.64 2.06 4.39 4.70 5.79 c 1,0CS1/10 7.4 5.13 6.35 3.77 5.40 4.78 5.89 1.83 3.89 4.15 5.13 c 1,0CS2/5 4.0 7.64 9.60 3.52 6.48 5.78 7.67 0.00 2.88 4.12 5.53 c 1,0 ,c 1,aCS2/10 8.0 7.66 9.63 3.53 6.48 5.79 7.68 0.00 2.88 4.12 5.54 c 1,0 ,c 1,aCS4/10 8.2 13.2 16.8 1.81 6.91 6.82 10.1 0.00 0.12 4.09 5.81 b 1,0CS4/13 13.4 10.9 13.8 1.40 5.58 5.53 8.17 0.00 0.02 3.31 4.70 b 1,0BS0.8/10 6.6 1.76 3.24 1.76 2.91 2.16 2.67 0.98 2.41 1.96 2.41 c 1,0BC0.8/10 17.0 1.30 1.50 1.04 1.29 1.22 1.39 0.67 0.99 1.09 1.25 b 1,0BC0.6/10 11.0 1.69 1.69 1.45 1.51 1.65 1.87 1.07 1.16 1.55 1.75 c 1,0a Format is a n,m : a = arching model (a = none, b = 2D, c = 3D), n = stress on wedge sides (1 = linear, 2 = incl.arching), m = K-value used (0 = K 0 , a = K a )b Format is ATn/m: A = Author, T = Type of Test, n = Overburden-Diameter Ratio, m = Diameter in m. Authors:B=Bezuijen [37], C=Chambon [60]. Type: S=Sand, C=Clay.Table 2.4: Comparison of centrifuge test results with models with different arching implementations
2.2. Wedge Stability Model 37with an overburden 2 times the tunnel diameter, the c 1,0 model again yields the closest match,but this time it gives an unsafe prediction of the required support pressure and the best safeprediction is obtained with the c 1,a model. For the deeper tunnels, with C/D = 4, the bestprediction is obtained with the b 1,0 model. In this case both the c 1,0 and the c 1,a model yield anunsafe prediction.The tests by Bezuijen on the other hand have been done in completely saturated sand (ϕ ′ =35.6 ◦ ) and soft clay samples (ϕ ′ = 23 ◦ , c ′ = 1kPa) with low overburdens, C/D = 0.6 or 0.8.The results of two tests are best predicted by the c 1,0 arching model. In one case this a slightlyunsafe prediction and the best safe prediction is obtained with the b 1,0 model. For the third testthe b 1,0 model yields the best safe prediction, although the c 1,a and the c 2,0 models are also veryclose.Based on this small number of tests it must be concluded that overall the c 1,0 model yieldsthe most accurate prediction of the minimal support pressure at which complete failure occursand the c 1,0 model will be used in further calculations. This model does however yield an unsafeprediction for several cases, especially the deeper tunnels with C/D = 4. In those cases the b 1,0model yields a better prediction. That the c 1,0 model yields the unsafe prediction that the faceis stable even without support may be due to an overestimation of the stress reduction causedby soil arching. Given the fact that the b 1,0 yields a safe prediction in all cases, this model maybe preferable from an engineering point of view. This choice may be further strengthened if itis desired to limit the deformations caused by the excavation process.The various arching implementations can be roughly associated with the amount of deformationthat occurs at the face. The support pressure found from the c models is the pressure atwhich total failure of the face occurs, at which point large deformations have already occurred.The b models on the other hand seem to yield the support pressure at which only limited deformationof the face occurs. Such limited deformations are needed to initiate the friction forcesand are inevitable in the boring process. The a models are equated to a situation where nodeformation has occurred and as a result the a model strongly overpredicts the minimal requiredsupport pressure. In combination with the effect of slurry infiltration and excess pore pressuresas described next, these models would yield extremely high required support pressures, resultingin extremely high overburden requirements, which are not backed by any field experience.The influence of the choice of the arching model and K y will be briefly illustrated in section2.3 for the reference case described there. Based on the limited evidence available, however,all further calculations will be made with the c 1,0 model in order to best predict the minimalrequired support pressure. The fact that it may yield unsafe support pressures, possibly due tovariations in the soil properties, should be overcome by the use of safety factors. And as is truein all cases where limit equilibrium models are used, the possible occurrence of failure by adifferent mechanism, in particular micro-stability, must be checked separately.2.2.3 Penetration of Support MediumAnother effect that has to be taken into account, in particular when boring in permeable soils, isthe penetration of the support medium into the soil. This infiltration may in turn lead to excesspore pressures in front of the TBM as well as a reduction of the effective support force.If a bentonite slurry is used, the bentonite should ideally form a thin impermeable filter cakeon top of the face. The entire support force from the slurry is then transported onto the soilskeleton at the face. In reality the slurry will always infiltrate the pores to a certain extent beforeclogging of the pores occurs and a filter cake is formed. The support pressure is then transportedonto the soil skeleton over this infiltration length. This situation is sketched in figure 2.33. In
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 and 48: 2.2. Wedge Stability Model 33q 02ad
Page 49: 2.2. Wedge Stability Model 35200400
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
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2.4. Comparison with Field Cases 87
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2.5. Further Groundwater Influences
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2.6. Conclusions 97the effective st
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2.6. Conclusions 99has been made th
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Chapter 3Horizontal Cone Penetratio
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3.2. Interpretation of Cone Penetra
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3.3. Calibration Chamber Tests on S
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3.4. Scale Model Tests 129Figure 3.
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3.4. Scale Model Tests 1315210Figur
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3.5. Field Tests 133Figure 3.35: Pl
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3.6. Modelling Horizontal Cone Pene
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3.7. Conclusions 141W H/V 043Ticino
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Chapter 4High-Speed Piezocone Tests
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4.2. Determination of Liquefaction
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4.2. Determination of Liquefaction
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4.4. Calibration Chamber Tests 149
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4.4. Calibration Chamber Tests 1518
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4.4. Calibration Chamber Tests 153v
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4.4. Calibration Chamber Tests 155-
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4.5. Conclusions and Recommendation
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4.5. Conclusions and Recommendation
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Chapter 5Conclusions and Recommenda
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5. Conclusions and Recommendations
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Bibliography[1] M.Y. Abu-Farsakh, G
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Bibliography 167[30] B. Belter, W.
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Bibliography 169[65] J.K. van Deen.
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Bibliography 171[99] E. Kreyszig. A
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Bibliography 173[133] Committee on
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Bibliography 175[171] F.W.J. van Vl
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Curriculum VitaeWout Broere was bor
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SamenvattingGraaffrontstabiliteit &
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Samenvatting 181spanningen ook in d
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NawoordIn de afgelopen jaren heb ik
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Appendix ABasic Equations of Ground
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A.1. Semi-confined System of Aquife
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A.2. Transient Flow 189withS s the
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....Appendix BBasic Equations of El
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B. Basic Equations of Elasticity 19
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