Tunnel Face Stability & New CPT Applications - Geo-Engineering

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2 1. Introductionmencement of the works. A typical site characterisation for a bored tunnel consists of (vertical)sampling and sounding tests at 50 to 100m intervals [68]. This interval is chosen as to obtainan optimum between the reliability of the investigation and the costs involved. However, belowcurrent and historical river beds, as found in many delta areas, like the western part of theNetherlands, this frequency may be insufficient to detect local variations of the stratification,such as sand lenses, or detect the presence of obstacles like large boulders [15]. Past tunnellingexperiences show that insufficient knowledge of the actual soil conditions or the exact locationof layer boundaries can lead to serious disturbances of the boring process, and therefore extracosts [26, 47].In many cases a more detailed knowledge of the soil conditions would not lead to an alteredtunnel alignment. It could however have an impact on the operation of the tunnel boring machine,in order to fine-tune the boring process and in that way minimize the risk of disturbances. Suchextra information could well be obtained after the commencement of the actual boring, and ithas therefore been suggested to use soil investigation techniques originating from the tunnelboring machine itself. Various techniques have been suggested, amongst which the use of acone penetration test. Although normally used from the soil surface as a vertical test, in this caseit would be rotated by 90 ◦ and executed horizontally in front of the tunnel face. Using such aHorizontal Cone Penetration Test, information about the soil up to some 30 metres in front ofthe tunnel could be obtained.The properties of the soil influence the amount of deformation that occurs around the tunnelboring machine due to the boring process, and thereby the amount of settlement that occursat the surface. They also strongly influence the forces needed to support the soil at the tunnelface during the actual excavation. The bandwidth of allowable support forces is limited. If thesupport force transferred onto the soil is too low, the soil may collapse into the tunnel boringmachine, if it is too high the soil may be forced away from the machine or the supporting mediummay escape to the surface, an event commonly called a blow-out. In all cases this may lead tostagnation of the boring process or undesired deformation of the surface, and in built-up areaseven to damage to surface structures.In order to reliably establish the allowable bounds of the support pressure, a detailed knowledgeof the boring process and the properties of the soil in front and above the tunnel boringmachine and a detailed understanding of the possible failure mechanisms is needed. And althougha number of different models is presented in literature to calculate the allowable supportpressures, there is only a limited understanding of the various aspects that may determine thenormative failure mechanism, its dependence on the soil properties and the interaction with theboring process. One of the aspects that has hardly been taken into account is the infiltration ofthe support medium into the soil and the interaction with the pore water.The determination of the limits of the support pressure is further complicated in heterogeneoussoils, as the presence of different soil types at the tunnel face may influence the governingfailure mechanism. This might lead to a situation where the overall stability of the face is undercutby a relatively thin layer with differing properties. An example would be the presence ofliquefiable sand lenses at the face.1.1 Aims of this ResearchFrom the problem areas signalled above, three aspects will be investigated in this thesis. Thefirst is the stability analysis of the face and the interaction of support medium infiltration on thelimits of allowable support pressure. A model will be developed to calculate the minimal required
1.2. Outline of this Thesis 3support pressure, which can deal with stratified heterogeneous soils and incorporates the effectsof support medium infiltration, but will also be applicable in cases where no infiltration occurs.Using this model, the influence of infiltration will be studied through a parameter analysis aswell as by comparison with recent Dutch field cases.The second part of this study will investigate the possibilities of horizontal cone penetrationtesting and attempt to find the similarities and differences between horizontal and traditional(vertical) cone penetration. To that end laboratory tests in a calibration chamber will be presentedand an analytical model will be derived. For practical reasons the calibration chamber tests willbe limited to sands at different densities.The third part will investigate the possibility of using a piezocone penetration test (<strong>CPT</strong>U)to determine the liquefaction potential of sands. To this end a number of tests will be performedin a calibration chamber using an adapted sounding installation and a regular piezocone. Againthese tests will be limited to clean sands at different densities.1.2 Outline of this ThesisChapter 2 deals with the stability analysis of the tunnel face. Within this chapter the first sectiongives a short introduction as well as an overview of the state of the art and literature. Section 2.2forms the central part of the chapter, where the new stability model is described and brieflyillustrated. In section 2.3 an extensive parameter analysis is presented, followed in section 2.4by a comparison with several recent field cases. Section 2.5 subsequently gives a short overviewof various influences on the pore pressures around the tunnel boring machine and section 2.6gives a very concise overview of the model and the main conclusions.Readers who want to gain a quick understanding of the stability model could start out withthese conclusions (section 2.6) and after that refer to the appropriate parts of section 2.2.Chapter 3 deals with the interpretation of Horizontal Cone Penetration Tests. After a briefintroduction, it start of with a concise overview of the interpretation of regular (vertical) conepenetration tests. Thern the various laboratory tests performed, and their results, are discussedin sections 3.3 and 3.4. Section 3.5 briefly lists the available data from field tests on horizontalcone penetration. In section 3.6 a simple analytical model is derived to aid in interpretingthe differences between horizontal and vertical cone penetration, followed by conclusions insection 3.7.The reader who is interested in a quick understanding of horizontal cone penetration mightstart with the conclusions of this chapter and after that skip back to the results of the laboratorytests, starting in section 3.3.3.Chapter 4 gives the results from the high-speed piezocone penetration tests. It starts out witha brief introduction, and shortly describes the determination of the liquefaction potential of soilsin section 4.2. Then an overview is given of the current literature concerning the influence ofthe penetration speed on the piezocone test results in section 4.3. Section 4.4 gives an overviewof the test conditions and results and is followed by conclusions.For a quick overview of the test results, and in view of the length of the chapter, the readermight opt to start reading at section 4.4.The final chapter gives a short overview of the main conclusions and a number of recommendationsconcerning the optimisation of the tunnel boring process.
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 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<
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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
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2.2. Wedge Stability Model 5140∆s
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2.3. Model Sensitivity Analysis 53P
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2.3. Model Sensitivity Analysis 55i
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2.3. Model Sensitivity Analysis 57
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2.3. Model Sensitivity Analysis 63t
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2.3. Model Sensitivity Analysis 65o
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2.4. Comparison with Field Cases 67
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Figure 2.57: Overview of soil strat
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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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