Hydro-Mechanical Properties of an Unsaturated Frictional Material

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66 CHAPTER 2. STATE OF THE ART - Janbu’s method (1969) Janbu (1969) proposed that the preconsolidation pressure can be determined from the plot of tangent modulus M versus effective vertical net stress (M − σ ′ ): M = ∆ε ∆σ ′ (2.27) where: ε is the strain and σ ′ is the effective vertical net stress (see Fig. 2.32). He found a drop in stiffness modulus near the preconsolidation pressure signifying a breakdown of the structural resistance. He defined the preconsolidation pressure as the point just before the stiffness modulus levels out. A detailed review of evaluation of of the preconsolidation pressure and a investigation of these various methods is given by Grozic et al. (2003). Investigations on silt (Rahardjo & Fredlund 2003) showed, that soil has not only a memory with respect to effective stress, but also with respect to suction. In the present study the methods given by Casagrande (1936) and Janbu (1969) are used to estimate, if there is an influence of the applied matric suction on the stress history behavior of granular material. The maximum stress to which the soil has been exposed (i.e. due to suction) is determined equivalent to the preconsolidation pressure and called here yield stress ˜σ0. 2.8 Summary This chapter summarizes important literature referring to unsaturated soils. In the beginning unsaturated soils are introduced and differences in hydro-mechanical behavior of several types of soils are given. Further stress state in saturated as well as unsaturated soils is explained. Several authors suggested single valued stress equations and other authors suggested the approach of independent stress state variable for describing unsaturated soils. In the present study the approach of independent stress state variables is preferred and used to perform experimental investigation on unsaturated sand. That is the application of suction and total net stress with reference to the air-pressure or water pressure. Phases in unsaturated soils as well as soil suction and its components are discussed. In case of granular materials as sand the matric suction is the main component influencing its characteristics. The definition and meaning of both hydraulic functions, namely the soil-water characteristic curve and unsaturated hydraulic conductivity function is given. Mainly the chapter is focused on the methods for determination of hydraulic functions. Most common methods are the one-step, multistep method and the continuous flow experiment that are used tradition- ally in combination with inverse methods to determine hydraulic functions. However, in the present work parallel measurements of water content and matric suction are carried out for the direct identification of hydraulic functions for drainage and imbibition cycles.
2.8. SUMMARY 67 Typical equipment and measurement techniques needed when dealing with unsaturated soils are introduced. Special features in the equipment used in this study allow to investigate granular materials that includes for instance measurement of volume changes using dial gauge with high resolution, attached burettes for application of small matric suction as well as matric suction changes and the development of modified pressure plate apparatus. An overview of several models for prediction of hydraulic functions is given. The review showed that there is a need for a simple equation that considers determination of scanning behavior of soil-water characteristic curve. Existent models are quite complex in use or their parameters are difficult to measure in the laboratory. Common type of test for prediction of the stress-strain behavior of soils is presented, that is the one-dimensional compression and rebound test. Usually this type of test is performed on saturated soils. The present study is concerned with unsaturated sand (the equipment and measurements have to fulfill appropriate requirements as given above). Relevant equations are given.
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Hydro-Mechanical Properties of Part
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Acknowledgement The present dissert
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3.2 Steps of Model Building . . . .
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11 Summary and Outlook 205 11.1 Gen
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2.16 Influence of Brooks and Corey
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6.2 Experimental results of soil-wa
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7.17 Unsaturated hydraulic conducti
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B.6 Experimental results and best f
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8.3 Constitutive parameters for the
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E ref ur Oedometer reference stiffn
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ρ Density (g/cm 3 ) ρd ρs Dry de
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2 CHAPTER 1. INTRODUCTION Figure 1.
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4 CHAPTER 1. INTRODUCTION - Model b
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6 CHAPTER 1. INTRODUCTION
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8 CHAPTER 2. STATE OF THE ART condu
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10 CHAPTER 2. STATE OF THE ART soil
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14 CHAPTER 2. STATE OF THE ART Figu
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116 CHAPTER 6. EXPERIMENTAL RESULTS
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136 CHAPTER 7. ANALYSIS AND INTERPR
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138 Observed values (-) Observed va
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164 Stiffness modulus (kPa) Stiffne
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172CHAPTER 8. NEW SWCC MODEL FOR SA
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186 CHAPTER 9. NUMERICAL SIMULATION
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CHAPTER 10. BEARING CAPACITY OF A S
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204 CHAPTER 10. BEARING CAPACITY OF
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206 CHAPTER 11. SUMMARY AND OUTLOOK
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214 APPENDIX A. DETAILS ZOU’S MOD
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216 APPENDIX A. DETAILS ZOU’S MOD
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218 APPENDIX B. SOIL-WATER CHARACTE
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230 APPENDIX C. COLLAPSE POTENTIAL
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232 Vertical strain (-) Vertical st
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234 APPENDIX E. NEW SWCC MODEL - DE
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240 40 50 30 APPENDIX E. NEW SWCC M
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242 Observed Values Number of obser
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244 BIBLIOGRAPHY Aubertin, M., Mbon
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246 BIBLIOGRAPHY Campbell, J. D. (1
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248 BIBLIOGRAPHY Davis, J. L. & Ann
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250 BIBLIOGRAPHY Ferré, P. A. & To
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252 BIBLIOGRAPHY Grozic, J. L. H.,
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254 BIBLIOGRAPHY Janbu, N. (1969),
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256 BIBLIOGRAPHY Lawton, E. C., Fra
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258 BIBLIOGRAPHY Mualem, Y. (1977),
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260 BIBLIOGRAPHY Phene, C. J., Hoff
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262 BIBLIOGRAPHY Rojas, J. C., Sali
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264 BIBLIOGRAPHY Stoimenova, E., Da
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266 BIBLIOGRAPHY Vanapalli, S. K. &
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268 BIBLIOGRAPHY Unsaturated Geotec
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Schriftenreihe des Lehrstuhls für
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Herausgeber: Th. Triantafyllidis 32
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Hydro-Mechanical Properties of an Unsaturated Frictional Material

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