Hydro-Mechanical Properties of an Unsaturated Frictional Material

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156 CHAPTER 7. ANALYSIS AND INTERPRETATION OF THE EXPERIMENTAL RESULTS as imbibition path. The imbibition curves start with an unsaturated hydraulic conductivity close to a zero value. With a decrease in the suction, the unsaturated hydraulic conductivity increases. The unsaturated hydraulic conductivity function increases first for the layers at the bottom of the (loose and dense) sand specimens where the voids are faster filled with water. In comparison to statistical models by Mualem (1976) and Fredlund et al. (1994), the scanning imbibition hydraulic conductivity curves derived using Childs and Collis George (1953) model begin at significant larger hydraulic conductivity values. In a second analysis (i.e. the instantaneous profile method) the profiles of hydraulic head gradient and water content are used to calculate the unsaturated hydraulic conductivity function directly for the drainage process. Figure 7.14 shows the unsaturated hydraulic conductivity for loose and dense specimens (1st drainage curve with a flow rate of 30 ml/min and 2nd drainage curve with a flow rate of 100 ml/min) calculated from both the instantaneous profile method (i.e. direct method) and the statistical models (i.e. indirect method). The instantaneous profile method is assuming that the water phase is continuous. The method is applicable in the saturated zone and in the unsaturated zone where water transport occurs in the wetting phase. The instantaneous profile method should not be applied in the residual zone, where water is believed to be exclusively transported in the vapor phase (non continuous water phase). The instantaneous profile method for the loose specimens shows unsaturated hydraulic conductivities in a range of approximately 0.3 × 10 −4 to 0.007 × 10 −4 m/s for a suction of 1.6 to 2.0 kPa respectively. For the dense specimen the hydraulic conductivities are in the range of approximately 0.4 × 10 −4 to 0.005 × 10 −4 m/s for suctions ranging from 1.7 to 2.2 kPa respectively. Similar to the results calculated when using the indirect method, the unsaturated hydraulic conductivity is decreasing rapidly along a narrow range of suctions. Results derived using statistical model by Mualem (1976) and Fredlund et al. (1994) are close to the results derived from direct method. Unsaturated hydraulic conductivity functions resulting from modified pressure plate appa- ratus (steady state tests) and sand column I (transient state tests) are compared in Fig. 7.15 for loose specimen and in Fig. 7.16 for dense specimen. The results are given for the indirect as well as for the direct approach. The soil-water characteristic curve is strongly related to the unsaturated hydraulic conductivity function and therefore their behavior is similar (including the effect of hysteresis). The unsaturated hydraulic conductivity functions are close to each other during the drainage path. The unsaturated hydraulic conductivity functions along the scanning pathes are located within the main drainage and imbibition loop. This behavior is consistent with drainage and imbibition soil-water characteristic curves. The following observations are made with regard to the effect of void ratio on the unsaturated hydraulic conductivity function. For low suction values the hydraulic conductivity for the loose specimen is higher due to the larger cross-sectional area available for water flow. When reaching the air-entry value, the unsaturated hydraulic conductivity for the loose specimen becomes less than the one for the dense specimen. The larger pores of the loose specimen
7.4. UNSATURATED HYDRAULIC CONDUCTIVITY 157 easily desaturate in this range whereas the smaller pores of the dense specimen are still available to conduct water. With an increase in suction, the unsaturated hydraulic conductivity decreases rapidly along a narrow range of suctions which is reflected in the interconnected and uniform pores. During the imbibition process the unsaturated hydraulic conductivity Unsat. hydr. conductivity (10 -4m/s) Unsat. hydr. conductivity (10 -4m/s) Unsat. hydr. conductivity (10 -4m/s) 10 1 0.1 0.01 10 1 0.1 0.01 Unsat. hydr. conductivity (10 -4m/s) Unsat. hydr. conductivity (10 -4m/s) 0.001 Matric suction (kPa) 0.001 1 10 1 10 10 1 0.1 0.01 0.001 1 Matric suction (kPa) 10 Instantaneous Profile Method: 1st drying - layer (210 mm) 2nd drying - layer (210 mm) Childs and Collis George (1950): 1st drainage 2nd drainage Unsat. hydr. conductivity (10 -4m/s) 10 1 0.1 0.01 0.001 0.001 Matric suction (kPa) 1 10 Mualem (1976): 1st drainage 2nd drainage Fredlund et al. (1994): 1st drainage 2nd drainage 10 1 0.1 0.01 10 1 0.1 0.01 0.001 Matric suction (kPa) 1 10 1 Instantaneous Profile Method: 1st drying - layer (405 mm) 2nd drying - layer (405 mm) Childs and Collis George (1950): 1st drainage 2nd drainage Matric suction (kPa) 1 10 Mualem (1976): 1st drainage 2nd drainage Fredlund et al. (1994): 1st drainage 2nd drainage Figure 7.14: Comparison of the unsaturated hydraulic conductivity resulting from 1 st drainage curve (flow rate 30ml/min) and 2 nd drainage curve (flow rate 100ml/min) from sand column test I (transient state test) derived from statistical models and instantaneous profile method (loose specimen)
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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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12 CHAPTER 2. STATE OF THE ART the
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14 CHAPTER 2. STATE OF THE ART Figu
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16 CHAPTER 2. STATE OF THE ART - Su
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18 CHAPTER 2. STATE OF THE ART - Re
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20 CHAPTER 2. STATE OF THE ART Volu
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22 CHAPTER 2. STATE OF THE ART Drai
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24 CHAPTER 2. STATE OF THE ART wher
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26 CHAPTER 2. STATE OF THE ART drai
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28 CHAPTER 2. STATE OF THE ART Tabl
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30 CHAPTER 2. STATE OF THE ART Tabl
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32 CHAPTER 2. STATE OF THE ART by W
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34 CHAPTER 2. STATE OF THE ART proc
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36 CHAPTER 2. STATE OF THE ART - Im
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38 CHAPTER 2. STATE OF THE ART auth
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40 CHAPTER 2. STATE OF THE ART 2.5.
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46 CHAPTER 2. STATE OF THE ART fitt
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48 CHAPTER 2. STATE OF THE ART Satu
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50 CHAPTER 2. STATE OF THE ART when
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52 CHAPTER 2. STATE OF THE ART Degr
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54 CHAPTER 2. STATE OF THE ART 1. T
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56 CHAPTER 2. STATE OF THE ART 0.2
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58 CHAPTER 2. STATE OF THE ART meth
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60 CHAPTER 2. STATE OF THE ART When
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62 CHAPTER 2. STATE OF THE ART Vert
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64 CHAPTER 2. STATE OF THE ART a) S
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66 CHAPTER 2. STATE OF THE ART - Ja
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68 CHAPTER 2. STATE OF THE ART
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70 CHAPTER 3. INTRODUCTION TO PROCE
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76 CHAPTER 4. EXPERIMENTAL SETUPS s
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78 CHAPTER 4. EXPERIMENTAL SETUPS 1
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80 CHAPTER 4. EXPERIMENTAL SETUPS D
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82 CHAPTER 4. EXPERIMENTAL SETUPS d
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84 CHAPTER 4. EXPERIMENTAL SETUPS b
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86 CHAPTER 4. EXPERIMENTAL SETUPS t
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90 CHAPTER 4. EXPERIMENTAL SETUPS D
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94 CHAPTER 4. EXPERIMENTAL SETUPS T
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96 CHAPTER 5. MATERIAL USED AND EXP
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98 CHAPTER 5. MATERIAL USED AND EXP
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100 CHAPTER 5. MATERIAL USED AND EX
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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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