Hydro-Mechanical Properties of an Unsaturated Frictional Material

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168 CHAPTER 7. ANALYSIS AND INTERPRETATION OF THE EXPERIMENTAL RESULTS Table 7.6: Yield stress for loose and dense specimen derived from Casagrande (1936) ψ = 1.5 kPa ψ = 3.0 kPa ψ = 20.0 kPa ψ = 50.0 kPa Loose 20 kPa 20 kPa 20 kPa 30 kPa Dense 30 kPa 30 kPa 30 kPa 30 kPa compression curves of loose specimen under applied constant suction are given. It was assumed to find an influence of the applied suction on the compression behavior (assumption: ψ = ˜σ0). But yield stress of approximately ˜σ0 = 20 kPa for loose and approximately ˜σ0 = 30 kPa for dense was found, which indicates that the applied suctions from ψ = 1.5 to ψ = 50 kPa do not influence the compression behavior (see also summary in Tab. 7.6). There is also the possibility to use Janbu’s method (1969), where the tangent modulus M is plotted versus the vertical stress σ. A drop in the shape of the curve identifies an influence of stress history on the mechanical behavior of the soil. As can be seen in Fig 7.24 (right) no drop and thus no breakdown in the structural resistance occurs. Also for the dense specimen it was observed, that applied suction does not influences the stress history. Results of the dense specimen are shown in Fig. D.1 in Appendix D. 7.6 Summary Based on the experimental results given in Chapter 6 relationship between suction and volumetric water content or saturation during initial drainage, main drainage and imbibition and scanning drainage and imbibition were derived using models proposed by several authors. The curve fit parameters are determined. The suction-water content models fit the experimental data well for drainage or imbibition process. But when using models dealing with hysteresis and also scanning drainage/ imbibition phenomena the experimental results are not in good agreement with the calculated results for several zones along the suction-water content curve. Also some models use to much parameters to identify this relationship or are rather complex in their application to experimental results. The interpretation of the results shows that the void ration and the loading path direction influence the shape of the soil-water characteristic curve. With decreasing void ratio the curves are shifting to higher range of suction values. Depending on the loading path direction for a certain suction value the water content is larger (drainage) or less (imbibition). This phenomenon is known as hysteresis. There are no sig- nificant differences found between curves carried out under steady state and transient state flow condition. Several statistical models in combination with the soil-water characteristic curve are used for prediction of unsaturated hydraulic conductivity function. The results from direct deter-
7.6. SUMMARY 169 mination of unsaturated hydraulic conductivity are close to the results estimated by Mualem (1976) and Fredlund et al. (1994). The relations between vertical net stress and void ratio as well as vertical strain and void ratio are analyzed using the concept of stress dependent stiffness. Stiffness modulus is calculated and the results show an increase of stiffness with increasing suction. After reaching an optimum value an decrease of stiffness during loading occurs. When unloading the specimen the stiffness is similar for the tests performed under several constant suction value. It can be concluded, that the stiffness of Hostun sand is influenced by the matric suction and the water content (volumetric water content, saturation) respectively during loading procedure. The collapse potential for loose specimen at several net stresses was found to be small. The suction induced to the sand specimen does not act as preconsolidation pressure.
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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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116 CHAPTER 6. EXPERIMENTAL RESULTS
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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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