Research on mechanical model of unsaturated soil taking account of its thermal properties

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The final aim of this research is to investigate the mechanism of slope failures, which often occur in the southern part of Kyushu Island when the heavy rains fall, and to apply the results to predict the scale and time of slope failure. The triaxial tests on unsaturated sandy soil, the field observation of suction and temperature in soil and the amount of rain fall, the numerical research to establish the mechanical model have been carried out to solve the problem above. Some consideration has also done to propose a new slope stability analysis for Shirasu ground.The triaxial test on unsaturated Shirasu sampled at Ohsumi Peninsula and Toyoura sand were carried out under drained-aired and different temperature condition to examine the thermal effect on mechanical behavior of soil. The range of confining pressure and cell temperature are 0.5-1.5 kgf/cm2 and 10-40ﾟC respectively. It is found out that the change in the surface tension and the coefficient of viscosity due to temperature caused the different stress-strain relation in the consolidation and shearing processes.The data acquired system in the field observation has been eatablished for suction, temperature and rain fall measurement, in which the data are automatically filed in the data loggers and the data in loggers are allowed to be acquired once a few months in the floppy disk by the note-type's personal computer.The mechanical model taking account of the phase change of pore fluid due to temperature and pressure was proposed and some numerical experiment was done to simulate the wetting and drying of soil due to the rain fall and sunshine. The results were compared with the data obtained by the field observation of suction in soil and temperature.The new slope stability analysis was proposed based on the consideration on the cohesion which depends on the water content and the effect of water content on the safety factor of slope was numerically investigated.