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

本研究的最终目的是探讨九州岛南部地区在暴雨过程中经常发生的斜坡崩塌机制，并将研究结果应用于预测斜坡崩塌的规模和时间。为解决上述问题，进行了非饱和砂土的三轴试验，现场观测了土体的吸力、温度和降雨量，并进行了建立力学模型的数值研究。通过对大须岛和托尤亚沙土的三轴试验，研究了不同温度和排水条件下的热效应对土体力学行为的影响。围压范围为0.5kgf/cm~2~1.5kgf/cm~2，室温范围为10~40ﾟC。在固结和剪切过程中，由于表面张力和粘度系数随温度的变化而产生不同的应力-应变关系。建立了现场观测数据采集系统，用于吸力、温度和雨量的测量。提出了考虑温度和压力引起的孔隙流体相变的力学模型，并对降雨和日照条件下土壤的干湿过程进行了数值模拟。将计算结果与现场土体吸力和温度观测数据进行了对比分析，提出了一种新的基于粘聚力的边坡稳定分析方法，并通过数值模拟研究了含水率对边坡安全系数的影响。

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.