| Summary: | 碩士 === 國立臺灣科技大學 === 營建工程系 === 103 === ABSTRACT
The majority of Taiwan’s hillsides belong to unsaturated soil slope. Seepage in these unsaturated slopes situated above groundwater level would easily lead to changes of hydrological characteristics (such as matric suction, etc.) when encountered rainfall, and then trigger subsequent slope stability problems. This study adopted a field case and used numerical analysis program SEEP/W and SLOPE/W module to conduct seepage simulation and stability analysis on unsaturated soil slopes under different rainfall scenarios. In addition to simulation and exploration of original alert modes (rainfall, groundwater level), this study also investigates changes of hydrological characteristics and stability in unsaturated soil slopes caused by rainfall infiltration, and then identify more accurate landslide disaster occurrence indicators also having a mechanical basis for potential application by related agencies in implementing disaster prevention and early warning measures.
This study found that the slope stability analysis results of unsaturated soil slope would vary under same cumulative rainfall but different durations. Therefore, only cumulative rainfall was used as indicator parameter of whether landslide will occur or not, in terms of this case study, its accuracy still has room for improvement. And under different rainfall scenarios the changes of water level in slopes with thick colluvium or deep groundwater are not significant. The majority of damage types of unsaturated soil slope belong to shallow landslide, and slope failures mostly occur along the wetting front, while the generation of wetting front represents the dissipation of matric suction, as a result the shear strength of soil will also drop, and this is one of the important factors causing slope instability. The analytical results exhibit critical value characteristic of volumetric water content prior to slope failure induced by rainfall infiltration. In addition, this critical volumetric water content would not be influenced by rainfall conditions and positions in the slope. Therefore, using critical volumetric water content as a landslide disaster occurrence indicator should be a feasible direction and warrants further study.
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