| Summary: | 碩士 === 國立臺灣大學 === 土木工程學研究所 === 101 === Lateritic-gravel tablelands are wide, flat, and easy to be developed for land uses such as dwelling houses or agricultural lands. However, the high steep edges of tablelands are prone to collapse after heavy rainfalls, which will endanger the lives and properties in the nearby area. Therefore, studying the engineering properties of lateritic gravels and its landslide mechanism is an important topic for research in the aspect of slope stability.
This study selected an area nearby Ping-Ding Village of Yun-Lin County as the study site; for there were several severe landslides occurred in this area in the past. Mosel tests were employed and carried out in a sand box to explore the failures of nonhomogeneous slopes (composed of laterites, gravels, and mudstones; from top to bottom) induced by rainfalls as well as the efficacy of the gabions used for slope protection. The bare slopes investigated were a 30º gentle slope and a 60º steep slope; while the slope protected by gabions was investigated only for 60º. During the experiment, the variations in pore water pressure and volumetric water content in the soil were measured. The characteristics of the failure mechanism, the responses of pore pressure and water content in the model slopes, as well as the performance of protection method are compared and discussed as functions of the variables. The finite element program PLAXIS was also utilized for numerical analysis.
The test results showed that the proposed new weight-replacement method (NWR) resulted in suitable testing soil that was in accordance with the law of similarity. In addition, the less permeable laterites at the upper part of the slope reduced rainfall infiltration and water accumulation within the slope; the tension cracks in the lateritic soil also affected the distribution of water in the slope. The subsidence at the top of bare slopes changed with infiltration depth. The mudstone at the bottom has small hydraulic conductivity, so the water accumulated in the upper gravel layer and formed seepage, causing gradual instability at the interface of gravel and mudstone layers and ultimate destruction of the slope. The slope face where gabions were installed induced more rapid infiltration than the bare slopes due to the small steps provided for installing the gabions. Nevertheless, the gabions effectively prevented the slope to deform and thereby improved slope stability and delayed slope failure. In addition, the mudstone is unlikely to result is mass sliding because of poor permeability.
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