Using TRIGRS to Assess the Effects of Rainfall and Infiltrationon Landslide Occurred at ShanTsunLaio, ChihChang

• Main Authors: Pei-Hsi Wang, 王姵兮
• Other Authors: Wei-Hau Wang
• Format: Others
• Language: zh-TW
• Published: 2007
• Online Access: http://ndltd.ncl.edu.tw/handle/44811127973291495327

碩士 === 國立中正大學 === 地震研究所暨應用地球物理研究所 === 96 === ShanTsunLaio landslide that continuously in motion is situated at Fu-Hsin village in ChihChang Township, Taitung County. An apparent landslide occurred after the invasion of Xangsan Typhoon on October 30, 2000. Xangsan Typhoon brought 603mm of rainfall that triggered the landslide on November 3th. TRIGRS was used in this study with the support of rainfall records from Typhoon Dujuan and Mindulle, field survey, and other important data as input to understand the effects of size of simulation domain, grid sizes, rainfall, and infiltration played during the landslide events. Simulations were first conducted to examine the impact of grid sizes on slope stability and pore pressure head. The results indicated that grid size affect both grid’s safety factor and pore pressure head. Larger the grid size is, less sensitivity the surface slope of the grid becomes which equally reduces the slope instability. On the other hand, finer detail of pore pressure head can be illustrated with finer grid size. Simulation results also showed the effect of initial groundwater level to both pore pressures and safety factor. If simulation started with low groundwater level, then number of grids with safety factor less than unity consisted 17.63% of the total grids in the biginning of a rainstorm event (t=1hr). If simulation started with high groundwater level, then 22.42% of the total grids posses safety factors less than critical. However, the effect of groundwater level diminished at the end of the rainfall event (t=60hr) with only 0.06% of increase in percentage of grid counts having safety factor less than 1.0. Right- and left-skewed rainfall events were used to assess the effect of rainfall pattern. The simulation results indicated that left-skewed rainfall events had higher influence on the rises of pore pressure and slope instability. Soil cohesion as well as friction angle also affects slope stability. Simulation results from this study indicated that the reduction of soil cohesion and friction angle apparently affected slope stability. Total of 25.58% of grid cells from the study domain possessed safety factors lower than the threshold when friction angle was set at 22°; whereas, 55.00% of grid cells possessed safety factors lower than the threshold when friction angle was reset at 15°. A 29.42% increase in instability cells was estimated. Therefore, the reduction of friction angle greatly affect TRIGRS simulation results in slope instability.