| Summary: | 碩士 === 國立中興大學 === 水土保持學系所 === 103 === At first, soil borings were performed along the C-C'' profile of You-Ye-Lin landslide and undisturbed samples were collected systematically for a series of physical and mechanical tests in laboratory. The soil boring logs and laboratory testing results were employed as references to determine the numerical model and soil material model parameters for sequential numerical analyses.
Further, using Geo-Studio 2012 numerical analysis tool, one can perform a series of rainfall induced seepage analyses on You-Ye-Lin landslide under the rainfall condition during Fung-Wong typhoon in 2014. Meanwhile, the groundwater variation of simulation was compared with those of measurement to calibrate and verify the validity of various material model parameters. The comparisons also show that the variation trend of the groundwater level of simulation is reasonably coincident with that of measurement.
Subsequently, a specific rainfall event (rainfall duration: 2015/06/01~2015/06/03, cumulative rainfall: 215 mm) was adopted for a series of rainfall induced seepage, displacement, and stability analyses along the potential sliding surface of C-C'' profile in You-Ye-Lin landslide. In the analyses, the influence of unsaturated Soil Water Characteristic Curves (SWCC or θ(u) ~ u curve, in which θ and u denote volumetric water content and pore water pressure respectively) on the numerical results was prudently inspected. In this study, two methods are employed to determine the SWCC, namely, physical property method (D10、D60、LL、θsat) and pressure plate experimental method.
In addition, the 13 years rainfall records of Ruei-Li rainfall monitoring station were used to determine the 24 hours design rainfall of 20, 50, and 100 years return period. The 24 hours design rainfall with different return periods were then used for a series of rainfall seepage and slope stability analyses. The numerical results indicate that the rainfall induced pore water pressure and lateral displacement of soil mass will increase with the extension of return period and which alternately reduces the factor of safety of the potential sliding surface.
The numerical results show that the soil water content θ(u), pore water pressure u, lateral displacement Δh, and factor of safety FS along the potential sliding surface are greatly relevant to the rainfall intensity. The θ(u), u, and Δh values will be promoted to response an immediate increase of rainfall intensity whereas a reduction of FS value is obtained simultaneously. For the volumetric water content of soil mass, the simulation is not coincident with observation well as expectation. In addition to the inherent limitation of two-dimensional (2-D) numerical analysis which is unable to consider the three-dimensional (3D) topographical and hydrological conditions, the deviation between simulation and observation of volumetric water content may be caused by the instability of in-situ time domain reflectometry (TDR) measurement of water content at initial adjustment stage.
Eventually, the numerical results also verify that the SWCC determined by pressure plate experimental method enable to provide better predictions on the pore water pressure, displacement, and factor of safety from rainfall induced seepage and slope stability analyses than the SWCC estimated by physical property method.
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