Stability and Scouring Analysis of the Slope Under Extreme Weather Condition

• Main Authors: Liu-Ming Hung, 柳名鴻
• Other Authors: Sung-Chi Hsu
• Format: Others
• Language: zh-TW
• Published: 2013
• Online Access: http://ndltd.ncl.edu.tw/handle/05296547924221505116

碩士 === 朝陽科技大學 === 營建工程系碩士班 === 101 === In 2009, the moderate Typhoon Morakot invaded Taiwan brought more than 2500mm of torrential rain. In central and southern Taiwan. It was measured as 3059.5mm in Alishan rainfall station which has been closed to the average rainfall (3684mm) per year in Alishan. This astonishing rainfall has exceeded the hundred year rainstorm frequency. The infiltration of heavy rainfall made the factor of safety of slopes to decrease and caused landslides initiated from the upper and/or downward slopes. The landslides may then cause and trigger mudslides or debris flow. The mud flow or debris flow may squeeze the main river channel and scour river banks and/or down slopes of the roads. Therefore, a lot of landslides had occurred during this typhoon along the road of Tai-21 in central Taiwan. In-situ exploration and sampling had been carried out in Sin-San Village in Nantou County after the typhoon to obtain the index properties of the soils. Large direct shear tests in the laboratory had been performed to measure the saturated and unsaturated shear strength of the material. The soil water characteristic curve (SWCC) of the soil was derived from the pressure plate tests. Guelph permeameter was used to estimate the in-situ hydraulic conductivity of the soil. These properties were necessary for later numerical analyses. The cross-section profiles of the failed slope before and after the typhoon at this area were obtained using digital elevation model (DEM) and 3D terrestrial scanner, respectively. The numerical softwares, SEEP/W and SLOPE/W, were used to analyze the slope stability under the similar rainfall by the typhoon. Different ground water level, river level, and friction angle of the soil were considered to compare the values of factor of safety and to reveal the failure processes of the slope. The possible failure of the slope may be due to scouring of the toe of the slope by the surge of rising river level and/or mud flow based on the investigated profiles and the numerical simulations. The estimated length of scouring was about 20m long. The possible mechanism of failure for this length of scouring could be due to multiple retrogressive failures after toe scouring based on the numerical modeling. The friction angle of the soil is around 46 to 54 degrees based on the direct shear tests and back analyses. Besides that, the one-day storm of 200-year recurrence interval was used to analyze the impact of different rainfall patterns. It was found back peak pattern of rainfall will lead to lower factor of safety.