極端氣候下道路邊坡穩定及淘刷模擬分析

Stability and Scouring Analysis of the Slope Under Extreme Weather Condition

柳名鴻(Liu-Ming Hung)

指導教授 ： 徐松圻

朝陽科技大學/理工學院/營建工程系/碩士(2013年)

摘要

在2009年中度颱風莫拉克侵台，在台灣中南部降下2500mm以上之豪雨，阿里山雨量站測得3059.5mm，已逼近阿里山年平均降雨3684mm，如此驚人的雨量已超越百年暴雨頻率，許多邊坡因降雨入滲使得整體安全係數下降，造成上或下邊坡發生崩坍，進而引發土石流，然而土石流淘刷許多下邊坡及擠壓主河道，下邊坡遭淘刷又引起道路的崩坍，使得臺21線沿線道路留下許多風災後的瘡痍。

本研究於南投縣信義鄉新山村現地勘查後取樣來進行試驗分析，並嘗試以大型傾斜直剪儀推估飽和與不飽和土壤剪力強度參數，同時進行基本參數試驗、壓力鍋、Guelph滲透計等試驗，來得到土壤水份特性曲線及滲透係數，以做為數值分析之輸入參數。由災前DEM及災後三維掃瞄得到之新山村邊坡剖面圖，配合SEEP/W及SLOPE/W來模擬分析及比較風災降雨條件下，在不同水位及河道淘刷破壞之情形，同時考量不同滲透係數、初始水位及土壤摩擦角來比較。由現地勘查及數值分析得知新山村邊坡破壞主要原因是因河水暴漲，導致坡趾發生淘刷，引發邊坡發生連續性的崩坍，使淘刷長度達20公尺。分析結果得到新山村摩擦角應介於46~54度之間。另以龍神橋200年重現期距之一日暴雨量，分析在不同降雨型態下，邊坡連續降雨之邊坡安全係數的變化，以後峰型降雨對安全係數影響較大。

關鍵字

數值分析 ； 河道淘刷 ； 降雨入滲 ； 崩坍 ； 極端降雨

並列摘要

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.

並列關鍵字

Numerical Analysis ； River Scour ； Infiltration ； Landslide ； Extreme Rainfall

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