考量降雨入滲於河岸穩定分析模式之建立與應用

Abstract

本研究結合Green-Ampt入滲理論與Boussinesq地下水流方程式，計算因降雨入滲及河道水位影響之地下水面線，再以靜水壓假設求得土體內孔隙壓力分佈，最後以極限平衡法(limit equilibrium analysis)計算安全係數，藉以評估河岸之穩定性。研究中分別探討土壤滲透性、降雨強度與河道水位變化對河岸穩定之影響，並以濁水溪為應用案例，模擬分析其在柯羅莎颱風(2007)期間，河岸穩定隨時間變化之情形。模擬結果顯示，高滲透性土壤伴隨降雨強度越大或低滲透性土壤，在河道水位下降速度越快之條件下河岸越容易發生破壞。

In this study, a model combining Green-Ampt infiltration theory with Boussinesq equation has been developed to simulate groundwater table variation under the condition of interactions between rainfall infiltration and variation of river stage. Depending on the calculated groundwater table, pore-water pressure can be estimated with the assumption of hydrostatic pressure distribution. Subsequently, riverbank stability can be assessed by factor of safety based on limit equilibrium method. The developed model was used to examine the effects of key parameters including various values of soil permeability, rainfall intensity and changing speed of river stage on the riverbank stability. In addition, Cho-Shui Creek during Typhoon Krosa occurred in 2007 was chosen as an application case. According to the simulated results, the riverbank failure is easily to be triggered with high permeability soil under heavy rainfall intensity or with low permeability soil under rapid drawdown.