以有限元素法探討暴雨時邊坡之穩定分析

Application of Finite Element Procedures on the Slope Stability Analysis in Stormy Condition

范嘉程(Chia-Cheng Fan) ； 馮道偉(Dao-Wei Feng)

《地工技術》 95期 (2003/03) Pp. 61-74

https://doi.org/10.30140/SG.200303.0002

摘要

傳統之邊坡穩定分析皆以極限平衡法求取邊坡抵抗滑動之安全係數，以為判定邊坡是否安全穩定之依據，然極限平衡法對邊坡因外在環境變化可能發展之位移與地層應力變化行為則無法掌握。本文就有限元素法應用於降雨情況下邊坡穩定行為與分析模式進行探討，以強度折減法（Strength Reduction Method）進行安全係數之求取，於不同邊坡坡角情況，有限元素法與極限平衡法分析之邊坡穩定安全係數甚為接近，另於一般合理之土壤凝聚力與摩擦角參數範圍，有限元素法分析之邊坡安全係數高於極限平衡法結果約10%～15%。本文將暴雨情況邊坡穩定分析分為三種地下水位深度加以探討，由於土層「浸潤帶」之形成，土壤含水飽和導致凝聚力損失，如損失程度高時，潛在邊坡滑動範圍有往淺層發展之趨勢，並產生一邊坡穩定安全係數之轉折臨界點。本文亦舉一實際邊坡地層位移案例進行有限元素分析，探討降雨等環境變化情況下，邊坡地層位移發展與時間之關係，分析成果並與地層位移觀測數據進行比較，初期此二者吻合程度尚可，長期預測結果則與監測值差異較大，有限元素法分析結果未能獲得確實之滑動面及現地地層之變異性為差異之主要可能原因。

關鍵字

邊坡穩定 ； 有限元素法 ； 安全係數 ； 極限平衡法 ； 暴雨情況分析

並列摘要

Slope stability is traditionally analyzed with limit equilibrium method. The factor of safety is used as a criterion for assessing safety of slopes. However, stress and deformation in the soil mass of slopes would not be possibly obtained with limit equilibrium analysis. Methodology along with the finite element procedure for analyzing slope stability problems in stormy condition is studied in this paper. Strength reduction method is used for determining factor of safety of slopes in the finite element procedure. Factors of safety analyzed with finite element method are close to those analyzed with limit equilibrium method for various slope angles. Also, factors of safety analyzed with finite element method are 10%~15% greater than those analyzed with limit equilibrium method for reasonable cohesion and friction angle conditions. A wetting zone in the slope is developed in the stormy condition. Softening of soils has a significant influence on loss of cohesion of soils. Procedures of slope stability analysis in stormy condition for three ground water levels are proposed in this paper. Failure of slopes in stormy condition may develop in the sallow depth and result in a sudden drop in factor of safety if loss of cohesion of the soil is significant. Finally, a case history of a landslip induced by chances in the environmental conditions is analyzed with the finite element procedure. The computed results of slope deformation with time effect are compared with the measured results. The computed results compare well with measured results for short period of time. However, discrepancy between measured and computed results becomes significant for long period of time. Failure in predicting precise slip surfaces and inhomogeneous geologic condition may be the primary reasons blamed for it.

並列關鍵字

slope stability ； finite element procedure ； factor of safety ； limit equilibrium method ； analysis in stormy condition