Prediction on landslides induced by heavy rainfalls and typhoons for Shih-Men watershed in Taiwan using SHALSTAB program

Abstract

In recent years, extreme weather made particular typhoons and heavy rainfalls under global warming effect, which caused enormous landslides and deadly debris flows in Shih-Men Watershed. Those disasters brought a great deal of sediment to a river course and silt up the some Sabo dams. Over flowing sediment would block up the route via downtown. Due to fine content of sediment, nephelometric turbidity unit (NTU) would grow up so highly that potable water could not be supplied to drink. Since the Chi-Chi earthquake, the main geological structure of Shih-Men Watershed became fragile and porous. After that event, the water table was apt to get rising highly when heavy rainfall infiltrated into slopes. In the meanwhile, the effective stresses of soil particles would be reduce and approach to be zero, and it would cause several shallow landslides over this region. In view of that, this study would apply hydrology model incorporated with infinite slope theory to analyze large-scale slope stability using SHALSTAB program. Prior to analysis, some soil parameters need to be determined using iterative procedure in rational range. Besides, soil depth was sensitive to the results in connection with terrain curvature and slope angle. It should be obtained from field investigation using hand auger and spade or based on empirical equations. Hydraulic conductivity and infiltration rate should be also considered within. Through the above procedure, it could help us realizing the sediment sources, distinguishing hazard-induced factors, and spatial distribution of slope failure potential. Moreover, engineers might find out how to mitigate the nature hazards and retrofit the hydraulic structure during the typhoon seasons