Case Study of The Slope Stability Under Rapid Drawdown of Nam-Pong bank at BaanTahGae, Mueng District, Khon Kaen Province

Abstract

This research studied the slope stability of the Nam-pong riverbank at Ban Tha Kae, Muang District, Khon Kaen Province, due to the rapid drawdown. The subsurface exploration was bored from the soil surface until a depth of 15 meters. The soil profile was divided into three layers; Lean Clay (CL), Clayey Sand (SC), and Silty Sand (SM). The consolidated undrained method determined an undisturbed clay sample's friction angle, cohesion, permeability coefficient, elastic modulus, and poison ratio from the triaxial test. The values ​​obtained from the test were analyzed by finite element method using Plaxis 2D program. In the analysis, the groundwater level was fixed, and the water level in the river was reduced by 25% from the groundwater level water level reach 75% of the groundwater level. The clay layer above groundwater was in an unsaturated condition. An unsaturated clay was analyzed as transition regime (the matric suction equal to 200 kPa) and residual regime (the matric suction equal to 300 kPa). Moreover, the specific date of reduction water level in the river was 60 days. Analysis shows that when water levels drop sharply at 75%, the safety ratio is the lowest. Soil movement was increase.