Abstract:
Rainfall induced landslides have become a cause for loss of life; they also obstruct traffic flow, which ultimately limits the road serviceability level and has an effect on the economy. This thesis includes detailed site and laboratory investigations for the selected failed cut slope sections on the Rebugebeya-Tamaweite road in Ganke Kebele to understand the rainfall induced slope failure using PLAXIS 2D. Along the selected failed slope locations, representative disturbed and undisturbed soil samples were taken from four selected test pits based on the slope angle and the material forming the slope through field observations. Laboratory tests were conducted to determine the index and engineering properties of the soil in the selected slope sections. Following the characterization and classification of the failed slope by detailed investigation and soil laboratory testing, the input parameters were determined for the analysis of the failed slope by PLAXIS 2D. The slope forming soil materials along the failed slope are classified as MH (silt with high plasticity) as per the USCS. It was observed that the road is highly affected by slope instability problems with a circular/rotational mode of failure. The factor of safety (FoS) for the identified slope failure was determined using the Finite Element software, PLAXIS 2D, modeled using Mohr-Coulomb failure criteria based on the strength reduction approach. The mesh and parameter sensitivities were conducted in order to understand the sensitive parameters affecting the slope stability. The result of the stability analysis of the slope for the initial conditions gives a FoS of 1.313. However, under rainfall loading conditions, the FoS reduced to 1.191. This shows that slope instability increases when rainfall infiltrates the slope, which is in line with the failure of the slope in the study area. Further, to reduce the instability of the slope in the study area, slope geometry modification, bamboo reinforcement, vegetation practice, retaining wall, and proper drainage have been recommended as remedial solutions to prevent failure of the existing slopes near the failed slopes.
Keywords: rainfall induced landslide, failed slope, PLAXIS 2D, slope stability, factor of safety, strength reduction approach, Sensitivity