Comparison on factor of safety using different method of analysis for slope stability

Currently, the construction of slope is increasing; thus, the risk of slope to fail also increases. The series of landslide that happened to man-made slope has been recorded since the early of 1993 until now. Many efforts such as treating the critical slope, redesigning the failed slope, and analysing the stability of the slope have been done. However, landslide is still happening in Malaysia. The factor of safety (FOS) from the stability analysis that is commonly used might not be adequate to determine the safety of the slope in Malaysia. Therefore, in this study, the optimum factor of safety was obtained by using three methods of slice; Bishop’s Simplified method, Spencer method, and Morgenstern-Price method which have been used in many projects. A study place was selected in Ladang Balau, Semenyih, in Selangor and from the CIU test, the important soil parameter for slope was extracted to analyse the slope stability using SLOPE/W and manual calculation. The lambda for Spencer method and Morgenstern-Price method was generated for further discussion on the relationship between lambda and factor of safety. The data generated from both calculation methods, from manual and software, were discussed and the next ideal method to achieve the optimum factor of safety was determined. The factor of safety for every method is basically influenced by the interslice shear force presence but not Bishop’s Simplified method as the moment equilibrium is insensitive towards interslice force function. For lambda, the factor that influences the value is the function used which included constant and half-sine function; however, for Bishop’s Simplified method, the lambda is equal to zero as the method ignores the interslice shear force. Thus, the Morgenstern-Price method was chosen to be the best method to generate a good factor of safet