The Mathematical Model on Lower Bound Values of the Shear Strength of Soils from Slope Failures

The main factor causing slope failures in tropical residual soils is the reduction of shear strength parameters of the soil slope as the soil becomes saturated during the prolonged rainy seasons. A total of 227 effective parameters were obtained from consolidated drained (CD) shear box tests under submerged condition shear strength. Disturbed soil samples were taken from slope failures in Penang Island and Baling. Field bulk density tests were carried out at all the locations where the soil samples were taken. The objective of the research is to determine the lower bound values of the effective shear strength parameters of soils taken from slope failures. The effective shear strength parameters were randomised into 2 subset data using Matlab software, the training and observed validation data. Performance indicator tests using Matlab software were conducted on the 2-subset data using normal, weibull, gamma and beta distributions to determine the best fit distribution. Normal distribution was found to be the best fit distribution for both subset data. The lower bound values of the effective shear strength parameters of the slope failures were determined from the normal distribution curves. It was found that the lower bound value for the effective cohesion c' = 0.86 kN/m(2) while the lower bound value for effective friction angle phi' = 16.21(0).