Parameters for curvilineared residual strength envelope

The residual friction coefficient was found to decrease with the increasing effective normal stress at the lower half of the effective normal stress, while it was constant at the higher half. Based on this finding, the curvilinered residual strength envelope was divided into two parts: the lower half and the higher half of the effective normal stress. The residual strength parameters were determined at each part, c_r was not zero at the lower half of the effective normal stress while it was zero at the higher half, and ϕ _r was greater at the lower half than at the higher half. The proposed method might be useful and rational to determine the residual strength parameters from the curvilineared residual strength envelope depending on the magnitude of the effective normal stress.