Abstract:The results of many large scale triaxial tests indicate that the Mohr failure envelopes for rockfill exhibit significant nonlinearity particularly in low and medium stresses,which means that,in low confining pressure,the angle of internal friction is relatively high,but in high confining pressure,it is relatively low. The strength of rockfill exhibits nonlinearity and the curved failure envelope could be described by logarithmic relationship. However,conventional strength is linear with an average friction angle. A computer program is developed for the stability analysis of circular arc slope with strength nonlinearity taken in account. The comparison of safety factors of 7 high rockfill dams with nonlinear strength and linear strength indicates that safety factor of non-linear analysis is bigger than that of linear analysis. The value of nonlinear safety factor is increased with increment of 20%. The slip surface of linear analysis is shallow,but that of nonlinear analysis is deep. The allowable safety factor based on linear rule should be properly increased with increment of 8%,according to the study result of this paper.