Abstract: In this study, two seismic failure mechanisms of L-shape retaining walls (i.e., long heel failure and short heel failure) were presented, and the failure mechanisms were influenced by geometric parameters and physico-mechanical parameters. The seismic stability of L-shape retaining walls and the determination method of sliding surface were investigated in this paper, and the critical condition of two failure mechanisms was defined. Based on the kinematical approach of upper bound theorem, the critical state equation of L-shape retaining wall was established, taking account of the occurrence of the second and third sliding surfaces condition. Then the multivariate function to calculate seismic acceleration coefficient was derived and optimized by extremum principle, so as to obtain the critical yield acceleration factor and the inclination of sliding surface. A case study and comparative analysis showed that the critical yield acceleration factor was smaller than that derived from the M-O method. When the heel of L-shape retaining wall was long enough, the angle between two sliding surfaces equaled to 90°-φ. It means that the result of using this method is the same as the result of slip-line field theory. When the heel of L-shape retaining wall was short, the angle between sliding surfaces was approximately 90°-φ.

Key words: L-shape retaining wall, critical yield acceleration factor, the second and third sliding surface, upper bound theorem