Inclined Plane Studies of the Newmark Sliding Block Procedure

This study considers the shaking-induced displacement and dynamic response of a rigid block and deformable columns of soil on an inclined plane. This work demonstrates that because of the coupled dynamic response and sliding of earth masses, actual deformations in these systems can vary significantly from those computed in a rigid block analysis proposed by Newmark in 1965. The rigid sliding block procedure was found to be generally unconservative when the predominant frequency of the input motion is somewhat less or about equal to the natural frequency of the sliding mass (0.2<= tuning ratio<= 1.3). Conversely, the sliding block procedure is generally conservative when the predominant frequency of the input motion exceeds the natural frequency of the mass (tuning ratio>1.3). While it was found that sliding surfaces might limit transmission of energy, high inertial forces can, nonetheless, develop in a sliding mass because of its stick-slip dynamic response. This was found to occur in many of the soil column tests when accelerations in excess of the yield acceleration were measured at the base of the sliding mass. Based on the results of this study, recommendations are made to aid practitioners in selecting an appropriate seismic slope deformation procedure.