A two-rigid block model for sliding gravity retaining walls

• We present a new two-rigid block model for sliding gravity retaining walls.
• Conceptual limitations of Newmark's sliding block method for retaining walls are discussed.
• We show that both the soil thrust and the absolute acceleration of the wall vary during sliding.
• Our model describes fully the kinematics of the soil wedge–wall system under dynamic loading.
• The method permits a simple computation of wall displacements during earthquakes.

This paper presents a new two-rigid block model for sliding gravity retaining walls. Some conceptual limitations of a direct application of Newmark's sliding block method to the case of retaining walls are discussed with reference to a simple scheme of two interacting rigid blocks on an inclined plane. In particular, it is shown that both the internal force between the blocks and their absolute acceleration are not constant during sliding, and must be computed by direct consideration of the dynamic equilibrium and the kinematic constraints for the whole system. The same concepts are extended to the analysis of the active soil wedge–wall system, leading to an extremely simple procedure for computing the relative displacements of the wall when subjected to base accelerations exceeding the critical value. A comparison with the results of numerical analyses demonstrates that the proposed method is capable of describing fully the kinematics of the soil wedge–wall system under dynamic loading. On the contrary, direct application of Newmark's method may lead to inaccurate predictions of the final displacements, in excess or in defect depending on a coefficient which emerges from direct consideration of the dynamic equilibrium of the whole system. This coefficient can be viewed as a corrective factor for the horizontal relative acceleration of the wall, related to the mechanical and geometrical properties of the soil–wall system.