Abstract
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.
Highlights
In recent literature several cases are reported of damage to gravity and cantilevered retaining walls due to severe seismic shaking [9,18]
By considering the dynamic equilibrium of the blocks, it is shown that the assumption that the absolute acceleration during sliding is constant and equal to its critical value is not correct, and this affects the internal force between the two blocks
Some conceptual limitations of direct application of Newmark's sliding block method to the case of retaining walls have been discussed with reference to a simple scheme of two rigid frictional blocks resting on an inclined plane and interacting with one another
Summary
In recent literature several cases are reported of damage to gravity and cantilevered retaining walls due to severe seismic shaking [9,18]. This work examines the dynamic behaviour of gravity retaining walls with dry cohesionless backfill, accumulating relative displacements solely by sliding on their base. Newmark's approach cannot be used directly to evaluate the permanent displacements of the soil–wall system unless a corrective factor for the relative accelerations is introduced in the computation. This factor is independent of the seismic excitation and, for realistic geometries of the wall and mechanical properties, takes values between about 0.7 and 1.1. The work does not examine the effects of shear strength reductions due to strain softening of dense sand on shearing
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