Threshold accelerations for rotation or sliding of bridge abutments

An analytic procedure for predicting threshold accelerations for movement of gravity-wall bridge abutments due to earthquake loading is first described in this paper. This method combines the well-known previous work related to the sliding mode of intermittent failure with a new theory on seismic reduction of bearing capacity leading to periodic vertical movement and consequent rotation of bridge abutments. Since the critical or threshold accelerations at which horizontal and vertical equilibrium are lost are different, mixed modes of seismic movement are also possible. The major emphasis of this paper is to then present laboratory observations on small-scale, retaining-wall bridge abutments subjected to seismic excitation to verify the critical acceleration levels predicted by this analytic analysis for the various modes of wall movement. Three different test series were performed on a shaking table on walls with different interface conditions between the wall and the foundation, backfill, and bridge deck. The abutment models were general in the sense that, while a particular mode of progressive failure could be anticipated, it was not forced.