Passive Force-Deflection Curves for Skewed Abutments

The passive force-deflection relationship for abutment walls is important for bridges subjected to thermal expansion and seismic forces, but no test results have been available for skewed abutments. To determine the influence of skew angle on the development of passive force, laboratory tests were performed on a wall with skew angles of 0, 15, 30, and 45°. The wall was 1.26 m wide and 0.61 m high, and the backfill consisted of dense compacted sand. As the skew angle increased, the passive force decreased substantially, with a reduction of 50% at a skew of 30°. An adjustment factor was developed to account for the reduced capacity as a function of skew angle. The shape of the passive force-deflection curve leading to the peak force transitioned from a hyperbolic shape to a more bilinear shape as the skew angle increased. However, the horizontal displacement necessary to develop the peak passive force was still between 2 and 4% of the wall height. In all cases, the passive force decreased after the peak value, which would be expected for dense sand; however, at higher skew angles, the drop in resistance was more abrupt. The residual passive force was typically 40% lower than the peak force. For nearly all skew angles, the transverse shear resistance exceeded the applied shear force on the wall so that transverse movement was minimal. Computer models using the plane strain friction angle were able to match the measured force for the no skew case as well as for skewed cases when the proposed adjustment factor was used.