Cyclic loading of loose backfill placed adjacent to integral bridge abutments

Abutments for integral (or jointless) bridge decks experience cyclic rotations/translations due to temperature induced expansion and contraction of the decks. These movements generate cyclic displacements within the backfill placed adjacent to the abutment. To assist understanding of the consequences of such displacements, an experiment is described here in which the movements within a laboratory scale model of an abutment and loose backfill are measured. The distributions of displacements and strains within the backfill are recorded using an optical measurement technique. It is found that the cyclic rotations of an abutment in loose sand results in significant volumetric contraction of the sand mass in the area where an active wedge is created. The degree of contraction is related to the abutment rotation and the number of such rotations. Many of the observed features, including the trend for large increases in lateral stresses on the abutments, may be attributed to the tendency of loose backfill to experience strain hardening due to repeated cyclic straining.