Performance Evaluation of Recent Improvements of Bridge Abutments and Approach Backfill TR-736

A bump at the approach of a bridge is an undesirable characteristic that causes bad ride quality and high maintenance costs. To mitigate bump formation, the Iowa Department of Transportation (DOT) revised its standards according to a former study completed in 2005. This current study evaluated the effectiveness of these revisions by investigating eight bridges in Iowa constructed after 2005, two of which were stub bridges and six of which were integral bridges. One stub bridge and three integral bridges were subjected to a detailed investigation including visual and borescope inspections, coring, GPR assessment, and elevation surveying. The other four bridges were subjected to visual and borescope inspections only. The data showed that components of the abutments were generally in good condition and the joints in the approach slabs were in the poorest condition; many joints were in need of maintenance. GPR assessment detected voids under the approach slabs leading to the integral bridges, and showed that voids were more extensive at the shoulders than at the centerline of the pavement. The stub bridge investigated with GPR had relatively limited voids. Borescope inspection of the access ports confirmed the presence of the voids in the integral bridges. The relatively large extent of voiding under the integral bridges is attributed to cyclic compression of the backfill due to abutment movement and failure of the joint between the barrier and the approach slab due to large differential movements between the two components, which would permit bridge runoff to enter and erode the backfill. Despite the presence of the voids and failed joints, the bridge approaches performed well. Several recommendation were made to improve inspection practices and performance of approach slabs, including the use of GPR assessment to investigate voiding beneath the approach slabs, a new design detail for stub abutments, and sealing or eliminating the gap between the barriers and approach slabs