Internal Reinforcement of Backfill behind Integral Bridge Abutments to Mitigate Approach Slab Distresses Final Report

Integral abutment bridges have become popular worldwide by eliminating movable shoes which are expensive to purchase, install, and maintain in conventional bridges. However, the behavior of bridge abutments subjected to air temperature changes for integral bridges is different from that of conventional bridges. Expansion and contraction of bridge girders due to temperature variations are accommodated by joints between bridge girders and abutments for conventional bridges. Expansion of bridge girders at high temperatures moves the integral bridge abutment toward its backfill, causing high lateral earth pressures behind the abutment, while contraction of bridge girders at low temperatures moves the integral bridge abutment away from its backfill, causing backfill surface settlements. The backfill behind the abutment cannot maintain its stability after the integral abutment moves away so that the backfill material within the upper portion slumps and moves downward and toward the abutment. Cyclic movements of the integral abutment due to temperature changes disturb the backfill and further reduce its self-stability when the integral abutment moves away from the backfill in the next cycle. In addition, soil erosion and compression of backfill and foundation soil can aggravate the backfill surface settlements for both integral bridges and conventional bridges. An approach slab is commonly used to provide a smooth transition between the backfill and the bridge abutment. The approach slab may lose some support from the backfill as the backfill surface settles. Consequently, more traffic loads on the approach slab are transferred to the end of the approach slab near the adjacent pavement, resulting in a differential settlement at the joint between the approach slab and the adjacent pavement. A sleeper slab has been proposed for placement underneath the joint between the approach slab and the adjacent pavement, thus minimizing this differential settlement. However, an excessive gradient may still develop for the approach slab due to the differential settlement between two ends of the approach slab. This situation may be aggravated by the concave deformation of the approach slab due to traffic loading. Therefore, backfill surface settlements and traffic loading are the two main causes for the distresses of the approach slab. These distresses may be mitigated by the use of geosynthetic reinforcement because it is expected to increase the stability of the backfill and reduce the settlement of the sleeper slab. However, the benefits of the geosynthetic reinforcement for this application are not well investigated and confirmed. The full report is available online from the Kansas Department of Transportation at http://dmsweb.ksdot.org/AppNetProd/docpop/docpop.aspx?clienttype=html&docid=11494558