Settlement of roadway pavement surfaces in the vicinity of highway bridge abutments often leads to abrupt grade differences at the abutments. These grade differences subject traveling vehicles to a "bump" which leads to driver discomfort and potentially unsafe driving conditions, causes vehicle wear and damages sensitive cargo, subjects the bridge structure to repeated impact loads, and requires costly and repeated maintenance work that usually impedes the flow of traffic. To eliminate the bump at the end of the bridge, WSDOT and other agencies often install an approach slab with one end supported on the bridge and the other on the soil at some distance from the end of the bridge. Approach slabs are often, but not always, effective in improving vehicle ride characteristics at bridge approaches subject to settlement.
A review of previous research indicated numerous potential causes of bridge approach distress, indicating that bridge approach settlement is largely a site-specific problem. A field investigation of nine distressed bridge approaches confirmed this observation. Recommendations for bridge approach design are presented.
The objectives of the research described in this report were to evaluate the effectiveness of bridge approach slabs, to identify site conditions for which approach slabs should and should not be used, and to present recommendations for the use of approach slabs.