Improvement of Approach Smoothness on Integral Abutment Bridges

Approach slabs span the embankment directly behind the bridge abutment backwall to provide a smooth transition between the bridge and pavement. Ride roughness at the approach slab has been a persistent problem, requiring significant maintenance for many highway agencies. The problem is so prevalent it is commonly referred to as “the bump at the end of a bridge”. Extensive research has identified time-dependent consolidation of the embankment and foundation soil along with inadequate compaction as primary causes for approach roughness. The natural movement of an integral bridge abutment, which the South Dakota Department of Transportation (SDDOT) uses extensively, can further compress the embankment material. Additional causes include design details, drainage, soil erosion, embankment material quality, and construction. The complexity of the problem is evidence that bridge approach roughness may be due to various conditions happening simultaneously, with a solution achievable by design engineers, geotechnical engineers, field engineers, and contractors working together. Over the past 30 years SDDOT has used various methods—including various embankment geometries, various backfill materials, addition and removal of geotextile fabric, different drainage configurations, and different joint details at sleeper slabs—to build and maintain smooth bridge approaches. However, the bump is still a major complaint for road users, still expensive to repair, and still a potential safety hazard. The objectives of this project are to: (1) Analyze and compare the performance of SDDOT’s current and past design, construction, and maintenance practices to resolve integral abutment bridge approach slab roughness; (2) Investigate the design, construction, and maintenance practices of other United States and European highway agencies to reduce approach slab roughness on integral abutment bridges; (3) Recommend feasible new designs and changes to SDDOT’s current design, construction, and maintenance practices to reduce approach slab roughness on integral abutment bridges; and (4) Recommend a strategy for future monitoring and evaluation of roughness at integral abutment bridge approaches.