Mitigating the bridge end bump problem: A case study of a new approach slab system with geosynthetic reinforced soil foundation

The Louisiana Department of Transportation and Development (LA DOTD) has initiated a major effort to minimize the bridge end bump problem associated with the differential settlement. As a result, a new design for the approach slab was proposed, which requires increasing the slab flexural rigidity (EI), and using reinforced soil foundation (RSF) to support the slab and traffic loads at the roadway pavement/approach slab joint (R/S joint). The Bayou Courtableau Bridge was selected as a demonstration project to monitor, evaluate, validate, and verify the new bridge approach slab design method. The west approach slab was designed using the proposed design method with slab thickness of 406 mm, while the east approach slab was designed using the traditional design method with slab thickness of 305 mm. The pavement end side of the west approach slab was supported by a 1.2-m wide strip footing with the soil underneath it was reinforced by six layers of geogrid placed at a vertical spacing of 305 mm. Two static load tests were conducted on both the west and east approach slabs at two different times after construction. The test results indicated that the east approach slab (with traditional design) kept losing its contacts from the underneath embankment soil starting from the bridge side towards the pavement side after about a year and half. Meanwhile, the west approach slab (with new design) lost most of its supports from the underneath embankment soil, but with less observed faulting at the R/S joint and improved rideability [i.e., lower International Roughness Index (IRI) values]. The field monitoring program at Bayou Courtableau Bridge demonstrated much better performance of the new approach slab design system (west approach slab) compared to traditional design (east approach slab).