This report addresses the causes and long-term solutions to the bumps that commonly develop at bridge/approach slab and/or approach slab/pavement interfaces. Moment capacities and applied moments of approach slabs for seven different State Departments of Transportation (DOTs) were determined using MathCAD, and compared. The value of internal moment capacity of the Ohio Department of Transportation (ODOT) approach slab was found to be greater than the value of applied moment capacity, indicating that a new approach slab would not fail even if soil support were lost. A 3-D finite element analysis (FEA) was performed using ALGOR to find the stresses and deflections for a new approach slab of 25 ft slab length under extreme HL-93 truck static loading, using ODOT design recommendations. Maximum deflection was predicted to be 0.19 in with soil support and 1.34 in without soil support. Repetitive loading may cause long-term damage to approach slabs when soil support is lost.
Laboratory tests for Sieve analysis, Liquid limit and Plastic limit were also performed on soil samples collected from one bridge site without a significant bump and four bridge sites with significant bumps around the greater Youngstown, Ohio, area. The results show that settlement of approach slabs was greater, and bumps more severe, for soils with larger percentages of silt and clay. This study indicates that efforts to reduce bumps at the pavement-bridge interface should focus on geotechnical factors and maintaining proper soil support under approach slabs.