Mitigating the bridge end bump problem: A case study of a new approach slab system with geosynthetic reinforced soil foundation Qiming Chen, Murad Abu-Farsakh * Louisiana Transportation Research Center, Louisiana State University, 4101 Gourrier Avenue, Baton Rouge, LA 70808, USA article info Article history: Received 30 November 2014 Received in revised form 29 June 2015 Accepted 1 July 2015 Available online xxx Keywords: Geosynthetics Reinforced soil foundation Bridge end bump Differential settlement International Roughness Index abstract 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 con- struction. 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 pro- gram 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). © 2015 Elsevier Ltd. All rights reserved. 1. Introduction 1.1. Background and problem Bridge approaches are normally constructed with reinforced concrete slabs that connect the bridge deck to the adjacent paved roadway. The slab is usually supported on one side by the bridge abutment and on the other side by the embankment. Their function is to provide a smooth and safe transition of vehicles from roadway pavements to bridge structures and vice versa. However, com- plaints about the ride quality of bridge approach slabs still need to be resolved. The complaints usually involve a “bump” that motor- ists feel when they approach or leave bridges (Cai et al., 2005). This problem is commonly referred to as the bump at the end of the bridge mainly resulted from the differential settlement of the concrete approach slab relative to the bridge deck (Long et al., 1998; Dupont and Allen, 2002; Lenke, 2006). It results in uncomfortable rides, dangerous driving conditions, and frequent repairs. Field observations indicated that either faulting at the roadway pave- ment/approach slab joint (R/S joint) or a sudden change in the slope grade at the approach slab/bridge deck joint (S/D joint) (as shown in Fig. 1) causes this “bump” (Cai et al., 2005). The settlement of the natural soil under the embankment, the compression of the embankment fill, and the stiffness of the con- crete approach slabs contribute to the development of such a bump problem. Concrete approach slabs can lose their contacts and supports from soil due to the settlement of embankment soil on which the slabs are built (Fig. 1). When settlement occurs, the slab will bend in a concave manner that causes a sudden change in slope grade of the slab. Traffic loads will be redistributed to the ends of the slab. Due to the redistribution of loading, vertical faulting at the R/S joint and a sudden change in the slope of grade at the S/D joint * Corresponding author. Tel.: þ12257679147; fax: þ12257679108. E-mail addresses: qchen1@lsu.edu (Q. Chen), cefars@lsu.edu (M. Abu-Farsakh). Contents lists available at ScienceDirect Geotextiles and Geomembranes journal homepage: www.elsevier.com/locate/geotexmem http://dx.doi.org/10.1016/j.geotexmem.2015.07.001 0266-1144/© 2015 Elsevier Ltd. All rights reserved. Geotextiles and Geomembranes 44 (2016) 39e50