Monitored Displacements of a Unique Geosynthetic-Reinforced Walls Supporting Bridge and Approaching Roadway Structures

A Geosynthetic-reinforced soil (GRS) system was used to support both the abutment shallow footings of the Founders/Meadows two-span bridge and the approaching roadway structures. This unique system has the potential to alleviate the “bump bridge” problem, and allowed for a small work area and construction in stages. This paper provides an assessment of the Founders/Meadows performance and behavior under service loads from displacement data collected through surveying, inclinometer, road profiler, and strain gages. Three sections of the GRS system were instrumented to measure movements of the front GRS wall, settlement of the bridge footing, and differential settlements between the bridge abutment and the approaching roadway. Data was collected during construction of the GRS walls, placement of the bridge superstructure and during 18 months after opening the bridge to traffic. The structure showed excellent performance: monitored overall displacements were smaller than those expected in the design and allowed by performance requirements, there were no signs for development of the bridge bump problem or of any structural damage, and postconstruction movements became negligible a 1 year after opening the bridge to traffic. The influence of compaction, construction season and construction sequence on the structure movements are discussed in this paper. Finally, design implications of the measured results and basis for estimating the movements of structures similar to the Founders/Meadows structure are presented. INTRODUCTION The Colorado Department of Transportation (CDOT) successfully completed in July of 1999 the construction of the new Founders/Meadows Bridge near Denver, Colorado. In this unique field application, geosynthetic-reinforced soil (GRS) walls support both the footing of the twospan bridge and the approaching roadway structure. Fig. 1 shows a picture of one of the segmental retaining walls. The “front GRS wall”, which supports the bridge superstructure, extends around a 90-degree curve into a “lower GRS wall” supporting the “wing wall” and a second tier, “upper GRS wall”. Fig. 2 shows a typical monitored cross-section (Sections 200, 400, and 800) along the front GRS wall and abutment GRS wall. The figure illustrates that the bridge superstructure load (e.g., from girders, bridge deck) is transmitted through abutment wall to a shallow strip footing placed directly on the top of a geogrid-reinforced segmental retaining wall. The centerline of the bridge abutment wall and front edge of the bridge footing are located 3.1 m and 1.35 m, respectively, from the back face of the front GRS wall (Fig. 2). A short reinforced concrete abutment wall and two wing walls, resting on the bridge spread footing, confine the reinforced backfill soil behind the bridge abutment and support the bridge approach slab (see Figures 1 and 2). 1 Geotechnical Research Engineer, Colorado Department of Transportation, Denver, CO 80222 2 Assistant Professor, University of Colorado at Boulder, Campus Box 428, Boulder, CO 80309 3 Bridge Design Engineer, Colorado Department of Transportation, Denver, CO 80222 Abu-Hejleh, N. , Zornberg, J.G. , and Wang, T. (2001). “Monitored Displacements of a Unique Geosynthetic-Reinforced Walls Supporting Bridge and Approaching Roadway Structures. ” Proceedings of the 80th Annual Meeting, Transportation Research Board, Washington, D.C., January 7-11 (CD-ROM).