Civil Engineering Association

Seismic Design of Geosynthetic-Reinforced Soil Bridge Abutments with Modular Block Facing

A geosynthetic-reinforced soil (GRS) mass is formed by placing closely-spaced layers of polymeric geosynthetic reinforcement in a soil mass during soil placement. The reinforcement in a GRS mass serves primarily to improve engineering properties of soil. The concept of GRS has been used successfully over the past few decades in many transportation facilities, including retaining walls, embankments, roadways, and steepened slopes. Tests and in-service installations have shown that GRS systems, particularly GRS walls with modular-block facing, are structurally sound, easy and fast to construct, and low cost compared to other designs. Interest in using GRS design for bridge abutments and approaches, in particular, has grown but a lack of rational and reliable design and construction guidelines for such structures has impeded more widespread adoption. NCHRP Report 556, "Design and Construction Guidelines for Geosynthetic-Reinforced Soil Bridge Abutments with a Flexible Facing," was produced as a first step effort toward developing such guidelines. The research described in that report addressed static loading conditions only. NCHRP Project 12-59(01), the subject of this report, was undertaken to develop design and construction guidelines for applications in seismically active regions. The research described here focused on single-span, simply-supported bridges subjected to seismic forces. Current seismic design methods for reinforced soil retaining walls – both pseudo-static methods and displacement methods – have been developed for situations where the self-weight of the soil is the predominant load. For a GRS bridge abutment, however, the abutment’s top surface is intended to provide a foundation of the bridge superstructure. The GRS abutment will be expected not only to maintain its stability as a soil mass but also to bear the additional large sustained and seismic loads associated with the bridge superstructure. The objective of this research was to extend the earlier research reported in NCHRP Report 556 to consider seismic loading conditions and thereby provide a more comprehensive basis for developing rational guidelines for design and construction of GRS abutments and approaches with modular-block facing.