Geosynthetic-reinforced soil (GRS) systems, in which the soil mass is reinforced in layers with a polymeric geosynthetic (e.g., strips, grids, or sheets) and, in most typically used systems, the layered reinforcement is fixed to facing elements that constitute the outer wall, have over the past several decades been used to construct retaining walls, embankments, and slopes. Experience has demonstrated that GRS systems, particularly those with modular-block facing, offer a low-cost, easily constructed, and structurally reliable design in many applications. An application that has gained increasing interest in recent years is bridge abutments and approaches, where GRS system advantages can include faster, less expensive, andt echnically less demanding construction. While full-scale tests and production bridges have shown excellent results, a lack of rational, reliable, and widely accepted design and construction guidelines for GRS bridge abutments has impeded adoption of the technology.
NCHRP Report 556: Design and Construction Guidelines for Geosynthetic-Reinforced Soil Bridge Abutments with a Flexible Facing, presented a first step toward developing such guidelines, addressing static loading conditions. To advance this new technology, especially in seismically active regions, it is essential to develop a rational design method and associated construction guidelines for GRS bridge abutments that address seismic loads and the dynamic interaction of GRS abutments with the bridge superstructure. Additionally, the data developed in this study must be adequate to support adaptation of the guidelines to enable inclusion of GRS abutments with modular-block facing in the American Association of State Highway and Transportation Officials Load and Resistance Factor Design (AASHTO LRFD) specifications.
This research was intended to be a further step toward developing effective guidelines. The research focused on single-span, simply supported bridges and built on current seismic design methods for GRS structures with modular-block walls. These methods--which can be divided into two categories, pseudo-static methods and displacement methods--have been developed for situations where the self-weight of the soil is the predominant load. The research included a shake-table test of a model GRS abutment parametric finite-element analyses to develop design and construction guidelines. Because the seismic behavior of GRS walls generally is not well understood, published data on seismic behavior of GRS walls without foundation loads placed at the wall top were used to provide additional validation of numerical models developed in this project. The objective of this research was to develop rational, reliable guidelines for seismic design and construction of GRS abutments and approaches with modular-block facing, applicable for single-span simply-supported bridges and compatible with AASHTO LRFD principles. Additional testing and analysis may be required to support widespread adoption of the proposed design methods and guidelines.
