Investigation of Required Tensile Strength Predicted by Current Reinforced Soil Design Methodologies

Abstract

Geosynthetic Reinforced Soil (GRS) is a promising technology that can be implemented in walls, culverts, rock fall barriers, and bridge abutments. Its use in walls and abutments is similar to Mechanically Stabilized Earth Walls (MSEW) reinforced with geosynthetics. Both GRS and MSEW are reinforced soil technologies that use reinforcement to provide tensile capacity within soil masses. However, the soil theories behind each method and the design methodologies associated with GRS and MSEW technologies are quite different.

Therefore, a study was undertaken to compare the required tensile strength predicted by these various reinforced soil design methodologies. For the purposes of this study, the required ultimate tensile strength was defined as the ultimate tensile strength needed in the reinforcement after all applicable factors of safety, load factors, and reduction factors were applied. The investigation explored both MSEW and GRS. GRS has been made an FHWA "Every Day Counts" initiative. Due to the push to implement GRS technology, it is critical to understand how GRS design methods differs from classic MSEW design methods, specifically in the prediction of ultimate tensile strength required.

A parametric study was performed comparing five different reinforced soil analysis methods. Two are current MSEW design methods and one was a proposed revision to an existing MSEW design method. The final two were GRS design methods. These design methods are among the most current and/or widely used design references in the United States regarding reinforced soil technology. There are significant differences between the methods in the governing soil theory particularly between GRS and MSEW design methods. The goal of the study was to understand which design parameters had the most influence on calculated values of the required ultimate tensile strength and nominal "unfactored" tensile strength. A base case was established and a reasonable set of parameter variations was determined. Two loading conditions were imposed, a roadway loading scenario and a bridge loading scenario.

Based on parametric study findings, conclusions were drawn about which design parameters had the most influence for different design methods. Additionally, the difference in overall predicted required tensile strength was assessed between the various methods. Finally, the underlying soil theory and assumptions employed by the different methods and their influence on predicted required tensile strength values was interpreted.