MSE walls as bridge abutments: Optimal reinforcement density

Abstract

Geosynthetics have become a common means of soil reinforcement in earth retention structures; however, the efficacy of its application can be enhanced dependent on use. Geosynthetic design often involves uniform spacing of reinforcements throughout a retaining structure. However, optimization of reinforcement spacing can have a significant impact on stability, especially when subjected to a finite surcharge, as demonstrated by a series of numerical simulations using Limit Analysis (LA). Use of a rigorous LA tool that employs an algorithm to computationally determine the critical collapse state allows for the determination of optimal reinforcement placement in Mechanically Stabilized Earth (MSE) walls based on both spacing and concentration – specifically at the toe or crest of the structure. The effects on stability are evaluated for two scenarios: (1) a “top-down” approach where reinforcement spacing density is progressively increased from the top of the wall downwards and (2) a “bottom-up” approach where the spacing density is progressively increased from the toe of the wall upwards. Presented within this study are the results of comprehensive parametric analysis varying reinforcement spacing, reinforcement strength and footing location, highlighting the stability benefits of top-down and bottom-up reinforcement density approaches. Placement of dense reinforcements near the crest of surcharge-supporting walls had a notable benefit for stability, while placement of dense reinforcements at the toe improved stability for walls without a surcharge. Hence, reinforcement spacing tailored to specific wall functions may provide significant economic benefits when considering reduced reinforcement needs, lessened tensile strength requirements, or shortened bridge deck length based on surcharge placement – all by concentrating reinforcement density at a specific height of a structure.