Effects of Surcharge Location on Serviceability of Mechanically Stabilized Earth Abutments

Use of mechanically stabilized earth (MSE) walls to support true bridge abutments has increased in the past decade. However, service state design of MSE abutments can be exceedingly complex, especially in consideration of reinforcement spacing, footing placement, wall geometry and other structural design aspects. A combination of these factors highlights the need to consider critical, and non-intuitive, design challenges – notably, effects on earth pressures, vertical and lateral displacements. To better understand the coupled behavior of these design factors, parametric studies were performed with Finite Element (FE) analysis to evaluate MSE abutment behavior under a variety of reinforcement and footing configurations. From these analyses, wall behavior (footing settlement, facing lateral displacement and vertical stress distributions) were observed, implicative of the complex response of MSE walls under non-uniform surcharge loading. Use of denser reinforcements enables improved service state performance, especially for footings placed closer to the wall face. Use of more reinforcement layers assists with reduced footing settlements (i.e., the “bump” at the end of the bridge) and facing deformations, facilitating closer placement of a footing near the wall face – subsequently reducing the required bridge deck length. Intuitively, as the footing is placed further from wall, the benefits of denser reinforcement spacing are lessened. One significant concern about higher reinforcement density is increased cost; however, the reduced bridge deck length presents a cost-benefit that may offset the increased abutment expenses.