Technical Review of the Back-to-Back Mechanically Stabilized Earth Walls

Back-to-back mechanically stabilized earth walls (BBMSEWs) have been increasingly used in the world, mostly for bridge abutments, highway and railway embankments, and coastal levees. The Federal Highway Administration (FHWA) provides guidelines for the design of BBMSEWs reinforced with steel reinforcements or geosynthetics under self-weight or vertical loads, which depend on gap or overlap distances between two-side reinforcements and wall height. However, BBMSEWs have also been used to support lateral loads or been subjected to seismic loading. Researchers have conducted numerical studies and centrifuge/shaking table tests to examine the behavior of BBMSEWs and compare some of the results with the FHWA design guidelines. This paper provides a technical review of recent studies on BBMSEWs and summarizes key findings from several important studies. The technical review is focused on the behavior of BBMSEWs, including critical slip surfaces, lateral earth pressures, tension in reinforcement, deformations of wall facing, and stability, and evaluates the effects of wall width to height ratio and reinforcement gap or overlap distance on the performance of BBMSEWs under static and dynamic loads, including seismic loading. The reduction of the back-to-back wall width reduces the lateral earth pressure behind the reinforced zone, the wall lateral deformation under self-weight, the maximum tensile force in reinforcement, and lateral resistance under lateral loading, but increases the factor of safety and the wall lateral deformation under seismic loading.