Investigating the performance of back-to-back mechanically stabilized earth walls as railway embankments using physical and numerical modeling

Back-to-back mechanically stabilized earth walls (BBMSEWs) are important derivative structures that are widely used for roadway ramps and bridge approaches. This type of MSE wall is typically used for railway embankments and consists of two opposing reinforced masses in a back-to-back configuration. The behavior of the BBMSEWs is significantly dependent on the horizontal distance between the opposing reinforced masses and reinforcement arrangement. Despite this dependence and the use of different types and arrangements of reinforcements in back-to-back MSE walls, the combined effect of these two factors on the performance of BBMSEWs, especially those used to support the railway tracks, remains unknown. Therfore, an extensive experimental and numerical investigation on 12 small-scale BBMSEW physical models reinforced by metal-strips and geogrid and 12 numerical ones reinforced by polymer strips and geotextile to assess the effect of reinforcement type, overlap length of the reinforcements and the position of the continuous reinforcements on the behavior of back-to-back MSE walls supporting railway tracks. Six reinforcement arrangements were chosen for reinforcing the wall models. The position of the continuous reinforcements was changed in the first three arrangements to evaluate the effect of connecting the two opposing walls at different points and overlap lengths of 0, 0.3H and 0.6H were used in the last three arrangements to assess the influence of the overlapping reinforcement length. The findings indicated that the reinforcement stiffness played a more prominent role in improving the bearing capacity than the pull-out capacity.   It was found that, although the use of extensible reinforcements increased the facing deformation and decreased the sleeper bearing capacity, it played an influential role in reducing the force mobilized in the reinforcements. The connection of two opposing walls with continuous reinforcements and the complete separation of them from each other were found to be the best and worst reinforcement arrangements. respectively, for improving the bearing capacity and reducing wall deformation in BBMSEWs. The respective use of these two arrangements mobilized the maximum and minimum forces in the reinforcements. Moreover, the creation of a proper connection between the opposing walls using continuous inextensible reinforcements or those with a sufficient overlap lengths were found to be efficient solutions to preventing the propagation of a failure plane across the back-to-back MSE walls.