Influence of Retained Zone Width on the Behaviour of Back-to-Back Mechanically Stabilized Earth Walls upon Rainwater Infiltration

The use of back-to-back mechanically stabilized earth walls (MSE) for highway ramps and bridge approaches has gained wide popularity due to their construction easiness and cost efficiency. The width of the retained zone (L) is a key parameter affecting the behaviour of such walls. Federal highway administration (FHWA) guidelines suggest independent design of two walls when the width of retained zone is more than the top width of active wedges behind the walls. This study has investigated the effect of retained zone width on the overall performance of walls with complete select fill, complete marginal fill, and marginal fill only in the retained zone, at the end of construction and subsequent to rainwater infiltration, through finite element approach. Results showed that effect of retained zone width on lateral pressure, facing displacement, and global factor of safety both subsequent to construction and rainfall infiltration was more significant in complete marginal fill wall. For a given retained zone width, lateral force behind the reinforced zone following the infiltration was found to be higher than FHWA values for complete marginal fill case, whereas reasonable agreement with FHWA was observed for complete select fill case. Variation in reinforcement tension was observed to be least influenced by L for all three fill cases. Furthermore, factor of safety was noticed to increase with decrease in L. Overall, the interaction between the walls was more prominent when L is less than half height of the wall.