The Effect of a Facing Unit on the Stability of Two-Tier MSE Walls

The facing of an MSE wall is composed of a number of discrete facing units (i.e., modular blocks or pre-casted concrete panels), which are connected to reinforcement (geosynthetic sheet or metallic strips) to provide lateral confinement for the reinforced soil zone. The adjacent facing units interact with each other through friction, and/or a connector or shear key. The current design methods checks the internal and external stabilities separately and does not consider the effect of facing unit on the stability of an MSE wall. This study, based on a series of numerical simulations and limit equilibrium analyses, investigated the possibilities of compound failure of two-tier MSE walls for various wall heights and setback distances. In the numerical modeling, the facing units was modeled a series of discrete blocks that interacts with each other through interfaces which allow relative movements but will yield once the shear stress exceeds the limit. Both the numerical simulations and limit equilibrium analyses show that critical slip surface may cut through the bottom region of the reinforced zone to form a compound failure plane. However, the critical planes obtained from the numerical simulations go through the facing, but, in contract, as the limit equilibrium analyses cannot consider the effect of the facing the obtained the critical plane is significantly different in terms of shape and location.