Numerical Investigation of the Effects of Geosynthetic Spacing on Failure Mechanisms in MSE Block Walls

The analysis used in design of mechanically stabilized earth (MSE) block walls is based on the premise that a failure surface will develop within the reinforced soil zone defining an active soil mass. Limit equilibrium analysis of this mass renders the reactive force in the reinforcement and connections. The objective of this work was to identify the effects of reinforcement spacing on failure mechanisms in block walls. A computer program, based on continuum mechanics and capable of dealing with soil at failure, was utilized. Geosynthetic connection to the blocks was purely frictional. Interfaces between stacked blocks, reinforcement and confining blocks, soil and blocks, and soil and reinforcement were modeled. In addition to spacing effects, computer simulations were conducted to study the effects of factors such as backfill strength, foundation strength, reinforcement stiffness, interface strength, and intermediate reinforcement layers. Results of the parametric studies on a surcharge-free wall show that, as the reinforcement spacing decreases, the likelihood of developing a failure or active zone entirely within the reinforced soil zone decreases. Nonexistent such failure zones, for closely spaced reinforcement, imply that current limit-equilibrium formulations and designs might be unrealistic leading to excessive reinforcement load and related length. However, based on the parameters used, it was observed that conventional failure modes, such as direct sliding and toppling, deep-seated failure, and compound instability, may occur. Current “external stability” design addresses the same identified modes and mechanisms; hence, reinforcement dimensioning based on these mechanisms seems appropriate.