Effects of Geosynthetic Reinforcement Spacing on the Performance of Mechanically Stabilized Earth Walls

The behavior of mechanically stabilized earth walls (MSEW) with modular block facing and geosynthetic reinforcement was investigated with numerical models that simulate construction of the wall layer by layer until it fails under gravity loading. The two-dimensional finite difference program FLAC (Version 3.4, Itasca 1998) was used to carry out the numerical analysis. The material properties were based on data reported in the literature, which represents typical values used in design practice. Failure mechanisms of MSE walls were identified as a function of geosynthetic spacing considering the effects of soil strength, reinforcement stiffness, connection strength, secondary reinforcement layers and foundation stiffness. The effects of reinforcement length on reinforcement stresses and wall stability were also investigated. FLAC predictions were compared with AASHTO design method. Additional numerical experiments were carried out to investigate the effects of some modeling parameters on wall response. Four failure modes of MSEW were identified: external, deep-seated, compound and connection mode. The reinforcement spacing was identified as a major factor controlling the behavior of walls. Two types of spacing were considered in studying the effects of spacing: small (less or equal to 0.4m) and large (larger than 0.4m) The increase of reinforcement spacing, decreased the wall stability and changed the predominant failure mode from external or deep-seated to compound and connection mode. Similar effects were identified when the soil strength, reinforcement stiffness, or foundation stiffness were decreased. Connection strength appeared to affect only the behavior of walls with large reinforcement spacing i.e., the increase of connection strength decreased wall displacements, improved wall stability and changed the failure mode. Similar effects were identified when secondary reinforcement layers were introduced in a model with large reinforcement spacing. The increase of reinforcement length improved wall stability and decreased wall displacements and reinforcement forces. A comparison between FLAC predictions and AASHTO calculations demonstrated a good agreement. It indicated that the existing design method is capable to distinguish the modes of failure identified by FLAC analysis especially these due to external instability. However, AASHTO disregards the effect of reinforcement spacing and thus considers an internal wedge to always develop internally.