The effect of upward and downward movement on the behavior of MSE wall

Mechanically Stabilized Earth (MSE) walls are used extensively to support various infrastructures. Limit equilibrium (LE) analysis has been used to design MSE walls. Presumably, the deflection of MSE wall can be limited to an acceptable range by ensuring sufficient factor of safety (FOS) for both external and internal stabilities. However, unexpected ground movements, such as movements associated with construction and/or volume change of expansive soils in foundation may influence both the stability and the serviceability of the MSE wall. In this study a lab-scale test and then followed numerical analyses were performed to investigate the influence of the upward movement of MSE wall leveling pad on the serviceability of the wall. The test MSE wall was built with a dimension of 600×1200×900 mm3. The MSE wall leveling pad was forced to move upward vertically in a displacement control mode. The induced vertical and horizontal movements of the wall, the induced lateral earth pressures, and the reinforcement strains were monitored at various locations.

Based on the lab-scale test, a numerical model was calibrated. The numerical simulation had three basic characteristics: 1) hardening plasticity model was used for simulating the backfill material with shear, compression and dilation hardening; 2) the MSE wall facing blocks were modeled as elastic elements with interfaces between themselves and with the backfill soil: 3) the geogrid reinforcement was modeled as linear elastic perfectly plastic 'strip' elements interacting with the backfill soil. Good agreement was found between the deflection profile of the backfill and geogrid strain for the laboratory test on MSE wall.

Utilizing the calibrated model, a numerical parametric study was performed to investigate the influence of surcharge, reinforcement stiffness, friction angle of backfill, reinforcement length, modulus number of backfill and height on the behaviors of the MSE wall subjected to upward and downward movements. All the parameters except the modulus number of soil were found to have significant influence on the behavior of the wall. The maximum increment of strain in geogrid reinforcement was found around the critical failure plane of the backfill for downward movement of the wall. For upward movement, this increment was exclusively near the wall where the geogrid was connected. The change in lateral earth pressure was negligible due to downward wall movement. For upward movement, considerable amount of increment in the lateral earth pressure was noticeable. The horizontal deflection of wall although was predicted as negligible for upward movement, while it showed significant amount of deflection due to downward wall movement. It could be concluded from this thesis that a careful selection of backfill friction angle, reinforcement length, reinforcement stiffness, height of wall and surcharge can significantly reduce the potential damage due to upward and downward movement of the wall. The scope of future work was outlined at the end of the study.