Study of the behavior of mechanically stabilized earth (MSE) walls subjected to differential settlements

The limit equilibrium (LE) analysis has been used to design MSE walls. Presumably, the deflection of MSE walls can be limited to an acceptable range by ensuring sufficient factors of safety (FOSs) for both external and internal stabilities. However, unexpected ground movements, such as movements induced by excavations, volume changes of expansive soils, collapse of sinkholes, and consolidations of underlying soils, can induce excessive differential settlements that may influence both the stability and the serviceability of MSE walls. In this study, a numerical model, which was calibrated by triaxial tests and further by a specially-designed MSE wall tests, investigated the behavior of an MSE wall as well as the influence of various factors on the performance of the MSE wall when the wall facing settled relatively to the reinforced zone. The numerical results showed that the differential settlement would cause substantial vertical and horizontal movements for the MSE wall, as well as an increase in lateral earth pressure and geosynthetic reinforcement strain. The maximum horizontal movement and increase of the lateral earth pressure occurred at about 1.0 m above the toe. The differential settlement resulted in a critical plane that coincided with the plane of 45°+?/2. The maximum increase of the strain for each geogrid layer occurred in that plane, and the bottom layer had the greatest strain increase among all layers of reinforcement. The study further indicated that the surcharge, backfill friction angle, tensile stiffness of geogrid, reinforcement length and MSE wall height had noticeable influences on horizontal and vertical movements, and strain in geosynthetics. According to the results, the MSE wall that had a higher factor of safety would have less movements and geosynthetic strain increase. In contrast, only the friction angle, tensile stiffness and MSE wall height showed some degree of influence on the lateral earth pressure due to differential settlements.     

Shaking table performance of reinforced soil retaining walls with different facing configurations

In this paper, a new type of MSE wall facing, termed as hybrid facing, is introduced and studied, which is built using a combination of concrete modular blocks and cast-in-place concrete. Two shaking table tests were carried out to compare seismic performances of model reinforced soil retaining walls with full-height vs. hybrid facing configurations. Results of this study show that the stability and performance of the hybrid facing model were similar to those of the full-height panel wall for peak input acceleration magnitudes less than 0.40 g. The amplification factors along the height of the facing were more uniform and smaller in the hybrid facing model as compared to the full-height panel wall, especially at higher peak acceleration amplitudes. Dynamic increment of lateral earth loads acting on the facing in both cases were found to be only 20% of the values calculated using pseudo-static methods. Connection loads in the hybrid facing model were smaller than those in the full-height panel wall, which was attributed to its smaller facing displacements.