Influence of Geogrid Stiffness on Shaft Lateral Capacities and Deflections behind an MSE Wall

Increased demand for right-of-way in urban areas has increased the use of Mechanically Stabilized Earth (MSE) retaining walls where elevation changes are required. Often in urban areas where right-of-way is adjacent to residential areas, sound barrier walls must be placed above the reinforced MSE mass behind the wall facing. Very conservative designs have often been used for this situation due to the lack of an accepted design approach. In some cases the foundation of the sound barrier wall has been completely isolated from the MSE mass and solely supported by shafts anchored in competent material below the MSE mass. Full-scale testing was conducted of an MSE wall 6.1m high and more than 45m long with laterally loaded cast-in-place shafts contained behind the facing of the MSE wall system. The tested system represents significant cost and time savings as it eliminated the need for socketed shafts below the MSE mass. This paper contains a discussion of the construction and calibration of three-dimensional finite difference computer models of the wall/shaft system used to extend the results to other wall/shaft configurations, with particular emphasis on the effects of geogrid stiffness on shaft capacities and deflections.