Laterally Loaded Shaft Group Capacities and Deflections behind an MSE Wall

Abstract

Design of laterally loaded cast-in-place shafts that pass through the reinforcement behind a mechanically stabilized earth (MSE) wall often requires isolation of the shafts from the MSE mass and socketing of the shafts into the underlying stable foundation material, such as bedrock. Sizeable cost and time savings could be realized, while maintaining stability if the shaft could be supported by the MSE mass alone with no rock socket. Construction, instrumentation, and testing of multiple 0.9-m-diameter shafts solely supported by the geogrid-reinforced mass behind a 6-m-high MSE block wall were conducted for the Kansas Department of Transportation (KDOT). This paper describes the design, construction, and instrumentation of the wall and shafts and the results from the lateral load tests of three shafts tested together as a group compared with shafts that were tested individually. This testing protocol was adopted to evaluate the shaft group effect and the effect of shaft distance from the back of the wall facing. All shafts discussed had lengths that were equal to the full height of the wall. Results for both load and deflection of the shafts and the deflections of the wall facing during loading are presented with preliminary design recommendations.