Capacities and Deflections of Laterally Loaded Shafts behind Mechanically Stabilized Earth Wall

Current practice for designing laterally loaded shafts that pass through a mechanically stabilized earth (MSE) wall often involves isolating the shaft from the MSE mass and anchoring the shaft into rock with a rock socket. Sizeable cost and time savings could be realized, along with continued effective performance and reliability, if a method were available to evaluate the lateral load capacity of a shaft supported by the MSE mass alone without a rock socket. The Kansas Department of Transportation assembled a team to develop such design methods: the construction, instrumentation, and loading of multiple 36-in. (0.914-m) diameter shafts supported within the reinforced mass of a 20-ft (6-m) tall MSE block wall designed according to existing FHWA procedures without consideration of lateral loads. The design and construction of the wall and the shafts, which were designed as drilled shafts, and the results from the lateral load tests of four shafts are described. These shafts had lengths equal to the full height of the wall and had spacings from the back of the wall facing to the center of each shaft of one, two, three, and four shaft diameters. Results for both load and displacement of the shafts, the width of shaft influence, and the relative displacements of the shafts and the wall facing during loading are presented, along with design recommendations.