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Testing Layout > Reaction Foundation

Composed of the two existing 4-ft diameter drilled shafts, spaced 12 ft center to center, that were buttressed with a sheet pile wall and two reinforced steel I-beams. The top 2 ft length of shaft above the ground surface are finished as a 4-ft square cap to facilitate loadings from previous testing. The west and east shafts extend to depths of 55 ft and 70 ft, respectively. Shaft reinforcement consists of eighteen #11 vertical bars extending to a depth of 35 ft below ground. These bars are wrapped with a #5 spiral pitched at 3 in with a 4.75-in clear cover of concrete. Half of the vertical bars extend from 35 to 55 ft with a spiral pitched at 12 in. The average compressive strength of the concrete in the shafts is 6000 psi.

To increase the lateral capacity of the shafts being used as a reaction foundation, a sheet pile wall was installed on the north side of the drilled shafts. AZ-18 sheet piling constructed of ASTM A-572, Grade 50 steel was used, being selected from sections readily available in the local area. Installation depth was controlled by the 40 ft length of the available stock. The piling, as built, extended to depths of 33.5 to 35.5 ft below the excavated ground surface. The sheet pile was installed by vibratory hammer, and the sheet piling was kept as vertical and flush with the faces of the shafts as possible.

To help ensure a composite behavior and proper load distribution, two 28-ft long, 64- by 16-in I-beams with numerous stiffeners were placed with the web horizontal on either side of the shafts and sheet piling. The reaction foundation was tied together with eight 2.5-in diameter high strength threaded bars that were post-tensioned to 10 kip.