Construction behavior of the first underground opening of the superconducting super collider project

Most underground structures of the Superconducting Super Collider (SSC) will be within the competent Austin Chalk (AC), an ideal tunneling medium; however, some structures will be within the very low strength Eagle Ford Shale (EFS). A 3 m diameter Exploratory Shaft, 82 m deep with a test adit at the AC/EFS contact was constructed as the first underground opening on the SSC to provide information on design parameters and construction behavior. The Exploratory Shaft was instrumented with piezometers, MPBXs, convergence anchors, inclinometer and heave gage casings, and an instrumented steel ring liner section. The shaft was deep enough to induce over-stress in the EFS. The geomechanical properties of the EFS and overlying AC, the instrumentation, and the insights gained for the SSC project are presented in this paper