Phase 1 of the Metro Exposition Line project was an 8.6-mile extension of the 73-station Metro Rail System in Los Angeles. It terminates in West Los Angeles at the Venice/Robertson Aerial Station, which is an aerial structure supported by 11, 12, and 15-foot diameter drilled shafts with depths of up to 112 feet. The 15-foot diameter shafts were constructed by stabilizing the surrounding soil with grout injections using the cutter soil mixing (CSM) technology. The 11-foot and 12-foot diameter shafts were constructed using polymer drilling fluids for shaft stabilization.
Eight CSM panels were installed in an octagonal pattern around each 15-foot diameter shaft with the ends overlapping by 3.5 feet to form a compression ring that eliminated the risk of caving ground conditions. Each panel was about 9 feet long and 3.3 feet wide and extended to depths of 118 feet below the ground’s surface. Since the CSM panels cut off the natural water table, shaft construction in the dry was possible. This eliminated the need for drilling fluid stabilization or the use of large diameter steel casings.