Deep Foundation Solutions for the Metro Exposition Line Extension
Phase 1 of the Metro Exposition Line project extended the 73-station Metro Rail System in Los Angeles by 8.6 miles. The line’s terminus is the Venice/Robertson Aerial Station in West Los Angeles, supported by a complex system of deep foundations. The station’s aerial structure is upheld by a combination of 11, 12, and 15-foot diameter drilled shafts, with depths reaching up to 112 feet. To ensure stability during construction, various techniques were employed.
The 15-foot diameter shafts were constructed using cutter soil mixing (CSM) technology, which involved stabilizing the surrounding soil with grout injections. The 11-foot and 12-foot diameter shafts, on the other hand, utilized polymer drilling fluids for shaft stabilization. A unique approach was employed to further enhance the integrity of the project.
Eight CSM panels were strategically installed around each 15-foot diameter shaft in an octagonal pattern, with overlapping ends to create a compression ring. This innovative design eliminated the risk of ground conditions collapsing. Each CSM panel, measuring approximately 9 feet in length and 3.3 feet in width, extended to depths of 118 feet below the ground’s surface. Notably, the use of CSM panels effectively cut off the natural water table, enabling dry shaft construction without the need for drilling fluid stabilization or large diameter steel casings.
