Horizontal Chemical Grouting Beneath the Hollywood Freeway, Los Angeles Metrorail C-311

摘要

A rigorous horizontal drilling and chemical grouting program was specificed beneath the Hollywood Freeway (U.S.Route 101) section of Los Angeles Metrorail Contract C-311. Twin 6.67-m (22-ft.) diameter starter tunnels were to be conventionally mined through a mixed alluvial and bedrock face consisting of silty sand, gravel, and weathered sandstone and siltstone of the Topanga Group. The contact between the alluvium and bedrock dipped toward the Crossover Excavation where the horizontal drilling and goruting operations were performed. The intent of this grouting program was to stabilize the mixed face to minimzie ground loss and surface settlement, and to reduce groundwater inflow into the tunnel headings. Given the highly variable mixed face conditions, horizontal drilling up to 86 m (284 ft.) resulted in upward trending trajectories which likely followed the bedrock contact.