Sewer Tunnel in Granite under I-210 Freeway

Joint Outfall “B” Unit 6J Relief Trunk Sewer, Phase II, La Canada Flintridge

Los Angeles, California

Geotechnical investigation and engineering support for construction of a 6-foot-diameter 10,000-foot-long sewer tunnel beneath Freeway 210, in granite bedrock, including a 72-inch-diameter 0.75-inch-thick steel casing as the initial support of the proposed tunnel. Geotechnical field exploration for tunnel, including drilling three continuous rock coring holes in granite bedrock and two soil borings; geotechnical laboratory testing, and preparation of Geotechnical Feasibility Report (GFR). Evaluated ground conditions for a 40 x 20 feet insertion shaft, a 35 x 15 extraction shaft, backfilling of shaft over-excavations to the desired grade, tunnel excavation, methods for Tunnel Boring Machine (TBM) and drill-and-blast, construction risk considerations, and recommendations for monitoring during construction.