Los Angeles metro rail project – geologic and geotechnical design and construction constraints

The Los Angeles Metro Rail Project is part of a planned 30 year transportation system development that will include over 480 km of light rail, heavy rail and commuter trains spanning the greater Los Angeles area. The backbone of the system and focal point of this paper is the Red Line Project which consists of a heavy rail subway system with 37 km of twin 6.6 meter diameter tunnels. Numerous geologic and geotechnical related issues involving regional seismicity, active faults, high groundwater, toxic and potentially explosive subsurface gases, abandoned oil wells and oil fields, and both soft-ground and hard rock conditions above and below the groundwater surface, have imposed constraints on the design and construction of the subway project. Complicating design and construction matters further, the project is routed through the heart of a major metropolitan area and has tunneled under freeways and high-rise buildings, beneath busy city streets and through oil fields and contaminated groundwater. Innovative solutions to natural and man-made problems have included unique tunnel support designs to accommodate or mitigate risks associated with earthquakes, chemical and compaction grouting to enhance ground performance and reduce surface settlements during tunneling, containment, treatment and disposal of contaminated groundwater, sophisticated gas monitoring equipment for tunneling in gassy ground, and use of magnetometers to detect abandoned oil well casings in front of advancing tunneling machines.