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Cal Park Hill Tunnel

The Cal Park Hill Tunnel in Marin County, California is being rehabilitated in order to convert the collapsed historic railroad tunnel into a dual use recreation trail and commuter rail facility.  The tunnel is approximately 1,100 ft long with concrete tunnel linings at both portals and timber ground supports within the interior.  The linings had severely deteriorated with a complete collapse of the tunnel lining near the southern portal, missing and severely rotted timber supports in the interior, and a partial collapse of the timber tunnel lining near the north portal.

Lachel provided independent constructability review services to the HDR-led team, including an assessment of the 90% tunnel and approach improvement related drawings and specifications.  The rehabilitation alternatives reviewed involved lining removal and sequencing; ground support schemes including shotcrete, rock bolts, contact grouting, steel ribs and steel lagging; and drainage control provisions.  The assessment was successful in identifying several aspects of the project where the proposed rehabilitation approach required further refinement and/or the use of alternative construction methods.