Contractor Implementation of SEM Tunneling and Comparison Between Design and Observed Ground Conditions, Caldecott Tunnel Fourth Bore, San Francisco Bay Area, California

摘要

The Caldecott Tunnel Fourth Bore was mined using Sequential Excavation Method (SEM)rntunneling. The SEM design identified 18 Rock Mass Types (RMT) grouped into seven Ground Classes thatrncorrelate directly with seven Support Categories. Selection of Support Category was implemented by arncooperative and interactive decision-making process between the Contractor’s and Owner’s geologists. Initialrnagreement established at the tunnel heading was typically adopted during daily SEM meetings. This paperrngives an overview of the design RMT’s, Ground Classes and Support Categories, followed by a discussionrnfrom the Contractor’s perspective that compares the design basis and actual observed geologic conditions,rnground behavior and initial support during construction. Tunnel construction resulted in a different distributionrnof Ground Classes than the design.