NATM Excavation and Support Design and Construction of the Caldecott Fourth Bore

Synopsis:
The two-lane, 1,036 m long (3,399 ft) Caldecott Fourth Bore opened to traffic in November 2013 and along with the original three Caldecott bores provides a key transportation link between Alameda and Contra Costa counties. Seven cross passages connect the new Fourth Bore to the existing Third Bore. This paper describes the design of the initial ground support and final lining for the tunnel. The paper also documents the construction of the tunnel, including the daily support selection process, organization of the construction support team, examples of predicted versus observed ground behaviors, contractual considerations regarding support selection criteria, and the management of community impacts.

2014 North American Tunneling Conference Proceedings
June 22-25, 2014
Los Angeles, California