Rock Mass Characterization and Initial Support Performance of the Caldecott Tunnel Fourth Bore, San Francisco Bay Area, California

摘要

The Caldecott Tunnel Fourth Bore was mined using Sequential Excavation Method (SEM) tunneling. Rock mass characterization was based on observations made during excavation and initial support performance was determined through daily surveying of monitoring points. Rock mass conditions observed during excavation were often better than anticipated by the GBR and the design, and often led to classifications at least one Ground Class better than anticipated in the design distribution. This paper provides a summary of the rock mass characterization as encountered during excavation as well as comparison of the performance of the rock mass and initial support systems relative to that anticipated by the design.