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)rntunneling. Rock mass characterization was based on observations made during excavation and initial supportrnperformance was determined through daily surveying of monitoring points. Rock mass conditions observedrnduring excavation were often better than anticipated by the GBR and the design, and often led to classificationsrnat least one Ground Class better than anticipated in the design distribution. This paper provides a summary ofrnthe rock mass characterization as encountered during excavation as well as comparison of the performance ofrnthe rock mass and initial support systems relative to that anticipated by the design.