A specialized Robbins EPB broke through to fanfare on June 11, 2014, marking the completion of twin tunnels at San Francisco’s Central Subway in California, USA. The first of the two machines holed through on June 2, with both Robbins machines achieving swift advance rates of up to 40 m (131 ft) in 24 hours and 513 m (1,683 ft) in one month. The Central Subway is the second phase of the San Francisco Municipal Transportation Agency’s (SFMTA) Third Street Light Rail Transit Project.
Two 2.5 km (1.5 mi) long tunnels were excavated through ground ranging from soft soils to thinly bedded siltstone, shale and sandstone bedrock, as well as concrete diaphragm walls. The TBMs, operated by the Barnard/Impregilo/Healy (BIH) JV, were designed with a number of features to efficiently navigate the varied geology, steep grades and turns along the alignment, and to bore in what was rated as “Potentially Gassy with Special Conditions” by Cal/OSHA. A mixed face cutterhead was selected and designed to excavate the anticipated wide variety of ground, while active articulation was integrated between the TBM shields to lessen the risks of segment damage, ring deformation, and settlement during boring through curves. Robbins continuous conveyors offered efficient muck removal throughout tunneling.
Content via The Robbins Company. To read more about this project, visit The Robbins Company website.