Challenges of Fully Assembled TBM Back-up Through Completed Tunnel Bore

摘要

To expedite the excavation schedule of the Metropolitan Transportation Authority CapitalrnConstruction (MTACC)’s East Side Access (ESA) Project (Contracts CM009 and CM019), a plan wasrndeveloped to prepare a newly-mined tunnel for retrieval of a fully-assembled Tunnel Boring Machine (TBM)rnthereby avoiding dis-assembly/re-assembly delays. Engineering analyses and constructability evaluations werernperformed to assess and address challenges of pulling back the double-shield TBM for subsequent re-launchrnfrom the newly-excavated wye cavern. Following a comprehensive geotechnical evaluation and risk assessment,rnmeasures including replacement of the existing initial support with equivalent minimal profile support systemsrnand enlargement/pre-support of the TBM bore within adverse ground conditions were implemented. This paperrnpresents lessons learned.