The 17.5m-diameter TBM, with a damaged seal system, mined through 20ft (6m) of unreinforced concrete to reach the interior of the pit.
Crews completed excavation on the 80ft-wide circular shaft, 120ft (37m) deep on January 30, and then built a concrete cradle on the bottom to support the TBM upon reception, before the TBM began mining on February 17.
