In April 2019, a Robbins 3.5 m (11.5 ft) diameter main beam tunnel boring machine (TBM) broke through into open space, completing its 2.8-km (1.7-mile) long tunnel. It was not the first time the machine had encountered open space. Twice during tunneling, the machine hit uncharted caverns, the largest of which measured a staggering 8,000 m3 (283,000 cu ft) in size.
