Bertha, the 57.5-ft-dia tunnel-boring machine attempting to dig a 1.7-mile state Route 99 tunnel underneath Seattle, is stuck again, having progressed 4 ft after a delay in December. Now, Seattle Tunnel Partners (STP), a joint venture of Dragados USA and Tutor Perini Corp., have decided to build a shaft in order to reach the TBM after discovering the 35-ft-dia seals surrounding the main bearing are broken.
STP and Hitachi Zosen, the Japanese manufacturer of the $80-million, 7,000-ton, 300-ft-long machine, already have started on the plan to build a 120-ft-deep, 80-ft-wide shaft in order to reach the cutter head's face 50 ft below the surface. The plan is to access Bertha from the front, instead of through the 1,023 ft already tunneled to its back end.