It is still unknown why the SR99 Alaskan Way TBM Bertha is being held up in her tracks at present but the design of the world's largest 17.5m diameter EPBM from Hitachi, Japan has been designed with all the features and operating installations needed for a safe and successful passage under the streets of Seattle. As work continues to identify and clear the current obstruction to progress, a tour last month by Shani Wallis, of the enormous machine, soon after its launch and before the current hold up, and to the incredibly large scale tunnel that it builds, provided the opportunity to know more of the design and planned operation of the machine by project contractor Seattle Tunnel Partners.
