Tour of the world's largest TBM - TunnelCast
  • VIP Polymers

December 2013: 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.


Technical details of record setting TBM

Shani Wallis reporting for TunnelCast
TBM length + back-up:
TBM weight:
6,664 tonne
Min horizontal radius:
350m (1,150ft)
Min vertical radius:
488m (1,600ft)
Max pressure in chamber:
10 bar
Max thrust:
Cutterhead displacement:
400mm forward
Cutterhead power:
24 x 560kW
No of disc cutters:
No of replaceable knife bits:
No of thrust cylinders:
28 x 2
Rotation speed:
0-1.8 rev/min
Max torque at 0.88 rev/min:
Break-out torque:
Screw conveyor diameter/ type/length:
10.5m + 23.8m
Total power installed: