Meet the Massive Tunnel Boring Machine that Excavated the New Crystal Springs Bypass Tunnel

On September 30, 2009, as the early morning sun was rising over the San Mateo hills, an amazing piece of machinery saw the light of day for the very last time. One of 87 critical Water System Improvement Program (WSIP) projects, the Crystal Springs Bypass Tunnel, was a critical link in the Hetch Hetchy Water System and ensure water delivery after a major earthquake.

With a torque of 593,920 foot-pounds and an operating thrust of 1,150,000 pounds-operating, the massive Tunnel Boring Machine (TBM), was carefully lowered 155 feet down into the depths of the south shaft by calm and skilled crane operator Lawrence “Larry” Cary. 

A closeup of the tunnel boring machine.
A closeup of the tunnel boring machine.

After months of controlled blasting to dig the north and south shafts, tail and starter tunnels, contractor Shank/Balfour Beatty detonated the final controlled blast on August 31. 

As workers hooked up and secured the TBM to the crane, project staff watched closely as the crane began lifting and moving toward the shaft opening. Workers carefully guided the TBM toward the shaft using ropes. Local media filmed and photographed the event and everyone on site held their breath as the TBM slowly began its descent into the darkness of the round shaft, and then into its starter tunnel. 

Crews prepare the tunnel boring machine.
Crews prepare to lower the Tunnel Boring Machine in the early morning hours.

SFPUC staff met with and kept the nearby neighbors updated from start to finish of the project with public notices, alerts, coffee gatherings, visits to the construction site and regular visits to neighbor homes to answer questions or address concerns.

In late October 2009, the TBM began chewing it way through rock and various soil types to create the new 4,200-foot-long New Crystal Springs Bypass Tunnel. The difficult excavation process took about five months and was completed ahead of schedule. Once excavation was complete, the TBM was abandoned in place.

A closeup of the tunnel boring machine.