Michigan Ditch tunnel bore slows, new cutters for boring machine on order

Michigan Ditch photo via AllTrails.com
Michigan Ditch photo via AllTrails.com

From The Fort Collins Coloradoan (Kevin Duggan):

A stretch of unusually hard rock inside a mountain near Cameron Pass has slowed a tunneling project aimed at shoring up Fort Collins’ water supply.

Progress on a 760-foot tunnel that will carry Michigan Ditch water to the city-owned Joe Wright Reservoir was stopped as of Thursday.

Crews are waiting for the arrival of replacement parts for the cutting head of a tunnel boring machine, or TBM, that was custom built for the project, said Owen Randall, chief engineer for Fort Collins Utilities.

Bearings on cutting disks on the rotating head have repeatedly burned out while dealing with a wall of pegmatite, a type of granite that can have various minerals and be exceptionally hard, Randall said.

Project managers are “literally looking around the world” for replacement disks, he said. When some will arrive at the work site is not known.

Rock conditions have varied tremendously during the course of the tunneling, which began in late June. Some layers of rock have been fractured and relatively easy to cut through, he said. Others have been difficult.

“We went 300 feet on the first set of disks,” Randall said. “We used up two sets going the next 8 feet. It’s just been very variable.”

Before the TBM was shut down, the cutting wheel was grinding out clouds of powder rather than chunks of rock, he said.

The machine was 482 feet into the mountain as of Thursday. Time and weather are becoming concerns as crews want to have the TBM off the mountain before heavy snow comes.

Randall said crews still expect to finish the project this fall.

Once the tunnel is cut, a 60-inch pipe made of fiberglasslike material will be put in place to carry Michigan Ditch. Randall said he wants to have water flowing through the pipe before the onset of winter.

“We are going to get through,” he said. “But safety will dictate how long we keep people working up here.”

Crews have been working seven days a week, 12 hours a day. That will increase to 24 hours a day Sept. 12. About 1,000 feet of pipe is expected to be delivered that week, Randall said.

The project is in response to a slow-moving landslide that has been affecting the ditch for several years. Damage was especially severe in 2015.

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