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At the end of the drive, the machine hit watery, soft mudstone that slowed progress. Crews added an intermediate jacking station to keep the gripper machine progressing in the soft material. In addition, bentonite was injected outside of the casing to make the pipe easier to push, as the soft material tended to collapse in around the casing.
New pieces of 8-foot long, 66-inch diameter pipe were installed every 45 minutes during the drive. The four-inch thick reinforced concrete pipe was jacked in behind the machine to serve as the primary liner. Muck was transferred through the cutterhead to a machine belt conveyor, which emptied into a single track muck car. Each muck car took about 10 minutes to exit the tunnel through the casing, where it was lifted out of the launch pit using a crane and emptied at a storage area on the project site before reentering the tunnel. Crews pumped heat into the pit nightly, in order to prevent water in the pit bottom from expanding and warping the rails or pipe jacking system.
On completion of the Confederation Trunk Sewer Crossing in mid-April, the machine broke through into a receiving shaft at the side of a parking lot and near the main road at 32nd Avenue. “We will be doing some pipeline rehabilitation in the area, as well as restoration of the jobsite,” said Rafih. “This is a special project for us. The residents in western areas of the city have had issues with sewer surges any time there is heavy rainfall. They have had flooded basements and insurance costs in the area are now very high. We have the opportunity to change that for them.” The pipeline is scheduled to be operational later in 2010.
In-Line is positive about the future use of tunneling machines in the Calgary area. “I think I first heard about Robbins machines maybe 15 years ago, when we rented an SBU-A for an auger boring job,” said Stace. “The equipment allowed us to get through some very hard ground that we couldn’t get through with our conventional auger boring equipment. We’ve been renting them off and on ever since, and hope to continue using the equipment.”
How The Equipment Operates
The Robbins Double Shield Rockhead (SBU-RHDS) is a tunneling machine for use on longer utility installations (usually over 600 feet) and in unstable ground. It also typically used for line- and grade-critical installations such as gravity sewers, as the machine can be continuously steered from an in-shield operator’s console.