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Midwest Mole Digs Multiple Sewer Crossings With Robbins Rockhead
Ground in tunnel 5 is predicted to consist of majority limestone with some shale. The route will undercut Shayler Creek with about 20 feet of cover. The final two tunnels needed to finish the job are expected to be much the same, and will measure 1,046 and 816-feet in length. Tunneling is expected to be complete in mid-2012.
Work on the launch/receiving shafts is ongoing; five shafts are now complete using a combination of drill and blast techniques and manual excavation. Some open-cut pipe jacking operations are also connecting existing, peripheral lines to the new sewer line. Midwest Mole recently utilized a 30-inch diameter Robbins SBU-A for a 150-foot long crossing of the creek, which will connect an 18-inch diameter PVC sewer to the main line.
Midwest Mole plans to use the Rockhead machine on future projects in the region after tunneling is complete. The contractor sees few limitations for the machine to excavate long bores. “One of the only limitations on distance is ventilation inside the tunnel. Our ventilation has a limited duct diameter due to the small diameter of the tunnel. We can adequately ventilate 2,000 foot tunnels, but we would need larger size fans for longer tunnels,” said Abernathy.
Overall, he feels that the method has worked well for the long tunnels at Shayler Run: “We have become very efficient at setup, launch, and conveyor installation during the start of each tunnel, as well as removal of the machine after it breaks through each shaft. We have gotten great production and are currently right on schedule.”