Cincinnati Seven

Midwest Mole Digs Multiple Sewer Crossings With Robbins Rockhead
April 2011 Vol. 66 No. 4
The Midwest Mole crew celebrates the most recent breakthrough at the Rockhead’s fourth tunnel in January 2011.

Legend has it that Cincinnati, like Rome, was built on seven hills. Contractor Midwest Mole Inc., Indianapolis, IN, is continuing the local history by constructing seven sewer tunnels in a landmark project that is challenging common trenchless methods for long bores.

Cincinnati’s rolling topography is a key component of the challenging project, resulting in tunnel alignments that range in grade. Ground conditions are correspondingly varied, consisting of interbedded layers of shale and limestone from dry consistency to sticky and wet. Despite the highly changeable conditions, Midwest Mole chose a single machine solution for the pipeline -- a small diameter, self-propelled tunneling machine with disc cutters.

The contractor is utilizing a 72-inch diameter Robbins Double Shield Rockhead, to excavate 9,430 feet of tunnel in total, with individual bores ranging from 816 to 2,014-feet long. The entire pipeline is being constructed for the Shayler Run Segment C Sewer Replacement Project in Clermont County, OH. Once complete, the $15 million project will upgrade an exposed sewer system and protect an area surrounding environmentally-sensitive Shayler Creek.

Cleaning up Clermont
The Shayler Run Segment C project is a priority for the project owner, the Clermont County Ohio Water Resources Department, because of severe pipeline erosion in the creek bed. “The existing sewer pipe was installed in 1978 directly into the creek. Since then, the creek has eroded, exposing the pipe to the environment and putting certain sections at high risk of failure. The exposed pipe has now dumped raw sewage into the creek on several occasions,” said Lyle Bloom, sanitation engineer for the Clermont County Ohio Water Resources Department.

The new pipeline is being installed well below the creek bed, crossing the creek multiple times. Cover ranges from 10 to 100 feet, with the majority of the pipeline running some distance from the waterway.

Final carrier pipe will consist of 42-inch diameter Hobas Reline, and will be much larger than the current 24-inch sewer line. “The larger pipe was decided on mainly to allow trenchless construction, though it has the added benefit of providing a larger capacity for future needs in the area,” said Bloom.

Midwest Mole is responsible for pipeline construction, which consists of seven tunnels crisscrossing the creek. Each crossing is connected by a 32-foot diameter launch and receiving shaft, with a total of eight shafts in all. The shafts will eventually become fiberglass manhole structures to access the new pipeline.