pipe, Hobas in this case, through the bore. This method ensured a highly controlled installation for contractor Minger Construction, which was essential given a need for high accuracy due to site constraints such as under- ground obstructions.. Hobas supplied 48-inch jacking pipe with an al- lowable pushing capacity of 400 tons, at a 2.5 factor of safety. This equates to a pipe with over a 1,000- ton capacity. “Jacking runs measured 400 to 1,200 feet in length,” said Minger Construction CEO Pat- rick Minger, whose com- pany has used standard centrifugally cast, glass- fiber-reinforced, polymer mortar Hobas pipe for more than a decade.
Beginning of pilot rod boring operations.
“Loads weighed between 100 to 190 tons and were a lot less than expected,” he added. “We figured on using intermediate jacking sta- tions; however, it's pretty amazing that the loads never got up there to justify the stations. None were used. At the end of the project, every foot of Hobas pipe was air tested and there were no problems.” The soils proved to be a good fit for the pipe jacking, with the stiff clays accounting for the low pressure of the jacking rates. Headquartered in Jordan, Minnesota, Minger Construction subcon- tracted some of the borings work to St. Louis-based J & J Boring. “They did an excellent job, so that probably accounted for why we ran four months ahead of schedule,” Minger noted of the accelerated construction timeline. An Improved Sanitary Sewer System When project restoration is completed in the spring of 2020, the East Trunk Sewer will add one million gallons of inline storage capacity to Mequon’s sanitary sewer system. This sizeable increase will halt the harmful effects of current wet-weather conditions. As the community grows, it will also ensure additional capacity for utility service exten- sions and future developments.
Trenchless Construction Hobas pipe was chosen because of its strength, pipe thickness, and resistance to corrosion. Joint integrity was an important factor and the pipe is also good for tunneling. For this undertaking, 8,056 linear feet of 48-inch Hobas pipe and 2,389 linear feet of 24-inch Hobas pipe were utilized over two trenchless and open-cut excavation phases. The project contained both microtunneling and guided boring. The 48-inch Hobas pipe on the bottom end of the project was all microtunneled, while the 24-inch on the top end was guided boring. During the microtunneling, an operator underground works directly with the tunnel boring machine (TBM) during the mining process. That operator controls the speed of the cutter head, which shaves the soil at the front of the machine into a tub on tracks that fills up. When full, the tub rides along tracks back to the jacking shaft where it is removed, emptied and put back to repeat the process. All of this occurs while another crew member runs the jacking pump unit, which is the machine that pushes the TBM and Hobas pipe, from the jacking pit. These workers are in constant communication for safety reasons. Guided boring, or pilot tube microtunneling, is different in that there is no one inside the tunnel during the mining process. The mining crew starts out with a pilot tube that sets the line and grade. Once the pilot tube reaches the receiving shaft, the bore diameter is increased in increments until reaching the desired size. Then the crew pushes the
KIMBERLY PAGGIOLI, P.E. is VP Quality Control and Marketing at Hobas Pipe USA. TROY HARTJES, P.E. is Senior Municipal Services Project Manager, raSmith.
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csengineermag.com
may 2020
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