Directional Microtunnel Design for I-84 Pipeline Crossing
Trenchless design to help Tennessee Gas Pipeline Company, LLC serve the Northeast’s growing demand for natural gas.
The Tennessee Gas Pipeline Company, LLC (Tennessee Gas), a Kinder Morgan Company, needed to increase the capacity of its pipeline system to serve the growing demand for interstate natural gas transmission service in the Northeast. As part of the upgrade, a 30-inch-diameter steel pipeline crossing was required at Interstate 84 and US Highway 6 near Matamoras, Pennsylvania. The crossing site was confining with difficult geologic conditions and traditional trenchless installation methods weren’t feasible.
When presented with the challenges at the site, GeoEngineers trenchless design team from Springfield, Missouri, drew on its experience with Direct Pipe™ technology, which had only been used on less than a dozen pipeline installations worldwide at the time of the initial project design. GeoEngineers’ design team combined the thrusting technology of the new Direct Pipe approach with the short interlocking segments of Permalok pipe to create a steerable, directional microtunnel. The project was a series of firsts not only for Tennessee Gas and GeoEngineers, but also for the field of trenchless design.
GeoEngineers developed an innovative directional microtunnel profile that reduced the depth and expense of entry and exit pits associated with conventional microtunneling. GeoEngineers also specified a casing pipe product, Permalok, that fits together in short interlocking segments, thereby reducing welding time and the need for an expansive pipe stringing area through nearby environmentally sensitive areas.
In addition, GeoEngineers developed a new design methodology for curved, jacked steel pipe (PDF – 703KB) to assess the stresses and the risk of buckling in the pipe to accomplish the curved microtunnel. This detailed engineering analysis helped validate the design approach and increase Tennessee Gas’ confidence in the safety of its pipeline.
Construction on the 30-inch-diameter, 470-foot crossing took a month to complete, allowing Tennessee Gas to construct the rest of the pipeline system as planned. The successful installation demonstrated that it is possible to conduct reliable engineering design and stress analyses for Direct Pipe crossings using the design procedures that GeoEngineers developed. The project went on to win the Grand Conceptor Award for the best overall project in the American Council of Engineering Companies (ACEC) of Missouri’s 2014 Engineering Excellence Competition, and was also featured in a special supplement of Trenchless Technology magazine.