Underground Installation Projects: Determining the Best Approach

August 2008 Vol. 63 No. 8

Cutting Edge Group recently completed a job that involved replacing roughly 30,000 feet of water main at a campus in Wassaic, NY, using a variety of techniques. “We replaced a 980 foot run of 12 inch pipe using a HammerHead static bursting unit,” Davey says. “After that initial shot, it got a bit tricky with lots of turning points. So instead of digging entry and exit pits every 50 feet or so, we used a horizontal directional drill to install a new line offset from the original line. We used a combination of directional drilling and pipebursting – and a lot of engineering ingenuity.”

Trenchless methods uncovered

There are several different trenchless methods available to contractors and each has its specialty in the type of projects it can complete.

Bursting: Defined as the breaking of an existing pipe, and expanding the broken pipe shards into the surrounding soil while simultaneously pulling in the new line. Static or pneumatic pipe bursting has several distinct advantages. First, it’s easy on adjacent utilities because it follows the existing pipe path. Second, pipebursting can be used to increase a system’s capacity by upsizing the service line where cured in place and sliplining cannot. Third, since bursting is a trenchless process, minimal excavation is required, allowing contractors access to congested areas without hampering traffic flow or affecting expensive surface structures.

Projects best suited for pipebursting include the upsizing of existing service lines and replacement of aged pipelines, specifically sewer and water. Pipes suitable for pipebursting are typically made of brittle materials, such as vitrified clay, cast iron, plain concrete, asbestos or some plastics. Reinforced concrete pipe (PCP) can also be successfully replaced if it is not heavily reinforced or if it is substantially deteriorated. Ductile iron and steel pipes can also be burst using pipe slitters.

Pneumatic boring: Typically, this method is used to “punch” a hole under existing landscape and/or structures from a city connection directly to the home or business. Bores typically are 50 feet or less in length and the diameter ranges from 1.25 to eight inches. With only two small operating pits, boring with small diameter pneumatic tools minimizes above ground disturbance to existing landscapes, reduces cost and the amount of time necessary to complete the connection.