Launch Slideshow

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Talking Trenchless

Talking Trenchless

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    This Phoenix, Ariz., sewer project is one of the largest-diameter VCP static bursting projects to date. It involved bursting and replacing 3,938 feet of existing 12-inch VCP with 18-inch VCP. Photos: TT Technologies

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    During the static bursting process, bladed rollers attached to bursting rods are pulled through an existing line by a hydraulically powered bursting unit (inset). As the bladed rollers are pulled through, they split the host pipe. An expander attached to the rollers forces the fragmented pipe into the surrounding soil while simultaneously pulling in the new pipe. The trench shown is shallow enough to require no shoring.

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Over the last decade, static pipe bursting has become the preferred trenchless method for replacing deteriorated or undersized gravity sewers, water mains, and storm drains. Using hydraulically powered static pipe-bursting systems, you can split and replace old ductile iron and steel pipes.

Recent advancements are making the static bursting method more versatile. Pipe manufacturers have been working with bursting equipment manufacturers to adapt various pipe products to pipe-bursting installations. With certain equipment modifications, the technique can now be used with fusion-welded or segmented pipe material, depending on site conditions and owner preference.

In the static bursting process, bladed rollers attached to bursting rods are pulled through an existing pipeline by a hydraulically powered bursting unit. As the bladed rollers are pulled through, they fracture or split the host pipe. An expander attached to the rollers forces the fragmented pipe into the surrounding soil, creating a temporary annular space large enough to accommodate the new pipe, which is pulled in simultaneously.

CHOOSING THE RIGHT CATEGORY

To decide between fusion-welded or segmented pipe, you need to know how the existing trench conditions will react to the compressive/expansive forces of the pipe-bursting action. A geotechnical consultant should perform a thorough soil investigation as part of project design and planning, as soil types vary dramatically from region to region, and sometimes from block to block. If the soil can maintain an annulus for a period of time, segmented pipe will probably work well. This temporary annular space must also accommodate the added dimension of segmented pipe bell joints, which may be problematic in some situations. In free-flowing sand and other similar conditions, on the other hand, segmented pipe may be problematic, and a fusion-welded pipe system should probably be used instead.

Polyethylene (PE), whether high-density (for sewer and water lines) or medium-density (for natural gas) accounts for a majority of pipe-bursting installations using both static and pneumatic equipment. Its fusion-welded joints produce a one-piece pipe section of whatever length is required. For example, to replace a 500-foot-long section, PE pipe is welded together into a string slightly longer than 500 feet and laid down in alignment with the launching pit. This procedure requires adequate lay-down area. Fusion welding of PE pipe is time-consuming and generally performed in the field.

Fusion-welded PVC is a relatively new type of pipe, just coming into use for water and sewer lines. Somewhat stiffer than PE, it requires longer launching pits (5:1 ratio, length to depth). Because of its stiffness, it also must be installed with a static pipe-bursting system; the heavy hammering action of a pneumatic bursting system can fracture the pipe's connection to the pipe-bursting tooling.

Welded steel pipe is installed by pulling with static pipe-bursting systems. The pipe is considered flexible enough to be welded together and then pulled in similar to PE pipe. In reality, however, it often must be welded together as each joint goes in.