Horizontal directional drilling for gravity sewers

A Trenchless Flowline-modified Ditch Witch JT2720 vertical drilling rig drills sight relief holes, 16 inches in diameter, for monitoring and adjusting grade during installation and evacuating borehole slurry. Placed at 30-foot intervals, the vertical holes play a key role in the ArrowBore installation method.

As another bore is completed, Trenchless Flowline employee Kelly Lindeman prepares the drill rods for pipe pullback. Photos: Trenchless Flowline.

During pullback, 10-foot joints of CertainTeed CertaFlo GreenLine integral bell PVC sewer pipes were loaded into the receiving pit and connected to the moving pipe string. The shorter pipe joints were beneficial, as they allowed smaller pit sizes and saved money.

Drilling fluid on the project was pumped from a Ditch Witch MM9 mud-mixing system.

Another joint of 12-inch CertaFlo GreenLine sewer pipe is added during pullback. A total of 1,900 feet was installed during the project.

Bore slurry was removed from sight relief holes during pullback by a trailer-mounted Vac-Tron MC855 SDT sewer jetter.

A close-up of a sight relief hole as bore slurry is vacuumed out. Using the sight relief holes to evacuate excess slurry is an important component of the ArrowBore method’s strategy for maintaining sewer grade.

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