Project of the Year – Rehabilitation Runner Up

No-DigTec burst the pipe in six runsPipe bursting specialist No-DigTec of Dallas upsized a 43-year-old, 24-in., reinforced concrete (RC) sewer pipe for The Trinity River Authority of Texas (TRA) with the pipe bursting technique.

The job was part of a larger Arlington and Fort Worth, Texas, wastewater sewer upgrade project undertaken by general contractor, Mountain Cascade. The upgrade was performed to accommodate anticipated future growth in this area of the community. Additionally, the flow and capacity of the existing pipe had been affected by root intrusion, bellies and offset joints. Pipe bursting was specified to preserve a playground, a concrete trail, and as many trees as possible of the bordering residential properties and within Stonecreek Park, through which the project ran.

No-DigTec prepared a narrow working trail with planking and more than 5 in. of wood chips. The contractor also protected the trees with redundant barriers to prevent any machine contact or pipe abrasion as pipe was drawn along the ground around curves and bends. Then No-DigTec burst the pipe in six runs, each with high-density polyethylene pipe (HDPE) to diameters prescribed in the project plan. The various lengths and diameters of the upgrade consisted of 175 ft of 28-in. HDPE, 1,826 ft of 32-in. HDPE, and 260 ft of 34-in. DR-17.

No-DigTec completed all six runs on time despite daily rains, a two-month delay and extra accommodations required within the Trinity River Recreation Area in Arlington. The length of the pulls, the complications of the original pipe’s layout, the tight working conditions and the size of the upgrade combined to make this a truly remarkable accomplishment. Five of the runs had upsized 24-in. diameter pipe to 32-in. HDPE. A sixth pull of 300 ft replaced 24-in. RC pipe with 34-in. HDPE — a five-step upsize. The pipe bursting specialist described it as one of the hardest projects the company has been contracted to perform.

No-Dig Tec owner John Newell calculated that each joint of 32-in. HDPE weighed 4,500 lbs. On the longer pulls he calculated the total weight of pipe and tooling being moved through the pipe was “60,000 lbs, not counting the force to overcome the existing pipe’s resistance.”

The contractor’s equipment had no difficulty making the pulls, but half of the job ran through Stonecreek Park in Arlington. Nearby residential properties and the highly valued trees and natural landscape required great care during the pulls. The pipe bursting plan was also designed to overcome complications due to the RC pipe’s original method of installation. The 24-in. RC pipe had been installed in trenches that took sharp turns around trees. At the RC pipe offsets in these turns, the original installers had poured cement over the joints, intruding into the pipe.

Digging was not permitted to locate these joints, but the contractor could tell when the expanding head encountered each one because the pipe bursting operation suddenly slowed to a fraction of its progression rate. Once the tooling had fractured and compressed the grouted joint away to the sides, the pull resumed its pace.

In places where the bends were judged to be too sharp to pull the massive pipe around, the runs terminated at manholes, creating junctions for the separate pipe runs. The lengths of 32-in. pipe had to be fused offsite and then towed to the park’s limited work area, a pathway not more than 10 to 12 ft wide in most places. A burst would require an entire workday, requiring equipment in the narrow corridor to be lined up correctly. Reorganizing equipment would otherwise have required each piece of equipment to be backed out and lined up again, delaying the burst until the next day to ensure a full day was once more dedicated to the bursting operation.

Equipment used for the project included a 38-in. expanding head made by HammerHead just for this job; a HammerHead 26-in.pneumatic bursting tool guided by a 20-ton HammerHead HydroGuide HG20 cable winch; and a HammerHead 20-inch pneumatic tool on the pipe’s trailing end.

Despite the daily rains, a two-month delay and continual maintenance of ground protection during the job, the 10-person No-DigTec crew completed the project on time within required specifications.

This project is currently the subject of a technical paper as testimony to the size and versatility pipe bursting represents as a trenchless replacement technique.
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