Environmental Protection

Case Study: Colorado Springs

Sliplining HDPE Solves High Traffic Dilemma

Officials in Colorado Springs, Colo., had two pressured water mains leaking clean, treated drinking water. One main was a 540-foot section running underneath Fountain Creek and the other was a 500-foot section running under Interstate 25 and two railroad tracks.

More than 100,000 cars travel each day through Colorado Springs on this route, according to the state Department of Transportation.

The city considered repairing the mains using microtunneling or horizontal direction drilling (HDD). With these technologies, tunnels are bored underneath the ground, making room to insert a new pipe. Another option was to line the existing pipe using a modified slipliner.

The advantage to installing a new pipe versus lining an existing pipe is that the existing pipe would remain in service while the new pipe was installed, eliminating the need for a bypass to provide service while the pipe is shut down. With modified sliplining, a temporary bypass would have to be set up for roughly one or two weeks. When costs are considered, microtunneling is one of the more expensive trenchless technologies and is limited in its scope. HDD and modified sliplining are both more cost-effective than microtunneling.

City officials and engineers decided to use a modified slipliner from the new Insituform Blue division of Insituform Technologies, Inc. The company specializes in the trenchless rehabilitation of underground potable water pipelines. The modified sliplining process would insert a high-density polyethylene pipe (HDPE) within the existing water main, eliminating the need for digging, drilling, or disposal of the deteriorated main.

While already accepted in European markets and in Canada, this was the first time this process was implemented in the United States.
 
The HDPE pipe was modified on-site to prepare for the installation process. Only two access pits, one for entry and one for exit, were needed for insertion. Sections of HDPE pipe were first fused together using butt fusion. The welded pipe then was altered by a machine that reduces the pipe diameter up to 40 percent. After this diameter reduction, the pipe was banded to ensure it retains the diameter reduction until the pipe pull-through was completed.

After pull-through, the line was filled with water until the bands snapped, allowing the pipe to return to its original diameter and create a tight fit with the existing host pipe. The final line pipe was considered fully structural according to American Water Works Association standards and had an internal pressure rating of between 170 psi and 230 psi. Crew members were at the job site for roughly a week and not a single lane of traffic was shut down on Interstate 25.

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