Officials in Colorado faced a tough infrastructure challenges in 2007. A 500-foot section of potable water pipeline running under a major highway and two railroad tracks was out of service, but needed to be reinstated to meet an increased demand in transmission main capacity.

Use of traditional dig and replace technologies would have required the complete reconstruction and closing of the multiple-lane, high-traffic highway, 10-ft tall noise barriers and two railroad lines. The pressurized transmission main needed of rehabilitation due to excessive leakage of clean, treated drinking water.

Choosing a Solution
There are a variety of alternatives to fix pressurized water mains. These include underground construction technologies including microtunneling and horizontal direction drilling (HDD). HDD and microtunneling are both trenchless installation methods for new pipes. With these technologies, tunnels are bored underneath the ground, making room to insert a new pipe underground. Another option was to line the existing pipe using a fully structural modified slipliner.

City officials and engineers ultimately decided upon using a modified slipliner from the new Insituform Blue division of Insituform Technologies, Inc. Insituform Blue specializes in the trenchless rehabilitation of underground potable water pipelines across the globe. 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. In fact, HDPE is the most widely used type of pressure pipe rehabilitation throughout Europe. HDPE is also the product of choice for industrial, gas and oil applications in the United States due to its resistance to corrosion and flexural properties. Studies are now being conducted by Cornell University researchers on the flexural properties of HDPE pipe and its reaction to seismic events and other ground movement. Preliminary research has found that, whereas many pressure pipe products tend to snap upon ground movement, HDPE bends, mitigating breaks and cracks.

Installation
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 on-site using butt fusion. With butt fusion, two ends of HDPE pipe are heated, brought together and then allowed to cool. This creates one long length of pipe. After butt fusion, the welded pipe is altered by a machine that reduces the pipe diameter up to 40%. After this diameter reduction, the pipe is banded on-site to ensure it retains the diameter reduction until the pipe pull-through has been 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 close-fit with the existing host pipe. The no-dig installation took roughly a week and not a single lane of traffic was ever shut down on the Interstate.