Although trenchless technology—the science of installing, repairing, or replacing buried pipes with little or no excavation—can be more cost-effective, environmentally friendly, and safer than traditional exhume-and-replace construction, it's still not universally embraced.
But that is changing. According to an exclusive survey of PUBLIC WORKS readers, 53% of respondents went trenchless in the past year on projects ranging from $100,000 to $500,000. Of the respondents:
- 47% used trenchless technology for sanitary or combined sewer rehabilitation
- 39% for new sanitary-sewer construction
- 35% for sanitary or combined-sewer repair
- 35% to construct new water mains
- 26% for manhole rehabilitation
- 23% for other applications such as gas and electric installations
- 12% for rehabilitating water mains
- 9% for repairing water mains.
“We do a lot of jacking concrete pipe and tunnel work,” says Steve Lilo, operator foreman with Mount Prospect, Ill.-based L.J. Keefe Co. The company uses pipe-jacking techniques to install sewer and water under interstates, toll-ways, and near airports where air traffic cannot be disrupted.
Proponents such as Lilo prefer trenchless technology because it's a non-invasive way of traversing environmentally sensitive areas such as wetlands. It's also less noisy and less disruptive to traffic patterns.
The no-dig aspect of trenchless methods also minimizes the chances of death and injury due to trench caveins, decreasing insurance costs and litigation and—more importantly—saving lives.
According to the TTC Technical Report No. 2001.02 (www.latech.edu/tech/engr/ttc/publications/index.htm), prepared by the Trenchless Technology Center (TTC) for the U.S. Army Corps of Engineers'Engineering Research and Development Center, trenchless techniques are most cost-effective when:
- There are few lateral connections reconnected within the replacement section
- The old pipe is structurally deteriorated
- Extra capacity is needed
- Restoration and environmental mitigation requirements are extensive.
The U.S. Environmental Protection Agency's Municipal Technology Branch's “Collection Systems O&M Fact Sheet” presents trenchless technique costs in 1998 dollars.
Project costs are influenced by pipe diameter, length of pipe to be rehabilitated, specific defects to be corrected, pipe depth and grade change, locations of access manholes, number of access points that need to be excavated, location of other utilities, provisions for bypass of existing flows, number of laterals in the section to be rehabilitated, and the number of directional changes at access manholes.
