When Trenchless Technology is Not Feasible
Three viewpoints tell at least part of the tale on when trenchless technology may or may not be the right choice.
Angie's List, a nationwide home contractor referral service in the US, says trenchless technology is a good option in many cases. Reliance Home Services, a California HVAC and plumbing contractor, says trenchless is appropriate in some, but not all circumstances and the San Francisco Chronicle says there are risks to going trenchless.
An open trench is the only other option, so how do you determine that trenchless technology isn’t feasible?
Trenchless Tech: Maybe Yes, Maybe No
Angie Hicks, the founder of the contractor referral service Angie's List, begins with the obvious: one advantage of trenchless technology is the minimal surface disturbance in a blog post, she cites the fact that trenchless work doesn’t damage "landscaping, hardscaping, driveways and other structures."
The blog post then cites the lower cost of trenchless work versus the cost of labor, which doesn't require heavy equipment to dig a trench for the placement of pipes and the cost of restoring the surface. The blog goes on to discuss the most common types of trenchless rehabilitation: pipe relining and pipe bursting. (Learn more in "Studies Claim the Trenchless Construction Cost Comparison is Massive.")
The one potential problem mentioned concerns pipe relining. Where there are a number of laterals or where a pipe has collapsed, the blog admits pipe relining may not work, but pipe bursting remains an option.
The final recommendation is to contact a reputable plumber or pipeline installer.
When Trenchless is Most Useful
Like Angie's List, Reliance Home Services aims its post at residential customers, but the trenchless paradigm remains the same: avoid excavation – which Reliance dubs "the dreaded e-word" - and the associated surface disturbance. Again, pipe bursting and pipe relining are the preferred methods, but with explanations.
Pipe relining requires an intact. The lining seals as soon as it's in place and is resistant to tree roots. The lining also enhances flow, as well, because its interior is smooth, as opposed to the inner surface of clay pipes. Learn more in "The History of Vitrified Clay Pipe in Trenchless Installation.")
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Pipe bursting is likewise described in some detail, with a discussion of the advantages of HDPE (high-density polyethylene) pipe, the requirement to dig access pits at both ends of pipeline being replaced and the winching of the pipe and the pipe bursting head through the existing pipe, destroying the host pipe as the new line is pulled into place. This process is called fragmentation.
The process is described as a replacement method for fully blocked pipes and those that are in a "state of collapse" or are leaking so excessively that mechanical spot repairs are unlikely to yield a good outcome.
Why Trenchless Represents a Risk
The authors of an article in the San Francisco Chronicle's online outlet, sfgate.com, began by admitting they were, "a little leery of the trenchless option," when asked about tree root incursion into century-old clay pipes. The authors recommended a mechanical spot repair using cast iron or PVC pipe to replace the section in which the tree roots had taken up residence.
An unidentified respondent to that online recommendation knew something about trenchless technology and recommended pipe bursting as a rehabilitative measure.
The owner of the faulty line read the follow-up comment advocating pipe bursting and contacted a city inspector, who warned that "this installation method might not pass inspection if water pools in a low spot in the line."
When Trenchless Cannot be Used
Changes in the horizontal and vertical direction of the pipe (deflection, belly, sag) can cause problems, such as pooling. Experienced trenchless installers know the extent to which deflections in an existing pipeline are removable. Generally, trenchless tech cannot be used for fix a line belly. (Read on in "Line Belly Vs. Channeling: When Trenchless Can't be Used for Repair.")
Predominantly sandy soil allows for the removal of a number of deflections; less forgiving, such as shale, prevents their removal.
The Proximity of Other Utilities
When the bursting head used in pipe bursting moves through the existing pipe, it splits it, forcing it out into the soil as the new pipe is pulled into place. Utilities in close proximity to the existing pipe can be pushed outward, resulting in damage to them. In a worst-case scenario, cut water lines and gas leaks can result from the passage of the bursting head. This requires the trenchless contractor to identify underground utility locations that nearby pipe bursting activities may affect. (Learn about the importance of nearby utilities in "The Science of Getting it Right: Locating Underground Utilities.")
A particular project's feasibility depends on many factors. Although the examples cited above are generally residential, the issues, caveats, and concerns raised – politics and government approvals, financial cost, the social impact of an undisturbed surface, the potential for damage to other underground facilities – apply to all trenchless projects. Trenchless technology may replace open trenches across busy urban streets or quiet country roads, but there are times when the trench is the only way to go. ￼
Written by Will Carpenter
A retired merchant seafarer, Will Carpenter sailed the world extensively before settling as far from the sea as possible. Now a technical writer, Will lives in the "hills and hollers" of Tennessee with two formerly feral cats.