Trenchless technology – the construction, repair or replacement of sewer and water pipes, underground utility conduits and other underground utility facilities – has gained increasing acceptance with government, contractors and the public over the last two decades. On its surface, it sounds like the best of all possible worlds but, as with any technology there are strong points and drawbacks. A primer on the advantages and disadvantages of trenchless construction and repair will include a discussion of materials, methods, advantages and the disadvantages of the trenchless method. (Learn more in 7 Types of Trenchless Rehabilitation Methods and How They Are Used.)
Trenchless technology brings state-of-the-art equipment to the table when it comes to sewer and drain repair, but that’s not all. High density polyethylene (HDPE) pipe, PVC and composite liners and pipe add to the heady mix of “pros” associated with no-dig construction, replacement and rehabilitation.
Trenchless technology has the advantage over traditional open-trench repair and rehabilitation in terms of time. Much of that advantage is the result of the very nature of the technology – there’s no time spent digging or filling in potentially extensive trenches. Some trenchless work may require an access pit, but the pit is substantially smaller than an open trench and creates less disturbance in ground-level activity.
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The lack of a trench is a very specific feature of trenchless construction and rehabilitation. An open trench presents several hazards, both to workers and to the general public. (Read Trenchless Operations Safety Do's and Dont's.) A trench’s walls may become unstable and collapse. If workers – or others – are present in the trench, such a collapse may become deadly. In the best case, a collapsed trench represents an additional disruption, because the trench must be reopened for the repair or construction to proceed, adding to the length of time required for the project.
Trenchless technology offers greater possibilities with regard to sewer pipe. A common cause of residential water or sewer disruption is the incursion of tree roots into a pipe. Homeowners have been familiar with the process of pipe auguring for many years, but that’s not the only repair or rehabilitation tool available to both large and small trenchless contractors. Methods such as cast-in-place pipe (CIPP) can be used to rehabilitate, rather than replace, damaged or leaking pipes by inserting a liner into the older pipe. The liner forms a new, intact interior lining for the pipe which allows it to continue in service without replacement, with minimum service interruption and without the disruption caused by a trench.
Less Invasive Process
Pipe replacement processes, such as pipe bursting, relining or even a new installation doesn’t disturb the surface of the ground above the pipe. (Read Pipe Relining: A Trenchless Alternative to Pipe Replacement.) This means fewer disruptions the service activities, safer conditions for contractors and the public, and less environmental damage. In pipe bursting, the new pipe follows the same pathway as the old pipe without the need to remove the pipe it replaces. As the old pipe is broken up by the bursting head its remnants are forced into the soil surrounding the pipe’s pathway. The new pipe is pulled through the pathway by the bursting head.
Relining, sometimes called sliplining, covers the interior of the damaged pipe with a flexible liner which adheres to the interior of the damaged pipe. Think of it as inserting a smaller, undamaged straw into a larger, damaged straw. The liquid then travels freely, without a leak.
New construction may be performed trenchlessly through a process called horizontal directional drilling (HDD). (Read A Step-by-Step Guide to HDD.) After a careful design process that includes engineering, design and geotechnical investigation, a specialized drilling rig bores through the earth horizontally, often starting in a manhole. The drill bit is steerable and its location underground is tracked electronically to ensure it stays within the pathway. When the drill bit reaches the access pit at the end of horizontal bore, the new pipe is connected to the bit which then pulls the new pipe back through the bore and the ends of the pipe are connected.
A noisier variation of trenchless technology called pipe ramming uses a hydraulic ram to drive new pipe beneath the ground’s surface without first creating a horizontal bore.
On the Other Hand…
For all its advantages trenchless is not a magic bullet. Pipes that are severely damaged, pipes that are misaligned and unstable geological or soil conditions (think of the San Andreas fault adjacent to San Francisco, California) may render trenchless processes ill-advised or even unlawful. In these circumstances, plumbing and mechanical contractors must resort to the old, tried-and-true open trench method.