By Chris Horgan, PE | Senior Engineer, Civil Engineering | Honolulu Office

Trenchless technology uses minimally invasive construction methods to rehabilitate or replace existing pipeline infrastructure in lieu of traditional replacement via open-cut excavation. Trenchless techniques generally use the existing pipeline as a guide or host pipe, and access is via existing structures or via small launching and receiving pits. By reducing the amount of excavation, trenchless technologies provide an option for extending infrastructure lifespan with less disturbance and less cost than traditional excavation approaches.

Examples of Common Trenchless Technologies

Pipe Bursting: Pipe bursting is a rehabilitation method by which an existing pipe is pushed apart with an expansion head pulled through the pipeline, creating space for the new pipe being pulled into place directly behind the expansion head. Due to the need for strength and flexibility during installation, the new pipeline material is typically high-density polyethylene (HDPE) or fusible polyvinyl chloride (PVC). Pipe bursting can be implemented for both gravity and pressure pipelines in sewer and water applications and is generally used for size-on-size replacements or for upsizing by one standard size. Service laterals must be reinstated along the newly burst pipeline and access for pipe bursting requires launching and receiving pits, so some excavation is required, making this a “mostly-trenchless” technology. Even with some excavation, the footprint is still smaller than a traditional excavation approach, and the cost is generally less. Click here to watch a video that shows the pipe bursting process.

Cured-in-Place-Pipe (CIPP): CIPP, not to be confused with slip-lining, is a pipeline rehabilitation method that involves inserting a resin-impregnated flexible liner inside an existing pipe, then curing and hardening the liner with heat or ultraviolet light. Service connections are reinstated once the liner is cured, typically with a cutting tool launched inside the pipe. For sewer, access for installing CIPP is typically accomplished via manholes, making CIPP one of the only true “trenchless” technologies with no excavation. This makes it an ideal solution for high-traffic areas, crowded utility corridors, or anywhere excavation needs to be avoided. This technology is mainly used for rehabilitating gravity sewer mainlines, but can also be used for sewer service laterals and pressure pipelines, including potable water. The expected lifespan of CIPP is 50+ years, and the cost can be 50% less than traditional excavation, making CIPP a very cost-effective way to extend the lifespan of existing infrastructure. Click here to watch a video that shows the CIPP installation process.

Spiral Wound Lining (SWL): Spiral Wound Lining uses continuous plastic strips (typically PVC or HDPE) to rehabilitate stormwater and sanitary sewer gravity pipelines and culverts. The plastic strips are wound to form a new, continuous pipe inside the old pipeline. The strips often have steel-embedded ribs to increase strength and rigidity. Similar to other trenchless technologies, access for installation is via manholes or launching/receiving pits, and any service laterals must be reinstated after the liner is installed. SWL differs from other trenchless technologies in that it can accommodate non-round shapes, can be installed around bends, and can be installed with live flow, eliminating the need for bypass operations during installation. SWL is a relatively new trenchless technology in the United States, meaning there are fewer contractors who are familiar with the process. This, coupled with potentially higher materials costs, makes SWL a slightly more expensive option, but often still lower cost than open-cut construction. Click here to watch a video that shows the Spiral Wound Lining installation process.

How do I know if Trenchless Technologies are right for my pipeline?

CCTV Pipe Inspection Crawler

The most important thing you can do to confirm if trenchless technologies are right for your pipeline is to perform a pipeline inspection using closed-circuit television (CCTV) inspection. CCTV inspection uses a robotic “crawler” with a camera to video the interior of the existing pipeline and notes lateral locations and pipeline defects. Videos and defects should then be reviewed with design engineers and contractors to determine which trenchless technologies best fit your project.

Is the pipeline via traditional open trench excavation still a viable option?

Yes! Often, the traditional excavation approach is still appropriate in lieu of a trenchless approach, including:
•If a significant increase in pipe size and/or slope is needed to improve capacity. Trenchless technologies are generally a size-on-size or one size bigger replacement.
• If the existing pipeline is extremely deteriorated or significant pipe defects exist that would preclude the use of trenchless technologies. Typical examples include offset joints, pipe ovality, pipe misalignment, and/or adverse grades.
• If a change in alignment is required. Trenchless technologies most often follow the alignment of the existing host pipe.

Connect with Coffman

Do you have a pipeline that might be a candidate for repair with trenchless technology, or do you want to learn more about Coffman’s Civil Engineering or Trenchless Technology services? Contact us to start a conversation with a local Coffman engineer.