- ENGINEERING INFO
- CASE STUDIES
The benefits and cost savings of trenchless construction are well documented in urban environments where asphalt and other surface restoration costs are high. The case history of trenchless construction in rural environments has been mainly reserved to stream, canal, and wetlands crossings, primarily using horizontal directional drilling (HDD). Pryor Mountain Engineering saw an opportunity to employ trenchless construction techniques when nearly six miles of 6-inch asbestos cement (AC) line was nearing the end of its useful life; bidding a trenchless option versus conventional dig and replace methodology.
|Pipeline Details and Project Summary|
|Project:||Town of Cowley West End Water Project; Cowley to Deaver, Wyoming|
|Engineer:||Pryor Mountain Engineering, Cowley, WY|
|General Contractor:||Mountain View Building, Sheridan, WY|
|HDD Contractor:||EBI Inc., Duluth, MN|
|Pipe Burst Length:||16,000 LF 10" DR18 Fusible C-900®|
|HDD Length:||8,600 LF 10" DR18 Fusible C-900®|
|Direct-Bury Length:||5,400 LF 10" DR18 Fusible C-900®|
The waterline serving the Town of Cowley (population less than 1,000) was a 6-inch AC line that originated in Deaver and ran along Highway 310, mostly through farm fields. With leaks becoming prevalent throughout the line (see photo on next page), significant amounts of precious water were being lost in this high desert area. Given the difficulty of disposing of AC pipe, in addition to potential cost savings, Pryor Mountain decided to bid a trenchless option that involved nearly three miles of pipe bursting and almost two miles of HDD. The Wyoming Water Development Commission (WWDC), the funding agency, was open to newer technology (pipe bursting with fused pipe), especially if it was able to reduce the overall installed cost. HDD was required in wetlands areas and in other locations where the existing pipe depth was less than five feet. There were also a few direct-bury locations due to re-alignment and other access/utility/depth challenges.
Contractors were offered the option to bid direct-bury/HDD with gasketed C-900 (PVC) pipe, or pipe burst/HDD with 10-inch DR18 Fusible C-900® pipe or 12-inch DR7 HDPE pipe (upsized HDPE pipe was required to maintain the same flow and pressure capacity as PVC). The engineer received seven bids. The low contractor was Mountain View Building (MVB), which came in $70,000 lower than the lowest direct-bury bid by proposing pipe bursting with Fusible PVC® pipe. Given the significant quantity of pipe to be fused and its positive past experience with Fusible PVC® pipe, MVB elected to get its crews trained by Underground Solutions for PVC fusion. MVB decided to perform the work in the spring when area farmers typically irrigate the fields; a decision that would normally pose a muddy challenge. Yet, taking advantage of the wet fields and the "lubricating" effect of the naturally occurring bentonite clay in the area, MVB was able to push the burst length limits from its already long planned distance of 800 LF to several exceeding 1,400 LF. Many of the irrigated fields and canals were simply bypassed with pits located on or near the access roads. One pull-in established a new record length for pipe bursting, with a measurement of 2,120 LF. Jason Spielman, President of Mountain View Building, stated, "When we bid the project we were optimistic about the soil conditions, however the burst lengths achieved with Fusible PVC® pipe exceeded our expectations which, in turn, minimized the impact to land owners and shortened the project timeline."
This was the first time that Willie Bridges, President/Owner/Chief Engineer of Pryor Mountain Engineering, had specified Fusible PVC® pipe: "I am extremely happy with the results we obtained using the pipe burst and boring methods along with Fusible PVC® pipe. This construction method saved the Town of Cowley thousands of dollars by not having to pay damages for cash crops to the area farmers whose land was crossed by the pipeline. I also believe that this process minimized the disruption of water service to customers along the route." The pipe passed pressure testing of 150 psi in July 2012, and went online shortly thereafter.