Jim Schill | Technical Writer
When it comes to trenchless pipe bursting, few contractors can claim the experience and success that PW Trenchless Construction can. The Surrey, British Colombia, Canada-based contractor has almost 20 years of pipe bursting experience and has performed some of the most notable bursting work in Canada, including a recent project for the city of Maple Ridge, British Columbia.
The ability to upsize, or increase the diameter of the host pipe, is one of the most significant capabilities of pipe bursting. For the Maple Ridge project, static pipe bursting was used to replace an undersized gravity sanitary sewer. The city’s south slope interceptor sanitary sewer runs along the riverfront area of Kanaka Creek Regional Park. With new residential developments and growth in the area, the sanitary sewer required major upsizing in order to keep pace. Because the sanitary sewer runs through an environmentally sensitive area, open-cut replacement was not feasible.
The city of Maple Ridge is considered part of the Metro Vancouver area. Located 30 miles east of Vancouver, the city has a population of approximately 83,000. In order to bring the city’s sanitary sewer inceptor in line with existing and projected growth, the project required upsizing the existing 15-inch PVC pipe. One section would require three nominal pipe size increase, or a 33 percent upsize, and the other nine nominal pipe sizes or 127 percent.
During the preliminary design phase, the city contacted several pipe bursting firms and solicited feedback on the feasibility of this major upsize. The response was clear. The project could be completed successfully, but only by an experienced pipe bursting contractor with the means and resources to undertake a project and a contingency plan. PW Trenchless was the ideal choice.
In addition to technical expertise, the contractor is very familiar with the conditions in Maple Ridge. “In 2014 we did a smaller upsize from 15 inches to 20 inches about a block away from this new project, and that gave the city some confidence to further explore the potential for a larger pipe upsize,” said David O’Sullivan, president of PW Trenchless. “This, however, was a more significant upsize, with four sections of 15 to 28 inches and three sections of 15 to 34 inches.”
For the project, O’Sullivan selected a Grundoburst 2500G from trenchless equipment manufacturer TT Technologies, of Aurora, Ill. The most powerful static pipe bursting system in the world, the hydraulic bursting unit offers 287 tons of pull force at 250 bars, with a maximum pull of 315 tons.
According to Mike Schwager, TT Technologies pipe bursting specialist, an upsize of this nature requires careful consideration. “Upsizing to these levels requires a lot of planning. You need to look closely at soil conditions, peripheral utilities, as well as surface conditions and obstacles,” said Schwager. “The job was really a progression, as PW Trenchless had completed several successful upsizes with several different sized bursting units in the years leading up to this project. This one, however, would necessitate much larger static bursting equipment than the preceding projects.”
While pneumatic pipe bursting paved the way for the trenchless method in the North America in the 1990s, static pipe bursting has made significant gains over the last 10 years, becoming as popular as its pneumatic counterpart.
For the of Maple Ridge project, static pipe bursting was the correct solution for the types of soil conditions encountered in that region of Canada.
A survey revealed that the first 15 feet contained well-graded, fill-sand and some gravel with occasional cobbles, but was primarily dry. In the next 15 to 20 feet, the was medium to coarse fill-sand, some rounded gravel and occasional cobbles. The existing pipe depth ranged between 9 and 20 feet deep and with minimal (0.02 to 0.1 percent) grade.
The western end of the project was close to Kanaka Creek. A large amount of rain in the spring season had raised the water level significantly where the creek meets the Fraser River. Because that was less than 330 feet away from the lowest manhole on the project, all means possible were utilized to protect the waterway. It was decided that the upper portion of the project would be completed first and bursting runs closer to the creek would be scheduled for later in the summer, in anticipation of lower water levels.
The bursting was divided into seven runs averaging 350 feet each, for a total of 2,456 feet. The design required replacement of the existing 15-inch PVC pipe with three sections of 34-inch DR 17 HDPE and four sections of 28-inch DR 17 HDPE. Maintaining the grade of the pipe was critical and with such a major upsize, ground heaving was also a concern.
The existing 41-inch-diameter manholes had to be replaced with four 47-inch and three 53-inch manholes. Launch and exit pits -10 to 15 feet deep and up to 60 feet long -were excavated at the manhole locations to help facilitate removal and replacement of the existing manholes after pipe bursting was completed.
Crews exposed the sanitary service connections in order to be ready for re-connection to the new pipe. All other adjacent services (water, gas) were also exposed before pipe bursting. Prior to each pull, the HDPE pipe was fused onsite and equipped with a special bursting head assembly.
O’Sullivan explained the unique approach: “We used a three expander bursting head assembly for this project. The three expanders increased incrementally in diameter. This triple expander configuration provided a staged movement of the soil, allowing it time to relax before the next expansion came along.”
In addition, PW Trenchless crews used lubrication to reduce the ground friction, pumping a mixture of bentonite and polymer through one pre-fused pipe.
During pipe bursting, some heaving occurred in the exposed service pits, but none on the ground surface, just some cracks along two sections of 34-inch pipe. Crews installed new inspection chambers for the re-connected services and all of the newly installed manholes in Kanaka Creek Park were sealed for odor control. The pit locations were restored and seeded.
And it was all done with no disturbance to existing utilities. “The CCTV post pipe bursting confirmed a successful installation,” said O’Sullivan. “Bursting times ranged between 3 to 4 hours per run, while removing the different cones took s6to 8 hours. Set up and break down was completed over several days.”