Pulling power pushes pipe upsizing
Pipe bursting proves the answer to a tricky B.C. replacement project
Maple Ridge, B.C., is a growing suburb of Vancouver that stretches along the north side of the Fraser River. With an increasing population, the municipality is steadily expanding its services, including water and sewer, and in some cases facing challenging terrain to do so.
A recent project called for replacement of a sanitary sewer that runs along the southern edge of the community, near the river. The existing line was made up of seven segments of 15-inch-diameter PVC pipe that was operating at capacity. That area of Maple Ridge is growing quickly with multiple developments on the horizon, so the city determined that an upgrade was needed.
The problem faced by City Council was how to go about replacing the sewer line. Cut-and-cover was iffy at best due to the existing route, which was along the shore of a creek as well as extending through a regional park and a green belt.
The city decided to go with pipe bursting to up the size of the sewer. A project in 2014 that upsized a 15-inch sewer to 20 inches provided a precedent for the selection. The problem was that to meet the needs of the new developments, the pipe size needed to increase significantly, with segments up to 34 inches in diameter in the plan.
Some contractors approached regarding the proposed project expressed concern over the size and soil conditions of the job, and in the end only PW Trenchless bid for the contract. The Surrey, B.C.-based company had completed the previous upsizing, had a familiarity with the city and the location, and most importantly had the gear to do the job.
Pipe bursting rig drives success
PW Trenchless has made a name for itself by successfully completing numerous challenging projects, many of them demonstrating the benefits of pipe bursting for municipal projects. Several years ago, the company purchased a Grundoburst 2500G static pipe bursting rig, which has provided the needed pulling power to successfully complete many of PW's bursting projects.
Grundoburst manufacturer TT Technologies describes the line of machines as versatile and capable to manage pipes from 4 to 48 inches in diameter and potentially higher. The machines are easy to move and set up, and have user-friendly controls to make bursting jobs easier.
Both PW Trenchless and the city of Maple Ridge approached this project as experimental, due to the sheer amount of upsize in the pipe – nine pipe sizes, compared to the earlier project, which was three – as well as the soil conditions throughout the jobsite.
The work also entailed installation of larger manholes along the pipe route; to facilitate that, the entry and exit pits for the equipment were placed at manhole sites. Seven separate sections were pulled from those sites, averaging about 350 feet per pull. An eight-inch bypass line was put in place to carry the existing flow while work was completed. Other services along the route were exposed and monitored to prevent any potential damage.
A flexible guide rod on the Grundoburst helps users prepare for each bursting run by easily pushing through existing lines.
Each pull was done by connecting a bursting head to the Grundoburst's Quicklock rods to cut the existing 15-inch pipe. Quicklock rods link together quickly and easily, according to TT Technologies, saving time over other methods that require bursting rods to be screwed together.
For this project, a trio of expanders followed the bursting head, pushing the surrounding material out to 21.6, 27 and 32 inches. A 34-inch HDPE pipe, fused on-site, was pulled through behind the assembly.
Lubrication was used to help the bursting assembly along, and to help surrounding material to migrate as it was pushed aside. The Grundoburst 2500G, which has a maximum pull of 287 tons of force, used about 280 tons during each pull of 34-inch sections.
PW Trenchless crews successfully completed each of the seven sections with few issues, and came away with some new knowledge about how existing soils behave under the compression of a bursting operation. A few heaves were reported in the service pits, but none occurred along the ground surface; some minor cracks were spotted along two sections of the 34-inch lines.
New inspection chambers were installed for reconnected services, and manholes in the park area were sealed for odour control. CCTV inspection after the bursting operation showed that installation was fully successful and the sewer is successfully in service.