The City of Langley, British Columbia knows the benefits of trenchless technologies, and in recent years many jobs have gone to tender that allowed for the use of these minimally invasive methods.
PW Trenchless bid a job in 2021 that involved the upgrading of a sanitary sewer under 200 Street between 48 Avenue and the Nicomeki River. The project, designed by R.F. Binnie & Associates Ltd., involved the upgrading of a 200-mm pipe to a 450-mm to increase capacity for the area.
200 Street is one of the most important arterial roadways in Langley. PW Trenchless opted to use static pipe bursting to complete the replacement project. Using this method of construction meant that – for the most part – at least one lane of traffic heading both North and South was kept open, and traffic was stopped for delivery trucks or when the pipe was staged.
Overall, the project consisted of five bursts, totaling 550 m, additionally there were two 50 m sections of open cut pipe replacement. The project spanned three months, and the existing 8-in. pipe, was replaced by approximately 300 m of 16-in. 450-mm HDPE pipe. All the manholes were replaced with new manholes including the bases.
Because there wasn’t a sewer nearby to divert flows through, this project called for a bypass system of pumps that could safely and efficiently handle the sewer flows 24 hours a day for an extended period. The engineering for the pumping system was handled in-house at PW Trenchless and utilized pipes, 6-in. Godwin Pumps, grinder pumps and generators.
Many sections of the sewer were 4 m deep and a soils engineer was used to provide safety for the crew and existing infrastructure.
Pipe Bursting Site Setup
Once the entrance and exit pits are excavated and shored with trench shoring cages, all other connections or pipe crossings are also excavated and shored. The HDPE pipe is fused together to the correct length for each run, often all the runs are fused at the same time and the lengths of new pipe are staged in one location and moved into place the day of the burst — or the day before.
A pulling head is attached to the end of the new HDPE pipe and staged close to the entrance pit.
The entrance pit varies in length due to the size and rigidity of the new pipe and the depth of the host pipe. While the new pipe string has some flexibility, the crew must align it aboveground so the new HDPE pipe is not damaged by excessive bending as it enters the pit and host pipe. Pipe bursting only works to replace an existing pipe, it differs in this way from horizontal directional drilling.
For a 4-m deep host pipe, the entrance pit needs to be more than 3-to-1 the length of the depth. Generally, a full depth trench is dug 2-to-1 of the depth, then a narrower sloped cage, or trench shoring is used to aid in the angle of entry for the new HDPE pipe and bursting head to enter the host pipe without too much upward stress on the HDPE pipe. Often during a burst, an excavator’s bucket will be used to help “persuade” a pipe to be more in alignment with the host pipe.
Before bursting on a section commences, all the pulling rods are inserted into the host pipe from the exit pit to the entrance pit. The entrance pit is the excavation where the pulling head and new HDPE pipe are inserted into the host pipe. The exit pit is where the pulling rig is placed and braced for the great forces exerted on the existing ground to pull the new HDPE pipe through the host pipe.
Great force is used because static bursting does not benefit from a percussive action as pneumatic bursting does. All the force of the bursting of the host pipe and the compression of the surrounding soils to make room for the larger new HDPE pipe come from the cone shape head and extreme force applied via the pulling rig of the pipe bursting process.
There are benefits to both, but the static pipe bursting system does away with air hoses and a cable winch that guides the pneumatic percussive pipe bursting head through the host pipe. For static pipe bursting, a much smaller less expensive pull back head is used, and pulling rods which have a much longer life than the winch cable.
The project was completed within the proposed time, and the area was restored so that the only evidence of the work is some fresher sections of asphalt. The use of pipe bursting over conventional excavation methods of pipe replacement required roughly 80 per cent less excavation, which meant less material trucked offsite and less fresh fill trucked in to backfill the excavations. Not only does decreased trucking directly contribute to the carbon footprint of the project, but it also decreases wear and tear to the roadways as well traffic congestion around the project site.
PW Trenchless completed the project during a fairly rainy time of the year and with proper planning was able to continue work during any inclement weather.
The Longest Burst – A Timeline
The longest burst of the project was 120 m in length and took place Dec. 9, 2021. This is a timeline of those activities.
- 9:10 a.m. – The pulling apparatus is lowered into place in the exit pit
- 9:30 a.m. – First rod is inserted into the host pipe from exit pit.
- 10:33 a.m. – The new HDPE that has been fused together and the pulling head already attached. It is moved from its lay down area and staged into position near the top of the entrance pit.
- 10:48 a.m. – The pulling rods enter the entrance pit. Elapsed time of inserting the pulling rods is 1 hour 18 minutes.
- 10:50 a.m. – The crew using a backhoe aligns the tail end of the new HDPE pipe out of the path of traffic coming off 50 Avenue entering 200 Street. Two lanes of traffic are kept open through out the bursting process.
- 11:04 a.m. – The new HDPE pipe is lifted into place into the entrance pit and moved into the pulling position near the rods coming out of the host pipe.
- 11:09 a.m. – The new pipe, with its pulling head attached, is fed through the series of trench cages up to the host pipe. There is a series of cages used in a row to help get the new pipe aligned with the host pipe 4 m below the surface.
- 11:18 a.m. – The pulling head is in place in the entrance pit and the connection to the pulling rods starts.
- 11:40 a.m. – The bursting head enters the host pipe, and the pipe bursting starts.
- 11:46 a.m. – The bursting head passes below an asbestos concrete watermain that has previously been exposed via hydro evacuation. The debris that is pushed into the excavation does not contact the watermain and the bursting head and new HDPE pipe pass under the watermain without issue.
- 12:28 p.m. – The bursting head passes through the first service lateral without incident.
- 12:40 p.m. – The bursting head reaches the first part of the pulling apparatus, and a reducing plate must be removed for the bursting head to enter the exit pit.
- 12:44 p.m. – The bursting head enters the exit pit.
Once the pipe is at the exit pit, the PW Trenchless crew was broken into three groups to finish the section. One group was tasked with removing the bursting head and the pulling apparatus and cleaning up the exit pit area. Another group cut the pipe in the entrance pit and make a mechanical connection of the previously installed HDPE pipe and the freshly installed HDPE pipe. The final group drills a hole into the newly installed HDPE pipe, install an Insert-Tee and connect to the new pipe to the service lateral.
All told, the installation of 120 m of HDPE pipe via pipe bursting was complete in 1 hour 4 minutes.