The City of Richmond, part of the Greater Vancouver Regional District, has a population of approximately 180,000 in a region of overall population of approximately 2.2 million.
Trenchless Technology
Preston Creelman
Richmond
The City of Richmond, part of the Greater Vancouver Regional District, has a population of approximately 180,000 in a region of overall population of approximately 2.2 million.
The City is located on a flood plain with elevations ranging from approximately 0.6 metres to 2.5 metres above sea level.
These physical attributes present numerous challenges and opportunities with underground utility design and construction. Design and construction of water mains in combination with soft soil, river delta ground conditions in particular, lends itself to trenchless construction opportunities.
Horizontal Directional Drilling (HDD) is gaining popularity in the Greater Vancouver area as an accepted method of installing watermains. In the City of Richmond, over three kilometres of aging 150mm diameter asbestos cement pipe was replaced using HDD and Cobra Lock PVC C900 DR18 pressure pipe, a first in Canada and possibly North America.
The Shellmont watermain replacement project was designed to be undertaken using the conventional “open trench” procedure. However, the contractor proposed the use of HDD and segmented Cobra Lock pipe as an alternative, “trenchless” method as an innovative opportunity and one that would minimize disruption to residents.
Initially, the contractor proposed using butt-fused HDPE pipe, however, public works staff at the City of Richmond requested that PVC C900 CIOD pipe be used. Public works preferred to work with PVC C900 for repairs or future expansion to the system.
They have over six years experience with segmented PVC C900 pressure pipe and wanted to maintain the standardization process underway going to PVC C900 water delivery system. HDD is one of several trenchless construction methodologies whereby a drilling bit is guided through soil to create a round cavity, which will stay intact for at least several days.
The drill head is propelled by adding segments of rod as the head proceeds forward. Once a cavity is created, the drill bit is removed and a pulling adaptor is attached to the drilling stem.
A length of PVC pressure pipe is affixed to the adaptor. As the adaptor is pulled back to the rig, segments of drill rod are removed. Simultaneously, segments of Cobra Lock PVC Water Pipe are coupled to the adjacent pipe.
This process is repeated until the adaptor returns to the rig and all of the watermain is in place. This PVC water pipe also kept the working area very compact, since no pre-assembly (butt-fusing) and stringing across driveways and roadways was necessary.
Cobra Lock water pipe is a PVC C900 CIOD pressure pipe which is manufactured in 6.1 metre lengths. Each pipe is beveled and grooved at each end. Along with each length of pipe, a coupling is provided. These couplings have two rubber o-rings placed in grooves which have been machined on the inside, near the centre of the coupling. Between the o-rings and the open end, there are corresponding grooves machined to align with the grooves at each end of the pipes, with an angled entry hole.
When a spigot end is inserted into a coupling, a square nylon spline is pushed through the entry hole and around the groove cavity until it goes around the spigot. The splines “lock” the pipe and couplings together, while the o-rings provide the pressure seal between pipes.
The resulting watermain can then be serviced by either direct tapping or saddle tapping as per usual procedures with conventional bell and spigot PVC C900 pressure pipe. Connection to standard appurtenances is made by removing the grooved spigot end with a field cut. The resulting spigot is then chamfered and an insert mark scribed similar to regular C900 PVC pressure pipe installation.
Trenchless construction methods are being used more commonly in British Columbia, with residents gaining the added benefits of less traffic congestion, reduced site dust and debris and minimal disturbance to yard landscaping and driveways.
All these attributes were realized on the City of Richmond project including reduced costs. These hidden/intangible advantages to the municipalities are recognized by industry as opportunities for future works.
James Young, P. Eng., is Manager Engineering Design and Construction, City of Richmond and Preston Creelman, P. Eng., is Specification Engineer, Royal Pipe Systems.
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