Environmental Science & Engineering - www.esemag.com - January 2006
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Mature neighbourhood benefits from tunneling concrete pressure pipe

By Butch Contreras

To preserve the ambience of this old established area with its mature trees, tunneling was selected as a viable option for the installation of the 400 mm diameter high pressure concrete watermain virtually in the centre of Aurora, a town as old as confederation. Photograph by Grant Lee

An old and vibrant residential and commercial neighbourhood in the Town of Aurora, north of Toronto, benefitted from the installation of a new concrete pressure pipe watermain, before it was commissioned to carry potable water. Started in August 2004 by North Rock Group, the service was not completed until October 2005 because the project had to be redesigned to accommodate poor ground conditions and the existence of underground utilities and services.

The project is located in the downtown core along Wellington Street, between Highway 11 (Yonge Street) and Berczy Street. The mature treelined avenue is home to residents and street-level businesses. In addition, it is a major east-west arterial road for traffic moving between Highway 11 and the commercial core of the town, and Bayview Avenue to the east and Bathurst Street to the west.

Type of installation of the pressure pipe supplied by Hyprescon, and choice of material were carefully considered, as prolonged disruption to the everyday activity of the street and adjacent neighbourhoods was not an option.

Design engineers decided to tunnel a 400 mm diameter watermain for 1,200 metres along the south side of Wellington Street, from west of Yonge Street to Berczy Street. The tunneled portion was part of a larger watermain installation project that extended between Orchard Heights Pumping Station and the Bayview Avenue Pumping Station. The alignment and depth of the tunnel along Wellington Street was determined to a great extent by existing services and utilities located above the tunnel.

The watermain project was divided into approximately four contracts beginning in 2001. North Rock Group had the last and longest tunnel section due to the redesign of the installation. Installations carried out by other sewer and watermain contractors included tunnelling to cross the rail line at Berczy Street and major intersections such as Bayview and John West Way which fronts on to the Aurora Municipal Offices.

Tunneling for the pipe required a cutting head at the leading edge of the pipe and the feed of slurry to the head for lubrication. As the pipe was advanced by hydraulic pushes behind the cutting head, a soil slurry was transported from the head of the tunnel along the inside of the pipe to the bore pit where it was removed. Once the tunnel digging machine (built by Technicore Underground Inc.) reached the receiving pit, it was removed by crane.

The advantages of microtunneling the pressure pipe included the accuracy of the tunnel alignment controlled by laser, the slurry was easily contained and removed, and since the need for workers in the pit was kept to a minimum, job safety was enhanced. Savings in construction, environmental, social and economic costs of the watermain through the neighbourhood by tunneling outweighed the open cut option. Once the concrete pipe was in position within the tunnel, the rigid pipe structure would interact with the surrounding soils to perform as designed.

Technicore installed a 3,000 mm diameter caisson shaft on the south side of the intersection of Victoria Street and Wellington. The second 3,000 mm caisson shaft was located on the south side of the intersection of Wellington with Berczy Street to receive the tunnel digging machine. The company also manufactured a special pipe handling machine to lower the pipe into the shaft to ensure proper installation without stress on the back pipe. All pipe joints were wrapped as they were installed.

Hyprescon manufactures 350 mm to 500 mm diameter bar-wrapped AWWA C303 and 600 mm to 1350 mm diameter lined cylinder pipe. Larger diameter sizes are produced as prestressed concrete embedded cylinder pipe. Lined cylinder pipe is manufactured horizontally. After a fabricated steel cylinder has been hydrostatic tested, concrete is applied to both sides of the cylinder while it is being spun. After the concrete has cured, the pipe is prestressed with high tensile wire. The outside of the pipe is then coated with cement mortar to cover and protect the wire. The cycle for producing a length of standard pressure pipe, in accordance with AWWA C301, is two to three days. Closure pieces for the pipe were manufactured as required.

The watermain along Wellington Street is part of the Aurora Newmarket Feedermain which will convey surface water from the Maple Reservoir in Pressure District 6 to the communities of Aurora and Newmarket in early 2006. This project consists of the North Maple Pumping Station and a large diameter trunk watermain from the pumping station to the Aurora Newmarket Reservoir at Bloomington Road. The Bathurst North watermain will convey surface water from the reservoir to the Wellington Street watermain in Aurora.

Prestressed concrete lined cylinder pipe is manufactured to meet the design life of projects require performance for generations. A minimum 100- year service life of the pipe provides an asset that enhances the value of a municipality’s infrastructure. Multiyear maintenance plans of the watermain along Wellington Street were developed with a high level of certainty that the structure will perform as designed. Tunnelling the concrete pressure pipe was an installation option that worked well in this case, with little disruption to a mature neighbourhood.

Butch Contreras is with Hyprescon
E-mail: bcontreras@h2ohyprescon.com

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