March 27, 2008

KMK CONSULTANTS

‘Tweety’ makes its way through all kinds of terrain during construction, defining it as a digging machine, not the usual boring machine.

KMK CONSULTANTS

When finished, the 4.5 km sanitary diversion sewer will first operate under gravity but as needs within the community change, its operation will be reversed to become a forced main.

Unique Design

New concrete pressure pipe will start as gravity pipe, then become forced main as needs change

DAN O’REILLY

correspondent

Burrowing under Highway 410 and through a number river crossings while staying clear of hydro lines, a 4.5-kilometre-long sanitary diversion sewer now under construction in Brampton may be the first of its kind in the Greater Toronto Area.

The 1,200-mm concrete pressure pipe will divert sewage by gravity from Peel Region’s near-capacity Fletcher’s Creek trunk sewer at Highway 10 east to its Etobicoke Creek trunk line in the Tomken Road area — at least for the next few years.

At some point, the flows will be headed in the opposite direction because the sewer has been designed and constructed to serve as both a gravity pipe and a forced main.

Scheduled for completion some time next summer, the project is divided into two contracts. Newmarket-based Technicore Underground Inc is tunneling the first 1.9-kilometre section from Fletchers Creek to Kennedy Road along the southern extremity of a hydro corridor just south of Highway 407.

With the exception of a tunnel under Highway 410, open cut construction is being used for the remainder of the route. Dom Meridian Construction Ltd. is the contractor for this phase. Concrete pipe suppliers are Munro Concrete Products Ltd. and Hyprescon.

At a cost of $27 million, the diversion sewer is considerably less expensive than the estimated $100 million cost of twinning the Fletchers Creek (or west trunk), says Simon Hopton, manager of capital works for the region’s wastewater division. “Although that (the twinning) will be necessary at some point in the future,” he says.

That’s when the diversion sewer will switch roles from a gravity pipe to a forced main. A yet-to-be built station will divert sewage from the Etobicoke Creek trunk to the Fletcher’s Creek trunk, says Hopton.

Identified as a crucial project in a water and wastewater master servicing plan approved in 1999, the diversion sewer is an effort to cope with major and fluctuating growth patterns in Brampton, he explains.

Right now, the Fletcher’s Creek sanitary sewer is operating at near capacity, while the Etobicoke Creek trunk has excess capacity. But as development patterns change in Brampton, that trend is expected to reverse itself, says Tony Mellegers, an associate at KMK Consultants Limited, consulting engineers.

“Sewage will then have to be diverted away from the Etobicoke Creek trunk,” he said.

Designing a sewer that could serve double duty as a gravity or forced main was just one of the many logistical and planning challenges the region and its consultants had to overcome before the project could proceed, says Mellegers.

Numerous regulatory approvals had to be obtained to use the hydro corridor, which was considered the best location to avoid disruption to residential and industrial areas and to minimize conflict with existing utility lines.

An agreement had to be negotiated with Ontario Realty Corporation, which owns the land, and the region also had to prove to Hydro One the sewer would not impact existing or future towers. Approximately 400 cubic metres of unsinkable fill had to be placed near each of 10 planned new tower sites, says Mellegers.

When it came to the actual construction, the first section had to be tunneled as depths of the sewer exceed 15 metres in many places. Technicore was awarded the contract because it is a tunneling machine manufacturer and a tunneling contractor, he says.

Because of the number of boulders along the route, a specially-designed digging machine was manufactured. “It’s digging not boring,” says Mellegers, explaining boring machines work well in either totally rocky or loose earth areas, but not where there’s a mixture of both.

Known as Tweety, the machine commenced work in early November and has been operating in two shifts from 7 a.m. to 3 a.m. with some down time for maintenance, says Technicore engineer and spokesperson Dave Marsland.

It requires fewer personnel to operate and consumes less power than a tunnel-boring machine, said Marsland, who was reluctant to provide any more details about its operation.

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