Microtunnelling goes deep for York Region sewer

Daily Commercial News
June 26, 2014
DAN O’REILLY

Microtunnelling was the option York Region chose for the installation of an urgently needed sewer line while, at the same time, minimizing disruption to homes, businesses, and traffic on a busy street in a well-developed part of the region.

The approximately 1,800-metre, 1,200-mm diameter North Don Sanitary Relief Sewer will relieve capacity constraints on the existing North Don Sanitary Trunk Sewer and permit growth in growth in Richmond Hill and Markham, say regional officials.

Construction of the approximately $17-million concrete pipe started last October and will be completed this fall. The general contractor is Pachino Construction and Ward & Burke Microtunnelling is subcontractor for the tunnelling which was close to completion in mid-June.

Design work by consultant MMM Group commenced in September 2012.
Although a section of the sewer is being installed on Carr-ville Road, the main route is along Bathurst Street.

“Bathurst is a major north/south collector road, so it is very busy,” says York Region project manager Claudio Micelli, in explaining why microtunnelling was chosen.

There are also plazas at the northwest, northeast, and southwest corners of the two streets, and number of homes along Carrville Road.

Even so, the tunnelling was an around-the-clock operation from Monday to Saturday with five launch and exit shafts being used.

And, while there was space at launch shaft locations for tunnelling and material storage, there was impact on drivers. To reduce that inconvenience, lane closures were restricted to non-rush hours between 9 a.m. and 3:30 p.m. to lessen the inconvenience, says Micelli.

The project has not been an entirely 100 per cent micro tunnelling operation. In one particular section about half-way along Bathurst Street open cut construction was conducted by the general contractor because the sewer route crossed over existing twin culverts “and there was very little clearance for the pipe.”

As a result of the open cut section, the microtunnelling had to be divided into three segments.

“The first tunnel run started at the south end of Bathurst and went north to the open-cut section. The second tunnel run started at Bathurst and Carrville and went south to the open-cut section. The third tunnel run started at the same location as the second but went east along Carrville to the east end of the project.”

Soil operations, however, have been very favourable and high water tables have not been an issue. Dewatering was not required for the construction of the shafts or the tunnel and only a little was needed for the open cut area, he says.

“They (the contractor and subcontractor) have been making really good progress.”
In an interview, Micelli said he was anticipating a completion of the microtunnelling by about the middle of the month.

But there is still plenty of work for the general contractor to complete. One of the most challenging duties will be the construction of a manhole and then breaking into the existing North Don sewer to install isolation chambers so that the flows can be redirected to the new relief sewer.

“It is more complicated than it sounds as the contractor must work in a chamber with running raw sewage, so maintaining health and safety will be important.”

Other work includes transforming the launch/exit shafts into manholes and site restoration, he says.