his summer the City of Saskatoon announced its plans for projected growth in the next 50 years- population one million. In June the city recorded a population of 246,300, up some 10,000 in just a year, and it foresees an annual growth rate of at least 2.5 per cent for the decades to come.

Growing quickly, not to mention the forecasts to meet this seven-figure milestone, requires expanding the city limits in a rural region-a task a forefront the City of Saskatoon’s agenda.

Among all the work to prepare for this on-going growth, the city is working on a development project that will add about eight new neighborhoods in an area called the East Sector (more recently renamed Holmwood).

The city awarded the design-build contract to Michels Canada for the McOrmond Drive Sanitary and Storm Sewer Trunks project in Spring 2012. Work consists of two parallel trunk sewers approximately 1,500m long, with a depth approximately 14m below ground surface. Michels Canada submitted the lowest bid at CAD 33,472,950 (USD 32,266,000) following a pre-qualification process in fall 2011.

These trunk sewers are the last step to opening up this major development of approximately 2,533 hectares, primarily residential, for the growing region. The design of the addition is based on a population of 82,000.

The tunnel alignment was selected 20 years ago as part of the city’s internal master planning. "In the past eight years, the pace of development has rapidly increased and our East Sector is now being planned for major residential developments," says Dan Willems, special projects manager for the City of Saskatoon.

"Trenchless methods were selected as the high demand for development in the neighbourhoods adjoining the alignment didn’t allow for construction of the trunks by open trench methods 10 years ago."

The two sewers will run along McOrmond Drive, from the downstream connection to existing trunk sewers on Attridge Drive to the southeast side of the intersection of College Drive (Highway 5) and McOrmond Drive. The sanitary sewer is a 1,200mm inside diameter tunnel and will be constructed using 2.6m diameter TBM. The storm sewer is a 2,400mm inside diameter tunnel and will be constructed using a 3.3m diameter TBM. Both tunnels will be a two-pass system with for the sanitary sewer, which, when complete will have a 48in (1,219mm) pipe installed inside.

Following the second drive, Michels Canada will install a 96in (2,438mm) pipe inside the storm sewer.

Both machines are launching from the same shaft located at the south (upstream) end of the alignment and tunnelling north. There will be 3m of clearance between the two drives. The launch shaft is about 15.2m long by 11.3m wide by 11.5m deep, and the reception shaft is about 6.1m long by 11.3m wide by 16.1m deep.

As shown in Figure 1, the tunnel alignment traverses a mix of firm and very stiff clay with occasional wet fine grained sand seams with cobbles.

The only grouting that will take place on the project is for the annular space between the outside of the carrier pipe (supplied by Hobas Pipe) and the tunnel lining. Michels Canada is working with Paci_ c International Grout to complete this work.

For the lining, Michels has selected a two-pass ring steel and timber lagging lining. The ring steel linings are made from three pieces of I-beam that are rolled and bent into a circular shape creating a ring set, and the timber lagging consists of 3in x 6in (76mm x 152mm) rough-cut timbers.

The rings are manufactured by DSI Underground Systems based in Louisville, Kentucky, and the timber was purchased from Welco Lumber Corp. of Burnaby, British Columbia.

The sanitary sewer tunnel TBM launched on May 7, with completion of the drive expected as this issue of Tunnels goes to print. And the storm sewer tunnel TBM’s launch should follow soon after.

Vandaelle says that the most challenging part of the job has been the ground conditions in which crews are mining, and the tough long winters experienced in this part of Canada.

Construction for the trunk sewers is required to be completed by 2014, in time to accommodate house sales starting in the East Sector.

According to the city’s population projections, current trends indicate new neighbourhoods in Saskatoon each average 10,000 people.

Maintaining a sustained growth rate of 2.5 per cent, the projected population increase will result in the need for the equivalent of three new neighbourhoods before the end of this decade. Should everything stay the course another 15 new neighbourhoods will be needed in the next 20 years