ENMAX - Downtown Calgary Transmission Reinforcement Project (DCTRP)

Somerville was contracted by ENMAX Power Corporation to construct a new underground single circuit 138kV transmission line (138-2.84L) from existing ENMAX No.2 Substation south-east of the city, to existing ENMAX No.8 substation downtown. This circuit was 5.3km long and involved a combination of open cut and microtunnel bore methods.   The open cut sections completed were approximately 3,800m in length, meandering through the City mostly in the travel lane portion of the road. Other trenched areas were through the medians, boulevards, Stampede Park Grounds, parking lots, and parkland. To facilitate the cable pulling limitations, 10 precast cable chambers (7.8m x 2.85m x 3.0m) were installed along the route, often in very congested areas.   5 microtunnels sections were completed by subcontractor Ward & Burke. The tunnels were 1,200mm dia., ranging from 87m to over 500m in length, under CP Rail and Blackfoot Drive, Elbow River, McLeod Trail, and under 9th Street and the CN mainline track downtown. This last tunnel was over 1,000m long with a launching shaft at the midpoint of the microtunnel. Difficulties during tunneling included building tie-backs, poor soil conditions, rock, and water ingress during ductbank tie-ins.