Eastside Water Supply Project Raw Water Intake Tunnel

Completed in 2013 by Southland Contracting, the Eastside Water Supply Project Raw Water Intake Tunnel Project consisted of the construction of one 45-ft-diameter shaft 170 ft deep; 6,000 lf of 114-in tunnel under Lake Ontario with a 4-in-thick shotcrete liner; six 60-in drilled pump shafts 100 ft deep; 220 lf of 12-ft main pump adit tunnel excavated by drill and shoot methods and two marine intakes (114-in- and 36-in-diameter, 60-ft deep in 60 ft of water) approximately one mile offshore on Lake Ontario. The 45-ft-diameter shaft was also lined with a 2-ft-thick concrete liner and had two 144-in roller wheel gates installed to regulate the intake water from Lake Ontario. The tunnel was excavated in the Queenstown Shale formation. The rock support for the tunnel included only rock bolts in the crown and rock bolts with wire mesh in the crown of the tunnel. As described below, we had a change in conditions on this project due to the shale formation encountered in the tunnel. We overran the bolts/mesh support by 200%+ due to the overbreak and slaking/drying of the shale. This created some challenges and safety concerns we had to overcome. At one point during the mining we had to cease operation and go back and re-support the entire tunnel and install mesh and shotcrete (only bolts were directed to be installed). Lesson learned was that the tunnel should have been supported with bolts and mesh the entire length of the tunnel due to the fallout of the shale formation. The marine work also had challenges of its own. The drilled intake shafts were approximately one mile offshore. The nearest launch site for the marine barge/tug equipment was over 15 miles away. To push the barges one way was an approximately 5- to 6-hour voyage. Within a matter of hours, the wind could pick up on the lake and cause very high, choppy waves that could damage cranes and barges. We always had to be on the lookout and make decisions each day regarding whether it was safe to work on the water. Due to the weather, we only had a short window to work on the lake from May to October. Due to the conditions on the lake, we invested in a jackup platform barge for the tendering crane operations. This setup allowed us to jack the barge up out of the water to ride out the storms, wind, and waves. There was not any soil overburden at location of the intakes in the lake. The bottom of the lake was essentially bedrock (shale). We had to drill and shoot a massive excavation out of the lake bottom. This required underwater blasting using divers to insert dynamite into the drilled holes. Once the rock was blasted, the rubble was removed with dredging, air lifting, and clamming techniques.