The findings from a recent seismic evaluation of Agnew Dam and the surrounding area raised safety concerns regarding the existing multi-arch dam. This emergency response project involved breaching the concrete shell of two of the dam arches to maintain a lower level at Agnew Lake and prevent water from being impounded by the dam prior to the snow runoff.
The scope of work included core drilling four 6-inch to 8-inch diameter holes, one at each corner of the 5-foot x 5-foot opening locations in the two arches. A concrete wire saw was set up by running the wire through the cored holes. One wire saw was used on each arch creating a even opening with no overcutting. The resulting openings were smooth and cut parallel to the axis of each arch. Before the final cut was made, anchors were attached to the slab to facilitate removal using the onsite excavator. To eliminate any potential downtime, a backup wire saw and spare equipment/wires were onsite and ready for use in the event of a primary equipment malfunction.
Once the holes were completed, cast-in-place reinforced concrete buttress walls were constructed on the downstream side to fortify the openings in the arches.
The project is in a very remote, environmentally sensitive location requiring extensive helicopter support to bring in crews, tools, and equipment.