For a new bridge spanning the Ottawa River between Hawkesbury, Ontario, and Grenville, Quebec, contractor Dufferin Construction Co. moved pier forms into place using a special marine railway and gantry barge and eliminated cofferdams by placing pier concrete by tremie. The bridge will replace the deteriorating Perley Bridge, which was built in 1931, 80 feet downstream from the new site.
Casting the nine concrete piers of the new 2,300-foot-long, four-lane bridge was no small feat. For each footing, a large 23x52x10-foot form was preassembled around a rebar cage on a railway cart on the riverbank. The first pier-shaft form was also assembled atop the footing form. With the help of winches, the cart was launched down a 260-foot railway, into the river and the arms of a specially modified barge. With the 60-ton form-and-cage assembly nestled between two pontoons, the barge’s gantry and four winches picked it up. Then the barge floated over to the pier location, and the winches lowered the assembly into place.
Placing the 600 cubic yards of concrete required for each footing took about 24 hours. A 28-meter boom pump on a barge, fed by a 32-meter boom pump on the old bridge, pumped concrete into one of 12 standpipes inserted into the submerged footing form.