Piers (provincial section)
The bridge engineers had to devise an innovative method to erect the bridge piers, given the thick layer of glacier marl over the rock, the river’s depth, and the speed of the current.
Since the St. Lawrence River is so deep at this point, the engineers decided not to use cofferdams and instead chose pneumatic caissons, a method that had not been used in Montreal in 25 years.
The Second Bridge
In 1963, it was felt that the Mercier Bridge’s two lanes were inadequate for the constantly increasing traffic travelling across it, so the Ministère des Travaux publics du Québec had a second bridge built downstream from the first.
In the federal section, the deck of the old bridge was modified so that it would have the same capacity as its “twin”. Minor changes were also made to the piers, as each pier was fully resurfaced with a new layer of reinforced concrete and were reshaped to match the piers of the new bridge.
Together, the new and old bridge doubled the number of lanes between both shores from two to four (two lanes per direction). Traffic to the South Shore then started passing over the old bridge, and traffic to Montreal was routed over the new one.