Building the new bridge, so far, has come with its own unique challenges. Heavy snow melt and rain last year, which caused the river to rise 35 ft above its normal level, effectively shut down the project for six months. "At one point, the water reached flood stage and crested," says Hetrick. "It was pretty much up to the door of the field trailers." The slide, which was originally scheduled for this September, has been pushed back to next April.
The pier strengthening also turned out to be a hassle. The owner relied on as-built plans, which were elusive at times, to plot out the submerged caissons. Extra core samples were required, and workers struggled to drill through the decades-old layers of concrete, lumber and other debris left behind from the old hand-dug pneumatic foundations. Finally, before installing and grouting bundled steel bars, workers drilled about 40 holes in each of the bridge's main piers, 4 to 5 in. in dia and extending about 55 to 70 ft deep, to make room for the reinforcement. "We are all glad to be above that point at this time," says Hetrick. "It's tough construction when you are down there."
This year the project also faced a safety-related setback when an ironworker was found unconscious in April pinned between the bucket of an aerial lift and a steel beam he was welding. He later died. The Indiana Occupational Safety and Health Administration is investigating the accident.
Weighing 15,260 tons, the Milton-Madison superstructure, which will measure 2,430 ft along its four-span truss and will extend 3,181 ft, including the approaches, is set to make use of eight 364-ton-capacity strand jacks supplied by Switzerland-based post-tensioning supplier VSL International Ltd. Operated by Walsh's craftworkers, the jacks on June 29 hauled up a 600-ft-long, 1,776-ton span that was prefabricated and floated into position prior to the lift. In August, Walsh plans to repeat the 80-ft-high maneuver for a 727-ft-long span weighing 2,000 tons.
With those two center spans clear of the main navigation channel and out of the way of busy barge traffic, Walsh plans to erect the end spans, measuring 500 ft and 600 ft, in cantilever. Early next year, traffic will be rerouted to the new bridge, which will bear on temporary piers made from 36-in.-dia steel pipe piles. After the old bridge is gone, the new bridge will be ready for the big slide upstream—20 in. at a time—using the eight strand jacks and 9-ft-deep, 125-ton sliding girders previously acting as temporary pier caps.
How long should the slide take? It will be slow and deliberate but much faster than a year of downtime. Johnson says, "We are planning to do it in a shift."