AEI Subsurface takes on complicated bridge project to help locate utility lines before support columns could be installed
Mission critical work is defined as anything deemed vital to a business or project. That pretty much describes what AEI Subsurface does every day: Locate and map underground utility lines so that contractors can safely and accurately perform excavation work.
The recent construction of the 4,735-foot-long, 150-foot-tall Pearl Harbor Memorial Bridge, which carries I-95 over the mouth of the Quinnipiac River in New Haven, Connecticut, provided a good example of AEI’s capabilities. The company, based in Warren, Rhode Island, was hired to locate utility lines so that the bridge’s massive support columns could be safely installed, says Pat Aubin, who co-owns the company with his son, Nick.
Twin 48-inch-diameter forced-sewer mains that run 100 feet under the bottom of the river represented one of many underground-infrastructure concerns. The mains carry millions of gallons of raw sewage a day; as such, the contractor building the bridge had to develop an emergency environmental plan, just in case the lines got damaged.
As it turned out, the margin of error was small. Using electromagnetic technology from Vivax-Metrotech, AEI determined that one of the shoreline foundations, which measured 11 feet in diameter and had to be placed atop bedrock 100 feet below the riverbed, would be installed a scant 15 inches from one of the sewer pipes.
The company usually relies on electromagnetic and ground-penetrating radar technology to locate utilities. But because those technologies don’t work under water, AEI had to mark the portion of the sewage pipe under the river bed by using survey coordinates provided by the general contractor. “We went out in a boat to mark the pipe under the river,” Aubin says. “We dropped buoys with heavy weights attached.”
To dig a hole for the support columns, the contractor used 11-foot diameter casings with teeth on one end that dig into the soil. “It literally liquefies the ground,” Aubin says. Since the drilling was occurring just 15 inches from the sewer line, officials were concerned about the stability of the ground underneath it; clearly, a sewer-line failure was not an option.
AEI solved the problem by locating the sewage line, then using air excavators to dig down and expose the pipe. Aubin also installed a monitoring device atop the pipe that would measure any vertical and horizontal movement during foundation-boring operations. All this work occurred 8 to 10 feet below the water table, alongside the river. The bridge opened in fall of 2015.