In 2020 and 2021, GLEG performed both the routine safety inspection and the fracture critical inspection. A fracture critical inspection consists of a “hands-on” inspection of all of the fracture critical members on a bridge. A fracture critical member is a steel component in tension that could cause a portion of the bridge or the entire structure to collapse. Typically, the routine safety inspection and the fracture critical inspections are conducted at the same time. A full bridge closure is required, and several pieces of equipment are needed to complete the inspections, including a bucket truck, a boat, and MDOT’s reachall. Because the Grosse Ile bridge is one of two crossings to the island of Grosse Ile, extensive coordination is required to even temporarily close the bridge. Additionally, overall the bridge is in very poor condition. Prior to the 2021 steel repairs, there were lots of steel members with holes rusted through (even after the 2021 repairs, there’s still a few members with holes rusted through).
Since 2019, GLEG has performed six underwater inspections on the Grosse Ile bridge. The underwater inspection frequency was set to 6 months, which is probably the lowest frequency for any underwater inspection in Michigan. During the November 2020 underwater inspection, GLEG found that the even-numbered piers (which were constructed on top of the original 1873 stone-filled timber crib foundations) were in really bad shape.
- Stones and boulders were missing
- There were large voids between the stones that were still in place
- There were gaps in the timber cribbing that allowed the stones and boulders to be removed by the swift flow in the channel.
As a result of the November 2020 inspection, GLEG recommended that the Grosse Ile bridge be closed to traffic until underwater repairs could be made to the even-numbered piers. THIS WAS A VERY BIG DEAL. The only other bridge that accesses Grosse Ile is a privately owned bridge with a 12-ton weight limit.
J.F. Brennan Company, from La Crosse Wisconsin, was hired to perform crazy underwater repairs. During the summer of 2021, they brought in several barges and cranes and used “flow deflectors” to reduce the velocity of the river around the piers and create safer working conditions. Once the flow deflectors were in place, cofferdams were installed around the even-numbered piers and grout was pumped inside the cofferdams to fill in the voids around the remaining stones and boulders. Brennen worked around the clock, with shifts of underwater divers working 24 hours a day, in order to complete the project prior to December 31, 2021. Throughout 2021, GLEG performed “verification dives” to confirm the integrity of the underwater repairs. Upon completion of the underwater repairs in November 2021, GLEG performed an “underwater open to traffic” inspection.
In addition to the underwater repairs Brennen worked on, C.A. Hull constructed steel repairs throughout the superstructure. Floor beams were replaced and bolted steel repairs were installed. After completion of the superstructure repairs, GLEG performed a new routine safety inspection and a new fracture critical inspection. Additionally, GLEG updated the load rating based on the steel repairs. The updated load rating increased the weight limit on the bridge from 26 tons to 40/65/80.
In the future, GLEG will have continued involvement with the Grosse Ile bridge by performing future inspections. By keeping public safety the number one priority, GLEG will assist Wayne County with maintaining the bridge for the foreseeable future.