Gary/Chicago International Airport Authority
Gary/Chicago International Airport Authority (“the Airport”) was required by the Federal Aviation Administration (FAA) to obtain additional airspace in their runway approach corridor for runway expansion. This necessitated relocation of two parallel 345 kV circuits, a 138 kV circuit, and a 34.5 kV circuit in the Northern Indiana Public Service Company (NIPSCo) transmission right-of-way.
The Airport selected Commonwealth to provide Owner’s Engineering and design services. As Owner’s Engineer, Commonwealth provided material procurement documents, bid documents, and construction packages and evaluated bidders’ submittals. Commonwealth also provided construction support. Eight design options were evaluated, and Commonwealth’s solution provided a 40 percent reduction in the total construction cost. This solution required the design and installation of a new 340 MVA 345/138 kV substation, two 138 kV underground transmission lines, one 34.5 kV underground line, and miscellaneous medium-voltage line construction.
Underground construction in this area presented some major challenges. As the water table varies with the direction of the wind on Lake Michigan, the required splicing vaults had to consider this and were designed for negative buoyancy. Due to the future construction and soils, the duct banks were designed for H20 highway loads. The design also made provisions for several future railroad relocations. Due to the existence of major industry related to oil refineries in the project area, several surprises were encountered during construction. Examples include a 50-inch concrete process water line and some abandoned crude oil lines. Since the underground construction occurred during winter, the concrete mix had to be readjusted for cold temperatures while retaining the necessary thermal properties to obtain the required transmission line power capacity.
All issues during construction were resolved successfully, and the project was completed ahead of schedule.