DYWIDAG Rock Bolts stabilize Chicago’s largest Flood Basin

Underneath the city of Chicago, a network of large tunnels connects a series of pumping stations and temporary holding reservoirs that collects all of the city’s storm and wastewater and diverts it to water reclamation stations around the city. The tunnels that feed into the reservoirs are typically located near the floor and require a concrete apron to prevent erosion at the tunnel entrances and exits.


This combined sewer system, called the Tunnel and Reservoir Plan (TARP), is managed by the Metropolitan Water Reclamation District of Greater Chicago (MWRDGC).

The purpose of the reservoirs is to eliminate flooding during severe weather events. Previously, floods frequently resulted in contaminated water seeping into the city’s canals and ultimately into Lake Michigan.

The McCook Reservoir is a former rock quarry and, when completed, will be the largest reservoir by volume in the system with the ability to store over 37.9 billion liters (10 billion gallons) of water.

This first project phase of McCook Reservoir was completed in December and has a storage capacity of approx. 13.2 billion liters (3.5 billion gallons) of water. The second phase is expected to be completed in 2029.


In order to protect the concrete apron at the McCook Reservoir when large volumes of water are flowing, high strength DYWIDAG Rock Bolts were used as tension piles for flotation control. A total of 480 epoxy coated, 46mm Ø, Gr 150 DYWIDAG THREADBAR® Bar Tendons with a total length of approx. 2,995m (9,825lf) including couplers, hex nuts and steel bearing plates were used to tie the concrete apron down.


The Metropolitan Water Reclamation District of Greater Chicago, USA

U.S. Army Corps of Engineers-Chicago District, USA