Thornton Connecting Tunnel & Gates


Walsh Construction

Completion Date



MWH Global


Thornton, Illinois

Delivery Method

General Contractor



Contract Value

$21 million
Thornton Construction in progress
Thornton Connecting Tunnel & Gates
Thornton Connecting Tunnel & Gates
Thornton Connecting Tunnel & Gates

Thornton Connecting Tunnel & Gates establishes connections between the existing underground water system and the Thornton Quarry through the construction of connecting tunnels and a gate shaft. The Thornton Quarry serves as a temporary holding reservoir for wastewater before undergoing treatment and eventual release into Lake Michigan.

The project was executed in two distinct phases. In Phase One, which spanned 18 months, a series of critical tasks were successfully completed. This included the excavation of a 63-foot-diameter shaft through a layer of common overburden measuring 14 feet in thickness. Additionally, drill and blast excavation was performed over a length of 335 feet through hard rock. Phase One also encompassed the drill and blast excavation of a bifurcation chamber, measuring 215 linear feet with dimensions of 60 feet in width and 40 feet in height. 970 linear feet of a 33-foot-diameter horseshoe drift were excavated. To ensure structural integrity, the excavation was reinforced using a combination of resin-grouted dowels, rock bolts, and fiber-reinforced shotcrete.

During the second phase of the project, the focus shifted to the drill and blast excavation of a tunnel connection, measuring 50 feet by 33 feet in diameter. Additionally, 70 feet of reinforced concrete lining with a diameter of 30 feet were installed. Access to Phase Two was facilitated through an existing shaft, measuring 340 feet in depth and 30 feet in diameter.