Maple Avenue Relief Sewer
The Village of La Grange is a suburb of Chicago in Cook County with a population of over 15,500. The Village features a historical downtown business district and residential buildings dating back to the late 1800s and early 1900s. In recent years, the Village has begun an ongoing infrastructure maintenance program to add capacity to their aging and undersized combined storm sewer system to improve operations, mitigate residential flooding, and help protect the natural environment.
The Maple Avenue relief sewer is a 60-inch reinforced concrete pipe installed along the approximate center of the Maple Avenue pavement, with junction chambers installed at all intersections for connection of combined and storm sewers along the side streets. The junction chambers also include overflow weirs and restricted outlets to limit the amount of wet weather flow to the downstream combined sewers. New storm sewers, inlets, catch basins, and manholes were installed as part of the Maple Avenue street reconstruction, and are connected to the new relief sewer — solving the downstream capacity issue by intercepting and redirecting flows to the Metropolitan Water Reclamation District of Greater Chicago’s deep tunnel system before reaching the smaller sewers downstream.
During preliminary design, soil borings indicated the depth of bedrock along Maple Avenue ranging from 4 to 15 feet below the street surface. Numerous methods of rock excavation were carefully investigated to minimize impacts to the residential properties located on both sides of Maple Avenue and the adjacent properties.
Structurally sound rock was removed with pneumatic breakers or rock saws, depending on the vibration effects at the adjacent buildings. Approximately 3,500 to 5,000 cubic yards of rock needed to be excavated during construction to install the relief sewer. Rock Removal Resources of Green Bay, Wisconsin, supplied a highly specialized piece of rock excavation equipment capable of trenching through solid rock up to 18 feet deep by 4 feet wide. The rock trenching equipment, while large, fit within the right of way without damaging the old growth trees, caused less noise than rock excavation via hammering, and the dust generated was easily managed with generic sprinklers.