Sixty Years of Rock Tunneling in Chicago

For more than 60 years Chicago has been constructing tunnels in rock, clay and glacial drift for its underground utilities including water supply, distribution and sewage. Of the city's 72.3 miles of water tunnels in service, or available for service in 1971, 57.6 miles were constructed on rock. The history and methods of rock tunneling, such as mole-mining, are reviewed. The Combined Underfloe-Storage Plan, which calls for construction of large rock tunnels under the surface waterways to collect and store spillages from combined sewers, is analyzed. These large tunnels would have the dual purpose of storage and conveyance. The plan also would meet Illinois's standards for water quality and provide flood control benefits with much less capital expenditure than by separation of sanitary and storm sewers, or any other method yet proposed. The writer forsees great progress in rock tunneling economics and technology as Chicago implements construction of planned improvements in the 1970's.