Design and Construction Challenges of a Major CSO Tunnel and Pump Station System in Indianapolis

Abstract: This paper presents the design and construction of a deep rock conveyance and storage tunnel and pump station cavern that was built about 70 m below ground surface for the City of Indianapolis. The TBM tunnel ran nearly 16 km in limestone with a finished inside diameter of 5.5 m. It provided a minimum storage volume of 205 million liters of untreated excess wet weather overflow. A pump station was planned for dewatering of the tunnel and discharging the CSO flow to a surface advanced wastewater treatment facility with a firm capacity of 340 million liters per day. The pumps were located within an 18.3 m wide and 24.4 m high deep mined rock cavern. Flexible design, advanced construction, and favorable geology allowed very high TBM production advance rates breaking daily, weekly, monthly world records in this tunnel diameter category.