Blasting Excavation for Connecting a New Tunnel to an Active Sewage Tunnel in a Wastewater Treatment Plant

Abstract

This study presents the controlled blasting method used to excavate the buffer zone between a new connection tunnel and an active sewage tunnel operating at full capacity at the Tuzla Advanced Biological Wastewater Treatment Plant in Istanbul, owned by ISKI. Treating up to 650,000 m3 of wastewater daily for a population of 2.6 million, the plant required new treatment units to be connected to the existing system due to increased capacity needs. Since the existing 2,200 mm-diameter sewage tunnel, built in 1998, could not be safely or economically shut down, blasting was selected for the excavation of the 40–60 cm thick rock buffer zone. The blast face area was 9.7 m2 and consisted of limestone with 25–35 MPa compressive strength. Due to unknown properties of the reinforced concrete lining of the existing tunnel and the presence of sensitive equipment above, a detailed risk analysis was conducted. Blasting design limited explosive charge per delay to 3.2 kg to stay below 15 mm/s particle velocity and 135 dB air shock. Electronic detonators and 27 mm cartridges in 33 mm boreholes ensured safety and precision. A total of 112 holes and 20 kg of explosives were used. Maximum measured vibration was 5.21 mm/s and air shock 132.3 dB. The operation achieved full breakthrough without disrupting sewage flow or causing structural damage. © 2025 International Multidisciplinary Scientific Geoconference. All rights reserved.