Connecting Shield Tunnels to Deep Undersea Caisson Arrival Shaft

Abstract: In a thermal power plant renewal project, seawater intake shield tunnels were connected to a seawater intake structure built by the pneumatic caisson method. The shield machine bored a tunnel to a point at the bottom of the seawater intake structure (caisson) doubling as arrival shaft. Due to high water pressure (0.34 MPa) at the shield machine arrival point, there was concern regarding sludge spray. To prevent this, a pressure-resistant hermetically-sealed arrival room was built inside the caisson arrival shaft. This paper reports our construction experience in connecting the shield-driven tunnels to the seawater intake structure (caisson arrival shaft) at high water pressure deep undersea.