Design guidelines for concrete lined pressure tunnels

This paper presents design guidelines for concrete lined pressure tunnels. It reviews and updates design methodologies, discusses existing concrete crack formulae, proposes a crack formula for immature concrete for pressure tunnel designs, suggests critical reinforcing ratios for crack control, and presents a qualitative observation for the lining-ground-crack interaction phenomenon. Mathematical proofs and laboratory tests can probably justify this observation in the future. It concludes that the critical issues for pressure tunnels are the hydrojacking and hydrofracturing of the ground and the seepage and leakage of water through lining to the ground causing tunnel and ground instability. It also concludes that high quality concrete practice is more important than crack predictions, and the preferred rebar location, for pressure tunnels, is at the outer face of a tunnel lining.