Evaluation on the Effect of Pressure Transients on Rock Joints in Unlined Hydropower Tunnels Using Numerical Simulation

Abstract Frequent pressure transients are identified as the cause of block failures in many unlined hydropower tunnels. The primary design objective such tunnels is to prevent hydraulic jacking at static and mass oscillation but neglects effect short transients, i.e., water hammer. issue has not been studied from perspective hydro-mechanical interactions due frequent pore changes rock mass. This article mainly focuses on different heads, or effective normal stresses across joints time period transient. Further, change behaviour mechanical properties joints, stiffness, friction angle dilation, investigated. Numerical simulations observed response during a transient carried out using distinct element code 3DEC. results show that relative joint deformation highest when 1.5–2.5 times higher than tunnel thus vulnerability weakening by fatigue higher. hammers can travel up 4 m into even stiff conditions sufficiently high stresses. Results further indicate impact hammer smaller compared oscillation. It concluded hammers, wherever applicable along waterway, still contribute addition cannot be neglected occur frequently. Tunnel filling/dewatering oscillations macroscopic displacements movements over long-term operation which major falls