Control of non-Darcian flow by consolidation grouting in the surrounding rocks of a concrete-lined pressure tunnel

Abstract

A concrete-lined hydraulic tunnel is currently under construction for water diversion and power generation in the Yangjiang Pumped Storage Power Station, Guangdong Province. This tunnel will be subjected to a maximum hydrostatic pressure of ∼ 8 MPa during operation. This will present an extremely high pressure gradient in the surrounding rocks, which in turn may induce non-Darcian flow and even hydraulic fracturing in the fault and fracture system. How to control this unfavourable effect becomes one of the key technological issues for design and reinforcement of this tunnel. In this study, the groundwater flow behaviours in the surrounding rocks are investigated with Forchheimer’s law-based numerical simulations. The hydraulic properties are determined by in-situ packer tests and a universal correlation between hydraulic conductivity K and non-Darcian coefficient β (i.e., ). The performance of high-pressure grouting in suppressing the non-Darcian flow effect is quantified. The numerical results show that when the depth of grouting reaches 6 m, the grouting zone is effective in controlling the groundwater flow in the regime of Darcian flow in the fault zones and fracture network, and in reducing the amount of leakage out of the tunnel and lowering the risk of hydraulic fracturing in the surrounding rocks. This work provides valuable insights for understanding the role of consolidation grouting in controlling the groundwater flow behaviours in fractured rocks surrounding high-water pressure tunnels.