Outstanding issues in excavation of deep and long rock tunnels: a case study

Abstract

Excavation of deep and long tunnels faces several distinctive challenges such as unknown geological structures, high groundwater pressure, and high in situ stress, as compared with conventional tunnels. The deep and long Taining tunnel in Fujian Province, South China, was excavated in complex geological settings. This tunnel had to pass through various squeezing fault zones and intensely jointed zones. Large deformations and high-pressure groundwater were frequently encountered during excavation. To predict the potential adverse geological structures, a comprehensive method, which included tunnel seismic prediction and ground penetration radar detection as well as horizontal drilling, was developed. Energy release and pressure reduction, as well as timely sealing, pre-excavation curtain grouting, and radial grouting were adopted to control the high-pressure groundwater. Countermeasures including improvement of support stiffness, double-layered primary support, and pre-support, increase of preset deformation, grouting reinforcement, and timely installation of permanent lining were taken to ensure safe construction in the surrounding rock masses under high in situ stress.