Optimization of radial drainage design for Water-Rich tunnel in sandy dolomite stratum considering pressure relief effect

Abstract

In the construction of tunnels in water-rich strata, the initial support behind the tunnel face bears significant radial water pressure. In particular, sandy dolomite strata have been found to be susceptible to water inrush disasters during tunnel excavation, highlighting the necessity for an optimized radial drainage system to mitigate water pressure. In this study, the effects of radial drainage on water pressure, deformation and stress of initial support are analyzed by considering six factors: drilling position, drainage hole length, transverse inclination angle, circumferential spacing, longitudinal spacing and longitudinal inclination angle. Firstly, radial drainage can further reduce the water pressure by 60% on the basis of curtain grouting. Notably, the best drilling position of the drainage hole is in the range of 90°-105°. Secondly, the drainage hole should pass through the grouting zone, and it is recommended that the drainage hole length be 0.4–0.5 times the width of the tunnel. Thirdly, 4–6 drainage holes are recommended for a section, and the longitudinal spacing is less than 4 m. Additionally, the longitudinal inclination angle range is recommended to be 0-30°. Finally, the radial drainage reduces the load on the initial support, leading to a reduction of 30% in support deformation and 20% in support stress. Through the field application, it is revealed that the optimized scheme can significantly improve the construction efficiency and economy, which has a wide application prospect.