Research on dynamic prediction method of the water inflow in tunnels under complex geological conditions based on the non-darcy flow-energy method

Abstract

To accurately predict tunnel water inflow under complex geological conditions, this study established a unified geomechanical calculation model for such environments. Using groundwater dynamics and Bernoulli's energy equation, a theoretical approach to calculate the tunnel face water inrush under non-Darcy flow conditions was proposed, which comprised a confined water formula and a phreatic water formula. This methodology considers temporal and geological variations to enable short-, medium-, and long-term dynamic predictions of water inflow. The research findings indicate that: for short-term predictions, the theoretical water inflow derived from both formulas exhibited at most 5% deviations from the actual measurements. When a 90% confidence interval was adopted for the medium-to-long-term predictions, the relative errors for both maximum and normal water inflow remained below 5%. Notably, during the decaying water inrush phase, the phreatic water formula predicted a 2–3 times slower decay rate than the confined water formula. The maximum water inflow positively correlates with the permeability coefficient (K), water head height (H), and diameter of the water inrush channel (d), whereas it negatively correlates with the length of the water inrush channel (L). Conversely, the normal water inflow negatively correlates with K and d but positively correlates with H and L. After the feasibility of this method had been validated in the Yongshun Tunnel and Zhongliangshan Tunnel, it was successfully applied to a mountainous tunnel project in southwestern China.