Calculation of the Allowable Drainage of Parallel Tunnels Based on Ecological Environment Protection

To determine a reasonable value of parallel tunnel drainage, a steady-flow calculation model is established. The differential equilibrium equation of seepage is established, and the equation of the falling funnel curve in a steady state with drainage parameters is solved by using boundary conditions. The maximum drawdown depth of the control point is used to calculate the allowable discharge of the tunnel. Then, the curve equation of the falling funnel is determined, the volume of the drainage funnel is calculated, and the total discharge in the steady state is calculated according to the water storage coefficient. Finally, the theoretical formula is verified based on an engineering case and numerical simulation. Considering the actual engineering geology and hydrogeological conditions of the tunnel site, the total drainage, allowable drainage, and initial support bearing head height calculated with the proposed method are different from the actual measurements collected on site by 10%, 18.9% and 13.6%, respectively. Therefore, the calculation method can provide a reference for similar engineering.