Sedimentation mechanism and influencing factors of drainage ditch in mountain tunnels

Objective This study investigates the evolution of sedimentation in drainage ditches by multi-factor coupling, due to the drainage failure and lining distress induced by sedimentation in drainage system of mountain tunnels, so as to provide theoretical support for the anti-sediment design of relevant projects. Method A combined technical approach of full-scale tests and numerical simulations was adopted. Variable combinations of sediment concentration, flow rate, slope, and four typical cross-sectional forms (i.e., narrow square, semicircular, inverted trapezoid, and square) were systematically designed. Model parameters were calibrated by using test data to ensure the reliability of simulation results, and the coupling influence mechanism of aforementioned factors on sedimentation was systematically analyzed. Result The sedimentation amount exhibits a linear positive correlation with sediment concentration (fitting slope of 0.87) and an exponential negative correlation with flow rate and slope (R2>0.90). In same boundary conditions, the rankings of both maximum flow velocity and sedimentation prevention capacity of drainage ditches with different cross-sectional forms are narrow square, semicircular, inverted trapezoid, square. A sedimentation prevention strategy for engineering was proposed, which involved appropriately increasing the slope and adopting a periodic centralized discharge mode to enhance sediment-carrying capacity through peak flow. On the premise of meeting drainage and flood control standards, the inverted trapezoidal or semicircular cross-sections are preferred. The flow velocity would be improved by reducing the bottom water-passing width, achieving the collaborative optimization on drainage smoothness and operational reliability. Conclusion This study clarifies the coupling influence rule of multiple factors on the sedimentation of tunnel drainage ditches, providing a scientific and quantitative basis for the structural selection, parameter optimization, and sedimentation prevention design of drainage systems of mountain tunnels.