Abstract: To study the transportation characteristics of gravel in the discharge pipe during the excavation of weathered rock layers by slurry shield tunneling, a three-dimensional model of gravel transportation in the discharge pipe was established based on the CFD-DEM coupling method. The velocity distribution, force characteristics, motion form, and the influence of gravel bed on mud during the gravel transportation process were analyzed. The effects of gravel size, shape, mud flow rate, and mud specific gravity on the sedimentation characteristics of gravel were studied. Research has shown that gravel particles move intermittently in a sand dune like bed; The velocity of gravel is layered along the height, and the velocity of surface gravel is fast, with collision and rolling as the main forms of motion. The velocity of gravel movement near the wall layer is low, mainly characterized by slip. There is a transitional layer between the near wall layer and the surface layer of gravel; The gravel bed layer locally increases the mud flow rate and pressure inside the pipeline; The velocity of the gravel bed increases linearly with the increase of mud flow rate; The height of the gravel bed increases with the increase of gravel size; The larger the mud density, the greater the drag force on the gravel; The smaller the coefficient of gravel shape, the greater the difficulty of transportation; Establish risk assessment indicators for gravel deposition, using the velocity coefficient α And boost coefficient β Evaluate the risk zoning of gravel deposition and propose targeted control methods for gravel transportation, providing reference for preventing and treating gravel deposition blockages.