Taking the No.1 tunnel of an irrigation district as the engineering background, the waterproofing design principle of “blocking water and limiting drainage” was adopted to explore the influencing factors of external water pressure under the composite lining condition of isotropic shallow buried tunnels. A simplified model of composite lining was established to analyze and derive the analytical solution of the variation in external water pressure and seepage volume in relation to the surrounding rock's permeability, grouting layer, lining permeability and head. At the same time, the Midas finite element software was used to calculate the water pressure and seepage volume under different conditions to verify the reasonableness of the analytical solution. The study shows that the permeability and thickness of the grouting ring have a greater influence on the water pressure and seepage volume outside the lining, and the construction of the grouting ring should be emphasized. With the increase of the depth of the drainage hole into the rock, the water pressure outside the tunnel lining gradually decreases. Therefore, in the environment of high groundwater head, setting drainage holes on the tunnel is the best effective measure to reduce the external water pressure.

water blockage and drainage  /  external water pressure of lining  /  seepage volume  /  analytical solution  /  numerical simulation