Numerical Simulation of the External Water Pressure in Seepage Anisotropy Under Heterogeneous Conditions

The external water pressure and seepage quantity are crucial factors in tunnel construction design, especially under complex geological conditions. Both analytical solutions and numerical simulations can be used to calculate the external water pressure in a shallow circular cross-section tunnel. Analytical formulas are usually derived based on homogeneous surrounding rock, which seems somehow unrealistic. In reality, the engineering geological conditions are complex and the surrounding rock is heterogeneous. Therefore, the results of analytical formulas may deviate from the actual results. This study takes the No. 1 shallow-buried tunnel in the north bank of the Xiaolangdi irrigation area as its research background. Based on heterogeneous and anisotropic analyses, the horizontal permeability, the vertical permeability, the parameters of the lining and grouting circle, and the position head are the main factors affecting the stability of the external water pressure. The result shows that the external water pressure increases as the ratio of the horizontal permeability coefficient to the vertical permeability coefficient increases. Moreover, when a grouting ring is used to block the water, the lining is guaranteed to have a certain degree of permeability, which helps to better achieve the purpose of reducing the external water pressure.