Dual channel seepage model of cracked soil tunnels under rainfall infiltration

A dual channel seepage model theory is proposed based on the phenomena and results obtained from the analysis of local seepage behavior in soil layers with a single crack. Based on the step function, the boundary conditions and transformation formula for rainfall induced seepage were derived. Based on the existing rainfall infiltration models in literature, the setting of the transition zone length for the step function was discussed. The results showed that the calculation results were more accurate when the transition zone length was 4 or 8 units. Applying the above results, the dual channel seepage effect was simulated using COMSOL Multiphysics multi physics field coupling software, and the deformation characteristics of tunnel surrounding rock with fractured soil under rainfall infiltration were explored. At the same time, a multi factor impact analysis is conducted based on factors that may affect the deformation characteristics of tunnel rainfall infiltration, including crack location, rainfall intensity, and crack width. The results show that with the increase of rainfall time, the settlement of the arch and upper horizontal displacement of the tunnel on the near crack side are significantly higher than those on the far crack side; The larger the crack width, the faster the rainfall infiltration and expansion, and the greater the displacement generated by the tunnel. Comparing the settlement of the arch crown with a crack width of 2mm and the upper horizontal displacement, when there is an 8mm crack width above the tunnel, the maximum settlement of the arch crown reaches 328mm, an increase of 6.5%, and the maximum horizontal displacement of the upper part is 26mm, an increase of 44%; The intensity of rainfall has a relatively small impact on the surrounding rock of the tunnel.