The unsaturated seepage field coupled with heavy rainfall-induced surface flow mainly accounts for the slope instability. If the slope contains macropores, the coupled model and solution process significantly differ from the traditional one (without macropores). Most of the studies on the variation of the water field under the coupled effect of runoff and seepage on the slope did not consider the macropore structure. In this paper, two coupled Richards equations were used to describe the MF (Macropore Flow), and along with the kinematic wave equation, they were applied to establish a coupled model of SR (Slope Runoff) and MF. The numerical solving of the coupled model was realized by the COMSOL PDE finite element method, and an innovative laboratory test was conducted to verify the numerical results. The effects of different factors (i.e., rainfall intensity, rainfall duration, saturated conductivity, and slope roughness coefficient) on water content and ponding depth with and without macropores were compared and analyzed. The results show that infiltration is more likely to happen in MF than UF (Unsaturated Flow, without macropore). The depths of the saturation zone and the wetting front of MF are obviously greater than those of UF. When SR occurs, rainfall duration has the most significant influence on infiltration. When macropores are considered, the ponding depth is smaller at the beginning of rainfall, while the effects are not obvious in the later period. Rain intensity and roughness coefficient have significant influences on the ponding depth. Therefore, macropores should not be ignored in the analysis of the slope seepage field.

为深入理解含大孔隙土体内部水分运移机理，本文基于计算机断层扫描(CT)与图像处理技术，构建了含大孔隙(>0.15mm)的三维(3D)等效孔隙网络模型(PNM)，并确定了最优代表性体积单元(REV)的尺寸为300×300×300体素，最后进行了大孔隙空间拓扑结构特征定量表征、PNM单相流动及3D大孔隙水-气两相流动模拟。研究结果表明：孔径较小的孔隙数量较多，超过80%的大孔隙孔径集中在0.15~1.00 mm。孔隙拓扑空间结构差异性较大，配位数主要集中在20以内，但部分可达60以上。孔隙平均配位数在3~7之间，平均连通孔隙半径>2 mm。单相流仿真表明，孔隙结构的复杂程度与CT扫描分辨率，共同导致模拟渗透率与测试结果出现一定差异，但主渗流方向误差仅为3.81%。两相流仿真表明，渗流初期驱替前缘近乎呈直线状，随后呈指进状，之后直至结束，呈不规则状。孔隙残余气主要以块状分布于孔隙边、死角和孔喉突变部位。随渗流时间增加，水相饱和度呈上升趋势(气相饱和度呈下降趋势)，之后逐渐趋于稳定状态，最终水相和残余气相饱和度分别趋于94.92%和5.08%。该研究能较好地揭示重构土的细观渗流机理，并为进一步认识土体孔隙流规律提供一定借鉴意义.

The two-phase seepage fluid (i.e., air and water) behaviors in undisturbed granite residual soil (U-GRS) have not been comprehensively studied due to a lack of accurate and representative models of its internal pore structure. By leveraging X-ray computed tomography (CT) along with the lattice Boltzmann method (LBM) enhanced by the Shan–Chen model, this study simulates the impact of internal pore characteristics of U-GRS on the water–gas two-phase seepage flow behaviors. Our findings reveal that the fluid demonstrates a preference for larger and straighter channels for seepage, and as seepage progresses, the volume fraction of the water/gas phases exhibits an initial increase/decrease trend, eventually stabilizing. The results show the dependence of two-phase seepage velocity on porosity, while the local seepage velocity is influenced by the distribution and complexity of the pore structure. This emphasizes the need to consider pore distribution and connectivity when studying two-phase flow in undisturbed soil. It is observed that the residual gas phase persists within the pore space, primarily localized at the pore margins and dead spaces. Furthermore, the study identifies that hydrophobic walls repel adjacent fluids, thereby accelerating fluid movement, whereas hydrophilic walls attract fluids, inducing a viscous effect that decelerates fluid flow. Consequently, the two-phase flow rate is found to increase with then-enhanced hydrophobicity. The apex of the water-phase volume fraction is observed under hydrophobic wall conditions, reaching up to 96.40%, with the residual gas-phase constituting 3.60%. The hydrophilic wall retains more residual gas-phase volume fraction than the neutral wall, followed by the hydrophobic wall. Conclusively, the investigations using X-ray CT and LBM demonstrate that the pore structure characteristics and the wettability of the pore walls significantly influence the two-phase seepage process.