Effect of colluvial soil slope fracture’s anisotropy characteristics on rainwater infiltration process

The SEEP/W module of the finite element software Geo-Slope was used to analyze the effects of fracture depth, permeability coefficient ratio, fracture angle and fracture number on the rainwater infiltration process. The effect of fracture seepage anisotropy on slope stability was studied along with the unsaturated seepage theory. Analysis result shows that when the rainfall duration is 1 and 7 d, respectively, the maximum pore water pressure in a 1 m fissure is 9.69 and 9.70 kPa, respectively, and the rainwater infiltration depth along the bottom of the fracture is 0.5 and 1.5 m, respectively. The pore water pressure in a fracture increases rapidly with the rainfall until it changes from a negative pressure to a positive pressure. The greater the fracture depth, the greater the pore water pressure in the fracture, and the greater the infiltration depth is when rainfall stops. The size of the saturated area is positively correlated with the fracture depth. When the permeability coefficient ratio is 1, the maximum permeability coefficient in the fracture range is 1.51×10^-7 m・s^-1. At this moment, the permeability coefficient along the fracture direction is less than the rainfall intensity, and the infiltration process is controlled by the soil permeability coefficient. When the fracture permeability coefficient along the fracture direction is larger than the rainfall intensity, the infiltration process is controlled by the rainfall intensity. The smaller the fracture angle, the greater the maximum pore water pressure in the fracture depth range, the greater the depth of the positive pore water pressure, and the smaller the range of surface saturation zone is. When there is no fracture, the slope still maintains a negative pressure state after rainfall, and there is no saturation zone. When there is a fracture, the rainwater infiltrates along the fracture and forms a saturated positive pressure zone inside the slope. The areas of the saturated zones formed by 1-5 fractures are16.4, 34.7, 60.9, 75.6 and 110.7 m², respectively. A power relation exists between the saturation area and fracture number. The influence range and degree of rainwater on the seepage field increase with the increase of fracture number. The concentration distribution of long fractures directly forms a large connected saturated zone and raises groundwater. 1 tab, 14 figs, 33 refs.