Temporal and spatial characteristics of moisture migration and instability mechanism of cracked soil slope under rainfall infiltration

To reveal the temporal and spatial characteristics of moisture migration and instability mechanism of cracked soil slope under the rainfall infiltration. The full-scale model test and fiber Bragg grating(FBG) displacement systems were developed independently to conduct the whole-process and multi-physical monitoring of slope progressive failure. The progressive deformation and failure evolution mode of cracked soil slope under the rainfall infiltration were revealed. Based on the progressive failure mode of cracked soil slope, the concept of soil saturation ratio was proposed. The sliding body within the crack depth range was divided into the saturated layer and unsaturated layer. The change of soil saturation degree was used to describe the water transport law of slope with randomly distributed cracks, and the slope instability mechanism controlled by cracks was discussed by combining with the rigid body limit equilibrium method. Research result indicates that the shallow deformation is controlled by the surface matrix suction in the case of continuous light rain for the slope without cracks. After the formation of cracks, the rainwater infiltrates rapidly along the cracks to form a transient saturated zone. It causes a rapid loss of shear strength contributed by the matrix suction with a drop of 82.50%-87.14%, and produces the initial slip flow, sheet erosion and other shallow deformations. After the rainfall stops, the slope is still in the creep process, and the displacements of slope foot and roof increase by 23.40% and 19.39%, respectively. After the evaporation, the development of crack increases the influence range of rainwater on the seepage field and slope failure scale. The soil becomes loose after experienced swelling, shrinking and creep process. The volumetric moisture content of soil at the deep layer of crack zone increases by 205.7% compared with the initial state. Under the same rainfall condition, the deeper the initial crack depth is, the lower the stability coefficient is, and the faster the failure occurs. For a slope with the same crack depth, its stability coefficient decreases with the increase of soil saturation ratio. The faster the soil saturation ratio increases, the wider the connected saturated zone inside the slope is. It is the main reason for the overall instability of cracked soil slope.