Rainfall infiltration characteristics and numerical simulation of slope instability in the basalt residual soil in the coastal area of Southeast China

Slopes in the basalt residual soil in the coastal areas of southeast China are easy to fall during the typhoon rainstorm. However, this aspect was seldom examined. In this paper, the Majitou landslide is chosen as a sample, and the undisturbed soil column tests are conducted to get the rainwater migration and distribution characteristics of the basalt residual soils under the central and advanced rainfall conditions. Geo-studio software is used to retrieve the soil column tests to obtain the unsaturated seepage parameters of the soil. The above results are applied to the numerical simulation to obtain the seepage field and slope stability of the Majitou landslide under the two rainfall conditions. The results indicate that the volumetric water contents in the upper and bottom parts of the soil column increase greatly during rainfall; under the rainfall intensity of 10 mm/h, the migration velocity of wetting front is low and unchanged with depths; while under the rainfall intensity of 30 mm/h, the migration velocity is 2-3 times greater than the former and decreases gradually with depth. Rainwater rapidly enters the basalt residual soil during the peak rainfall, and after three days’ rainfall, the soil saturation and the pore-water pressure of the Majitou landslide increase rapidly. The perched water appears at the foot of the slope, the soil shear strength decreases sharply, and the slope is unstable. The rainwater movement velocities under the central rainfall conditions are faster, which lead to the larger perched water area, and the landslide is easier to induce. The results in this paper may provide theoretical background for the stability evaluation and treatment for slopes in the basaltic residual soil in the coastal regions in southeast China.