Field Study on the Soil Water Characteristics of Shallow Layers on Red Clay Slopes and Its Application in Stability Analysis

Red clay is widely distributed in Zhejiang Province, China. Rain-induced shallow landslides easily occur on red clay slopes due to the reduction in shear strength caused by rainwater infiltration. The aim of this paper was to study the soil–water characteristic of red clay and its application on analyzing the stability of red clay slope. A series of field tests at different depths of red clay slope were carried out to monitor the variations of water content and matric suction under typical climate conditions. The results showed that the distribution of water content in red clay slope is complex because of long-term wetting–drying cycles. The water content within shallow layer is sensitive to external environment, and the response time of the water content is related to rainfall intensity. It is also observed that the soil water characteristic curve (SWCC) varies at different depths. The SWCCs of red clay can be fitted by linear function. The SWCCs from laboratory tests illustrated that saturated water content is more than 40%. Most of the SWCCs obtained at the depth of 90 cm are within the hysteresis loops of the SWCCs from laboratory test. The short-term rainfall has less effect on the stability of the slope, but the stability continuously decreases after the rain stops. The SWCCs obtained from laboratory were applied to analyze slope stability. Considering the influence of cracks, the computed results are close to field data. The study has a certain directive significance to the design of red clay slopes.