Rainfall Experiments And Numerical Analysis Of The Shallow Landslide In The Red-Bed Area In East Sichuan

Many landslides occurred in the rainy season or during heavy rainstorms. Thousands of shallow soil landslides were triggered by rainfall on September 16 th in Nanjiang, causing much loss of people's lives and property. At present, there were some studies on development environment, distribution law, formation mechanism and influence factors of this kind of landslide. But few studies were carried on the internal mechanism of the rainfall-induced landslides when analyzing the slope stability, and the failure mechanism of the slopes along a bedrock surface is not clear yet. Therefore, study on the pore-water pressure variation of the slope and the instability due to rainfall is theoretically significant and has a practical engineering application implication.Field geological survey, hydrologic monitoring, combined with a series of rainfall-induced shallow landslide experiments were conducted. A physical model of shallow landslide was also established, and the coupled fluid and solid in the unsaturated slope was discussed using numerical methods. The main results of this study are drawn as follows:1.In-situ hydrologic monitoring was carried at Gufenping landslide, combined with the precipitation monitoring, we analyzed the infiltration characteristics and hydrological response of the residual soil slope, and the impact of rainfall on the seepage for the soil slopes with different structures.2.The model tests of rainfall-induced shallow landslide were conducted. Based on the monitoring of hydrology and deformation, we analyzed the infiltration and the cumulative rainfall amount at the critical state in the red-bed area in Southwestern China. A failure mode was summarized for the shallow landslide in the test, the impacts of rainfall intensity, rainfall type and initial water content on slope stability was also discussed.3.Combining a modified G-A infiltration model with slope stability analysis, we established a physical model of shallow landslide considering the impact of underground water. The changes of slope safety factor under two conditions were compared, the sliding surface is located at the wetting front or at the bedrock surface, the early-warning models of landslide were also determined. Then, we analyzed the effects of underground water and initial unit weight on slope stability.4.Based on the coupled seepage-deformation theory for saturated-unsaturated soil, we examined the effects of antecedent rainfall, the initial matrix suction, and saturated infiltration coefficient on landslides. The results indicated that antecedent rainfall has a very weak effect on the pore-water pressure changes and the slope stability. The impact of the initial matrix suction is time-dependent. The greater the initial matrix suction is, the lower the slope angle is, the more stable the slope is. Slopes with high permeability are prone to pond at the bedrock surface, which causes shallow landslides.