Effects of changes in soil properties caused by progressive infiltration of rainwater on rainfall-induced landslides

Abstract

Slope failure is associated with changes in pore water pressure induced by rainfall, this paper further attempt to bridge knowledge gaps that exist in understanding the relationship between mechanism of rainfall-induced regional-scale widespread shallow landslides in cohesive soils and change in pore water pressure. We designed in situ slope experiments with pre-designed vertical profiles at the toe of the slope, and used pore water pressure, conductivity, and moisture content sensors to capture the changing characteristics of soil properties during slope failure. The experiment finds that failure occurred first where internal material was continuously taken out of the slope, even before the maximum static pore water pressure is reached. However, the slope remains stable when the pore water pressure near the failure surface reached the maximum static pore water pressure that could be provided by rainfall. Instead, slope failure during subsequent rainfall periods, even if the pore pressure is then lower. Meanwhile, the soluble minerals in the soil continuously dissolve and migrate, causing the electrical conductivity before slope failure is approximately 1.38 times that after failure, on average. Here, we estimate that the changes in soil properties caused by progressive water infiltration only may have decreased test slope stability by an average of approximately 33.0%. Therefore, we suggest that the early attenuation of soil strength caused by the gradual changes in soil properties makes a significant contribution to soil failure caused by pore water pressure. This was verified in the case of the 7.25 Tianshui group-occurring landslides. Finally, by using an automatic laser particle size analyzer, scanning electron microscope, X-ray diffraction, ion chromatography, and quadruple direct shear instrument to analogize the changes in soil properties exposed to different leaching environments on loess platform, we further show that the early attenuation soil strength is caused by deteriorate in soil properties in the processes of successive years of rainfall, where the content of cemented minerals tends to decrease, fine particles tend to be lost, and pore structure tends to take the form of single macro-pores, which are more likely distributed around mineral particles >10 μm. Our results provide a new perspective on the widespread shallow landslides caused by changes in pore water pressure in a region and their associated gradual deteriorations in soil properties.