Failure mechanism of gently inclined shallow landslides along the soil-bedrock interface on ring shear tests

There were many gently inclined shallow landslides along the soil-bedrock interface at a depth of 3-5 m in Nanjiang County, Sichuan Province, China. To explain why slope failure occurs at the soil-bedrock interface at a depth of 3-5 m, we conducted ring shear tests on samples of the slip zone soils, slip zone soil-to-the smooth bedrock, slip zone soil-to-the natural bedrock, and slip zone soil-to-the rough bedrock interfaces under various normal stresses. Twelve specimens of the slip zone soils and the slip zone soil-to-the bedrock of the gently inclined shallow landslides were tested by means of a ring shear apparatus. The results show that the peak shear strength and residual strength of the slip zone soils were larger than those of the slip zone soil-to-bedrock interface under a normal stress of 60-100 kPa. Thus, the slope slides along the slip zone soil-bedrock interface at a depth of 3-5 m. This can explain why the slope fails along the slip zone soil-bedrock interface at a depth of 3-5 m. The peak shear strength and residual strength of the slip zone soil-to-bedrock were larger than those of the slip zone soils under a normal stress of more than 100 kPa. Thus, the slope slides along the slip zone at a depth of more than 5 m. This can explain why the slope does not fail along the interface between the slip zone soils and the bedrock at a depth of more than 5 m.

Automated summary

The study found that under normal stresses lower than 100kPa, the peak shear strength and residual strength of the slip zone soils were larger than those of the slip zone soil-to-bedrock interface, leading to slope failure at a depth of 3-5m. Conversely, under normal stresses higher than 100kPa, the peak shear strength and residual strength of the slip zone soil-to-bedrock interface were larger than those of the slip zone soils, causing the slope to fail at a depth greater than 5m.