Shear behavior of sliding zone soil of loess landslides via ring shear tests in the South Jingyang Plateau

Since the 1970s, a large number of loess collapses and landslides have occurred in the Loess Plateau of China due to water diversion and irrigation projects. A large amount of ancient landslide deposits are accumulated at the foot of the tableland, which is likely to slide again in the case of a rapid increase in short-term rainfall or long-term irrigation. The weak characteristics of the sliding zone soil often become the key factor affecting the revival of old landslides. To explore the effects of water content and shear rate on shear behavior of the sliding zone soil, a series of ring shear tests were conducted on reconstituted loess in the South Jingyang Plateau. Experimental results suggest that under the condition of normal consolidation, the soil sample with the optimum moisture content has the highest shear strength. The increase in the shear rate effectively reduces the strength of the soil. Because of the high shear rate, the pore water that cannot be dissipated and fine particles accumulated at the shear plane form a weak base (slurry making theory), which cannot be easily stopped once the landslides start, leading to high-speed and long-distance landslides. In addition, the changes in the soil particles and pores were observed using a scanning electron microscope (SEM), and the observations were consistent with macroscopic results. From these studies, we come to the conclusion that the motion mechanism of reactivated landslide was associated with the interaction of water content and shear rate, which reduces the shear strength of the displaced materials to a great extent.