STUDY ON SHEAR STRENGTH OF DEEP-SEATED SLIDING ZONE SOIL OF ZHOUCHANGPING LANDSLIDE IN MAOXIAN, SICHUAN

The Zhouchangping large deep creeping ancient landslide is located on the left bank of the Minjiang River in Maoxian County, Sichuan Province. It had a large-scale rapid reactivation and dammed the Minjiang River in 1982. Based on field investigation and drilling analysis, the landslide is currently in deep-buried creeping deformation. Rainfall has an important influence on the deformation rate of the landslide. The moisture content of sliding zone soil and the sliding rate of Zhouchangping landslide have a great influence on its mechanical strength characteristics and the occurrence and development of the landslide. In order to study the influence of moisture content and sliding rate on the mechanical strength, this paper carried out ring shear tests of sliding zone soil with different moisture contents(8%, 15%, 25%) and different shear rates(0.1 mm·min^-1, 5 mm·min^-1, 100 mm·min^-1). The results show that the shear strength of sliding zone soil decreases with the increase of moisture content, and the reduction is greater under high moisture content conditions. The strain softening phenomenon of the specimen becomes more obvious with the increase of shear rate, and its peak strength and residual strength generally increase first and then decrease. The internal friction angle of the strength parameter, linearly fitted by the peak strength and the residual strength, first increases and then decreases. Research suggests that in the case of rainfall conditions, high moisture content significantly reduces the shear strength of the sliding zone soil, which is likely to cause the Zhouchangping landslide to periodically creep. The accelerated sliding rate can again reduce the shear strength of the sliding zone soil, which can cause the landslide to reactive and block the Minjiang River as a whole again.