Study On Mechanism Of High-speed And Long Run-out Landslide Induced By Prolonged Low-intensity Rainfall In Zhaojiagou,Zhenxiong,Yunnan

On 11 st January 2013 a catastrophic landslide due to a prolonged lowintensity rainfall occurred in Zhaojiagou,Zhenxiong,Yunnan.Based on geological survey,centrifugal model tests,ring shear tests and numerical simulation,the possible mechanism and behavior of the landslide from initiation to runout were examined,main results are as follows:(1)The “shoe-like topography”,loose soil structure,humid climate and prolonged low-intensity rainfall are the main reasons for the instability.(2)The instability mechanism of the Zhaojiagou landslide was studied based on a centrifugal model test.A new media atomizing rainfall simulation equipment and the method of minimizing the inclination of raindrops due to Coriolis effects are used to simulate the prolonged low-intensity rainfall condition.The results indicate that the formation mode of the Zhaojiagou landslide is gradually collapsed in form of traction to sliding,and the sliding of slope is associated with pore water pressure dissipation.(3)The shear behavior of soil samples collected from the sliding surface and runout path were examined by means of ring shear tests.The results show that the increase of pore water pressure and decrease of the shear strength due to the instability of the metastable structure in the loose soil resulting in the failure.While the sliding surface liquefaction resulting in the long-distance migration of the sliding body.(4)The back analyses by Geo-studio show that the groundwater level was redistributed and lifted significantly by the rainfall infiltration.When the rainfall lasted for 40 days,the groundwater level was raised to foot of the slope,rainfall and groundwater soften the sliding belt,causing a rapid increase of the volumetric water content and pore water pressure near the sliding belt,which significantly increased the weight of soil and weakened the effective stress of the soil,the safety factor reduced from initial state 1.05 to 0.97 after 40 days of rainfall.(5)The simulation result by DAN-W reveal that the landslide can be simulated perfectly by a combination of the Frictional model and Voellmy model,and the landslide had a duration of about 48 s and an average velocity of 16.7 m/s.