The formation and failure process of Yigong landslide in Tibet Plateau

Abstract

Yigong landslide is located in Zhamunong gully, Yigong Township, Bomi County, Linzhi region in Tibet, the volume of which is 3×108m3. Firstly, we analyse the formation mechanism of Yigong landslide in 2000, based on the field investigation and data collection. Secondly, we analyse the failure mechanism of Yigong landslide in 2000, combined with the mechanical test results of granite rock and stability calculation results of slumped mass (BH01). Under the combined effect of rapid incision and seismic activity in Yigong Lake zone, the basic factor of landslide formation is that the rock mass structure for controlled slope rock mass evolution has entered a stage of progressive failure in Zhamunong gully, and precipitating factors of landslide are excess melt-water and continuous rainfall under the temperature rise before landslide hazard happens, according to the results of the study. The formation process of landslide can be divided into 4 stages. (i) Trailing edge fracture of slope rock mass is in rapid development stage due to the effect of fast incision in the valley. (ii) The frequent seismic activities in Yigong Lake district facilitate the development and evolution of granite rock mass’s structural plane; (iii) The combined effect of excess melt-water and continuous rainfall at the prophase of the disaster makes the high angle fissure in trailing edge of BH01 rock fall body further develop. (iv) The high-speed rock fall block of BH01 rock fall body triggers the liquefaction of detrital accumulation materials at the source of gully, which forms landslide and finally transforms into high-speed granular mass flows. The stability-losing distruction mechanism of landslide is as follows. Under the combined effect of many conditions, such as fast incision of valley in Yigong district, earthquakes, temperature change, and continuous rainfall and so on, the high angle fissure in trailing edge of BH01 rock fall body develops quickly, and continuous creeping deformation occurs in rock fall body along weak structural plane or fracture surface, forming mid ‘locking section’. When the depth of cracking segment in trailing edge of BH01 rock fall body Hcr >363m or the length of rock mass’s locking section L<455m, sudden brittle failure occurs in the mid locking section of BH01 rock fall body, and rock fall occurs in rock fall body.