Research On The Reactivation Mechanism Of A Huge Landslide In Yangmaoping,Maoxian County,Sichuan Province

The eastern margin of the Qinghai-Tibet Plateau is characterized by complex topography,deep-incised rivers and strong neotectonic activities,where ancient landslides are extremely developed.Recent years,as human engineering activities and climate change intensifying,many giant ancient landslides have reactivated,which seriously threaten the safety of important infrastructure and public life and property.This paper is mainly focued on the key scientific issues of landslide prevention and mitigation in the Minjiang River Basin,and takes the Yangmaoping ancient landslide in Maoxian County,Sichuan Province as an example to systematically stduy the development characteristics and reactivation mechanism of the huge old landslide by field investigation,UAV,geophysical exploration,drilling,geotechnical tests and numerical simulation,etc.The main results or understandings are as follows:(1)The Yangmaoping landslide is located on the left bank of the Minjiang River,with a longitudinal length of 1200-2400 m,a lateral width of 200-1800 m,an average thickness of 35 m,and a volume of 11900×10~4 m~3.It is a giant ancient landslide during the Late Pleistocene.(2)At present,the landslide has partially reactived and formed three secondary landslides(H1,H2,H3),whose reactivation modes are traction-pushing type,pushing-traction type and push type,respectively.(3)The analysis of indoor triaxial test and direct shearing test show that the cohesion of sliding soil is more sensitive to the change of water content in the shear strength index,while the internal friction angle of slip zone soil is more sensitive to the change of water content.The ratio of illite to chlorite content in the slip zone soil is large,which means slip zone have been formed.(4)Using Geo-Studio software,the numerical simulation model is established to research the effects of seepage field and stress field of landslide on the landslide stability under heavy rainfall condition.The trigger mechanism of the landslide reactivation is proposed.(5)Combined with the reactivation characteristics and evolution process of the Yangmaoping landslide,the landslide monitoring and early warning design scheme is proposed.The obtained preliminary understanding and achievements in this paper have guiding significance for the prevention and mitigation of Yangmaoping landslide reactivation.