Research On The Development Characteristics And Formation Mechanism Of Damming Landslides At Alpine Canyon Area In The Upper Reaches Of The Minjiang River

The upper reaches of the Minjiang River are located on the eastern edge of the Qinghai-Tibet Plateau.Since the late Cenozoic,with the strong uplift of the Qinghai-Tibet Plateau,the Neotectonic activity in the region was intense,and the earthquakes were frequent and high intensity,resulting in the development of a large number of landslides in the geological history.Firstly,on the basis of summarizing previous data,field investigations,experimental analysis,numerical simulations were used to conduct detailed studies on the development characteristics and formation mechanism of the landslides in the upper reaches of the Minjiang River.Then,The analysis of the geomorphic effect,the significance of disasters,the environmental effects,and the relationship between tectonic activities and paleoclimate in the damming landslide were discussed.Finally,taking Jianshan landslide as an example,combined with dating analysis,numerical simulation and other methods to analyze the its development characteristics,formation age,and formation mechanism.Through research,we have the following conclusions:(1)The development and distribution of geological disasters in the upper reaches of the Minjiang River mainly include the following aspects:(1)Landslides developed on the banks of the Minjiang River and on the highway slopes.(2)Landslides are mainly developed in phyllite,slate,siltstone,and loess strata.The dominant gradient of landslides is 20~45°.(3)The collapse in the study area mainly develops on high and steep rock slopes,loess steep slopes,and highway excavation steep cliffs.(4)Wenchuan earthquake induced a large number of geological disasters.The number of geological disasters after the earthquake was3.1 times that before the earthquake.Among them,the collapse was 10.1 times before the earthquake,the landslide was 2.6 times before the earthquake,and the debris flow was 2.6times before the earthquake.(2)According to the formation time,the upstream of the minjiang river can be divided into four periods:damming landslides in the late pleistocene period,damming landslides in the holocene,ancient damming landslides and modern damming landslides.The triggering factors of the damming landslide are dominated by the earthquake and rainfall.The earthquake damming landslides are mainly large-giant scale and rainfall landslides are mainly medium scale.The damming landslides mainly occurred at 15~25ka.B.P in the geological history of the eastern Tibetan plateau.Massive damming landslide events are related to strong earthquake events induced by tectonic activities during this period.Since the 17th century damming landslides concentrated at three time points:corresponding to the luding-kangding Ms7.75 earthquake in the Dadu river in 1786,the Ms7.5 earthquake in the Minjiang river in1933 and the wenchuan Ms8.0 earthquake in 2008,Which indicates that in a certain period,the mass of the damming landslides is often associated with strong earthquakes.(3)The formation of Koushan landslide is related to the strong earthquake induced by Maowen fault in the 24000 years ago.The landslide volume is 1.5×10~8 m~3~1.8×10~8 m~3,which once blocked the Minjiang River and formed a large lake.The formation process of Jianshan landslide can be divided into four stages:the vibration of the trailing edge,the smooth sliding of the soft layer,the shearing of the front“locking section”,and the accumulation of the collapse vibration.The numerical simulation results show that:(1)potential slip surface is obvious under seismic conditions.According to the slope,the slip surface can be divided into three sections:steep surface in the trailing edge,the middle bedding slip surface and shear surface in the toe.(2)The hysteresis effect of the horizontal and vertical acceleration of the monitoring point is obvious.Because accelerations begin to increase gradually after seismic waves are input for 15 seconds.Seismic accelerations have obvious topographic amplification effect on the isolated parts of the slope top and shoulder,and the vertical acceleration amplification effect is greater than the horizontal acceleration.This study has a certain reference value for the study of the Minjiang landslide and the geological planning for the Chengdu-Lanzhou Railway.