| In all natural geological disaster,landslide is the main component of geological disaster is a distributed widely in the world and destructive geological disasters.It often causes major losses of lives and property.In some alpine valleys areas,the steep slope often fail to slide,forming landslide and some large landslides block rivers forming the disaster chain mode.Based on the analysis of the basic characteristics and formation mechanism of Qiaojia ancient landslide,this paper uses ESR dating data to determine the formation age and classify the active periods of the ancient landslide,analyzes and summaries the particle size characteristics and sedimentary environment of ancient landslide dammed lake sediments through the lacustrine sediment particle size analysis experiment and takes advantages of the PFC2 D numerical model to establish the numerical model of Qiaojia ancient landslide front under the condition of normal storage water level of 825 m,and the stability of an accumulation body at the ancient landslide boundary under the conditions of rainfall and earthquake is analyzed and researched.The following conclusions is drawn through research and analysis:(1)Through interpretation remote sensing and field investigation,the basic characteristics of Qiaojia ancient landslide are described.It is found that Qiaojia ancient landslide has obvious boundary,an obvious armchair landslide landform,a typical phenomenon of double gully homology of landslide,and the Jinsha River channel has an obvious left bend at the front of the ancient landslide body.The river system on the landslide body is disorderly with high degree of fragmentation and low integrity,and there are multi-level terraces.(2)Based on the research of the ancient landslide exposed slope on the opposite side of Qiaojia ancient landslide and lacustrine sediment the qiaojia lacustrine sediment granularity characteristic and sedimentary environment are analyzed and summarized by means of mechanical analysis,comprehensive grain size frequency curves parameters and the cumulative probability curves by the average particle size,standard deviation,skewness,kurtosis 4 grain size parameters studied sediment granularity characteristic and depositional environment,It is speculated that the lacustrine sediments may be formed by the barrier lake deposits formed by the failure of Qiaojia ancient landslide to block the Jinsha River.(3)The analysis on formation mechanism of Qiaojia ancient mainly from the characteristics of geological structure,geological environment and seismic activity conditions.Among them,the Xiaojiang fault passing through Qiaojia county has the biggest influence on the landslide,and the Qiaojia ancient landslide with huge volume may be caused by the strong earthquake caused by the intense activity of the Xiaojiang fault zone.At the same time,the geological disasters in Qiaojia are developed seriously,which are mainly small and medium-sized ones.The distribution of geological disasters has spatial and temporal characteristics,and the distribution of geological disasters is uneven.The disaster sites in the central and eastern part and the northern part are developed more,and the density is high,and the time is mainly concentrated in the rainy season from May to September.It is mainly affected by factors such as landform,tectonic activity,stratum,earthquake and rainfall,and human engineering construction activities.It has the characteristics of wide area,short period of disaster,chain development of disaster and mass occurrence.(4)There is a large cementation layer on the sliding surface of Qiaojia ancient landslide.A recrystallization sample is collected on the sliding surface for ESR dating.According to the ESR dating results,it is speculated that two sliding events occur in Qiaojia landslide,and the cementation may have formed in different periods of landslide activity.One occurred 94 ± 7 ka ago and the other 61 ± 5 ka ago.At the same time,combined with the photoluminescence dating data of lacustrine sediments,there may be three active periods of the ancient landslide,the latest one is 10,000 to20,000 years,and the middle one is 60,000 to 70,000 years.The oldest dates from90,000 to 100,000 years ago.(5)Uniaxial compression test and Brazil splitting test in particle flow discrete element software PFC2 D are used to calibrate the meso-mechanical parameters of sandstone in the model to obtain the meso-mechanical parameters of particles.According to the slope geological model,the discrete element numerical model of Qiaojia landslide is established by using the contact bond in the PFC software.The numerical simulation of the deformation,failure and instability of the front edge of the ancient landslide slopel under the condition of water level 825 during the normal impoundment are carried out.It is found that the slope had a slight instability and sliding phenomenon at the front edge of the slope under the condition of water level825 m.PFC2D is used to simulate and analyze deposit slopes,reveal the characteristics under the working condition of heavy rainfall and earthquake deformation and destruction,the results show that the department of ancient landslide boundary deposit in heavy rain and strong ground motion under the inducing factors will still happen failure.Appropriate engineering measures such as cutting slope of ancient landslide deposit boundaries and governance should be taken,the real-time monitoring of the ancient landslide boundary should be continue to be strengthen,a monitoring and early warning system should be set up to eliminate the danger caused by the slide of potential dangerous rock mass in time. |
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