Study On Reactivation Deformation Of Ancient Landslide Accumulation Body And Mechanism Of Blocking River

The ancient landslide is the product of the long-term complicated evolution process of the slope.It has complex material composition,special geotechnical mechanical properties,and strong susceptibility to disturbance.With the intensification of human engineering activities and frequent occurrence of extreme weather,a large number of catastrophic events such as the destruction of transportation,hydropower engineering and other important facilities and casualties caused by the resurgence of ancient landslides,especially mountain railways,highways,hydropower stations and other human projects Activity disturbances are becoming stronger and stronger,and the risk of ancient landslide disasters is becoming increasingly severe.This paper takes the typical case of Jiangdingya landslide in Nanyu Township,Zhouqu County,Gansu Province on July 12,2018.Taking the ancient landslide body's resurgence deformation characteristics and instability blocking river mechanism as the main research content,using multi-temporal optical satellite remote sensing dynamic monitoring,Radar satellite time series In SAR deformation analysis,drone aerial survey,detailed on-site investigation,and indoor physical model test and other technical methods have carried out in-depth research on the formation of Jiangdingya landslide instability history,resurrection deformation characteristics and river blocking mechanism.The following main understandings and conclusions are made.(1)Through historical data analysis and remote sensing interpretation,it is believed that the Jiangdingya landslide in Nanyu Township,Zhouqu County,Gansu Province on July 12,2018 is a typical resurgence event of ancient landslide accumulations.The resurgence of the ancient landslide accumulation body is mainly affected by the erosion of the front edge of Bailong River and the intense human engineering activities on the accumulation body.Eventually,large-scale instability under the action of heavy rainfall and the formation of a river blockade lake.The area of the resurrection area is 1.3×105m2,the average thickness is 26.5m,and the volume is 338.1×104m3.This time,the river channel in the Nanyu Township of Bailong River was blocked.By the afternoon of the 13 th,the narrowest part of the river was5 m wide,the upstream water level rose 7-8m,the national highway 345 was washed away,and the traffic was interrupted.The nearby low-lying areas of Nanyi Village and Naner Village 135 private houses are flooded.(2)Through comprehensive analysis of historical documents and historical remote sensing images,the Jiangdingya ancient landslide mass occurred in 1986,1988,1990,and 1991,respectively,and large-scale slippage occurred,and the river blockage event occurred in the following three times.Through comparative analysis of multi-temporal remote sensing images,it was found that as early as March 21,1971,satellite images showed obvious signs of small-scale collapse and other deformations at the front of the landslide,but no obvious staggering threshold was seen at the trailing edge of the landslide.According to historical records,a large-scale landslide occurred on June 13,1991 in Jiangdingya.At the same time,satellite images on July 20,1991 showed that the landslide blocked the Bailong River to form a dammed lake.The scale of the dammed lake was the same as that of 2018.The dammed lake formed by the landslide on July 12 was of similar size.Comparing the satellite images in 2010 and 2014,it can be seen that the source area of the landslide has undergone a total slippage during this period.The trailing edge has formed a clear offset,the overall deformation of the landslide area has further intensified,and a clear shear exit has been formed in the lower part of the landslide.(3)Through the In SAR deformation analysis of 14 scenes of Sentinel-1A ascending image data from January 9,2018 to June 26,2018,the information of the deformation before sliding was obtained.The results show that the landslide itself has undergone more obvious deformation than the surrounding area,and the maximum deformation rate can reach 80mm/a.Combined with the deformation rate results,point P1 was selected on the landslide body,and its historical deformation curve was drawn.It can be found that the landslide has been deforming at a uniform speed for half a year,and the deformation of the landslide body increased sharply between June2 and June 14.Large,it is presumed that the slope body was affected by continuous rainfall,and the deformation was intensified.From the 14 th to the 26 th,the deformation basically recovered to the previous uniform deformation state,and the cumulative deformation amount at this point reached 291 mm.After the occurrence of the landslide,the deformation of the landslide after instability was studied through 4high-resolution Planet satellite remote sensing images.The results show that the landslide is still in the stage of slow deformation after the instability on July 12,2018,July 14.After that,the landslide tended to be stable.(4)Research on the mechanism of Jiangdingya landslide instability and river blocking through landslide physical test.First,the 52-minute rainfall was applied to the landslide model.Its purpose was to allow the rainfall to better infiltrate the landslide model.It was also to simulate the strong rainfall before the prototype of the Jiangdingya landslide was destabilized,and then to carry out water erosion on the front edge of the slope body.The leading edge of the model is gradually washed away by the current under the action of water erosion.At this time,the landslide model has formed a good free surface.Under the effect of rainfall,the slope body slides slowly forward,and the forward sliding The erosion of the slope body was further strengthened by water flow and caused small-scale instability,which eventually led to the instability of the first half of the landslide model and caused blockage;the model was temporarily stable after the first blockage,under the effect of rainfall The slope body continued to slide forward slowly,which eventually caused the overall landslide model to become unstable,and the second slope was blocked after the overall slope body became unstable.The state of the landslide model is:stable?unstable?stable?unstable,which is also consistent with the instability and blocking model of the Jiangdingya ancient landslide that resurrected and blocked the river many times.