| The active tectonic movement and intense erosion in the Qinghai-Tibet Plateau lead to the development of geological disasters in the steep and deep gorge area,and the disaster chain effect is prominent.In October and November 2018,the landslides occurred on the right bank slope of Jinsha River in Baige Village,Jiangda County,Tibetan Autonomous Region for two consecutive times.Due to the high location(840m above the river surface at trailing edge of landslide)and the large volume(1866×10~4m~3and 620×10~4m~3respectively)of the two landslides,the Jinsha River was blocked,thereby forming barrier lakes.Nine days after the second landslide,the landslide dam broke,which made floods to flow downstream and bringing huge property losses to the Tibetan Autonomous Region,Sichuan and Yunnan Province in the Jinsha River.In addition,due to the landslide disturbance and offloading,the deformation of the trailing edge and both sides is obvious and multiple fractures are developed after the occurrence of two landslides.As a result,there are potential unstable areas,named as three zones CZ1,CZ2 and CZ3 in this paper,which may lead to another landslide and disaster chain.Therefore,it is of great importance for disaster prevention and mitigation in this area to grasp the development mechanism of Baige landslide in 2018 and make a reasonable study and judgment on the characteristics and laws of continuous deformation in the cracked zones.Under the support of the National Key Research and Development Program"Research on Key Technology of Dynamic Disaster and Risk Prevention and Control of Major Landslides on Qinghai-Tibet Plateau"(2018YFC1505000),this study comprehensively analyzes the development and movement mechanisms of Baige landslide,and proves the internal law and deformation trend of the continuous deformation of Baige landslide through detailed field investigation,UAV aerial survey,geological drilling,deep displacement and water pressure monitoring.The main results are as follows:(1)The Baige landslide is located in the Jinshajiang suture zone,and the trailing edge of the landslide is only a few hundred meters away from the Boluo-Muxie fault.The tectonic activity of Jinshajiang fault zone in the area is strong,which makes the slope body show distinct features of complex rock mass.The lithology of the slope is fully weathered serpentinized gneiss,strongly weathered gneiss,and moderately weathered gneiss from top to bottom,which controls the two platforms of 3500m and3100m elevation.The strength of rock mass gradually increases from top to bottom,and the structural crumpling is obvious.However,the overall occurrence of the foliation plane is about 223°∠47°,which tends into the slope.(2)There are obvious signs of geomorphic deformation in the trailing edge before the two landslides,which is the result of the long-term deformation of slope body under the control of gravity after the valley cutting formed the open surface.The"10.10"landslide was developed in the middle and upper part of the slope body,and the shear outlet was about 100m above river surface.A large number of deformed platforms were developed on the surface of the slope body in the landslide region,and the gneiss strata exposed in the north side of the landslide area showed obvious topping deformation,indicating that the landslide area had experienced deep gravity deformation for a long time.The"11.3"landslide occurred in the middle of the"10.10"landslide to the north,and the sliding body was located in the cracked zones of CZ1 and CZ3.The wedge cleaving effect caused by the steep approach and gravity made the sliding body in CZ1 region to slide.The sliding body in CZ3 region slid down because of the disturbance of CZ1.(3)According to the kinematics mechanism,the"10.10"landslide can be divided into the source zone,the accumulation zone and the impact zone.Further,the source zone can be divided into the trailing zone,the major sliding zone and anti-sliding zone.The sliding body of the major sliding zone and anti-sliding zone hit the left bank after sliding out of the shear outlet and rose up to 176m on the slope of the left bank,thus forming debris-eroded zone.In the process of reentry,they collided with the sliding body in the trailing zone sliding down from the right bank,thus forming waterjet-eroded zone and silt-polluted zone respectively.(4)The process of moving and scouring can be divided into six steps:startup of the major sliding zone and anti-sliding zone,initiation of the trailing zone,formation of the debris-eroded zone,collision between debris and surge of the waterjet,second slipping of the landslide dam,and surface flush in the accumulation zone.The"10.10"landslide had a severe impact on the left bank,and the feature point on the impact arc on the opposite shore was extracted.By using the law of conservation of energy and the derivation formula,the results show:the sliding body in the major sliding zone and anti-sliding zone started at the initial speed of 2.2m/s,and the elevation of the impact point was 2933m and the velocity was 67m/s when it reached the Sichuan shore.The sliding body in the trailing zone was then started.The sliding body had a speed of 47.9m/s when it reached the shear outlet.(5)The long-term monitoring data of deep displacement and seepage pressure in the field shows that there is no stable groundwater level in the cracked zones.The deformation has not converged,and part of the slope at the back edge is in a creeping deformation state.The shear zones of CZ1-1,CZ2 and CZ3-1 had been formed.The deformation depth of CZ2-1 was the smallest(18m),CZ1 was the largest(67m),and CZ3-1 was in the middle(22.5m).The average deformation rate was the largest in the CZ2-1 region,which was estimated to be greater than 20mm/d.The CZ3-1 zone was the second,reaching 3.33mm/d.The CZ1 region was the smallest,which was0.21mm/d.The CZ1-1 and CZ2-1 zones are at the greatest risk of landslide blocking the river at present.In the later stage,attention should be paid to the fracture deformation characteristics and the disintegration of local bedrock. |
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