| In October 11th and November 3rd,2018,two large-scale landslides occurred at Baige Village,Jiangda County,Changdu City,Tibet Autonomous Region,which dammed the Jinsha River impounding a barrier lake and caused flooding of many villages downstream and destruction of road facilities.The landslide also caused the rock mass at the top of the slope to loosen,and there were growing cracks in many places,with the risk of destabilization again.Therefore,this article takes the Baige landslide as the research object,the formation mechanism of the landslide was analyzed,and provided a theoretical basis for the landslide control in this area.It also has great practical significance for ensuring the safety of people's lives and property and maintaining social order.Through literature review and analysis,the geological evolution process of the valley is clarified.Using field investigation,drilling,historical satellite images interpretation,numerical simulation,and deformation monitoring methods to understand the engineering geological conditions of Gege landslide,it clarified the development history of Baige landslide,analyzes the formation mechanism of Baige landslide and the formation mechanism of Baige landslide.It also analyszes the development trend of the trailing edge residual body and possible damage modes.The main knowledge gained is as follows:?1?The section where the Baige landslide is located belongs to the deep-cut canyon section of the Jinsha River,and most of the valleys are"V"shaped valleys.The slope shape is"steep-slow-steep-slow-steep".In addition to the top platform,there are two levels on the landslide.platform.The elevation of the first-level platform is about 2940-2960m,the range is relatively small,the terrain is relatively slow,and it is near the landslide shear outlet;the development of the second-level platform is relatively small,the elevation is about 3550-3450m,there is no farmer's residence,the front edge of the second-level platform The terrain is steep,and many collapses and deformations occurred during the historical period.?2?Signs of deformation and failure for a detailed site survey,the slope body is divided into main sliding area,anti-slip area and influence area from top to bottom.The main landslide area is mainly located on the steep slope and above the front edge of the second stage platform,about 3250m above the elevation.The slope body is mainly composed of fractured serpentine and gneiss;the anti-slip area is mainly located before the second stage The local gneiss area under the steep slope section of the margin has an elevation range of about 3100?3250m,and the structural surface of the gneiss body is poorly developed;the affected area is the lower slope range of the anti-slip zone,and part of the rock and soil body of the slope is affected by scraping take away.?3?The Baige landslide had a small-scale collapse deformation as early as 1966,and the deformation development has lasted for nearly 52 years.Initially,small-scale collapse deformation occurred on the left side of the trailing edge of the landslide and on the right side of the middle of the slope;afterwards,local creep slippage occurred in the gneiss area on the right side of the trailing edge.Edge boundary;thereafter the deformation intensified,and the whole middle and upper part of the landslide experienced creep deformation and squeezed the lower part of the slope.?4?The formation and evolution of the Baige landslide are mainly divided into four stages:?1?shallow collapse-cracking deformation stage:the left side of the trailing edge of the landslide and the shallow rock and soil body between the first platform and the second platform collapse Deformation and form certain tensile cracks;?2?Deep creep-downward deformation stage:the right side of the trailing edge of the landslide is affected by the left side sliding deformation,and it starts to develop from local creep to overall creep.The left tensile crack penetrates and constitutes the overall trailing edge boundary of the landslide;?3?Shearing stage of the“locked segment”:the deformation of the middle and upper parts of the landslide is further intensified,the stress in the lower gneiss body is further concentrated,the stress and strain are further increased,and the stress is higher.Energy and large strain energy,and eventually evolve into a locked segment;?4?"locked segment"shearing stage:the rock mass in the upper and middle parts of the landslide squeeze the lower part of the slope,the trailing edge of the trailing edge continues to develop downward,and the stress continues to concentrate With the effect of rainfall,the locked section was finally cut off and a landslide occurred.The deformation and failure mode can be attributed to"shallow sliding-deep creeping-squeezing-shearing".?5?The Baige landslide 1-1'engineering geological section was selected,and the sky landslide was modeled and calculated by FLAC-3D.The displacement and deformation,stress state and shear strain increase of the landslide model at 5000 time steps,50000 time steps and 100000 time steps were selected.The results show that:the Baige landslide has a small range of displacement and deformation in the initial state,and the deformation is small;the shear deformation area in the slope body is mainly concentrated in the serpentine area where the middle and upper structures are broken.When the calculation reaches 50000 steps,the surface tensile stress range of the slope increases,the landslide deformation develops deeper,the shear stress is concentrated downward,and the shear strain appears in the middle and lower gneiss locking section.When the calculation reaches 100,000 time steps,the deformation of the landslide intensifies and the potential shear plane gradually penetrates.?6?The trailing edge residual body is divided into 3 strong deformation zones.The overall stability of K3 zone is better than that of K2 zone,but worse than that of K1zone.After the treatment of the K1 deformation zone,the overall deformation tends to converge and the stability is relatively good.It is speculated that there are 3 potential sliding surfaces in the zone.Deformation is relatively strong in the K2 area,small-scale slumps continue,and the stage of accelerated deformation has been entered.The stability is poor.The frontal steep change is likely to be unstable under the inducing factors such as rainfall.It is speculated that there are 2 potential slips in the area surface.The K3 area is generally in the stage of uniform deformation,and the front of the block has a tendency to accelerate.It is speculated that there are two potential sliding surfaces in the area. |
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