| Luoyang and Sanmenxia,in western Henan Province,located in the transition zone of the second-stage step to the third-stage step of topography,with large topographic relief and complex geological environment conditions,are prone to landslides.Landslides with locked section characterized by sudden failure,have strong capacity to cause disasters in a large scale.In addition,there was no accurate identification method due to the concealment of the position,quantity and type of the locked segment in landslides.The types and distribution characteristics of landslides with locked segment in western Henan have not been fully identified,and its failure process and mechanism need to be further revealed.According to statistical analysis,rainfall is the main triggering factor of landslides in western Henan Province.Therefore,it is of great scientific and practical value to study the evolution mechanism of rainfall-induced landslides with locked segment in western Henan Province.Field investigation and extensive collection of materials of landslide disaster,large size physical model tests,and numerical simulation were conducted.Then the disaster environment of landslides was clarified,the classification and the frame system of comprehensive identification,based on the development and evolution characteristics of landslides with locked segment,were put forward,and the failure process and mechanism were revealed.Finally,the identification criterion depending on the evolution state of landslides with locked section in western Henan Province was established.The main research contents and achievements include the following aspects:(1)Disaster environment of landslides in western Henan ProvinceLandslides disaster environment was analyzed depending on the results of field survey and analysis of landslides data.The relationship between landslides distribution and geological environmental factors,such as topography and geomorphology,types of rock and soil,and structure of slopes were established.The results showed that the geological structure of landslides mainly include five types;sandstone,mudstone and all kinds of soft soil and rock are prone to landslides in western Henan.The relative height,shape and angle of slopes affect the distribution of landslide severely.Rainfall and human activities were the main inducing factors.(2)Classification and identification of landslides with locked section in western Henan ProvinceAccording to the development characteristics,landslides with locked section in western Henan Province were divided into three categories: landslides with anti-tipping locked segment,landslides with wall-like locked segment and landslides with arch-like locked segment.The geological structure of landslides with anti-tipping locked segment was characterized by gravel soil covering over bedrock,with one or more groups of rock layers with a formation tendency opposite to the potential sliding direction,forming anti-tipping locked segment in the front of slope.The landslides with wall-like locked segment mainly developed in slope with both soft and hard mass,while hard rock mass at the middle part along the potential sliding surface forms a wall-like locking segment.Landslides with arch-like locked segment were characterized by rock and soil mass with relatively high strength at both sides of a narrow opening.According to the geological environment conditions and failure process of landslides with locked segment in western Henan province,landslides with the same locked segment have similar material composition,mass structure,failure mode and evolution characteristics.However,landslides with different locked segments have obvious difference in the above aspects.The comprehensive consideration of the development characteristics and the evolution process of the landslide is an important way to conduct the identification of landslides with locked segment in Western Henan Province.(3)Evolution process of landslides with locked section induced by rainfallBased on the classification of landslides with locked segment in western Henan Province,a large-scale model test device for landslides failure process induced by rainfall was constructed.Multiply information of the whole failure process of landslides with locked segment was obtained by using 3D laser scanner,unmanned airborne high-definition camera,miniature pore water pressure gauge and earth pressure gauge.Eight large-scale physical model tests were conducted to reproduce the failure and evolution process of landslides with no locked segment,anti-tipping locked segment,wall-like locked segment,or arch-like locked segment.The experimental results showed that landslide without locked section was characterized by the stepped sliding with progressive collapse in the front.For landslide with anti-tipping locked segment,the slide deformed coordinately.The evolution process of landslide with wall-like locking section was similar to that of landslide with arch-like locking section,sliding occurred rapidly after the failure of the locking section.(4)The identification criterion of landslides with locked segment based on deformation characteristicsThe displacement of characteristic points and deformation of slope surface were recorded by 3D laser scanner,the results showed that the deformation process can be divided into two stages: general stable and accelerated growth,and the accelerated growth rate of displacement played an important role in predicting the failure time of landslide.The characteristic points of the front edge of the landslide without locked segment first accessed the accelerated growth stage,then the middle and rear part of the landslide accelerated in turn.The displacement curve of each characteristic point in the front,middle and rear of landslide with anti-tipping locked segment was almost the same,with similar acceleration rate.The displacement of the front part and rear part of landslide with wall-like locked segment and arch-like locked segment accelerated firstly,followed by the middle part.The displacement accelerated growth rate of characteristic points in the middle part was obviously higher than those in the front part and the rear part.The records showed that,in the accelerated deformation stage,the horizontal displacement growth rate of landslide with anti-tipping locked segment was about 5.5 mm/min,about 7.5 mm/min to 7.75 mm/min for landslide with wall-like locked segment,and about 9 mm/min for landslide with arch-like locked segment.Thus,velocity and distribution of displacement acquired by field monitoring could be used as identification for landslides with different locked segment.(5)The identification criterion of landslides with locked segment depending on the variation process of internal stressDepending on the analysis of pore water pressure recorded,the response of the pore water pressure in the sliding body under rainfall infiltration was divided into three stages: the slow growth,the acceleration growth and the rapid decrease.The accelerated growth stage occurred basically synchronous with the displacement acceleration increasing stage,and could be used as predicting information of the landslide deformation.For the middle part,the acceleration growth rate of the pore water pressure for landslide with anti-tipping locked segment was about 0.013-0.014 kPa/ min,about 0.025 kPa/ min for that of landslide with wall-like locked segment,and about 0.193 kPa/ min for that of landslide with arch-like locked segment.The acceleration rate of pore water pressure for landslide with arch-like locked segment was about 14 times that of landslide with anti-tipping locked segment,and about 2 times that of the landslide with wall-like locked segment.The rapid accumulation of pore water pressure may be used as an important indication of the strain energy accumulation of the locking segment in landslides with wall-like locked segment and arch-like locked segment.(6)The failure mechanism of Huaipa landslide with anti-tipping locked segmentThrough field investigation,geological drilling,engineering geological analysis and three-dimensional numerical simulation,the material composition,geological structure,characteristics of locked segment and failure mechanism of Huaipa landslide in western Henan Province were studied.Besides,identification of locked segment was conducted considering the development characteristics and evolution process.The anti-tipping rock layer in the front part constitutes the anti-tipping locking segment,providing resistance to sliding forward.The slide body was in a critical stable state after the anti-tipping rock layer was destroyed by human activities.The decrease of the strength parameters of the slide body caused by continuous rainfall infiltration was the triggering factor of landslide failure.Deformation characteristics presented by both landslide with no locked segment and landslide with anti-tipping locked segment in model tests were found in Huaipa landslide.The results of three-dimensional numerical calculation showed that the stability coefficient of the landslide was 1.35 in natural and 1.26 when the sliding body was saturated by continuous rainfall,when the anti-tipping locked segment in the front part was not destroyed.After the anti-tipping strata was destroyed by human activities,the stability decreased significantly and was in a critical stable state(the stability coefficient was 1.04).The whole failure occurred when the sliding body was saturated by continuous rainfall(the stability coefficient is 0.88). |
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