Research On Mesostructure And Evolution Of Rock-soil Aggregate Landslides In Deeply Incised Valleys

Affected by both the continuous uplifting of Qinghai-Tibet Plateau since the Quaternary and the deep incision of valleys such as Yangtze River and its tributaries,Southwest China forms the typical deeply incised mountain and ravine region.Numerous rock-soil aggregate slides,which have composed by glacioflurial deposit,alluvial deposits,collapse,landslide and debris flow deposits,are distributed in Southwestern areas of China,many of them have occurred obvious revived deformation,forming a certain type of landslide that is called "revived landslides".Which have the characteristics of multiple formation types,complex evolution mechanism,sudden occurrence,difficult to predict the developing trend,huge damage,and so on.Studing this type of landslide has very important theoretical value and applied engineering meaning.Funded by the National Science Foundation and the Geological Survey of China,the author uses the methods such as: high precision remote sensing interpretation,field investigation,engineering investigation,geological mapping,image acquisition and recognition,long-term field monitoring triaxial tests,qualitative analysis,quantitative calculation and numerical simulation,to do study on the mechanism and movement processes of the Danba valley in the upper of Dadu River,the mesostructure and mechanical properties of rock-soil aggregate,the spatial and emporal distributing,catastrophic process and early identification of rock-soil aggregate landslides.The main research findings and progresses are given as follows.(1)Systimatically revealed development characteristics of rock-soil aggregate landslides in the Danba reach of the Dadu River.The comprehensive analysis methods including field detailed engineering,data collection long-term monitoring and comparative analysis has been carried out to analysis development characteristics,spatial and emporal distributing,geologic times and hazard of 45 rock-soil aggregate landslides in Danba reach.Then,the typical landslides such as Jiaju landslide,Zhongluxiang landslide,Suopo landslide,Jianshejie landslide were further researched and defined the concept,formation conditions,characteristics of rock-soil aggregate landslides and disaster effects.(2)Study on mesostructure and quantitative parameters of rock-soil aggregate in deeply incised valleys,and the model of typical rock-soil aggregate is constructed.rock-soil aggregate is as a kind of special rock and soil mass in deeply incised valleys area,which has multiple genetic types and complex mesostructure.The macroscopic,mesoscopic and microscopic structures of rock-soil aggregate in the Danba reach of the Dadu River were observed,and the macrosructures could be divided into soil-like structure,stone-like structure and stone-like structure.The stability of rock-soil aggregate slops was better,with the increasing of the stone content of coarse particles and the mosaic degree of particle contact surface,and the better cementation property.The mesostructure was observed mainly from the characteristics of particle and pore development,and the characteristics and parameters of particle plane morphology,arrangement,contact,quantity,particle size and so on were greatly different.The description of microstructure,including grain group,grain morphology,grain contact,pore morphology and interparticle interaction,was clearly defined and expressed by 17 quantitative parameters.The spatial structure of typical rock-soil aggregate was studied in detail by observation of 6 typical sections and 36 grillage tests,3 CT(computerized tomography)scanning,12 SEM(scanning electron microscopes).The mesostructure model of typical rock-soil aggregate was constructed.(3)Thoroughly studied the response of the mesostructure of rock-soil aggregate to its catastrophic process.rock-soil aggregate is a special geological body with high dispersion in dimension and structure of grain,and then its mesomechanical property has unique.The definition of 11 indexes and 12 quantitative parameters,such as mesomechanical properties of strength,dilatancy and shrinkage,stress-strain relationship,hardening and softening,were systematically analyzed,then,the index system of mesomechanical properties was constructed.Based on the direct shear and triaxial tests of typical rock-soil aggregate in the study area,the mechanical parameters of mesostructures were obtained,and combined with a lot of previous research results,the effects of rock-content and load the confining pressure,and mechanical parameters of rock-soil aggregate were deeply discussed.Then,this paper also introduces the Shenzhujiang theory of binary medium consisting of bonded blocks and weakened cells and combines the homogenization theory of micromechanics to analyze the correlation between the mesostructure change and the mechanical and deformation characteristics,and preliminarily discusses the constitutive relationship between the strength and deformation characteristics of rock-soil aggregate.(4)Summarized the geomorphologic evolution process of incised valleys,and the formation mechanism and evolution processes of typical rock-soil aggregate landslides in deeply incised valleys.In this study,according to the evolution of valley in Danba reach,the macroscopic structure of slope and mesostructure of rock-soil aggregate landslides and their mechanical properties,the formation mechanism and evolution processes of four typical rock-soil aggregate landslides,such as layered-dumbbell,block-soil lock,banded block-soil,and block-soil open types were analyzed.A comprehensive monitoring system including GPS(Global Position System),In SAR(Interferometric Synthetic Aperture Radar)and inclinometer and numerical simulation have been carried out to study evolution and stability of Jiaju landslide.The evolution process of Jiaju rock-soil aggregate landslide was verified by UDEC(Universal Distinct Element Code),and the stability and development trend of landslide were simulated by FLAC3 D.The results show that the deformation and failure modes of Jiaju landslide are as follows: instability and collapse of the shallow surface,creep deformation and failure of multistage multistage sliding in the deep.(5)Constructed the early identification method and index system of rock-soil aggregate landslides in deeply incided valleys.An integrated Space-Air-Ground early identification system for rock-soil aggregate landslides in deeply incised valleys,aerial image such as high-precision remote sensing interpretation,In SAR(Interferometric Synthetic Aperture Radar),Li DAR(Light Detection And Ranging),aerial image and field detailed survey,was established.The indexs selection should consider the principles of operability,chromatography and universality.A three types of 13 indexes of early identification system including geological conditions(landform,stratum lithology,geological structure,ground water,surface structure,etc.),slope structures(the gradient,height,shape,body structures,etc.),the structures of rock-soil aggregate(genesis,grain morphology,grain dimension,contact relationship and pore morphology),was established.Then based on In SAR(Interferometric Synthetic Aperture Radar)interferometry and GIS(Geographic Information System)mapping quantitative analysis was carried out on the early identification authentication.The identification system was used to identify and verify the earthen rock-soil aggregate landslide in the deep valley of Danba river reach,45 rock-soil aggregate landslides were identified,and a typical earthen rock-soil aggregate landslide,Jiaju landslide,was selected for verification.