Study On Effective Reconnaissance And Control Of Badong-type Landslides In The Region Of Western Hubei-eastern Chongqing

The Badong formation landslides owing to its instability have constantly been restricting the regional engineering construction and economic development.Areas under the severe impact of the landslides are the western and southwestern part of Hubei province,including Zigui,Badong,Xuan'en,Jianshi,etc.And the eastern part of Chongqing city,including cities and counties like Wushan,Fengjie,Yunyang.Researches indicate that western Hubei and eastern Chongqing area including Three Gorges reservoir area are prone to developing geological hazards with following characteristics: wide distribution,high frequency,severe destruction and strong abruptness.Landslides developed in The Middle Triassic Badong Formation strata are the most typical landslides in these areas.The typical landslides include Huangtupo landslide,Huanglashi landslide and Zhaoshuling landslide in Badong;Er-langmiao landslide in Wushan;Baiyi-an landslide,Houzishi landslide and even a mega one,Sanmashan landslide,in Fengjie.The Middle Triassic Formation is characterized by its rich content of hydrophilia clay minerals such as montmorillonite and illite,which have significant water swelling and disintegration properties and are recognized as one of the easily sliding stratum,therefore they gain much attention from production units and research departments in geological field.As a result,the research and prevention of the Badong formation landslides have been specially paid attention,which is of great theoretical and practical significance to deepen the understanding and promote the prevention and control of geological hazardss.In this thesis,taken the geological hazards prevention implemented in or after phase?and phase ? of the Three Gorges reservoir region as examples,based on the essential characteristics of some relatively typical landslides,the impact factors system in formation of the Badong formation landslides was established according to the theory of engineering geology.The quantitative analysis of the impact factors' effects in the formation of the Badong formation landslides was conducted by applying conventional statistical method,and principal component analysis method was adopted to identify the main controlling factor beyond the hazards,then the system of the Badong landslides' fundamental types was proposed,and generalized three main types of the Badong formation landslides.Secondly,utilizing numerical simulation methods,discussion on the geological background of hazards-concealed slope was made from the combination of three aspects including the distribution of the stratum where the Badong formation landslides occurred,geological structure and the incision history of landform and rivers.Based on the forming process of the Badong formation landslides involved in this paper,in allusion to the Badong formation slope after its formation,researches on the evolutionary process and deformation mechanism of this type of landslides were conducted,from aspects of the Badong formation slopes' structure transformation and qualitative changes of rock mechanics.Thirdly,study was conducted in allusion to implement effective investigation method to the Badong formation landslides.Five key problems including the recognition and investigation of landslide deformation,recognition of sliding belt,comprehensive geophysical investigation,selection of strength parameters and the stability state were analyzed practically and discussed in detail.Effective and feasible investigation methods were proposed,which were suitable to the Badong formation landslides.Valid basic datum were provided to correctly identify the deformation stability state of the Badong formation landslides.Fourthly,in allusion to the generalized main types of the Badong formation landslides,this thesis systematically studied the optimal time to prevent and treat the Badong formation landslides,key positions to prevent and measures of prevention that aim at the deformation mechanism,from the combination of theoretical aspect and evolutionary phase of landslides.Based on this,it combined the examples of two typical landslides in the Badong formation to demonstrate the effectiveness in current prevention and treatment projects,and analyzed the optimal time and key positions(or factors)to prevent landslides.It specified the appropriate measures to prevent and treat landslides through comparisons of stress adjustment condition in the slope,displacement changes and control status under different circumstances.Lastly,combining basic geologic features and deformation features,the thesis proposed effective prevention and treatment scheme to the main types of landslides in the Badong formation.Through the analysis and research,the main conclusions and achievements are listed as follows:(1)The strata of mid Triassic Badong formation was extremely widely distributed in the eastern Chongqing and western Hubei in stripped shape.It has a controlling effect on the stability of the slopes in this region.The landslides of the Badong Formation are known for their large scale,the conditions and mechanism of formation,the serious deformation under the condition of water storage and reservoir operation,the severity of the damage,the difficulty of decision-making,the representative and the typicality.(2)The terrain and topography in the concave slope,the underground slope of 25 ~ 30 °,relative elevation above 200 m,the lithologic combination of marlstone in slope characteristics,0 ~ 20° obliquity of rock slope,the dip slope structure,the deformation characteristics of the local deformation and damage in the sliding body,the material composition of the rock-soil mixed,the destructive extent reaches maximum when the position factor characteristic,as one of the sliding belt characteristics,is developing in weak intercalated layer;slope structure,dip angle of strata,topographic slope,material composition and deformation characteristics are five main internal controlling factors.The environmental factors of the external disturbance are mostly affected by the rainfall infiltration.(3)In general,there are three main types of landslide in the Badong Formation in the Three Gorges reservoir area.The first type of Badong Formation landslide is characterized by mudstone,local deformation and fracture,rock-soil mixed sliding body,deformation along the weak intercalated layer,and can be divided into two subcategories of landslides,namely,dip slope with gentle inclination and reverse slope with steep inclination.The second type of Badong Formation landslide is characterized by mudstone plus sandstone,slowly creep,and can be divided into two subgroups of landslide,namely,dip slope with gentle inclination in rock-soil mixed sliding body that deforms along the layer surface,and reverse slope with steep inclination in soil sliding body that deforms along the contact surface of rock and soil.The third type of Badong Formation landslide has the characteristics of gentle inclination,dip slope,rock-soil mixed sliding body,and has properties of limestone,local deformation and fracture,deforms along the weak interlayer and mudstone plus sandstone,slowly creep,deforms along layer surface.The proposed basic type system of the Badong formation landslides provides a reference and basis for the identification and control of the Badong formation landslides.(4)Through the numerical simulation analysis of the forming process of the Badong formation landslides,it was discovered that slope in both shores generated obvious unloading rebound during the process of river valley undercutting.The deformation range of such unloading rebound mainly concentrated upon the slopes which were above the elevation of riverbed at that time.As the river valley was undercutting,the rebound deforming area expanded downward gradually.For the slopes in left shore whose structure are reverse slope,the overlying marlstone strata in the third segment of Badong formation obtained more subsidence space owing to the compressive deformation of underlying strata,which aggravated the gravity subsiding deformation,and reached maximum displacement on the stratum contacting surface.For the slopes in right shore whose structure are dip slope,the overlying marlstone strata in the third segment of Badong formation slid along the layer surface,the underlying strata of mudrock plus sandstone creep integrally as a deformation characteristic.(5)The high and steep slope providee a large area of the free face,which is the terrain condition to generate the Badong formation landslides.Rainfall is the main natural factor to induce the landslides of the Badong Formation.The characteristics of mudstone decided the process of deformation and fracture of type one Badong formation landslides should go through the following procedures: under the effects of external weathering and eluviation and internal development of fissures,the slope underwent intense structural loosening and passed into phase of intense deformation,and continuously developed till the integral structure collapsed and disintegrated,and subsided rapidly to form mingle accumulated body.While the process of deformation and fracture of type two Badong formation landslides characterized by mudrock and sandstone go through the following procedures: under the effects of physical weathering,some diversity changes happened to the rock particles,for example,the granularity declined,number of fissures increased,size of fissures declined,as a result the integrity of rock mass was continuously undermined,the landslide stability deteriorated gradually.Besides,the interbedding of mudrock and sandstone is actually an uneven spatial distribution,it led to the easily displaced deformation on the contact surface of mudrock and sandstone.(6)The key problem in the Badong formation landslides survey is to identify the elements of the landslides,especially the sliding belt and its development.For the landslides segments developed in the marlstone stratum in the Badong Formation,the argillization-weaken intercalated layer is a perfect development site for the sliding belt.For the landslides developed in the mudstone plus sandstone stratum in the Badong Formation,the layer surface and surface where soil and rock contacted were perfect development sites for the sliding belt.(7)Aiming at several types of landslides in the Badong Formation,this paper put forward the method and order to identify the landslides of the Badong Formation from a macroscopic point of view: Engineering Geological Surveying-Geophysical Prospecting-Trenching – Drilling.This set of surveying methods can effectively find out the boundary of the Badong landslides,material composition,distribution of groundwater depth and distribution of sliding belt's depth in the Badong Formation.It proposed to master the lithology,microstructure characteristics,grain composition,mineral composition and physical and mechanical properties of the Badong formation landslides from micro perspective,and the effective survey method of the Badong formation based on comprehensive physical prospecting methods,and the method to auxiliary identify sliding belt utilizing the groundwater distribution characteristics,and the method to select soil strength parameter of the sliding belt in the Badong formation landslides.From three aspects including material characteristics,structural characteristics and deformation characteristics,the thesis proposed the identification indexes of stability status of the Badong formation landslides as follow: the disintegrate degree of rock mass,the degree of weathering,joint fissures,acoustic emission,deformation features,deformation rate.Furthermore,it provided criteria to use different index to judge the stability status of landslides.Comprehensive utilization of these indexes and judgements can help us master the stability status of the Badong formation landslides in reality.(8)For the Badong formation landslides with gentle inclination and dip slope structure,the effective control method combination is: surface water engineering + monitoring engineering + anti-slide pile support + slope cutting load engineering + reinforced concrete lattice slope + barricade in slope's front edge.For the Badong formation landslides of the reverse slope structure,the effective control method combination is: drainage engineering(surface water truncation + underground drainage)+ monitoring project,and simultaneously select anti-slide pile support and slope load shedding project according to the specific situation.(9)Considering the complexity of the stratum in the Badong Formation,the effect of the landslide control in the Badong Formation should be evaluated from the aspects of preventing and treating scheme and stabilization effect according to the principle of analytic hierarchy process.The research results have important theoretical significance for prevention and treatment of regional landslide.