| The complicated geological conditions in Three Gorges Reservoir(TGR)area leading to the occurrence of reservoir landslides.It is of great significance to study landslide formation mechanism and evolution regularity for landslide prevention and mitigation.Huangutpo landslide,as one of the most typical reservoir landslide in TGR area,the deep and comprehensive research on Huangtupo landslide is important in revealling the evolution characteristics of such landslides.Various companies and scholars have been conducting field investigation into Huangtupo landslide since this site was selected as the new address of Badong county in 1979 for the construction of Gezhouba Water Conservancy Project.However,as a large complicated ancient landslide,there are still problems unsolved about the material composition and spatial structure of Huangtupo landslide.There is no exact conclusion about the spatial model and the slip zone distribution.The study on basic information of Huangtupo landslide is not so comprehensive to reveal its spatial and temporal evolution regularity.The selection of topic in this thesis is based on the National Basic Research Program of China(973 Program)(No.011CB710600)and the Key National Natural Science Foundation of China(No.41230637).A further and complete research on No.1 sublandslide,the most unstable part of Huangtupo landslide,was conducted based on the insitu investigation tunnel.In this paper,the spatial structure of Huangtupo landslide is studied through regional geological data and the monitoring data.A spatial structure model of Huangtupo landslide was established from the aspects of the covering order of the four sub-landslides,material composition and deep structure.Then,slip zone soil samples were abstracted through the in-situ investigation tunnel.A serial of laboratory tests was carried out to reveal the macro and micro behaviors of slip zone soil.With the systematic data and information of Huangutpo landslide,the formation era,general geological environment and influencing factors of Huangtupo landslide are analyzed so as to reveal the deformation mechanism.The long term deformation of Huangtupo landslide is revealed with monitoring data from the shallow and deep part of the landslide.In view of the mentioned study,the simulation on the evolution of Huangtupo landslide on the condition of water fluctuation and rainfall is conducted to reveal the characteristics of Huangtupo landslide on real condition.The results and conclusions are of great significance no matter in theory or in practice.The main results are as follows:(1)According to the geological survey and data analysis,the regional profile of Huangtupo landslide was studied based on the natural history analysis method.It is found that the Three Gorges area spans two natural geography units in China.On the whole,the area is formed with low and middle mountain,gorges as well as erosion landform.The overall topography is low in the middle and east-west part while high in the south-north part.The stratigraphic distribution of the Three Gorges area in the Yangtze River has a completely different pattern of eastward and westward transformation of the crystalline rocks in the Huangling anticline core.In tectonic history,the Three Gorges area experienced three intense tectonic movements,Jinning movement,Yanshan movement and Xishan movement,forming a series of fold structure and fault structure.The intermittent uplift,oblique and slow subsidence of the tectonic movement period resulted in the stratigraphic surface of the Three Gorges area,and the river undercutting erosion formed a multi-level terrace.The whole tectonic structure is mainly composed of the fissures of the slopes,and the whole slope system is formed by the late-stage geologic transformation of the south wing.These effects lead to soothing folds or strong crush and deformation in some area.The slope system of Badong is formed by the fan-shaped single slope that tilts northwards.The system is divided into five units by four large scale northsouth gullies and many landslides were formed on each units.Under the rapid cutting of the Yangtze River and the later transformation of human activities,gravitational lateral unloading effect caused by the relatively rapid formation of the mountainous geologic structure of the slope makes the shallow surface of Badong slope area deformed.(2)A systematic study is conducted on engineering geological condition of Huangtupo landsldie.The results show that Huangtupo landslide is located in the south bank of Yangtze River between Wu Gorge and Xiling Gorge.The area of Badong county is in subtropical monsoon climate characterized by being warm and rainy and has four distinct seasons.The landforms and geomorphic types belong to the middle and low mountain gorge areas formed by the tectonic action.Huangtupo landslide has a multilevel slope platform and the overall slope shape is characterized by being steep in the upper and riverside part but gentle in the middle part.There are many gullies as well as faults and folds developed in Huangtupo area.The groundwater in the landslide area can be divided into four categories according to the water medium characteristics,water dynamic and the runoff discharge characteristics: carbonate karst water,carbonate rock clastic and rock fracture karst water,clastic rock fracture water and pore water in loose accumulation.According to then content,groundwater in the landslide area are calcium carbonate water(HCO3-SO4-Ca)and calcium bicarbonate type water(HCO3-Ca).A comprehensive monitoring system including the monitoring of precipitation,water level,GPS satellites,boreholes and so on are arranged in the landslide area.In addition,the large in-situ investigation tunnel is constructed in No.1 sub-landslide to reveal its geological spatial structure as well as providing access to slip zone soil samples.(3)The spatial structure of Huangtupo landslide is revealed from shallow to deep,local part to the whole with the combination method of borehole data,field investigation and laboratory tests.From the overall spatial structure of Huangtupo landslide,it is composed of four secondary landslides,which are No.1 Sub-landslide,No.2 Sublandslide,Substation landslide and Garden spot landslide.No.1 Sub-landslide and No.2 Sub-landslide are located in the front part near Yangtze River,forming the main part of Huangtupo landslide.Substation landslide covers the back edge of No.1 Sub-landslide and No.2 Sub-landslide while the north-east side of the front of Garden spot landslide covers the north-east side of front of substation landslide and the back edge of No.1 Sublandslide.Through the further revealing by in-situ investigation tunnels,there are two slip zones inside No.1 Sub-landslide,indicating there are two independent landslides forming No.1 Sub-landslide.From the view of the composition,the slip body of Huangtupo landslide is mainly composed of gravelly soil while the slip bed is composed of the stratum from Middle Triassic Badong Formation.The bedrock of the two sub-landslides near Yangtze River is composed of middle and thick layers of limestone from the third section of Middle Triassic Badong Formation.In the meantime,the bedrocks of the back Substation landslide and Garden spot landslide are from the second section and the lower third section of Middle Triassic Badong Formation.For the slip zone of Huangtupo landslide,it is composed of silty clay with gravel particles.Borehole drilling and the insitu investigation tunnels are adopted to reveal the deep structure of No.1 Sub-landslide.In the vertical direction,the rock color turns from dark gray,yellowish green,pink,brown to yellowish,and the rock integrity is poor.Along the path of the main tunnel,the color,lithology and strength varies from place to place and the rock grade from the entrance to the exit of the main tunnel has the trend of first increasing and then decreasing.Spatial variability exist in vertical direction and the plane direction of tunnel.(4)Based on the study of deep structure of Huangutpo landslide,slip zone soil samples were abstracted from the in-situ investigation tunnel to reveal the micro-structure,mineral composition,strength and so on.The spatial distribution of slip zone of Huangtupo landslide is revealed with the particle-size distribution analysis results.Specifically,in terms of microscopic characteristics,it is found that a large amount of clay minerals exists in the slip zone soil and there is scarcity of scratches on the surface.The slip zone soil is consist of granular,massive mineral crystals and layered flaky clay minerals.In the aspect of macroscopic physical and mechanical properties,the partical content,liquid limit and plastic limit,liquid index,saturation,shear strength parameters and compressive modulus of the slip zones of the four secondary landslides were obtained with laboratory tests.A large scale triaxial compression test was conducted on the in-situ slip zone soil sample of No.1 Sub-landslide to reveal the shear strength parameters under real conditions.Particle-size distribution curve was obtained through particle analysis of slip zone soil and the structure is quantified with fractal theory.Based on the mass-size fractal model,it is found that the fractal dimension can be a good index in presenting particle size distribution.Through drilling information,the slip zone soil of No.1 Sublandslide and No.2 Sub-landslide varies from place to place and the fractal dimension value increases along the main sliding direction.This indicates that the particle size distribution can in some extend present the spatial variability of slip zone distribution.(5)Huangtupo landslide is formed between 54×104a~5×104a from now.No.1 Sublandslide and No.2 Sub-landslide are originated in 54×104a~19×104a from now and experienced five times of intense movement ever since.The first three times were in the period of 40×104a~38×104a?31×104a~30×104a?22×104a~18×104a from now,which composed the basic shape of No.1 Sub-landslide and No.2 Sub-landslide.Then Substation landslide and Garden spot landslide moved and formed in 16×104a~13×104a and 13×104a~12×104a from now and covered the back edge of No.1 Sub-landslide and No.2 Sub-landslide,leading to the re-activation of the two landslides near Yangtze River.No.1-1 Sub-landslide and No.1-2 Sub-landslide were formed in 10×104a and 5×104a from now respectively.The evolution of Huangtupo landslide experienced four stages of slope development,falling,moving and reconstruction.The formation of Huangtupo landslide is controlled by composition material,boundary condition and the environment.The formation mechanism of Huangtupo landslide in general is that: the soft rock from second section of Middle Triassic Badong Formation and relatively hard rock from the lower third section of Middle Triassic Badong Formation provide easily deformed stratum in this dip slope area.Under the cutting of Yangtze River,the height of free face inceases,providing the potential energy for sliding.In the end,when the concentrations of the stress in the small pleat section reach a certain degree,there will be landslide.(6)A further analysis on the deformation of Huangtupo landslide is conducted with the monitoring system.It is found that the displacement vectors are not pointing the same direction but on the whole the main deformation is along the direction of NE20°.The cumulative displacement at the front of No.1 Sub-landslide is between 157.23 mm and 199.09 mm.The value in the middle part of No.1 Sub-landslide is 256.78 mm and 184.7mm from two monitoring site.At the edge of No.1 Sub-landslide,the cumulative displacement is 72.51 mm.Multi-fractal dimension was adopted to reveal the shallow deformation evolution characteristics of No.1 Sub-landslide.The results show that the multi-fractal dimension values are relatively big and the affects a lot by rainfall and water level but the landslide is in a relatively stable condition.In the study of deep formation of Huangtupo landslide,in No.1 Sub-landslide,the cumulative displacement at the slip zone increase steadily from 0mm to 54.32 mm.The maximum value of monthly deformation rate of the slip zone decrease from the front to the edge of No.1 Sub-landslide.The multifractal dimension of the deep displacement shows similar trend with that of shallow part of No.1 Sub-landslide.(7)Based on the combination of geological survey,in-situ monitoring and numerical simulation,the evolution characteristics of Huangtupo landslide is studied under water fluctuation and rainfall condition.The real condition of water fluctuation and rainfall in one year is selected as boundary conditions and the one hydrological year is divided into four conditions so as to reveal the evolution of the landslide.The results show that when the water level just began to increase or decrease,the infiltration line inside the landslide show the lag behind.The impact of rainfall on landslide is mainly concentrated in the middle and edge of landslide.For the deformation characteristics,in the period of water decreasing,the deformation extends gradually from the front to the middle and then the rear part.With the occurrence of heavy rain,the shallow deformation of landslide changes from forward extending to backward.Finally,Bishop,Janbu,Morgenstern-Price and Ordinary methods are used to evaluate the stability of all stages of the Huangtupo landslide.In general,the results obtained by Bishop method are the most conservative.The No.1-1 Sub-landslide have lower factor of safety than No.1-2 Sub-landslide.Under the real water condition,the stability of No.1 Sub-landside is more affected by rain than water fluactuation. |
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