| The complicated hydrodynamics environments & the special hydro-engineering structure of reservoirs determine that the impacts of this kind of landslides are usually very destructive and disastrous.Especially for major water conservancy projects,due to their large water storage impact range and strong water level fluctuation power,the impact has become a major hydrodynamic environmental problem in this field that must be studied and solved.Therefore,how to establish appropriate and effective monitoring and early warning parameters and models according to the mechanism and law of hydrodynamic catastrophe of reservoir landslide has become one of the major issues that need to be researched and solved in the field of landslide monitoring and early warning and prevention.The research will have important theoretical value and practical significance for the scientific prediction and prevention of not only the landslides of the Three Gorges Reservoir area,but also similar landslides in large-scale water conservancy projects with fluctuating water environment dynamic conditions in China.In this study,based on the reasons and mechanism of deformation and instability of reservoir landslides,the compound hydrodynamic load-unload effect of landslides,the weakening effect of landslide parameters and the evolution of landslide stability were considered as a complete landslide analysis system for cross-coupling research.By exploring the variation law of the compound seepage field of reservoir-type landslides as well as the impact of the compound hydrodynamic load-unload effect and the weakening effect of landslide parameters on the stability of landslides,we established a prediction model of the compound hydrodynamic load-unload response ratio of reservoir-type landslides.On this basis,the basic principles of damage mechanics were applied to establish the quantitative relationship between the load-unload response ratio and landslide stability coefficients.The above research findings provide a theoretical basis for the prediction and prevention of reservoir-type accumulation landslides.The main research findings are as follows:(1)Based on the regulation scheme and precipitation characteristics of the Three Gorges Reservoir,the seepage field conditions with different permeability coefficients,reservoir water change rate and precipitation intensity were determined,the variation law of landslide seepage line and porewater pressure under the combined action of reservoir water and precipitation under different conditions was analyzed,and the variation law of landslide seepage dynamic under different lithological permeability coefficients was quantitatively evaluated: 1)When k?100m/d(the landslide rock mass is composed by gravel),the hydrodynamic force of the landslide is manifested by the floating support weight reduction(hydrostatic pressure)effect;2)When1m/d<k<100m/d(the landslide rock mass is composed by silt and fine-grained sand),the hydrodynamic force of the landslide is represented by the mixed floating support weight reduction and seepage force effect;3)When k?1m/d(the landslide rock mass is composed by clay and silty clay),the hydrodynamic force of the landslide is reflected by the dynamic water pressure effect.(2)The load-unload patterns of different types of landslides were determined based on the value range of the permeability coefficient:(1)For landslides featuring floating support weight reduction,as the water level of the reservoir rises,the stability coefficient decreases and the variation of the water level is characterized by a loading effect;as the water level declines,the stability coefficient rises and the variation of the water level is characterized by an unloading effect.(2)For composite landslides featuring floating support weight reduction and dynamic water pressure,as the water level rises,the stability coefficient of the landslide first rises and then decreases,and the variation of the water level is characterized by first an unloading effect and then a loading effect;as the water level declines,the stability coefficient of the landslide first decreases and then increases,and the variation of the water level is characterized by first a loading effect and then an unloading effect.(3)For landslides with dynamic water pressure,as the water level rises,the stability coefficient of the landslide rises,and the variation of the water level is characterized by an unloading effect;as the water level declines,the stability coefficient of the landslide decreases,and the variation of the water level is characterized by a loading effect.(3)Based on the weakening of the shear strength caused by precipitation infiltration,the weakening process of the landslide can be roughly divided into thefollowing three stages: the stage of rapid reduction of the shear strength when the moisture content varies from 10% to 15%,the stage of slow reduction of the shear strength when the moisture content varies from 15% to 25%,and the stage during which the shear strength weakens toward a fixed value when the moisture content ranges from25% to saturation.Moreover,an empirical formula indicating the variation of shear strength of different rock masses with the change of moisture content was proposed and determined accordingly.In addition,based on how the shear strength of rock masses in the reservoir water fluctuation zone changes with the number of drying and watering cycles,it was found that as the number of drying and watering cycles increases,the cohesion and internal friction angle of different types of rock masses are characterized by a generally consistent weakening trend,i.e.gradually decreasing.The weakening of the cohesion of rock masses is apparently stronger than that of the internal friction angle,and the weakening of the shear strength of the rock mass is mainly found during the early phase of the drying and watering cycle.(4)According to the formation mechanism and instability causes of landslides triggered by the compound water environment,the dynamic influencing factors(i.e.precipitation and reservoir water)of the reservoir-type landslide as well as its displacement response law and the corresponding formation mechanism were quantitatively and organically studied.A prediction model of the compound hydrodynamic load-unload response ratio of reservoir-type landslides was established with the compound dynamics of precipitation increment and monthly change in reservoir water level used as the load-unload dynamic parameters,and the corresponding monthly change in displacement as the load-unload dynamic displacement response parameters.Besides,the accuracy and feasibility of the load-unload response ratio in landslide stability evaluation were verified based on the site monitoring data of landslides in Shuping Village.With this parameter used,we can not only describe the dynamic causes and formation mechanism of changes in the stability and displacement of reservoir-type landslides,but also quantitatively monitor and assess the dynamic stability of such landslides.(5)Based on the basic principles of “damage mechanics”,the damage variableevaluation parameters were applied to reveal the internal connection and quantitative relationship between the stability coefficient of the limiting equilibrium method and the load-unload response ratio.On this basis,the judgement standards of instability of reservoir-type landslides were established,providing the load-unload response ratio with stability evaluation significance and value equivalent to that of the landslide stability coefficients.What's more,the load-unload response ratio is more convenient,practical and monitorable than stability coefficients used by the conventional limiting equilibrium method.(6)The prediction model of the compound hydrodynamic load-unload response ratio and the judgement standards of instability of reservoir landslides were used to conduct the coupling analysis and evaluation of the load-unload response ratio of the strain and stress fields of typical reservoir-type accumulation landslides,and determine the spatial distribution characteristics and evolution pattern of the displacement dynamic coupling parameters of landslides.Furthermore,the damage area of the landslide was defined based on the variation trend of the displacement dynamic coupling load-unload response ratio.In addition,the distribution range of the plastic zone of landslide,the degree of plastic failure and its spatial evolution were evaluated based on the damage state of each element of the landslide. |
PDF Full Text Request