Numerical Calculation Of Seepage-deformation Coupling Characteristics Of Earth-rock Dams

With the development of dam construction technology,earth-rock dams are widely used in dam construction in the world due to their advantages of local materials,strong adaptability to topography and geology,flexible construction,fast speed and low cost.With the development of construction machinery,geotechnical mechanics and calculation theory and technology in recent years,and the use range of dam materials is relaxed,and the construction period is greatly shortened,so that earth-rock dams have become the fastest growing dam type in dam construction in the world.For earth-rock dams,the soil is usually subjected to stress deformation and seepage at the same time.The stress deformation of the soil leads to the change of permeability,and the change of permeability will change the seepage field.The change of the seepage field will further affect the stress deformation of the soil.This interaction and mutual influence feature,namely,the coupling effect of seepage and deformation.The seepage-deformation coupling effect of soil is usually the main reason for the failure of earth-rock dam engineering.Therefore,the research on the seepage-deformation coupling effect of soil is of great significance to the practical engineering.In this paper,through the establishment of the ideal homogeneous earth dam calculation model,combined with the finite element analysis software Auto BANK and Duncan-Chang E-B model,first of all,the seepage field analysis,reveals the dam material for different initial permeability coefficient of stable and unstable seepage general law.Secondly,the obtained seepage field is superimposed on its stress field,and the seepage-deformation coupling calculation under stable and unstable states is carried out and its variation law is analyzed.Then the ideal core dam calculation model is established,and the seepage-deformation coupling calculation is also carried out.The coupling results of homogeneous dam and core dam are compared and analyzed.Furthermore,taking the ideal homogeneous dam as the prototype,combined with previous research results,the results of soil permeability coefficient k changing with time t are obtained,and the corresponding function formula is fitted.Finally,combined with the engineering example of Lianghekou high core rockfill dam,the fitting function formula is used to calculate the variation of the permeability coefficient of the core wall material,which is compared with the calculation results without considering the variation of the permeability coefficient of the core wall material,and certain rules and conclusions are obtained.As follows :(1)Through the steady seepage and the corresponding seepage-deformation coupling calculation,it is concluded that the permeability coefficient of the ideal homogeneous dam body material is no matter how large,the final seepage and seepage-deformation coupling results are consistent,which shows that the distribution of water pressure,head and infiltration line is the same,and only the single width seepage flow and steady seepage flow velocity are linearly and positively correlated with the permeability coefficient.Horizontal displacement,vertical settlement,principal stress and stress level distribution are the same.(2)Through the calculation under the condition of unsteady seepage-deformation coupling,it can be seen that when the permeability coefficient of homogeneous dam body material is constant,all the elements in the unsteady process change rapidly in the water level rising period,and the change rate gradually slows down until the reservoir is stable after full impoundment,such as water pressure,total head,saturation line,displacement deformation,major and minor principal elements.When the permeability coefficient of homogeneous dam body material is changed to be calculated respectively,it is concluded that the change rate of all factors decreases with the decrease of permeability coefficient,and the time to reach a stable state is longer.(3)Through the calculation and analysis of the ideal core dam,it can be concluded that the change of water pressure mainly occurs within the core wall,and the uplift of the saturation line mainly occurs during the change of water level.After the high water level,this change will become relatively slow until it is stable.The arch effect of the core wall can be observed obviously from the deformation results of the core wall dam during the completion period and the stable state,which is due to the inconsistent and uncoordinated deformation of the core wall and the rockfill of the dam shell.(4)Combined with the mathematical model of clay permeability change established by predecessors,based on the calculation of ideal homogeneous dam,it is concluded that in the whole process of unsteady seepage,the permeability coefficient of dam body material decreases rapidly and then gradually decreases and converges to a stable value,and the functional relationship between the permeability coefficient k and time t is fitted.(5)Taking Lianghekou high core rockfill dam as an example,the calculation considering the change of permeability coefficient of the core clay is carried out.By comparing the calculation results of the core clay k unchanged and k changed at the end of the impoundment period and in the stable state,it is found that the calculation results of the core clay considering the permeability coefficient change are more reasonable.