| Seepage damage is one of the main causes of dam failure,which has the characteristics of long time span,large spatial scale and high degree of damage.The scaled centrifugal test has the characteristics of"size reduction"and"time reduction",which can restore the real stress field of the dam model in a small scale and reduce the time cost and space demand of physical simulation.However,at present,the influence mechanism of high gravity on the seepage characteristics of soil is not clear.The seepage characteristics of soil are comprehensively affected by body force and surface force and other factors,and the existing high gravity seepage erosion test results are quite different from the theoretical results,which seriously restricts the effectiveness and reliability of the seepage failure test of dams under high gravity.Based on zju-400high gravity centrifuge platform and one-dimensional seepage erosion test device,this paper theoretically analyzes the seepage model under high gravity,and carries out experimental research on seepage and flowing soil failure of cohesionless soil under high gravity,including:1.The hydraulic loading system,control system and data acquisition system of the constant gravity one-dimensional seepage erosion device are optimized,so that it can have the functions of precise and stable regulation of high head（i<140）,determination of multi-point head pressure of soil samples,and determination of long-span seepage flow velocity（1-10000ml/min）.Based on the force balance relationship of micro elements,the influence of uneven centrifugal acceleration on the seepage model is analyzed,and the error of seepage force between the model and the prototype caused by uneven acceleration is discussed.The error is only 0.58%,which can be regarded as a uniform gravity field.Through theoretical analysis,the relationship between the flow velocity under centrifugal hypergravity field and the total pressure difference at both ends of the sample,the applied pressure difference（surface force）and the position pressure difference（body force）is given,and the influence on the seepage characteristics when the proportion of body force and surface force changes is considered,which lays a theoretical foundation for the later experimental design.2.The seepage comparative tests of three graded cohesionless soil one-dimensional soil columns were carried out under the environment of high gravity of 10-60g and normal gravity,and the influence of centrifugal acceleration on the flow characteristics of porous media was explored,considering the seepage characteristics of different body and surface forces.The results show that the permeability coefficient of soil and the critical Reynolds number of fluid（the critical Reynolds number of Darcy to non-Darcy flow transformation）have not changed under high gravity.The samples of group A and B are in the Darcy flow range（Re<3.8）,and the non-linear phenomenon can be observed in the test of group C,and the critical Reynolds number Recritical=4.8of the flow regime transition;Body force and surface force can be mutually transformed in the process of seepage.3.The flowing soil comparative tests of three kinds of graded cohesionless soil one-dimensional soil columns were carried out under high gravity（30g,50g）and normal gravity environments,and the evolution law and failure mechanism of homogeneous cohesionless soil flow soil under different gravity fields were observed.The results show that the failure process of homogeneous cohesionless soil under super and normal gravity can be divided into two stages.In the first stage,the soil did not experience erosion,and its permeability coefficients were basically equal,satisfying Darcy’s law;Then the particles in the soil were continuously eroded,and experienced the stage from the slow change of the permeability coefficient to the sudden change.At this stage,the soil evolved into a"occurrence→development→destruction"flowing soil failure process,and the hydraulic screening phenomenon occurred,and the flowing soil failure degree is more severe under the hypergravity.It is found that the similarity ratio of the critical hydraulic gradient during the failure of fluid soil is（χLess than and close to 1,and decreases with the increase of centrifugal acceleration）,the test value is less than the theoretical expected value,and the reason for the change is analyzed by using the lateral earth pressure coefficient model under over consolidation.Combined with scale factorχThe relationship between critical hydraulic gradient and centrifugal acceleration is given.The above research results provide the necessary theoretical support for the subsequent centrifugal model of infiltration erosion. |
