Simulation Of Seepage Failure Law Of Layered Permeable Layer Based On Discrete Element

In order to study the generation and development process of seepage failure from the micro perspective,based on the basic theory of discrete element,triaxial test and fluid solid coupling principle,the quantitative relationship between the macro parameters(c and ψ)and micro parameters(bs and μ)of cohesive soil is established by using the particle flow software(PFC3D)and its built-in fish language,and the program of the repose angle particle flow model of cohesionless soil is compiled.The micro parameters of materials are calibrated quickly and accurately.In this paper,the model of contact scour particle flow between sandy gravel and sand is established,and the models of contact scour under different D10/d10 ratios(D10 and d10 are the effective particle size of sand gravel and sand respectively)are simulated.The evolution process of porosity,fine sand loss and particle trajectory of sand and gravel layer with seepage action time in contact erosion process is analyzed.The influence of unsteady flow,particle shape and porosity of sandy gravel layer on contact erosion is discussed.According to the different content of fine materials in the coarse-grained soil overlying the multi-layer embankment foundation,the development process of the seepage deformation of the embankment foundation is simulated,and the micro parameters and migration characteristics of the seepage deformation are obtained,and the change rules of the parameters such as the particle loss amount are analyzed.The conclusions are as follows:(1)The method of control variable and Mohr Coulomb criterion are used to calibrate the micro parameters of cohesive soil,which effectively reduces the trial work of the traditional calibration method.The relationship between the macro strength parameters(c and ψ)and the micro parameters(bs and μ)is established.The relationship between macro and micro parameters is as follows:cohesion c is positively correlated with shear bond strength bs,and internal friction angle ψ is exponentially correlated with shear bond strength bs and friction coefficient μ.(2)When D10/d10 ratio is less than or equal to 12,the change of particle loss and porosity is small,and the model is not damaged.When D10/d10 ratio is greater than or equal to 14,the particle loss and porosity of the fine sand suddenly increase,and the model is damaged.It can be concluded that the critical ratio(D10/d10)of model failure is between 12 and 14.The fine sand layer particle loss first occurs far away from the contact surface between the fine sand layer and the sandy gravel layer at the pressure head end.With the increase of calculation time,the fine sand layer particle loss gradually develops along the contact surface between the sandy gravel layer and the fine sand layer towards the pressure head end.When the fine sand layer particle loss reaches a certain degree,the upper sandy gravel layer will settle.The migration path of fine sand particles in the upper sandy gravel pores is irregular and random.(3)It is found that the loss of fine sand decreases with the increase of the loading stages of the pressurized water head,and the faster the loading of the pressurized water head,the greater the harm of the contact scour.When the upper sandy gravel particles are irregular,the loss of particles in the fine sand layer is slightly smaller than that when the upper sandy gravel particles are spherical.In the process of contact erosion,the change of porosity in the upper sandy gravel layer has a great influence on the loss of fine sand particles.The loss of fine sand particles increases with the increase of porosity in the upper sandy gravel layer.(4)It is found that when the fine content of the coarse-grained soil layer is 10%and 20%,the fine particles flow in the pores of skeleton particles under the action of seepage force,which shows piping failure.The less the fine content of the coarse-grained soil layer is,the more easily the fine sand layer is damaged.When the content of fine material is 30%,the soil near the pipe mouth is firstly damaged by flow soil,and then the skeleton particles of the overlying coarse-grained soil and the fine sand layer particles are lost synchronously and gradually develop to the upstream,which is shown as the piping failure,and the overall particle loss is transitional seepage failure.