Research of similarity law of seepage deformation and Microscopic mechanism of piping based on the statistical particle modelXiaodong NiTunnel and urban rail transit reaearch Institute, Hohai UniversityAbstract: Seepage failure is a complicated fluid-solid coupling process, Involving large deformation and the flow theory of granular media. The process of particle migration is closely related with time. At present,the continuous medium method from the Macroscopic level is used in most case to solve this question.It is obviously that the continuous medium method is helpless to describe the physical process of seepage deformation dynamically.Statistics particle flow method has the discrete traits which can be used to simulate the physical processes more convenient.Seepage deformation is a dynamic process of interaction between soil and water.When carry out relevant experiment, it is necessary to make sure that the time between the analysis model and research objects is coordinated. In other words ,it must obey time similarity criterion .The ongoing indoor model test or centrifuge model test are based on the assumption of Darcys law. Under the assumption, it has been confirmed by tests that the time similarity criterion does not satisfy again. In this case , it is impossible to achieve similar between porototype and model in the corresponding period.So there will be a certain deviation between porototype and model. Based on the basic equations of fluid dynamics in porous media, the similarity criterion about seepage deformation is deduced. Statistical particle model can meet the the conditions in the similarity criterion. Therefore, the model is used to verify the correctness of the similarity criterion.Based on the above results, seepage deformation model test is conduct, then taken it as the prototype. Corresponding statistical particle model is established according to the similarity lawThe result shows that this method is applicable to research the phenomenon of piping. Final,this method is used to explore the microscopic mechanism of Piping.1.PrefaceDescribes the relevant numerical methods of seepage deformayion, highlighted the problems existing in the current method. Describe the advantage of statistics particle model in carry out seepage deformation.2.Seepage deformation characteristics 302003 200 ()(,(1)() ()1sT sVtijktnQtk dttggJFlow :Function of time and space.3.Nature of seepage deformation3.1 Basic equations Continuity equation/Momentum conservation equation( ()ffntnnput vvgv()=fluid-particle friction coefficient：21150.75f fndd the driving force applied to a particle by fluid is :3int 6)(1pijjdufjij v3.2 Processing method4. Similarity law in the process of seepage deformation4.1 Hydrodynamic similarity lawContinuity equation/Momentum conservation equation22pv vgtlll vtidemStl22idemFrgl 2idemEuvvlidemR4.2 Similarity law of fluid dynamics in porous mediaMomentum conservation equation( ()ffnnput vgv)=fluid-particle friction coefficient:2312ffnkgFig.1 Schematic diagram of fluid-structure interaction Solid particlesLiquid：ContinuousImpermeable layer Pressure point Velocity pointFluid flow in micro-poreporeSolid：DiscretePore-Averaged N-S solution equationImpermeable layerParticles-SPM solution2/1()/()vtlgpvlkgldabcef5. confirmation similarity criterion by Statistical particle model Fig.3 Nuniacal poroto and model(a) Numerical prototype(b) Centrifugal model(c) Model satisfies the similarity criterion6. Indoor Model test and Statistic particle model test00.050.10 0.1 0.2 0.3 0.4M-II: po=1.7kpa d=do/10 =1、0.1M-II: po=2.0kPa d=do/10 =1、0.1M-I: po=1.7kPa d=do =1、10M-I: po=2.3kPa d=do =1、100.15Velocity(m/s)time /sFig.4(b)Surface velocity changes with time in model under different hydraulic gradientsFig.5(a)Schematic diagram of the indoor modelPiezometer0.3HBC A0.30.2 0.8Permeable platePiping hole0.020.040.060.080.100 1 2 3 4Velocity(m/s)Fig.4(a) Surface velocity changes with time in prototype under different hydraulic gradientsP: po=2.0kPa d=do =1P: po=1.7kPa d=do =10Time (s) Fig.5(b) Schematic diagram of numerical model7. Microscopic mechanism of piping8. Conclusion基于统计粒子模型开展渗透变形相似律及管涌细观机理研究Impermeable boundaryUpstream head boundaryP=0Impermeable boundary摘要：渗透破坏过程是复杂的流固耦合过程，涉及固体大变形和颗粒介质的流动理论，该过程中颗粒运移与时间密切相关。当前大多从宏观角度采用连续介质方法对该问题开展相关研究，显然无法从本质上对该物理过程进行动态描述，统计粒子流方法具有的散粒体特质可以实现对该物理过程的模拟。渗透变形是一土水相互作用的动态过程，开展渗透试验研究时必须确保分析模型与研究对象间的时间协调，亦即需满足谐时准则。当前开展渗透变形室内模型试验或离心试验研究均基于达西渗流假定，该假定下渗透破坏时间比尺不满足谐时准则已为试验所证实。模型与原型中对应时间点将很难保证相似，最终试验结果与原型之间必将存在一定的偏差。本文基于多孔介质流体动力学基本方程推导了渗透变形相似准则，统计粒子模型的优势恰能满足渗透变形相似的各项条件，因此采用该模型对相似准则的正确性进行了验证。基于上述成果，开展渗透变形模型试验，以其为原型，按照相似律建立相应的统计粒子模型，通过分析验证统计粒子模型研究管涌问题的适应性。最终，采用该方法开展管涌细观机理研究，从细观层面揭示发生管涌破坏的机理。