Study On The Calculation Method Of Graded Granular Particle Packing Density

Particle packing density is one of the most basic parameters which reflect the internalstructure of granules medium. It is one of the key design parameters in civil engineering andis a point of penetration of many particle mechanics problems. In view of the importance ofstudying particle packing density, numerical test is carried out in PFC3D numerical platformbased on the deep water cofferdam project. Relevant factors of particle packing density arestudied and computational formula of particle packing density is established in thisdissertation. Meanwhile, physical model test and centrifugal model test are also carried out tocheck the result of computation. The research contents and results are as follows.1The computational formula of particle packing density.is set up. Based on the mechanism ofparticle "filling" and particle "replacing", the estimation model of particle density is extendedfrom mono-size particle and binary particle to multiple size particles. The influence of theparameters in computational formula is studied by the numerical test. A whole set of methodand computational formula estimating particle packing density is set up respectively for thedifferent situations2. Particle shape information is extracted and its shape is reconstructed based on the imageprocessing in Matlab.Weighted roundness of the particle is defined as shape indices. Thereconstruction process can be state as follows: fetching roundness information from threeviews of particles which are shooted by digital camera firstly, then calculate the averageroundness is weighted by the areas.3D convex hulls which have certain weighted roundnessare created in Matlab and then extract three-dimensional information by means ofvoxelization and skeletonizing. The clumps are created according to the three-dimensionalspace coordinate information in PFC3D.3. The influence of particles characteristics on packing densityis studied. Knowing thatpacking density are influenced by factors such as friction coefficient between particlesparticle shape and gradation of particles, correlative numerical test are carried out and therelationship between the packing density and factors is clear. The relationship between macro-frictional angle of granular media and micro-friction coefficient between particles isdiscussed and defined the calculative process of width of size distributions.4. The packing density in the condition of fluid-structure interaction studied. The particlesyielded force such as gravity, buoyancy, resistance and disturbing force between particles inthe fluid. Packing density will be modified due to the external force. Numerical tests ofgradation particles were designed to study the influence of still water on packing density.5. The influence of packing depth and vertical press on the packing density is studied. Fittingformula of void ratio varied with depth and vertical press is established according to Janssenformulas and numerical experimental results. Meantime, the confined compression numericaltest is carried out by PFC3D and its results can be the basis of variation of void ratio with theimpact on cover load. Also the fitting formula whose void ratio varied with depth and verticalpress is improved.6. Physical model and centrifuge model testing are designed to verify the validity of packingdensity estimation model. Glass marble and weathered sand are poured to cylinder in differentheight and weathered sand with graduation are packed in centrifugal machine in the conditionof different acceleration to simulate self-weight compression. The calculated results agreewell with those of the physical model testing and centrifuge model test.