Study On Migration And Evolution Mechanism Of Caved Ore And Rock Based On The Particle Flow Theory

The caving mining method has been widely used in metal mines around the world.However,due to unreasonable structure parameters and poor draw control,the loss and dilution of ores are relatively large,which are directly impact by gravity flow of caved ore and rock.At present,the understanding of migration and evolution mechanism of caved ore and rock is still inadequate,which needs to be further investigated.In light of the current problems existing in the study of draw theory and technology,the migration and evolution mechanism of caved ore and rock is investigated in this doctoral dissertation based on the particle flow theory.And taking the Meishan Iron Mine in Nanjing as the background,the research work is financially supported by the National Natural Science Foundation of China(No.51374032).More specifically,using the three-dimensional physical model,a series of bottom and side draw experiments were carried out.Based upon the particle flow theory and PFC program,macroscopic and mesoscopic physical and mechanical parameters of caved ore and rock were matched,and the numerical models that can reflect the actual draw state of caved ore and rock were constructed.Several problems related to the migration rule of caved ore and rock,secondary fragmentation and ore loss and dilution under different boundary conditions were investigated based on physical draw experiments and numerical draw tests.The main research results and conclusions are as follows:(1)Based on physical draw experiments and numerical draw tests,it is observed that the shape of IEZ(isolated extraction zone)or IMZ(isolated movement zone)is the upside down drop shape,rather than a standard ellipsoid.The maximum width of the IEZ is mainly related to the mass drawn and the height of the IEZ,and is not significantly influenced by factors such as the granular media size,drawpoint size and column height in the range of values studied in this thesis.(2)Different boundary conditions,stope structure parameters and draw modes have different effects on the IEZ's shape and the ore loss and dilution.(3)Under both infinite and semi-infinite boundary conditions,the mass drawn has a power function relation with the IEZ's height and has an exponential function relation with the IEZ's radius.The change trend of the IEZ's height can be divided into the following two stages:in the initial draw stage,the IEZ's height increases exponentially and its growth rate decreases gradually with the increase of mass drawn while in the second stage,the IEZ's height grows linearly with increasing mass drawn.(4)The particle diameter ratio of the fine and large particles and the shape of particle are important parameters significantly influencing percolation characteristics of fine granular media.The rate of percolation of fine particle decreases in the form of negative exponent with the increasing of the particle diameter ratio of the fine and large particles.The closer the diameter of the fine particle size to that of large particle size,the more difficult it is for the fine particle to penetrate.(5)The isolated numerical draw tests are carried out with the construction of the cluster model and rolling resistance contact model,which have further improved the accuracy and reliability of numerical draw simulations.And draw migration and evolution mechanism of caved ore and rock is studied from a mesoscopic view:the gravity flow of fragmented rock is controlled by collapse of the arch on the upper part of the IMZ and erosion of its sides as granular material flows at its boundaries.The secondary fragmentation of caved ore and rock mainly takes place in the shear zone that forms the boundary between the stagnant and movement zones.In summary,the research of migration and evolution mechanism of caved ore and rock based upon the particle flow theory and PFC program can reappear the actual draw state,make up for the deficiency of the existing laboratory experiment and numerical simulation,and eventually provide beneficial scientific basis and technical support for the optimization of stope structure parameters and prediction of indices of ore loss and dilution.