Study On Crack Propagation And Expansion Of Phosphorite Under Triaxial Compression

This paper focuses on the mechanical and acoustic properties of the rock of the phosphorite and its top and bottom floor rock.The three-axis loading instrument and the acoustic emission testing system are used to study the crack propagation law of internal cracks under pressure.It is of great significance to analyze the research results and apply them to practical projects not only for the scientific exploitation of mineral resources but also for the prevention of geological disasters scientifically.Complete phosphorite is a brittle material whose strength is strongly dependent on the presence of internal defects and microcracks.When the compressive load exceeds the limit of proportionality,the microcracks will first develop from defects and stress concentrations,resulting in the stretching and convergence of the microcracks and the generation of macro-cracks.When the peak stress is reached,many micro-cracks will appear in the whole rock sample,and the tendency of micro-crack expansion will be more intense.Because the rock mass of phosphorite is not homogeneous,the stresses inside the rock are not uniform.After the compression,the stress concentration phenomenon is likely to occur at the tip of the crack,resulting in the formation of microcracks and stress redistribution,resulting in the rupture of the adjacent fractures.At this time,some macro-cracks and fractures have been formed in the rock samples and the number of fractures has increased,but they are not connected to each other and have not reached the highest level.After the peak,the micro-cracks rapidly expand and merge into the macro-fracture surface.With the decrease of the internal resistance area of rock samples,the rock stiffness decreases rapidly,and the formation,expansion and fusion of microcracks are accelerating.Acoustic emission frequency is high.This shows that for brittle rocks such as phosphorous blocks,the compression failure time is earlier than the acoustic emission peak,which means that the actual warning time will be longer than expected if acoustic emission is used as monitoring and warning indicator for stope collapse and rock burst Short time,rock damage earlier than expected.Under the different confining pressure,the acoustic emission of phosphorite differs widely.Comparing the acoustic emission time of phosphorite under the three stress conditions,the number of acoustic emission decreases when the confining pressure is 2MP 3MP 4MP,Can be seen,the higher the confining pressure,the lower the acoustic emission of rock activity.The relationship between damage and strain of phosphorite under triaxial compression is obtained.From the damage process of phosphorite,it can be known that the phosphorous rock specimen initially produced the fracture damage and then the microcracks expanded,and the ultimate crack eventually led to the whole damage to the complete damage,which was a gradual development.The physical parameters of phosphorite were input to SPSS for data regression analysis to calculate the formula of triaxial compressive strength of phosphorite.Numerical simulation was carried out by using Abaqus platform to expand the finite element correlation module to establish similar numerical model with the experimental sample.The maximal failure stress which is obtained by fitting the physical and mechanical parameters of phosphorus block into the fitting formula is about 2% different from the maximum failure stress that is simulated by ABAQUS.Within the allowable error range,it can be proved that the triaxial compressive strength formula of phosphorous block fitted in the previous article is feasible,and to a certain extent,it can be used to estimate the strength of unknown phosphorite.