Study On Non-uniform Deformation And Re-breaking Characteristic Of Crushed Coal Gangue During Confined Compression

There are numerous and huge gobs in our country.Long-term mining leads to the formation of"three zones"from top to bottom in gobs:bending subsidence zone,fracture zone,and caved zone.The caved zone is formed by the broken rock-coal particles in the gob.The re-breaking of the broken rock mass in the caved zone during the compaction process are the main reason for the change of the porous structure in the caved zone in the gob.And the change of the porous structure of the broken rock-coal mass in the caved zone will lead to changes in the parameters such as stress,density,porosity and permeability of the caved zone itself,which will change gas and water enrichment laws in gobs.Thus,understanding the re-breaking law and pore structure evolution of broken rock-coal in the caved zone is crucial for accuracy permeability estimation of mining gob and safety and efficient production for coal mining.In this paper,through laboratory compaction-acoustic emission test,PFC numerical simulation test and other scientific methods,a systematic study has been carried out on the scientific problem of"non-uniform deformation characteristics of broken coal gangue during axial compression".Based on the existing research,the crushed coal gangue compaction-AE experimental method and experimental device are improved.Then the evolution characteristics of AE parameters in different compression stages are studied,and the spatiotemporal evolution of AE positioning points in different horizons is quantitatively analyzed.The PFC^2Dnumerical model of crushed coal gangue is established,and the research on the internal layered deformation and porous structure evolution law of broken gangue in the process of axial compression realized from a mesoscopic point of view.We achieved some research results as follows:（1）Using the improved crushed coal and rock mass compaction-acoustic emission experimental device and method,the internal layered deformation characteristics of broken gangue during compaction were studied.During compaction,the breaking rate of each particle size sample at different layers is:upper layer>middle layer>lower layer.The re-breaking rate of gangue in the same layer grows with the increase of particle size.Larger particle size samples have weaker resistance to deformation.In the final compaction state,the larger the particle size is,the greater the porosity of the sample in the same layer;and for a certain particle size,the porosity of different layers is upper layer<middle layer<lower layer Layered.（2）The corresponding between the cumulative parameters of AE and the stage of axial compression is explained.In the initial stage,the accumulative count and energy of AE are low.In the early stage of linear compaction,the curve of AE cumulative count and energy with time shows a"downward convex"trend,and the curve shows a linear growth trend in the later stage.During the plastic compaction stage,the curve shows an increasing trend related to particle size.In the plastic consolidation stage,the curve shows an increasing trend related to particle size.The distribution of AE locating is related to the stage of compression.It has obvious layerd characteristics:in the early stage of axial compression,the locating points first appear in the middle and upper layers.With the continuous axial loading,AE locating points appear in the upper,middle and lower layers,and are more concentrated in the middle layer.In the later stage of axial loading,the number of AE positioning points increased significantly,and more concentrated in the middle and upper layers.（3）PFC^2D is used to construct the flow numerical model sample of crushed particle in uniaxial compression test,and the meso parameters of the numerical model are calibrated based on the laboratory test results.The results show that the stress-strain curve of particle flow numerical simulation test can also be divided into three stages according to the change of curve slope.The stress is transmitted from top to bottom along the force chain network.The force chains continue to destabilize and recombine and gradually formed more stable force chain skeletons.The deformation characteristics of particles under pressure are non-uniform.The temporal and spatial evolution characteristics of breaking point are from top to bottom.In the whole compression,the voidage of each layer is:upper layer<middle layer<lower layer.Under the same strain,the larger the particle size,the greater the void fraction of the sample.