Research On Compaction Characteristics And Re-crushing Mechanism Of Graded Broken Coal And Rock

In the process of coal mining,there are a large number of broken coal rocks in the collapse zone of the mining area.Due to the high porosity,strong permeabitity and poor bearing capacity of such coal bodies compared with the original rock body,the geological environment is relatively complex.It is an important factor affecting the safe management of the mining area.In addition,the green mining technology of infill mining,is proposed for the problems of surface subsidence and waste of resources caused by the collapse method of the mined area treatment method.Moreover,in infill mining,the control effect of overlying rock movement and surface subsidence depends on the compaction characteristics of the infill material.Therefore,the basic mechanical characteristics and compaction characteristics of the crushed coal ro ck are studied by scientific means,so as to analyze the influence of its re-crushing characteristics and pressure-bearing stability on the movement of the overlying rock layer.It can provide a strong theoretical basis for surface subsidence.In order to study the compaction characteristics of crushed coal rock mass,the compression test system of crushed coal rock mass was designed independently in the way of graded loading.The paper carries out compaction tests on crushed coal rock mass under different stress conditions,and analyzes the effect of different axial stresses on the compression modulus of crushed coal samples.The paper obtains the compaction law of the crushed coal rock mass under certain stress conditions,so as to obtain the compaction characteristics of the crushed coal rock mass.And by fitting the relationship between the cut-line modulus of the crushed sample under the action of stress ?i and temperature,the intrinsic structure relation.ship of the compacted crushed coal body is obtained.And the accuracy and reasonableness were verified by bringing the experimental data into the intrinsic constitutive relationship equation.According to the compaction test research results of crushed coal rock body,the compaction process of crushed coal rock body was divided.Moreover,the thesis investigates the variation law of compression modulus of crushed coal rock mass under compression with different Talbol power index n.The fractal characteristics and stability analysis of graded coal rock mass are combined with particle size fractal theory and bulk mechanics.The compaction process is divided into three stages:plastic destabilization stage,stress recovery stage and primary rock-like stress stage according to the stress characteristics of the crushed coal rock body in the compression process.The deformation of the crushed coal body in the stress recovery stage has two ways:displacement reorganization and crushing reorganization,and the deformation in the pre-loading stage is mainly displacement reorganization.When the degree of compaction reaches a certain degree and the strain of broken coal body is ?1,the deformation is mainly in the form of crushing reorganization.The deformation caused by particle displacement reorganization in the whole process of compaction deformation is larger than the deformation caused by particle crushing filling.In order to study the re-crushing characteristics of the crushed coal rock body,the continuously graded crushed coal rock body was used as the test object.The fractal test of continuously graded crushed coal rock masses was designed and carried out with the self-designed fractal test system of crushed coal rock masses.The paper analyzes the effects of different grading structures and different stresses on the fractal dimension of particle size,and obtains the effects of grading structures on the re-crushing pattern of crushed coal bodies.The following conclusions are obtained:with the increase of stress,the particle mass difference between the mixed crushed coal bodies of different grades decreases gradually in the same particle size interval,and the particle size distribution of coal samples of different grades is more similar after the axial stress of 16 MPa.After a certain axial stress,the particle size distribution of the pressurized mixed crushed coal body with arbitrary grading structure will tend to be similar.That is,the grading structure will tend to be the same stable structure,which has smaller porosity and stronger load-bearing capacity.The denseness is higher and less prone to compression deformation and re-crushing,which can provide an important theoretical basis for the prevention of surface subsidence.Combining with the particle size fractal theory,the study of compaction and re-crushing mechanism of pressurized and crushed coal rock body was carried out.The paper analyzes the characteristics of coal rock particle re-crushing and obtains the relationship between fine view crushing and macro compaction deformation of crushed coal rock particles.Then the distribution coefficient of coal rock particles after compaction and the particle crushing difference and particle crushing weight are analyzed in one step to get the particle distribution mechanism of the compacted coal rock body after compaction.Finally,the evolution law of particle re-crushing state of pressurized and crushed coal rock body is deduced.The article considers that the graded crushed coal rock particles can be regarded as a combination of several single particle size intervals which are independent of each other.The particle gradation in the crushed state can be obtained by the assembly matrix proposed in this paper using the evolution function of the particle gradation in the crushed state for a single particle size interval.