Energy Evolution Law In The Process Of Failure Of Coal And Rock Mass In Fissure Of Soft Coal Seam

After the coal and rock mass in the soft coal seam are mined and subjected to in-situ stress,the primary cracks on the coal wall begin to develop and expand,which weakens the strength and stability of the coal body.Therefore,it is of great engineering significance to carry out the scientific research on the mechanical properties and deformation and failure process of the rock mass in the soft coal seam.By analyzing the fracture expansion process of soft coal mass from the Angle of energy and exploring the influence of energy evolution of coal-rock mass with different fracture inclination angles on the fracture expansion mode,the deformation and failure law of coal-rock mass with fracture in soft coal seam can be studied more deeply.In this paper,by combining numerical simulation and laboratory tests,the DNS200 electronic universal testing machine and digital image correlation technology are used to obtain the deformation and failure law of coal and rock mass in soft coal seam fissure and the energy evolution law in the process of deformation and failure,and the following research results are obtained:(1)In order to study the evolution process of deformation and failure cracks of coal and rock mass in soft coal seam,physical and numerical simulation tests of coal and rock mass with different inclination angles were carried out according to the different initiation and propagation modes of coal and rock mass fractures in different prefabricated fractures.Through numerical calculation,the characteristics of crack initiation stress in the process of deformation and failure of coal and rock mass are obtained.The digital speckle correlation measurement technology was used to obtain the data of strain field and displacement field on the surface of coal and rock mass deformation and failure,and the crack propagation law and failure mode on the surface of coal and rock mass were analyzed.(2)The sliding crack model of the prefabricated crack under compression was selected to analyze the stress distribution at the crack tip under the action of in-situ stress,and the applicability of the model was verified by numerical calculation.The experimental results show that the fracture initiation characteristics are as follows:when 0???45°,both ends of the prefabricated crack are subjected to tensile stress;When 45°???60°,one end is subjected to tensile stress and the other end is subjected to shear stress.When??75°,both ends are subjected to shear stress and crack initiation.In addition,under the action of compressive stress,there are compressive stress and tensile stress concentration around the crack,resulting in shear crack in the direction of vertical stress.(3)In order to identify and locate the crack propagation path,the digital image correlation method was used to carry out the deformation field evolution test of the soft coal body with crack.The results show that:near the stress peak stage,the strain field differentiation rate-axial strain curves of samples with different crack inclination angles show obvious growth point P1 and "sharp point" P2 successively,which correspond to the starting point of tensile crack and shear crack,respectively.The increase of inclination makes the P1 point occur earlier in the deformation process.At the same time,the stress value corresponding to the point P2 is closer to the peak stress.(4)In order to study the law of energy conversion of coal-rock mass with different dip angles in soft coal seam,a self-inhibition evolution model between pre-peak accumulated energy and axial strain of coal-rock mass with different dip angles was established.The model can reflect the inhibition effect of dip angles on energy conversion.By fitting the constitutive equation of the model with the laboratory test results,the applicability of the model is verified.The mechanism that inhibits energy conversion plays a decisive role in the final result of pre-peak energy accumulation.The self-inhibition of pre-peak energy in fractured coal-rock mass increases first and then decreases with the increase of prefracture inclination Angle,the energy accumulation rate decreases first and then increases,and the energy storage limit at the corresponding peak point decreases first and then increases.(5)In order to explore the relationship between the energy dissipation and the failure mode of coal-rock mass in the fissure of soft coal seam,the energy dissipation of coal-rock mass in different failure stages was compared and analyzed.The results show that the coal and rock mass have no obvious failure stage before the peak,and the system input energy is mainly stored in the sample in the form of accumulation,and the accumulated energy is released along the direction of crack and crack after the peak.In the process of deformation and failure of coal and rock mass with small dip Angle fissures,tensile fissures are easy to occur,which can easily lead to deformation and failure of coal mass in coal mine engineering.