Study On Uniaxial Compression Mechanical Properties And Fracture Evolution Law Of Coal Rock Combination

Compared with the surrounding rock of single rock roadway,the uneven deformation of surrounding rock of thin coal seam roadway is more prominent.This uneven deformation characteristic of thin coal seam surrounding rock between the different surrounding rocks has greatly hindered the mining of thin seam coal mines.The research on the deformation characteristics of surrounding rock provides a theoretical basis for optimizing the supporting measures of semi coal rock roadway and improve the bearing capacity of surrounding rock which are the keys of the problem.In this paper,the deformation characteristics,fracture evolution and failure characteristics of"sandstone coal sandstone"combination under uniaxial compression are studied.In order to study the mechanical properties of different rock formations and reveal the uneven deformation characteristics of rock and coal formations.Through the uniaxial one-time and uniaxial cyclic loading tests of"rock coal rock"combination with different height ratio,the loading failure law of coal rock combination with different height ratio is analyzed,which shows that the strength of combination is affected by the height of middle coal body,and the uniaxial compressive strength increases with the increase of coal body height;the energy evolution of combination with different height ratio is compared and analyzed,and the test results of coal rock combination are obtained The results show that the internal energy dissipation of the specimen decreases suddenly when the height ratio is between rcr-0.5 and rcr-1;the failure of the composite specimen is dominated by the coal body,and the sandstone at both ends constrains the middle coal body,so as to improve the strength of the coal body;the constraint in the middle of the coal body is the smallest,and the influence on the middle part decreases rapidly with the increase of the height of the coal body;the failure mode of the specimen changes from splitting to splitting with the increase of the height of the coal body The failure turns to shear failure and finally becomes the extrusion of middle coal.The fracture evolution law of coal rock combination in uniaxial compression process is summarized by calculating the damage variable of specimen in uniaxial compression test and recording the number of fractures in PFC numerical simulation.In the whole process of specimen fracture evolution and compression in indoor test,the fracture development begins to increase rapidly when loading to 0.8?₁,while the numerical simulation results show that the fracture begins to develop at 0.7?₁ and increases at 0.8?₁ The reason is that the numerical simulation can not reflect the original micro cracks.According to the synchronous monitoring method,a monitoring device is designed which can be used to monitor the axial force of the bolt when conducting similar simulation experiments in the laboratory.It is a monitoring equipment which can monitor the deformation of roadway surrounding rock and stress of anchor bolt simultaneously in practical engineering.Under the influence of coal rock height ratio,the failure mechanism of coal rock combination can be divided into unstable failure and unstable failure:in this paper,when the height ratio of sandstone and coal rock combination is equal to 1,and the height ratio is lower than 1,the sandstone and coal rock successively enter into the stage of unstable fracture development,and then fail at the same time When the height ratio of the specimen is greater than 1,the coal body will be destroyed after the sandstone and the coal enter the stage of unstable fracture development,and the sandstone does not reach the critical state at this time,so the failure is instability.