Study On Fracture Evolution And Instability Mechanism Of Large Dip Coal Seam Roadway Considering The Effect Of Mining

The surrounding rock of large dip roadway is often subjected to the effect of the non-symmetric loads.However,the shear stress components generated by the nonsymmetric loads is beneficial to the crack initiation and expansion.This is one of the main reasons of the failure and instability of large dip roadway.Revealing the fracture evolution and instability mechanism of large dip roadway from different aspects can provide an important reference for the support design of such roadway.Although domestic and foreign scholars have carried out a series of studies on the failure mechanism and control technology of the roadway with large dip angle,there still exists many shortcomings.For instance,it is still a blank to reveal the influence of shear stress composition on the fracture behavior of coal or rock specimens under combined compression-shear loads from the perspective of laboratory tests due to the lack of responsive experimental systems;meanwhile,there are still few reports on the instability mode of large dip roadway considering the sliding effect of weak roof layer under mining;In addition,from the mechanical analysis aspect,the study on the influence of mining intensity and inclination angle on the stress and deformation behaviour of surrounding rock of large dip roadway still needs to be supplemented.In this paper,the laboratory test,numerical simulation,theoretical analysis and field test are used to study the fracture evolution and instability mechanism of large dip roadway under mining,and the corresponding control theory and technology are proposed.The main conclusions are summarized as follows:(1)Firstly,a new combined compression and shear test(C-CAST)system is developed,and the specific assembly steps and application methods of C-CAST system are described in detail,and the strength calculation principle of coal or rock specimens under combined compression and shear loads is provided.Compared with the traditional uniaxial compression experimental system,this new test system can realize inclined uniaxial loading of the specimens.The loading method can effectively reflect the compression-shear coupling mechanical status of the large dip roadway.(2)Based on the C-CAST system,the influence of loading rates and inclination angle on the stress-strain curve,shear stress-displacement curve,stress,elastic modulus,shear stress component and strain energy of the specimens are analyzed,and then the macroscopic fracture mode and progressive fracture process of coal specimens at different loading rates and inclination angles are analyzed,the effects of loading rates and inclinations on the fracture tendency of coal specimens were revealed.Finally,based on the BP neural network algorithm,the prediction model on peak stress and elastic modulus of coal samples under different loading rates and inclination angle is established to quantitatively characterize the mechanical properties of the coal specimen subjected to the effect of complex stress conditions.(3)The acoustic emission(AE)behavior of coal specimens in the inclined uniaxial compression test are investigated,and then the evolution law on the AE parameters,crack initiation and damage threshold with the loading rates and inclination angles are analyzed;Meanwhile,the evolution law of tensile and shear crack of coal specimen in the inclined uniaxial compression processes are also discussed with the increase of loading rates and inclination angles,and the influences of inclination angles and loading rates on the fracture behavior of coal specimens are revealed from the microscopic perspective.Finally,the mechanical models on crack initiation model under uniaxial compression and combined compression-shear condition are established,and the crack initiation behavior under different load conditions are revealed from the mechanical perspective.(4)Combined the practice engineering,considering different weakness plane conditions,the influence of inclination angle,mining intensity,weakness plane parameters and stress release coefficient on the displacement,stress,plastic zone and weakness plane shear displacement of surrounding rock of large dip roadway are analyzed in detail by using FLAC3 D software,and the difference on instability mechanism of the roadway with different roof conditions is discussed.From the perspective of engineering,the fracture and instability process of large dip roadway is revealed under the effect of complex stress environment.(5)Based on the conformal transformation and complex function theory,considering the effect of mining intensity and inclination angle,the mechanical model on stress and deformation of surrounding rock of straight wall arch roadway with large dip angle is established,and then the analytic solution of stress and deformation of surrounding rock are also obtained based on the genetic algorithm.This can reveal the instability mechanism of large dip roadway form the mechanical aspects.(6)According to the results of numerical simulation,the mechanical model on the roof structure self-stability of large dip roadway is established under support condition.The mechanics criterion of roof structure self-stability is deduced and the relationship between rock-layers contact force and support strength located in spandrel is also discussed.Based on the above analysis,the “High pretension asymmetry” support theory is proposed and used in the 1201 working face transportation roadway.Finally,the support design flow of large dip roadway under mining is given.There are 136 figures,33 tables and 187 references in this dissertation.