Research On Mechanics Characteristics Of The Sandstone With Structural Plane In Coal-Bearing Strata Of Shendong Coal Field

Rock mass is a complex structure formed by a long geological evolution process,which has obvious structural features.A large number of engineering practices show that the structural characteristics have a great impact on the mechanical properties of rock and rock mass.Therefore,the mechanics characteristics of the sandstone with structural plane in coal-bearing strata of Shendong coal field were used as the main line for the study.First,more than 1000 meters core was analyzed to investigate the structure surface type,and the macro and micro structural characteristics of the structure plane were analyzed by X ray diffraction,scanning electron microscopy and 3D laser scanner.And then,the mechanical properties and acoustic emission characteristics of sandstone with structural planes were studied by CMT5000 tensile testing machine,RDS-200direct shear apparatus,RMT-150C mechanical testing machine and DS5-8b acoustic emission monitor.Finally,based on the basic damage theory model,a new damage theory model was established considering the AE,structure and porosity parameters.The research results were obtained as follows:?1?The structure plane of coal-bearing strata in Shendong coal field can be divided into two types through statistics of more than 1000 meters of cores.But the I class can be divided into 3 subclasses?I₁?I₂?I₃?.I class structural plane formed by the plant leaf carbonization;I2 class structural plane formed by the plant trunk carbonization;I3 class structural plane formed by the small granular coal;II class structural plane formed by the Muscovite.The macro-microscopic features of structural plane are described quantitatively by X ray diffraction,scanning electron microscopy and 3D laser scanner.The experimental results show that the four kinds of structural planes have obvious differences in composition characteristics,microstructure surface and the three-dimensional shape characteristics.?2?The natural structure plane has obvious influence on the peak tensile strength,peak strain,shear strength and elastic modulus,and the peak value of acoustic emission in the process of direct and direct shear of sandstone.However,it has no effect on the uniaxial compression strength,peak value of acoustic emission and cumulative count under uniaxial compressive.?3?The thickness of the interlayer has obvious effect on the peak strength,peak strain,elastic modulus,peak value of acoustic emission,cumulative count and waveform parameters.However,the thickness of the interlayer has no effect on the cohesion and internal friction angle.The failure mechanism of the two types of sandstone has a certan difference.The theory model of strength weakening of the two kinds of structural planes is proposed.?4?The inclination of the structure plane has obvious influence on mechanics and acoustic emission characteristics.The uniaxial compressive strength,elastic modulus,triaxial compressive strength,peak strain,peak count and total count with increasing obliquity,first decreases,then increases,showing a quadratic function relation.The inclination of structure plane for 0o,15o,75oand 90o,sandstone does not along the structural plane failure.However when the inclination of structure plane is 30o,45oand60o,sandstone along the structural plane slip failure.It was found that a single weak plane theory can't fully adapt to the surface structure of certain thickness through comparative analysis the experimental data and theoretical analysis results.The piecewise function was proposed to describe the situation.?5?The stress loading path has a certain influence on the mechanics and acoustic emission characteristics of sandstone in the failure process.The frequency of the acoustic emission during the initial densification period and the stress at failure increases with the increasing of confining pressure under the conventional triaxial compression.A positively correlated was present among the confining pressure,strain difference,maximum principal stress difference,peak value of acoustic emission,cumulative counts and the initial confining pressure under triaxial unloading confining pressure.The unloading rate was positively correlated with the confining pressure and the peak value of acoustic emission.While there is a negative correlation among the strain difference,maximum principal stress difference,the cumulative count and unloading rate.?6?A new damage model was established,considering the AE cumulative counts,inclination of the structure plane and porosity based on the Lemaitrc damage theory.And,the model is verified by experimental data.