Study On Strength Characteristics Of Fluidized Coal Based On Hoek-Brown Criterion

The three-phase system consisting of gas pressure,ground stress and groundwater has a great influence on the mechanical properties of the coal.Especially for the tectonic soft coal with III-V structures affected by gas pressure and groundwater and other factors,the coal and gas outburst and other dynamic phenomena are prone to happen,which seriously threaten the life safety of field operating persons,therefore,the acquisition of mechanical properties of tectonic soft coal is very important for the safety mining of soft coal seam.In this paper,experimental study on the strength characteristics,unstable failure characteristics and AE laws under uniaxial compression,triaxial compression of raw coal and coal briquette were done,contrast the difference between the two;the experimental study on the strength characteristics under direct shear,uniaxial compression and triaxial compression of the tectonic soft coal with III-V structures of granular raw coal and coal briquette were done,and analyze the variation of strength characteristics of coal samples under different moisture content and pore pressure conditions;the Hoek-Brown criterion and the GSI of coal body structure was introduced to establish the coal body strength parameter.Research results are:(1)the unstable failure characteristics of raw coal is mainly splitting failure along axial occurred in uniaxial compression experiment,while the coal briquette failure mode is mainly spalling from both ends like a cone,finally unstable failure occurred in middle of coal sample,under confining pressure within a certain range,as the confining pressure increases,both coal sample strength increases.(2)In experiments of uniaxial compression,the AE events of different degrees of coal briquette took place on every stage,AE events of coal briquette in the stage of compaction are more active than raw coal,the AE events of raw coal occurred in small amount in previous plastic stage,while AE counts and energy of both two were quite active and enhanced rapidly in late plastic stage,and achieve peak counts and energy near peak strength.(3)the fractal dimension of the tectonic soft coal with III-V structures are increases in the order with the degree of crushing gradually increased,the internal friction angle is negatively linear correlated with the fractal dimension of the particle distribution,and the cohesion of granular raw coal increases first and then decreases with the increase of moisture content.However,the internal friction angle decreases as the moisture content increases.(4)The consistent coefficient of coal samples is a major factor influencing the strength of coal briquette compared to particle gradation,the cohesion of coal briquette is exponential positive correlation with the fractal dimension of the particle distribution.(5)As the moisture content of coal briquette increases,the strength of coal briquette increases first and then decreases,but the pore pressure weakens the strength of the coal briquette,however,the difference in strength of coal briquette with III-V structures is significantly reduced under pore pressure.(6)The strength parameters of coal sample and GSI value of coal body structure have a great influence on the accuracy of estimated value of coal body strength parameter,and the estimated value of the coal body strength parameter should be closer to the site actual.