Influence Of Horizontal Stress On Coal And Rock Failure And Cave Shape

In the process of coal mining,coal working face outburst is more common,the horizontal stress under the effect of bedding is a typical high outburst type,the difference of tectonic stress(horizontal stress)is the key to decide the scale and level of the outstanding capability of disaster,is the main factor to determine the outstanding cave form.In order to study the mechanical characteristics of coal and rock and the characteristics of cave body under horizontal stress,the coal and rock specimens of the outburst mine are selected to carry out the true three axis compression test under the different stress conditions.Various possible complex stress conditions under horizontal stress are simulated,and the mechanical properties of coal and rock under different stress conditions such as deformation,strength and failure characteristics are compared and analyzed.Through acoustic emission monitoring,the influence of horizontal stress on acoustic emission signal characteristics of coal and rock failure is studied under different stress conditions.According to the test results,several widely used criteria for coal rock strength are analyzed and evaluated.Based on the experimental results and strength criterion,combined with elast-plastic mechanics,the true three axis constitutive model of coal and rock is inferred.Reference the coal and rock mechanics properties and stress distribution in the scene of Pingdingshan NO.8 mine,the stability coefficient R of coal and rock is introduced,the reliability and feasibility of the numerical simulation are verified.The development law of cave body under different horizontal stress conditions is obtained,and the results of the study have certain theoretical and practical value.The results show that the horizontal peak strength of the coal rock specimen increased with the increase of stress in either direction of ?h and ?v,and the influence of ?v on the peak value was greater.The peak strain ?h and ?v of coal and rock specimens are all in good linear relation with stress ?h and ?v.The rate of increase of peak strain ?H is obviously greater than that of ?h and?v.It was indicated that the compression deformation of coal rock specimen was mainly due to horizontal ?H compression.The failure modes of specimens were mainly compressive shear failure.The number of fractures,the fracture angle and the degree of grinding caused by the failure of coal and rock increases with the increase of stress level,and the fracture angle of the fracture was quadratic function related to the equivalent confining pressure.The experimental data were analyzed by D-P intensity criterion,Mogi strength criterion and improved H-B intensity criterion,and the results show that the D-P strength criterion had the best fitting effect.The length of the cave along the roadway and the length of the vertical tunnel increased exponentially with the horizontal stress,and horizontal stress ?h has a higher influence on the length along the roadway.The length of orifice increased linearly with horizontal stress and the coefficient of influence was small.When the horizontal stress increased to a certain value,the growth rate of cave was obviously improved.