Experimental Study On The Failure Law Of Saturated Coal Samples Under Falling Hammer Impact

With the increase of coal mining depth and mining intensity year by year,rock burst disasters are becoming more and more serious.Mine rock burst is the result of the combined action of static and dynamic disturbances of coal and rock mass.Coal seam water injection is an effective method to prevent rock burst,and it is of great significance and practical application value to study the instability and failure law of water injected coal samples under combined dynamic and static loading.In this paper,dynamic and static combined loading tests are carried out on natural coal samples,coal samples saturated with water for one day,and coal samples saturated with water for two days by using the developed drop-weight impact loading device.The law of instability and failure,and the acoustic signal monitoring of coal sample failure combined with acoustic emission technology,the main work and understanding are as follows:(1)Develop a drop-weight dynamic and static combined loading test device,which consists of a frame,a static load application system,a drop-weight impact system,a data acquisition system,etc.Dynamic and static combined loading experiments of standard specimens.(2)Carry out dynamic and static combined loading tests of natural coal samples and different saturated coal samples.The static loads of the test are selected as 0.6σ_c,0.7σ_c,0.8σ_c,0.9σ_c,and the impact loads are selected as 0.1σ_c and 0.2σ_c,and the combined loading effect of the coal samples is studied.The lower stress-strain relationship,impact time,strain rate,peak stress and other mechanical parameters change with the load.In the combined loading,the uniaxial compressive strength value of the natural coal sample is the largest,and the uniaxial compressive strength of the coal sample decreases gradually with the increase of the saturated days of the coal sample,and the peak stress of the coal sample after the saturated water treatment decreases obviously.(3)The variation law of the influence of static load and impact load on the stress peak value of natural coal sample and water-saturated coal sample was studied.When the static load is the same,the peak stress of the natural coal sample and the water-saturated coal sample increases with the increase of the shock load,but the variation range of the water-saturated coal sample is smaller than that of the natural coal sample.The more stable it is with the change of static load.When the shock load is the same,the peak stress of the natural coal sample and the water-saturated coal sample increases with the increase of the static load,and the peak stress of the water-saturated coal sample changes less than that of the natural coal sample.(4)The effects of the severity of coal sample damage and the damage degree of water injection coal samples were analyzed.The damage severity of natural coal samples,coal samples saturated with water for one day,and coal samples saturated with water for two days decreased in turn,and the damage patterns of coal samples were different.After the saturated water treatment,the coal body is softened and the brittleness of the coal body is reduced.The saturated water treatment of the coal sample can reduce the damage degree of the coal sample.(5)The change law of coal sample impact failure time was analyzed.When the static load is the same,the impact time decreases as the impact load increases.The shock load is constant,and with the increase of the static load,the failure time of the natural coal sample,the one-day-saturated coal sample,and the two-day-saturated coal sample decreases successively.(6)The variation law of acoustic emission signal of coal samples in different loading stages was studied.The change trend of the damage energy signal of coal samples is different.The natural coal sample has the most concentrated energy signal and the largest signal intensity in the damage stage,while the saturated coal sample has the largest energy concentration and the largest signal intensity in the middle and late elastic stage and the early stage of the damage stage.The signal strength of the ringing count corresponds to the variation law of the energy signal strength,and will enter the stage of signal strength concentration in advance with the increase of the number of days when the coal sample is saturated with water.There are 50 figures,9 tables,and 116 references.