Experimental study on the stiffness of waste rock of gob of fully mechanized mining with large mining height

In order to reveal the changing law of gangue stiffness of goaf,in terms of the shortage of stiffness measurement data for waste rock at the working face of fully mechanized mining with large mining height,the experimental device of gangue compression was self-designed and developed. Taking limestone,medium sandstone and coarse sandstone as samples and combining with testing machine of rock mechanics,18 schemes were designed. The procedure of experimental was described briefly below:the crushing of rock→screening particle size of rock→mounting sample into experimental device→compression test by testing machine→cleaning up compressed debris→repeating experiment.The relationship between the compression displacement and the force on the condition of same lithology but different particle size (10-20 mm,20-25 mm and 25-35 mm),the same particle size assemblage but the different lithologic assemblage (combined sandstone with limestone and combined sandstone with the coarse sandstone) and the same particle size combination but different single lithology were tested. According to the principle of similar material experiment,the curve relation was converted,and the stiffness value formula of different combination rocks and different fragmentation degrees in gob was fitted. The results show that the stiffness of limestone caving zone is larger than middle sandstone caving zone,and the stiffness of middle sandstone caving zone is larger than that of coarse sandstone.The stiffness of large diameter limestone gangue is larger than that of medium size,and the stiffness of limestone gangue is larger than that of small particle. The stiffness of composite rock is between two kinds of rock rigidity. Under the same crushing condition,when the same amount of gangue is compressed,the harder the gangue is,the higher the stiffness of the gangue will be.