Experimental Study On Anomalously-Low Friction Effect Of Interface Between Combined Coal And Rock Under Impact Loading

Resource development is gradually developing towards the deep underground.With the increase of mining depth,deep rock mass tends to be broken into a block medium.The special mechanical environment of "three high and one disturbance" promotes the anomalously-low friction effect of deep underground block rock mass.So it will induces the disasters as rock burst.Taking the combined coal and rock mass as the research object,the self-developed deep rock mass anomalously-low friction effect test system is used to carry out experimental research.The study focuses on the influence of the properties of the interface between combined coal and rock layers on the anomalously-low friction effect of combined coal and rock under impact loading.The research conclusions can provide scientific reference for preventing and controlling the occurrence of anomalously-low friction rock burst in deep underground coal and rock mass.The results show that:(1)The influence of lithology on the horizontal displacement and acceleration of the working block is analyzed.In the same stress environment,the horizontal displacement of coal and rock combination and rock and rock combination working blocks can be divided into four stages: static stage,sudden increase stage,slow increase stage and stable stage.Their horizontal accelerations can be divided into three stages: initial stable stage,abrupt change stage and second stable stage.Compared with rock and rock combination,coal and rock combination have shorter horizontal displacement mutation time and horizontal acceleration amplitude time,and larger irreversible displacement and horizontal acceleration amplitude.In the same stress environment,the coal and rock combination is more prone to anomalously-low friction effect.(2)Through comparative analysis of the horizontal displacement and acceleration characteristics of the combined coal and rock working block subjected to the vertical impact disturbance,it is found that the vertical impact disturbance promotes the occurrence of anomalously-low friction effect.The larger the amplitude of vertical impact disturbance,the more significant anomalously-low friction effect of combined coal and rock.The frequency of vertical impact disturbance has a critical value of 2.6 Hz.When the frequency of impact disturbance is less than 2.6 Hz,with the increase of the frequency of vertical impact disturbance,the anomalously-low friction effect of combined coal rock is more significant.The low frequency vertical impact disturbance is favorable for the occurrence of anomalously-low friction effect of combined coal and rock.(3)The roughness of combined coal and rock contact surface affects the anomalously-low friction effect of combined coal and rock,and it has a critical value of 3.98.When the roughness of the contact surface is greater than 3.98,the friction between the coal and the roof sandstone is reduced due to the pulverized coal generated between the coal and rock contact surface under the action of impact disturbance.As the roughness of the contact surface increases,the anomalously-low friction effect of combined coal and rock becomes more significant.(4)The anomalously-low friction effect of the combined coal and rock has a nonlinear relationship with the thickness of the weak interlayer between the combined coal and rock layers.The thickness of the weak interlayer has a critical value of 4 mm.When the thickness of weak interlayer is less than 4 mm,the probability of inducing anomalously-low friction effect increases with the increase of the thickness of weak interlayer.With the same thickness of weak interlayer,the different position of weak interlayer affects the anomalously-low friction effect of combined coal and rock.When the weak interlayer is located on both the upper and lower surface of coal block,the anomalously-low friction effect of combined coal and rock is the most significant.(5)By analyzing the effect of the particle size of pulverized coal on the horizontal displacement and acceleration of combined coal and rock working block,it is found that the larger the particle size of the pulverized coal,the more likely the combined coal and rock to have anomalously-low friction effect.So it will induces the disasters as rock burst.