Study On The Mechanical Effect Of Some Issues Of Coal-rock Cutting And Stope Roof And Floor Under Deep Mining

With the deepening of coal mining level,complicated geological conditions and serious underground working situation,more accurate cognition about pick cutting and safety of mining roof and floor is in need.Firstly,based on theory analysis and laboratory test,the calculation method of peak cutting force of coal-rock is proposed,and the mechanical test of coal cutting under lateral pressure is designed and carried out.Secondly,considering the variety of supercharged load in coal resource mining,the characteristics of deformation,internal force and fracture step distance of hard roof are studied systematically.Finally,according to the condition of asymmetric force of floor along coal roadway,the bottom lift mechanism is expounded,and the deformation and internal force of floor are studied.The main conclusions are as follows:(1)Based on the mechanical condition of coal rock on working face and the interaction of rock-pick during mining process,based on Evans theory,this paper puts forward a method of calculating the peak force of pick cutting on coal-rock.The results show that the theoretical calculation based on the curve strength criterion is in good agreement with the experimental results.With the increase of the cutting pressure,the peak load of cutting increases firstly and decreases later.The broken angle shows logarithmic properties,the upper limit is 180 degrees.Moreover,with the increase of the tensile strength of coal-rock,broken angle decreases and the floor limit of angle is 120 degrees.With the increase of cutting thickness and cone angle,the peak cutting force increased.(2)Through the preparation of classified coal-rock with similar materials,the cutting test of pick cutting on coal-rock with confined pressure was carried out.The effects of pressure,cone angle,cutting thickness,intrusion rate,intrusion angle,material hard coefficient and cutting spacing on cutting mechanics effect and energy consumption characteristics were studied.The results show that cutting factors have important effects on cutting peak force,intrusion coefficient,caving weight and energy consumption.Although the existence of lateral pressure increases the intrusion coefficient and peak load,it will result in a significant increase in the weight of the caving body,thus reducing the specific energy consumption.Due to the increase of the lateral pressure,the optimal truncation ratio is increased: while the pressure is 4MPa,the optimal truncation ratio is 3,while the pressure is 0MPa,the optimal truncation ratio is 2.(3)Based on the principle of elastic foundation beam,a method for calculating the deformation and internal force of hard roof is proposed,which is suitable for arbitrary supercharged load.The results show that the analysis results of 100 m roof on coal wall are accurate,although the calculation error will cause the deviation of the inner force and deflection of the distant roof girder.With the stiffness of the foundation smaller,the deflection of the roof span is obviously increased,and the roof on coal wall may be bent many times under supercharged load.With the support resistance,the minimum bending moment in the coal wall decreases obviously,and its position is close to the coal wall.The foundation stiffness has little effect on the fracture step distance,the lower the initial fracture step distance,and the smaller the beta and L,the closer the position of the failure near the middle of roof.(4)Based on the method of analysis of the roof over elastic foundation beam theory,the deformation and internal force of the floor of roadway are studied.The results show that with the increase of the depth of coal roadway,the bottom lift and bottom bending moment increase,and the relationship between the depth of coal roadway and the bottom lift pole is obviously linear.Combined with the coal mining rate and the maintenance of the floor of coal roadway,narrow coal column protection method should be adopted.The increase of bending stiffness of the floor leads to the decrease of the bottom lift,but the excessive bending stiffness will raise the bending moment of the floor and cause the fracture on it.