Instability mechanism of narrow coal pillar roadway floor considering dynamic load disturbance

The floor of a narrow coal pillar mining roadway often exhibits asymmetric failure characteristics. When the overburden suddenly breaks and releases energy, it will have a dynamic load disturbance effect on the narrow coal pillar roadway. Under the action of dynamic load disturbance, the phenomenon of rock fragmentation and even rock ejection is more common, which makes it difficult to maintain the stability of the roadway floor. In order to grasp the failure mechanism of narrow coal pillar mining roadway floor and the influence of dynamic load disturbance on the stability of roadway floor, a comprehensive use of theoretical analysis and on-site measurement methods, a mechanical model of the floor of the narrow coal pillar roadway is established, and the stress, energy and excavation unloading characteristics of the roadway floor are analyzed. The results show that：after excavation, the stress on both sides of the narrow coal pillar roadway floor is asymmetrically distributed. The stress of the solid coal floor and the roadway floor is greater than that of the coal pillar floor, and the side floor near the solid coal is prone to shear failure. After the excavation of the roadway, the coal pillars and the roadway floor are in a state of unloading axial pressure and confining pressure, and the solid coal floor is in a two-way loading state. After the dynamic load is disturbed, the energy increment of the coal pillar and the roadway floor is greater than that of the solid coal floor, and the side floor near the coal pillar is more affected by the dynamic load disturbance. Considering the disturbance of the dynamic load, the coal pillars and the roadway floor are in a state of discharging energy after excavation, the solid coal floor is in a state of energy accumulation, and the "unbalanced" stress state of the surrounding rock is an important reason for the instability and asymmetric failure of the roadway floor. Increasing the deformation modulus of coal pillars and roadway floor or applying compensation stress, reducing the stress concentration of floor and storing energy are the two main ideas to improve the "unbalanced" degree of roadway floor. Through the implementation of asymmetric support technology for a narrow coal pillar roadway in a certain mine, the floor near the coal pillar side is grouted and reinforced, thereby improving the "unbalanced" state of the floor and effectively controlling the floor heave of the roadway.