Damage water inrush mechanism of loading unloading stress path of mining floor in deep coal seam.

The mechanism of water inrush from the stope floor has always been the key and difficult point in the research field of coal mine water disaster prevention and control. The mechanical essence of water inrush from the mining floor is the loading-unloading stress state transformation process. To reveal the joint action mechanism of principal stress state transformation and water pressure in the process of water inrush from the stope floor, the author studied the water inrush criterion, the characteristics of saturated rock damage test and the characteristics of principal stress transformation of coal floor using theoretical analysis, laboratory test and numerical calculation. Research results: The results show that the threshold of water inrush criterion of the mining floor is 1, based on the discrimination index of disturbance degree of mining floor strata, the threshold of floor cracking pressure, and the instability index of floor aquifer. The damage to the limestone floor samples has an obvious delay effect after pressure relief, but it produces a stress drop phenomenon when it is unstable. The maximum principal stress of the back floor in front of the working face is converted from horizontal stress to vertical stress. After the floor is unloaded, the maximum principal stress is transformed from vertical stress to horizontal stress. The difference between the maximum principal stress and the minimum principal stress of the mining floor presents different distribution characteristics at different depths, but it increases overall and is concentrated near the front and back coal walls of the working face. The research results will help to further reveal the mechanism of water inrush from the stope floor.