Abstract:
Water inrush from the floor of the coal mining face is one of the main disasters in deep coal mining in China, and its occurrence is related to the geological conditions of the coal seam and the mining activities. In the process of coal mining, the floor can be perturbed and damaged, and the original fracture zone for fluid uplifting above the limestone aquifer can also gradually extend upwards under the joint effect of secondary tensile stress and confined water pressure. When it is connected with the failure zone of the coal floor, water inrush occurs. The rock fracturing induced by floor damage can produce microseismic events. From the spatial and temporal distributions of microseismic events, the spatiotemporal distributions of the floor damage zones can be determined. At the same time, in the process of the upward invasion of confined water, the water can interact with the surrounding solid media to produce oscillations, which can propagate outwards in the form of elastic waves. By using the microseismic monitoring system for mining group A coal layer of Pan’er Coal Mine of Huainan Mining Group, in addition to monitoring large amounts of microseismic signals related to floor rock fracturing, the oscillation signals related to the interaction between fluid and solid medium was also detected for the first time. The corresponding waveform is screw like and lasts for more than 20 s, whose amplitude is mainly in the range of 10-5-10-4 V and frequency range is 20-40 Hz. Therefore, based on microseismic locations of floor fracturing signals, the authors can further analyze and locate fluid flow induced oscillation signals, and determine the temporospatial distribution of the fluid filled fractures overlying the limestone aquifer. As a result, the floor damage depth and the spatial distribution of uplifting zone for the confined water and their connections can be determined. Therefore, based on the joint analysis of microseismic locations and fluid induced oscillation signals in time and space, a new idea and method is proposed for monitoring and early warning of water inrush from coal limestone floor. The new strategy have been applied in the monitoring and early warning of water inrush from coal floor of group A of Pan’er Coal Mine of Huainan Mining Group.