Research on the application of fiber bragg grating monitoring for deformation of coal pillar in sections

When the coal mine passes through the overlying coal pillars in close proximity to the coal seam, the superposition of dynamic and static loads induces strong mining pressure, leading to deformation and instability of the coal pillars in the section, resulting in casualties and equipment damage. In order to explore the real-time monitoring of deformation and development characteristics of coal pillars in sections based on fiber Bragg grating, and analyze the mechanism of rock pressure manifestation in the stage of entering and exiting residual coal pillars, the optical measurement methods of FBG and grating stress meters are combined with on-site measurement to study the spatial distribution law of coal pillar strain and the time-domain response characteristics of internal strain of coal pillars in front of the working face during the mining process, Feasibility study on verifying the optical measurement method for observing the strain level of coal bodies. The results indicate that during the process of mining the overlying coal pillars, the roof of the section coal pillars is affected by concentrated stress, and the upper rock block is broken and rotated, resulting in an increase in the load on the coal pillars. As the working face advances, the overlying rock fracture further propagates upwards, and the key layer fracture recurs, causing pressure on the working face. The overlying rock rotates downward, ultimately leading to deformation and instability of the section coal pillars. Based on the amplitude of on-site grating strain increment, the severity of local deformation inside the coal pillar is determined. Under the influence of concentrated stress, the maximum strength that occurs during the deformation of the section coal pillar is 650 με on the left and right sides, the concentrated stress in the overlying strata causes the peak horizontal strain of the coal pillar to be located at the 11.5 m position of the coal pillar width. The strain along the width direction of the coal pillar shows a trend of first increasing, then decreasing, and then stabilizing. The internal strain field has an impact range of about 5 m during the mining process. A comprehensive study is conducted on the characteristics and laws of deformation and instability of coal pillars in the section caused by strain when the mining face passes through the overlying coal pillars. Combined with changes in strain level and physical and mechanical properties of the coal pillars, the precursor characteristics of coal pillar failure are obtained. Before reaching the peak deformation under external force, safety measures are taken to relieve pressure and protect the coal pillars before lifting them.