Abstract:
Studying the temporal and spatial evolution of the roof microseismic response during passing through the old roadway is of great significance for mastering the damage degree and migration characteristics of the roof strata. The paper takes the 9212 working face of Dongpang Coal Mine as an example. First, the division of the research stage is based on theoretical analysis and microseismic monitoring. Then the plane, section distribution and spatial position relationship of microseismic events in different stages are analyzed. The energy dispersion coefficient (AE) and spatial double factors (S, α) are used to study the energy difference and accumulation characteristics of microseismic events on the roof; Then, the comprehensive weight is determined by principal component analysis and entropy weight method, and the risk assessment model is established based on vulnerability index method; Finally, GIS technology is used to draw the risk level zoning map of three stages. The research shows that:① The period when the working face passes through the old roadway is divided into three research stages, namely the normal mining stage, the advanced influence stage of the old roadway, and the old roadway passing stage. Each stage is divided into “low frequency, low energy” and “ Low frequency, high energy”,“high frequency, high energy” are the main microseismic response characteristics;② There are two AE abnormal areas before and after the roof key layer breaking. The former abnormal area takes the stress anomaly as the main inducing factor, which leads to the AE value suddenly increasing to more than 7; The latter abnormal area takes the periodic weighting as the direct inducement, which leads to continuous large-scale strong earthquakes. The important sign is that the former abnormal area ends and the A E value suddenly drops.③ The angle factor α is generally concentrated in the range of 30° to 60° but it is less than 30° during periodic weighting. And the α before the fracture of the key layer will be inoculated upward at a high angle of>60° and then fracture at a small angle of <30° . The area factor S will increase suddenly when the high-level key layer is broken and periodic weighting occurs. Although the S caused by the advanced fracture of low key stratum is small, the degree of coal and rock fragmentation is large;④ The three research stages are divided into six risk levels, in which the red “grade I” risk area is the most likely to occur roof collapse and large-area weighting, which mainly concentrated in the range of 0-60 m above the coal seam in the old roadway stage and 0-30 m above the roof in the advanced influence stage of the old roadway, and presented the distribution pattern of upper small and lower large.