Characteristics of strata pressure behavior of working face under typical roof conditions in China

Roof failures have always accounted for a large proportion of coal mine disasters for a long time, and have always been a problem that plagued coal mine safe production in China.The analysis of strata pressure behavior is very important to the effective prevention and control of roof disasters.At present, most studies only focus on a single mine or individual mining areas, and there is no unified understanding of strata pressure and roof disaster characteristics of different roof conditions.There is insufficient research on the commonalities and differences of pressure manifestation, and the effective evaluation indexes and methods of mining pressure manifestation characteristics have not yet been formed.Based on the above problems, the roofs of coal mines in China are classified into three typical conditions: shallow depth, hard roof, and non-hard roof.Among them, the non-hard roof working face includes two types of strong rock pressure roof and weak rock pressure roof.Through the analysis of a large amount of rock pressure data, the comprehensive analysis method based on the support working resistance P-T curve, the rock pressure cloud chart, the statistics of the typical working face pressure characteristics and the homogenization cycle fitting is used to analyze the characteristics of the working face rock pressure under various typical roof conditions.The following conclusions are drawn:① Shallow coal seam face has the characteristics of increased resistance by incoming pressure, slight increase or negative resistance increase by non-incoming pressure, frequent and long duration of incoming pressure, and large influence of ground pressure on surface shape.The homogenization cycle curve during the pressure on the working face is characterized by a logarithmic + exponential compound function.The resistance increase rate of the support during the pressure is much higher than that during the non-pressure period, and the growth rate of the working resistance shows a slow growth trend afterwards;② Hard roof working face has the characteristics of increased resistance by incoming pressure, large step distance of incoming pressure, sometimes dynamic load impact.The resistance increase rate during the non-compression period is small, and the homogenization cycle curve shows a slight resistance increase characteristic similar to a linear function.During the pressure period, the resistance increase rate of the support is significantly increased, and the characteristics of the homogenization cycle curve are similar to the resistance increase characteristics of the shallow coal seam;③ The non-hard with strong mining pressure type roof face has the characteristics of inconspicuous definition of incoming pressure and non-incoming pressure, and continuous and progressive roof disasters.The resistance increase rate under non-incoming pressure is higher than that of shallow buried and hard roof working faces, while the opposite is the case when under pressure; the non-hard with weak mineral pressure type roof working face has the features of weaker pressure appearance, lower resistance increase rate, and frequent local pressure, etc.The homogenization cycle curves of the two non-hard roof working faces are in line with the characteristics of logarithmic function, and the resistance increase rate shows a rapid increase in the early stage of the frame shift, and then a rapid growth trend.When pressure is applied, the resistance increase curve is lower than that of the shallow buried and hard roof working face.