Abstract:
To investigate the influence of abrupt changes in coal dip angles within deep and complex geological structures on the evolution characteristics of coal and gas outburst and impact evolution characteristics, an interface with an abrupt change in dip angle is established by taking into account the practical situation of coal and gas outbursts. The upper side of the interface consists of virgin coal, while the lower side consists of briquetted coal, which are utilized to simulate the virgin and the tectonic coal, respectively. With monitoring units, such as impact force testers, acoustic emission detectors, and data acquisition systems, coal and gas outburst simulation experiments under three-dimensional stress conditions are conducted considering different conditions of abrupt dip angle (the initial angle of coal dip angle mutation
θI, the mutation angle
θM) changes. The influence of coal dip angle mutation on outburst intensity and impact parameters (peak impact force, maximum negative pressure, and duration of sharp change) are analyzed. The research results show that within the range of 10°<
θI≤20° and 10°≤
θM≤20°, a critical value of coal dip angle mutation
θT exists. When both
θI and
θM are greater than or equal to
θT, low-index outbursts are prone to occur. Given a constant
θI, the critical gas pressure exhibits a negative correlation with
θM, while the outburst intensity per unit shows a positive correlation with
θM. The evolution process of impact force in the simulated roadway can be divided into rapid change stage, fluctuation change stage and stable change stage. The number and density of high-frequency pulse A in the positive pressure stage and high-frequency pulse B in the negative pressure stage are closely related to
θM. With the increase of
θM, the fluctuation of the impact force in rapid change stage becomes more complex, and the high-frequency pulses A and B gradually show a highly concentrated trend in this stage. The peak impact force and the maximum value of negative pressure stage have a negative linear relationship with the gas concentration factor
Iθ, while the duration of the rapid change stage has a positive linear relationship with the gas concentration factor. The peak velocity of impact airflow and the cumulative AE energy show basically the same trend. Both of them have a negative linear relationship with the gas concentration factor, and exhibit more significant changes when
θM is greater than or equal to
θT.