Study on stress evolution law during coal winning of hanging wall working face of step fault

When the working face is mined under complex geological conditions,the stress-concentrated area is formed with the change of tectonic stress,and a large amount of elastic strain energy is easily accumulated in the coal rock. The distribution and dynamic evolution of stress field and energy field have a significant induction effect on the dynamic phenomena such as underground rock burst. In this study,the UDEC numerical simulation software was used to study the distribution and evolution law of the advanced support stress when the working face was mined over the step fault (combined normal fault). Combined with the energy distribution and fault activation, the dangerous area and grade of the impact during coal wining of hanging wall working face of step fault were comprehensively identified. The results show that the working face has a stress barrier effect during fault mining,and gradually forms a stress concentration in the mining plate. The barrier effect aggravates the accumulation of elastic strain energy and is an important factor inducing the occurrence of rock burst in the working face. During the mining period from the first fault to the next fault,the advance abutment stress of the working face is relatively small,but the energy in the roof area between the two faults increases,presenting a potential impact risk. When the working face is advancing towards the step fault,the subsidence deformation of the near-fault roof in front of the working face is easy to cause fault activation. When the working face is less than 20 m away from the fault,the step fault activation is obvious. The research results can provide reference for the prediction of rock burst and the division of dangerous areas,the layout of working face and the selection of mining sequence under the condition of similar step faults.