Precursor of microseismic energy and stress evolution induced by rockburst in coal mining: a case study from Xiashijie, Shannxi, China

Abstract

Rockburst has become one of the most frequent dynamic disasters in coal mines when mining activities proceed towards greater depths. The goaf near the working face is the dominant factor, resulting in a high risk of rockburst and seriously threatening the safe production of coal mines. In this paper, to systematically analyze the stress and energy evolution of surrounding rock in the stope and reveal the rockburst precursory characteristics of the working face adjacent to the goaf, the microseismic (MS) monitoring technique and numerical simulation method were utilized based on the case of the Xiashijie Coal Mine in Shaanxi Province, China. The results indicated that the presence of the nearby goaf could lead to a dense high-energy event distribution in the overlying rocks owing to the fracturing of the hard main roof, which is closely related to periodic weighting and could be manifested as a periodic trend. Based on the source parameters of the energy index (EI) and cumulative apparent volume (CAV), lgCAV/lgEI could effectively evaluate the risk of rockburst and exhibits the advantages of convenience and thresholding. The risk of rockburst tended to increase with increasing lgCAV/lgEI. In particular, rockburst was prone to occur when lgCAV/lgEI exceeds 10. The distribution of the elastic strain energy derived via numerical simulation agrees well with that of the microseismic energy density measured via MS monitoring. The simulation results further indicated that when rockburst occurs, the average maximum principal stress in the main roof of the working face sharply dropped, while the average maximum principal strain significantly increased. Affected by the adjacent goaf, the advanced abutment stress of the roof and floor of the working face was distributed asymmetrically, with the characteristics of high stress concentration close to the goaf. Therefore, under dynamic disturbance due to notable energy release in the hard main roof, rockburst easily induced.