No abstract

In-situ stresses are significantly important for underground mining geotechnical design and coal seam gas management in underground coal mines. Aiming at regions with geological structures, this paper proposes an in-situ stress inversion method combining Rhino precise modeling and transverse isotropy theory, and tests it near the Guodishan fault. The results show that the application of Rhino precise modeling and transversely isotropic model in in-situ stress inversion shows advantages in improving the accuracy of in-situ stress calculation. In addition, based on the inversion analysis of in-situ stress near the Guodishan fault, we believe that the fault structure has a significant impact on the distribution of in-situ stress. Within the elevation range of − 400 m to − 800 m, the horizontal stress and vertical stress of the footwall are greater than those of the hanging wall. Moreover, the K ratio near the fault is generally less than 1, but the K ratio in the footwall is usually greater than that in the hanging wall, indicating that the tectonic stress has a stronger influence on the footwall. It is worth noting that the stress gradient near the fault is higher, which may lead to higher disaster risk.

In-situ stresses are significantly important for underground mining geotechnical design and coal seam gas management in underground coal mines. The past research always assumed an isotropic elastomer in the rock mass so that they could propose multivariate linear regression to predict the in-situ stresses. However, such a method normally led to a huge error if some extreme ground conditions presented such as massive bedding structures and frequent variations in the dip angles of discontinuities. The Guodishan fault area has complex geological conditions. In order to study the distribution characteristics of regional geostress field, this paper established an accurate 3D geological model of the area near the Guodishan fault by Rhino. Combined with the idea of large-scale transverse isotropy, we successfully extrapolated the original in-situ stress near the fault by using finite difference software, and determined the relationship between the gas hazard of coal seam in the fault and the in-situ stress. It was found that the 3D model development in Rhino could increase the accuracy of the geological conditions so that the accuracy of the in-situ stress inversion can be improved consequently. Based on the transverse isotropic modelling methods for numerical calculations, a more accurate in-situ stresses field could be obtained. The coal seam F16-17 at the foot wall of the fault has a K ratio greater than one indicating a significant influence of the fault structures on the in-situ stresses distribution. Between levels − 300m and − 900m, the seam at the hanging wall area of the fault is deeper than seam at the foot wall area leading the original in-situ stress at hanging wall as much as 1.69 times that at the footwall. This would pose a greater gas risk in the hanging wall area than the foot wall area. The area close to the fault has a higher stress gradient which might lead to a higher risk of hazards.

The crack closure in impact coal seams induced by high-pressure air blasting greatly affects gas drainage efficiency. The length of the crack closure was calculated and analyzed based on energy and elastic theories. The closure region was then determined to be 3.8 m from the blasting hole. The results of a high-pressure air blasting experiment in the underground of one coal mine in China showed that the effect of crack closure on gas drainage efficiency manifested as a decreased amplitude of gas emission in the crack closure region. At 1.0–4.0 m from the blasting hole, the amplitude of gas emission in the observation holes first increased and then decreased with increasing distance from the blasting hole. At 1.8–2.5 m from the blasting hole, the amplitude of the gas emission was maximal. At 4.0 m from the blasting hole, the crack was nearly closed, and the gas emission in the observation holes was minimal. The theoretical calculation had good consistency with the field test results; thus, it can provide an important reference for an appropriate arrangement of gas drainage boreholes.

The gas storage conditions in a fold area are complex, and there are many influencing factors. Therefore, it has been the focus and challenge of regional gas control. Based on the analysis of the forces acting on the geological structure in a fold area and the law of gas migration, this study derives six factors controlling the gas content in the fold area. Then combined with grey entropy correlation theory, a grey entropy correlation analysis method is proposed to screen the key factors of gas occurrence in complex fold area. Finally, taking the anticline fold area of a mine in western China as an example, the main factors controlling the gas content in this area are studied using the grey entropy relational analysis method. And the fitting equations of the regional gas content and main controlling factors are obtained using the multiple regression method. This study provides a basis for mine gas disaster prevention and control. These results show that the entropy degree of the burial depth of the coal and the distance between the measuring point and the outcrop of the coal seam are 0.996 and 0.989, respectively, which are the key factors controlling the gas occurrence in this area. Then we use multiple regression method to get the regression equation of regional gas content and main control factors, which provides a basis for mine gas disaster prevention and control.