Effect of geological structures on in-situ stress distribution in underground coal mines

Using the hydraulic fracturing in-situ stress testing rig with small boreholes, stress measurements were carried out at 14 sites near the large syncline structure in the Huating coal mining area, where steep and extremely thick coal seams are typical in China, to analyze the in-situ stress variation in different parts. Measured data point out that the tectonic stress predominates in the Huating coal mine and Yanbei coal mine. Along the wing of the syncline structure, the horizontal stress is comparatively small; however, the horizontal stress near the axis of the syncline structure increases far more quickly than the vertical stress; and the syncline structure greatly influences the stress distribution in the coal mining area. Based on the in-situ stress data measured in the Jincheng coal mining areas in Shanxi Province, the effects of faults on the magnitude and orientation of in-situ stresses were analyzed. Some areas near the faults show the lower horizontal stress than the normal level, and large faults may alter the orientation of the maximum horizontal principal stress. On the basis of measured in-situ stresses, numerical models were built to analyze the stress distribution around the large syncline structure in the Huating coal mining area by means of FLAC3D code, and the numerical results were compared with the measured ones. The combination of in-situ stress measurement and numerical simulation will provide an effective approach to fully understand the characteristics of in-situ stress field in underground coal mines.