In-situ stress measurements and distribution laws in Lu'an underground coal mines

60 points of in-situ rock stresses have been measured in 13 coal mines of Lu'an coal mine area by means of hydrofracturing stress measurement rig with small borehole. The stress measurement data point out that: the maximum horizontal principal stresses on 55% of the total measuring points are greater than the vertical stresses in Lu'an coal mine area; and the in-situ stress values exist great differences in various mines because of different buried depths and geological structures. However, the magnitude of the stresses is generally moderate value. The orientations of the maximum horizontal principal stresses change greatly from southern part to northern part, the tectonic stress fields present changeable state. Based on the field data, the stress distribution map of Lu'an coal mine area was drawn up; the stress variation with buried depth, and the relation between the specific value of the mean horizontal principal stresses to the vertical stresses and buried depth were analysed. The stress measurement results provide reliable fundamental parameters for engineering practices, such as mine field development, roadway layout and support design, and improve the scientific degree, rationality and reliability of engineering designs.