Abstract
For non-directional drilling cores, the sample selection and test method for Kaiser effect (KE) in-situ stress measurement were proposed, and the magnitude and direction of its principal stresses were theoretically derived. Based on this method, the KE of 423 samples in Burtai and Baode coal mines in northern Ordos Basin (NOB) were tested. The results show that σH, σh and σv vary with depth and location, and their values increase with increasing of depths. Generally, horizontal stresses play a leading role. There are main stress regimes in NOB: σH > σh > σv (Burtai, <172m; Baode, <170m) and σH > σv > σh (Burtai, 170-800 m; Baode, 170-400 m), and the σv > σH > σh stress regime is mainly distributed in moderately deep to deep coal mines. For rock masses with a depth of 350m, k ((σH + σh) / 2σv) tends to 1, indicating that deep critical state will gradually emerge. The test results were compared with those of overcoring method (OC), elastic strain recovery (ASR) and micro-hydraulic fracturing (HF). The relative errors of σH, σh and σv are 14.90%, 19.67%, 15.47% (Burtai) and 10.74%, 22.76%, 19.97% (Baode), and they are all within a reasonable range required by the project, which verifies the reliability of KE method. The dominant orientation of σH (Burtai, NE-NNE; Baode, NEE) was obtained by using paleomagnetic technology, which is consistent with that (NE-NEE) of earthquake focal mechanisms in this area. Based on Byerlee-Anderson theory, the stress accumulation level of mine rock mass was discussed. Under dry rocks or hydrostatic pressure rocks, the friction coefficient of faults is both low, which is less than the lower limit (0.6) of strike-slip faults slip, indicating that the fracture stress with a low level around the study area is lower than the friction limit stress. The stress accumulation level in Baode mine is slightly larger than that in Burtai mine.
The Prediction of Distribution Characteristics of the In-situ Stress for Liuhuanggou Mine Field
