EXPANSION OF MICRO CRACKS UNDER UNIAXIAL AND BIAXIAL COMPRESSION LOADS AND THE EFFLUENCE OF LOADING DIRECTION CHANGES ON THE KAISER EFFECT

摘要

Micro-defects are widespread in rocks, and rock structures always have heterogeneity and anisotropy. Assuming that micro-cracks of rocks contain wing cracks, by using the elastic fracture mechanics method, the propagation of micro-cracks is deducted under uniaxial compression. The formulas to calculate the stress intensity factor and the critical stress under biaxial compression were deduced. The relationship between the crack dip angle and the critical stress are obtained under two conditions. When the far field stress is the compression, the influence of the loading direction on the Kaiser effect is discussed. The results show that, if the first loading direction is perpendicular to the crack and the range of the rotational angle is from 0° to 90°, the critical stress of crack propagation and the value of FR (Felicity Ratio) will increase. When the rotational angle is the same on two continuous loadings, the value of the critical stress will not change with the same ratio. When the rotational angle is small, the memory of rock pre-pressure is obvious and the memory of the Kaiser effect is more accurate. When the rotational angle is close to 90°, the critical stress of crack propagation and the value of FR are almost infinite, the crack is not able to propagate, and the Kaiser effect disappears.