大深度高応力鉱山でのルーチン的な採掘ハザード定量化に資しうる岩盤コア絶対差応力DCDA測定法の試評価

抄録

It is difficult to mine-widely, routinely measure absolute stress in the highly stressed rock mass in deep mines in the world because the drilled holes or cores are damaged during and immediately following the drilling. We evaluate the use of the Diametrical Core Deformation Analysis (DCDA) method, developed by Funato and Ito. The method can evaluate non-destructively the absolute differential stresses and measurement errors in the planes orthogonal to the core axes by precisely measuring the ellipticity of the core section orthogonal to the borehole axis. The five readings required to evaluate a single core take only about ten minutes to make. The measurement system is compact enough for a single regular courier parcel or flight check-in luggage. Absolute differential stresses were determined for thirty-five core samples from fourteen holes in different directions in the highly stressed rock mass in a South African gold mine. We were able to constrain an average 3D differential stress field, consistent with the 3D stress field measured in-situ with an overcoring method, with the maximum principal stress larger than 100 MPa, with a root mean square of residuals of several MPa. Interestingly, the results represent relaxation in shear stress near the fault intersected by the boreholes. The measurements require a core diameter larger than ca. 40 mm, and a core is longer than ca. 10 cm. The method assumes that there is no significant inelastic deformation and that the rock is isotropic.