ボーリング採取試料の応力解放に伴う弾性変形を利用した岩体応力測定原理の数値シミュレーション

抄録

A cylindrical rock-core obtained by borehole drilling expands radially into a slightly elliptical shape along its transverse cross-section when the rock sample is relieved of its in-situ anisotropic stress by drilling. The magnitudes and orientation of in-situ stresses can, in principle, be estimated from the circumferential variation of core expansion. However, it is not possible to evaluate the expansion from a core collected in a conventional way, with a single drilling bit, since it will be in its expanded state when extracted and lacks information about its required pre-expansion dimensions. To overcome this problem, we propose an innovative way of core drilling referred to as Dual-bit Coring. This approach results in a single core that has two signature transverse cross-sections: the first has an elliptical shape resulting from core expansion and the second records the initial circular shape prior expansion. We simulated numerically the process of cutting a rock column out as a core by the Dual-bit Coring method and examined how the column deforms during core drilling.