취성파괴수준과 파괴개시시점에 관한 진삼축 모형실험연구

At low in-situ stress, the continuity and distribution of natural fractures in rock mass predominantly control the failure processes. However at high in-situ stress, the failure process are affected and eventually dominated by stress-induced fractures preferentially growing parallel to the excavation boundary. This fracturing is often observed in brittle type of failure such as slabbing or spalling. Recent studies on the stress- or excavation-induced damage of rock revealed its importance especially in a highly stressed regime. In order to evaluate the brittle failure around a deep underground opening, physical model experiments were carried out. For the experiments a new true triaxial testing system was made. According to visual observation and acoustic emission detection, brittle failure grades were classified under three categories. The test results indicate that where higher horizontal stress, acting perpendicular (SH2) and parallel (SH1) to the axis of the tunnel respectively, were applied, the failure grade at a constant vertical stress level (SV) was lowered. The failure initiation stress was also increased with the increasing SH1 and SH2. From the multi-variable regression on failure initiation stress and true triaxial stress conditions, f (SV, SH1, SH2) was proposed.