Initial Stress in Underground Rocks

由于初始应力状态对洞室围岩的力学行为具有显著的控制作用，因此，对大型洞室进行初始应力测试是必不可少的。另一方面，为了评价岩体洞室的稳定性，控制岩体洞室的施工，对施工期和开挖结束后的围岩应力状态，即诱导应力的评价是十分重要的。这些应力状态被认为是受地质不连续性的影响，例如节理和断层。为了确定地质不连续性的影响，需要对现场进行系统的应力测量，如对岩石洞室周围的应力分布进行系统的测量，而半球形端部钻孔技术是一种通过单孔测量来确定应力张量的方法。在这项研究中，初始应力测量的半球形结束钻孔技术在这两个地区进行。一种是片麻岩中活动断层附近的测量，另一种是节理石英岩中的测量。根据这些结果，阐明了断层运动与初始应力状态之间的关系，提出了预测隧道开挖失稳区的可能性，并将现有的两种方法结合起来，提出了一种双向初始应力条件下地下洞室弹塑性应力分析的新方法。弹性力学的边界元法和塑性力学的特征线法。讨论了DDM分析裂纹问题精度的提高和DDM在节理岩体应力分析中的适用性。结果表明，采用本文提出的方法可以充分准确地分析应力场和位移场。

The initial stress measurement is indispensable to construct large rock cavern, because of the fact that mechanical behavior of rock mass around the rock cavern is dominated by the initial stress state remarkably. On the other hand, in order to estimate the stability of the rock cavern and control the construction of it, it is of important to evaluate the stress state around the rock cavern on construction or after the completion of the excavation, namely the induced stress. These stress states are considered to be affected by geological discontinuities, e.g.joints and faults. Systematic stress measurement of the field, e.g. systematic measurement of the stress distribution around the rock cavern, are need to confirm the influence of the geological discontinuities.Hemispherical-ended borehole technique is one of the methods that the stress tensor can be determined from the measurement in a single borehole. In this study, the initial stress measurement by the hemispherical-ended borehole technique are performed for the two areas. One is the measurement adjacent to active fault in gneiss and the other is the measurement in jointed quartz diorite. From these results, the relation between the movement of the fault and state of initial stress is clarified and the Possibility of predicting the unstable region for the excavation of tunnel is suggested.Furthermore, a new method for elasto-plastic stress analysis of underground rock cavern, under the condition of biaxial initial stress, is presented by jointing two existing methods, a boundary element method for elasticity and a characteristics method for plasticity. Improvement of the accuracy of DDM analysis on the crack problem and the applicability of DDM to the stress analysis of the jointed rock are also discussed. As a result, it is confirmed that the stress and displacement fields can be analyzed sufficiently and accurately using those methods proposed by this study.