Initial Stress in Underground Rocks

由于洞室周围岩体的力学行为明显受初始应力状态的支配，因此在大型洞室施工中，初始应力测量是必不可少的。另一方面，为了评估洞室的稳定性和控制洞室的施工，在施工时或开挖完成后对洞室周围的应力状态，即诱导应力进行评估是很重要的。这些应力状态被认为是受地质不连续的影响，例如节理和断层。需要系统地进行应力场测量，例如系统地测量岩洞室周围的应力场分布，以确认地质不连续的影响。半端钻孔技术是一种通过单孔测量确定应力张量的方法。在本研究中，采用半端钻孔技术对这两个区域进行了初始应力测量。一种是片麻岩中活动断层附近的测量，另一种是节理石英闪长岩中的测量。通过这些结果，阐明了断层运动与初始应力状态之间的关系，并提出了预测隧道开挖失稳区域的可能性。在此基础上，结合已有的两种方法——弹性边界元法和塑性特征法，提出了双轴初始应力条件下地下岩洞室弹塑性应力分析新方法。讨论了提高DDM分析裂缝问题的精度，以及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.