Initial Stress in Underground Rocks

大型洞室围岩的力学行为受初应力状态的影响很大，因此对于大型洞室的施工来说，初应力测量是必不可少的。另一方面，为了评价洞室的稳定性，控制洞室的施工，对洞室围岩在施工时或开挖完成后的应力状态即诱发应力进行评价是非常重要的。这些应力状态被认为受到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面的影响，需要对现场进行系统的应力测量，如系统地测量岩洞周围的应力分布。半球形端部钻孔技术是根据单孔测量确定应力张量的方法之一。在这项研究中，利用半球头钻孔技术对这两个地区进行了初始应力测量。片麻岩中活动断裂附近的测量和节理石英闪长岩中的测量。在此基础上，结合已有的弹性边界单元法和塑性特征线法，提出了双向初应力条件下地下洞室弹塑性应力分析的新方法。文中还讨论了裂隙问题DDM分析精度的提高和DDM在节理岩石应力分析中的适用性。结果表明，利用本文提出的方法可以充分、准确地分析结构的应力场和位移场。

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.