Miniaturization of the system and improvement of the accuracy for Hemispherical Ended Borehole Technique

在岩石洞室施工中，高精度地测量洞室周围岩体的初始应力状态和诱导应力分布，对洞室的设计和稳定性评价具有重要意义。本计画发展半球端钻孔技术以量测岩石应力，并进行系统小型化及精度提升之研究。该系统应用于洞室围岩应力的测量。1）提出了一种在单孔中测量岩石全应力状态的新技术--半球形端孔技术。应力张量是根据钻孔半球形底面上的16个应变计算的。本文讨论了高精度测定应力张量的应变片布置方法，并研制了一种将应变片直接粘贴在指定测点底面上的球形应变盒。2）通过理论分析和岩石空间试验，证实了本文方法比传统方法能测定更高精度的岩石应力。3）用该方法对洞室围岩进行了现场应力测试，确定了洞室围岩应力分布。根据应力分布，可以估计洞室周围破坏区的范围和形成地拱的岩体的实际强度。

In the construction of rock cavern, it is important for the design and stability estimations of the rock cavern to measure the state of intial stresses as well as distribution of induced stresses in the rock mass around the cavern with high accuracy. In this project, the Hemispherical Ended Borehole Technique is developed for measurement of in-situ rock stresses and the miniaturization of the system and the improvement of the accuracy are performed. This system are applied to measure rock stress in the rock mass around the cavern. The results obtained in this project are as follows:1) A new technique to measure the complete state of in-situ rock stresses in a single borehole are developed, which is called Hemispherical Ended Borehole Technique. The stress tensor is computed from 16 strains on the hemispherical bottom surface of a borehole. An arrangement of strain gauges to determin the stress tensor with high accuracy is discussed and a spherical strain cell to bond the strain gauges directly to the bottom surface at the designated stations is developed.2) It is confirmed that the rock stresses with higher accuracy can be determined by using of the proposed method in comparison with the conventional method from the theoretical analyses and experiments using rock spacimens.3) The in-situ rock stresses in the rock mass around the cavern are measured by the proposed method and the distribution of the stresses is determined. The extent of the failure zone around the cavern and the practical strength of the rock mass forming the ground arch can be estimated from the distribution of stresses.