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

在岩洞施工中，高精度地测量洞室周围岩体中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。在本项目中，发展了半球形端部钻孔地应力测量技术，并对系统进行了小型化，提高了测量精度。该系统用于测量洞室围岩中的地应力。1)提出了一种测量单孔地应力完整状态的新技术--半球形端面钻孔技术。应力张量是由钻孔半球形底面上的16个应变计算得到的。讨论了一种高精度确定应力张量的应变片布置方式，并研制了球面应变盒，将应变片直接粘贴到指定站点的底面上。2)通过理论分析和岩石空间实验，证实了该方法比传统方法能更精确地测量岩石应力。3)用该方法测量了洞室周围岩体中的地应力并确定了应力分布。从应力分布可以估计洞室周围破坏带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.