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

在洞室施工中，准确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。在本项目中，开发了半球形端孔技术，用于测量地应力，并进行了系统的小型化和精度的提高。该系统应用于洞室周围岩体的应力测量。本项目取得的成果如下：1)开发了一种测量单孔地应力完整状态的新技术——半球形端孔技术。应力张量由钻孔半球形底面上的16个应变计算得到。讨论了一种高精度测定应力张量的应变片布置方法，并研制了一种球形应变单元，将应变片直接粘接在指定站点的底面上。2)理论分析和岩石空间试验结果表明，与传统方法相比，该方法可以获得更高精度的岩石应力。3)利用该方法测量了洞室周围岩体的地应力，并确定了地应力的分布。根据应力分布可以估计出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.