Rock Stress Measurement by Means of Conical-ended Borehole

岩石应力对地下洞室等岩石结构的施工至关重要，因为围岩的力学行为主要是由岩石应力决定的。因此，岩石应力测量被认为是岩石工程中的一项重要的现场测量。特别是近年来在地下洞室结构稳定性预测方面的发展表明，需要进行系统的应力测量，如系统的初始应力测量。为了确定岩体内某一点的完整应力状态，提出了锥端钻孔技术，利用应力解除法高精度、低成本地测量岩体中的三维应力状态，并讨论了底面的最佳形状和量规布置。文中说明了如何由单孔锥底表面的应变确定应力张量，以及如何从理论上评估应力测定的误差。讨论了该方法的敏感性和实用性，并与传统的地应力测量方法进行了比较。随后，通过对单孔多次应力测量所得到的应力分布的检验，讨论了断层类地质不连续的存在往往会损害地应力的均匀性和连续性。

Rock stress is of fundamental importance for the construction of rock structures, such as underground openings, since the mechanical behavior of surrounding rock masses is mainly dominated by rock stress. Therefore, the rock stress measurement is considered to be an important field measurement in rock engineering. Particularly, recent developments in relation to the prediction of structural stability of underground openings have indicated th e need for systematic stress measurement, e.g. the systematic initial stress measurement.In order to determine the complete state of stress at a certain point within a rock mass, the conical-ended borehole technique is proposed to measure the three dimensional state of stress in a rock mass with a high accuracy and low costs by the stress relief method, and the optimum shape of the bottom surface is discussed as well as the gauge arrangement. It is shown how the stress tensor can be determined from the strains on the conical bottom surface of a single borehole, and how the error of stress determined can be evaluated theoretically. The sensitivity and the practicality of the present method are discussed, comparing the conventional methods of in situ stress measurement. Subsequently, by examining the stress distribution obtained by the multiple times stress measurement in a single borehole, it is discussed that the uniformity and the continuity of the field stress are frequently injured by the presence of the geological discontinuities like faults.