Crustal stress, and especially its orientation, is one of the key parameters in geotechnical mechanics and engineering. Because of the complexity of traditional crustal stress testing methods, especially in deep holes, the determination of crustal stress orientation is difficult, which is hindering the development of crustal stress testing technology. Therefore, the quick, effective, and accurate measurement of crustal stress in deep boreholes has important practical significance. This paper presents a method for the fast, effective, and accurate determination of deep crustal stress orientation by using panoramic stereopair imaging technology and stressed borehole geometric shape. Firstly, borehole panoramic stereopair images of the borehole wall are acquired using a biconical mirror, and the geometric features of the wall, are characterized by constructing a digital elevation model (DEM) of the borehole wall. The borehole geometric shape under crustal stress state is then analysed. In general, the circular borehole will become elliptical in shape. This paper presents the standard equation of the ellipse and establishes the relationship between the elliptical shape parameters and crustal stress. Lastly, from this relationship and the borehole geometric shape obtained by stereopair imaging, the orientation of crustal stress is determined utilizing the positioning capability of this technology. Simulations show that the borehole geometries and orientations are in agreement with the actual crustal stress orientations without the help of petrophysical parameters. This is a direct method of crustal stress orientation assessment based on the analysis of borehole geometric shape obtained by using the latest borehole stereopair imaging technology. This constitutes a new way of measuring deep crustal stress, which overcomes technological problems and promote the development of crustal stress measurement technology.

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