In-situ stress measurement is an important subject in the field of rock mechanics. At present, the relief method widely used in engineering is limited to the testing depth, and the testing process is complex. This paper presents a new in-situ stress measuring technique based on the principle of borehole shape and stress relief method. Firstly, in theory, the proof that the geometric shape of a circular hole is ellipse after being deformed by force is completed, the relationship between stress and ellipse geometric shape parameters is established, and the method of measuring and calculating ellipse geometric shape is put forward, and the in-situ stress calculation based on ellipse parameters of boreholes is realized. Secondly, in the aspect of measuring technology, a multi-contact type micro-optical diametrical measurement technology aiming at ellipse geometry shape is proposed. The measuring principle, system structure and key technology are introduced. The feasibility of technical principle, correctness of measurement method and operability of practical application are verified by indoor calibration test and loading test. Thirdly, in practical application, the in-situ stress test is carried out by using this technology, and the stress relief test at 424m depth is realized. The whole test only takes 1 hour and 38 minutes. After the result analysis and the in-situ stress calculation, the maximum, minimum and maximum principal stress directions are 21.61MPa, 14.72MPa and 335°, respectively. Combined with the structural characteristics of stylolite structure obtained by the borehole camera, the result is verified. The analysis results are basically consistent with the measured maximum principal stress direction, and the correctness of the test results is verified from the stress direction. This paper carries out in-depth and systematic research from the aspects of measuring principle, testing technology and result analysis and provides a new method and device for in-situ stress measuring in deep boreholes, which has the advantages of rapid testing and deep borehole testing.

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