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Abstract. Observation and estimation of the stress state in the deep crust is a crucial challenge in in situ stress measurement work. The hydraulic fracturing method is an important borehole-based technique for absolute in situ stress measurement. The small-diameter hydraulic fracturing in situ stress measurement system described in this article consists mainly of underground measurement components (serial small-diameter packers and dual-circuit connecting installation rods) and surface control components (hydraulic fluid control system, data acquisition system, and high-pressure oil pump with controllable flow). It enables series measurement of small-sized boreholes for in situ stress and provides a maximum measurement range of 30–45 MPa. The subsequent calculation of in situ stress data adopts a uniform design method to discuss the influence of various external factors on rock fracturing values. The small-diameter hydraulic fracturing in situ stress measurement system has the advantages of simple and lightweight structure, short testing time, high success rate, and low requirements for rock integrity and pressurization equipment. It has formed a series of small-diameter in situ stress measurement equipment which has been innovatively promoted to the field of underground tunnel safety assessment in coal mines and metal mining areas. It has an important practical value and economic significance in accurately determining the in situ stress state of deep development areas.
Liu et al. (Tue,) studied this question.