Abstract: The rock fracture caused by disturbed stress field change in deep underground engineering is a common issue receiving continuous attention. After analyzing the test data of disturbed stress field in Jinping underground laboratory phase II project, the variation law of disturbed stress field under different construction processes was interpreted, and the change mode of principal stress direction was analyzed. Through the comparative analysis about in-situ drilling imaging of rock mass, the influence of principal stress direction change on surrounding rock fracture was revealed. The results show that the disturbed stress field changes the most actively at the stage of middle pilot tunnel excavation, the change mode of principal stress direction is mainly gyration when the tunnel face is advancing toward the monitoring section, and the change mode is mainly rotation when the tunnel face moves away from the monitoring section. The position where the principal stress direction change reaches the maximum is 4.5 meters away from the design profile of test tunnel. During the expanded excavation of sidewall, the change mode of principal stress direction is mainly rotation, and the position where the change reaches the maximum is 2.5 meters away from the design profile of test tunnel. The change in disturbed stress direction directly affects the pattern and trend of rock fracture development, the stress with large-angle rotation tends to cause tensile crack and tensile-shear mixed crack, and the stress with small-angle rotation tends to cause the shear crack with concave and convex morphological features whose deflection angle equals the stress rotation angle. The stress with large-angle gyration mostly causes X-shaped shear crack. The results based on the measured disturbed stress can provide a reference for studying the variation law of disturbed stress field during deep high-stress hard rock excavation and its influence on rock facture development.

Key words: deep rock mass, hard rock excavation, disturbed stress, stress direction, rock facture