Analysis on the three-dimensional in-situ stress state and underground cavern stability of a pumped storage hydropower project area in Xinjiang Uygur Autonomous Region

[Objective] In order to investigate the characteristics of the in-situ stress field and the stability of surrounding rock in underground caverns of a large-scale, deeply buried pumped storage power station on the southern margin of the Tianshan Orogenic Belt in Xinjiang, and to ensure the geological safety of the underground powerhouse and water diversion tunnels. [Methods] This study conducted the following work: First, two sets of three-dimensional hydraulic fracturing stress measurements were carried out in the underground powerhouse to obtain fundamental data on the in-situ stress field. Subsequently, a 3D geological model of the project area was established, and the 3D in-situ stress field was inverted using finite element numerical simulation. Finally, based on the distribution characteristics of the 3D stress field, the stability of the underground caverns was evaluated from two aspects: the rationality of the cavern axis layout and the risk of rockburst in the surrounding rock of the underground powerhouse and water diversion tunnels. [Results] The results indicate:  (1)The 3D in-situ stress measurements in the underground powerhouse reveal that the maximum principal stress (σ1) ranges from 16.19 to 16.23 MPa, oriented N43.98°E–N54.44°E with a dip angle of -4.81° to 6.93°; the intermediate principal stress (σ2) ranges from 9.82 to 12.23 MPa, oriented approximately SE with a dip angle of -18.89° to -14.52°; and the minimum principal stress (σ3) ranges from 6.90 to 10.41 MPa, exhibiting a near-vertical orientation. (2)The 3D stress field inversion shows that the maximum principal stress (σ1) in the underground powerhouse ranges from 16.54 to 17.21 MPa, with an azimuth of N47.88°E–N56.32°E, while along the axis of the water diversion tunnel, σ1 ranges from 14.86 to 24.32 MPa. [Conclusion] The angles between the axes of the underground powerhouse and water diversion tunnels and the measured maximum horizontal principal stress (S_H) deviate by ≤10°from the optimal angle (62.84°) for an SHV-type stress field, which is favorable for cavern stability. Based on multiple criteria, including the rock strength-stress ratio method and Tao Zhenyu’s criterion, the surrounding rock of the underground powerhouse and water diversion tunnels is generally classified as having a slight rockburst risk. [Significance] The findings provide a scientific basis for the design and construction of the underground powerhouse and water diversion tunnels of this pumped storage power station, while also supplementing the lack of 3D in-situ stress measurement data on the southern margin of the Tianshan Orogenic Belt in Xinjiang.