In-Situ Stress Measurement of Lower Rock Mass and Rockburst Prediction of Underground Caverns in Zhumadian Compressed Air Energy Storage Power Station

To investigate the characteristics of the in-situ stress field in the lower rock mass of underground gas storage caverns at the Zhumadian compressed air energy storage (CAES) power station, and to predict the risk level of rockburst in the caverns for ensuring geological safety, a series of studies were conducted. Firstly, hydraulic fracturing in-situ stress tests were carried out in the lower rock mass of the CAES power station to obtain the basic data of the in-situ stress field in the storage cavern area. Subsequently, indoor rock mechanics tests were conducted on the core samples from the corresponding test sections of the stress measurement boreholes to determine the saturated uniaxial compressive strength of the rocks. Finally, the rockburst risk level in the caverns was predicted using the rock strength-to-stress ratio. The results indicate the following: (1) The measured in-situ stress in the underground gas storage caverns is at a low-to-medium level, with the maximum horizontal principal stress (SH) ranging from 4.48 to 9.61 MPa and the minimum horizontal principal stress (Sh) from 3.15 to 5.79 MPa. Within the measured depth range, both the maximum and minimum principal stresses exhibit a linear relationship with burial depth, increasing as the depth increases. (2) The orientation of the measured maximum horizontal principal stress is NE-SW (N43.3° E), which is generally consistent with the regional principal stress direction. The coefficient of the maximum horizontal principal stress in the rock mass of the underground storage caverns ranges from 1.12 to 1.62, while that of the minimum horizontal principal stress ranges from 0.79 to 0.97. The horizontal stress coefficient within the measured depth ranges from 1.29 to 1.68, indicating a strike-slip faulting stress regime. (3) The tensile strength (T) of the rocks obtained from hydraulic fracturing tests ranges from 1.72 to 11.97 MPa, with an average value of 4.71 MPa. The overall tensile strength of the rocks is relatively high, which is generally consistent with the values obtained from the indoor rock mechanics tests. (4) Through a point-by-point analysis of rockburst risk during tunnel excavation, the surrounding rock at a burial depth (H) of 187.20 m is classified as having a slight rockburst susceptibility, while no rockburst is expected at other test points. (5) These research findings provide a scientific basis for the design and construction of the underground energy storage caverns at this CAES power station, and also fill the gap in the measured in-situ stress data for this region.