Hydraulic Fracturing In-Situ Stress Measurements and Large Deformation Evaluation of 1000 m-Deep Soft Rock Roadway in Jinchuan No. 2 Mine, Northwestern China

Reliable in-situ stress information is of great significance for the stability assessment and the large deformation mechanism research of deep soft rock roadways. We characterized the stress field of Jinchuan No. 2 Mine using the hydraulic fracturing stress measurement method. A total of 17 hydraulic fracturing measurements and 7 impression tests were conducted in three boreholes to estimate the stress state and variation characteristics at different locations 1000 m below the surface. The results indicate that the main characteristic of the stress field is S-H > S-h > S-v, which is a strike-slip faulting regime stress, suggesting that horizontal compressive forces dominate the regional stress field. Based on the compiled hydraulic fracturing measurement data (a total of nine boreholes), we indicate that the maximum (S-H) and minimum (S-h) horizontal principal stress magnitudes are 7.10-56.73 MPa and 6.44-24.91 MPa, respectively. The S-H is dominantly oriented in the NE-NNE direction, which is consistent with the regional tectonic stress field. Finally, the squeezing large deformation analysis and risk assessment of the deep soft rock roadway in the Jinchuan No. 2 Mine were discussed. Significant squeezing deformation may occur in the sublevel 850 m. The radial strain epsilon of most roadways is between 2.5 and 10%, and only a few are greater than 10%, suggesting a very severe to extreme squeezing large deformation. The results of this study are of great significance for the study of the large deformation mechanism and the selection of matching support technology for the deep soft rock roadway in the Jinchuan No. 2 Mine in the future.