Abstract:

The newly built Sichuan-Tibet railway line extends across the Xianshuihe active tectonic zone, along which the tectonic stress field is extremely complex, and the risk of tunnel rock engineering failure is prominent. To reveal the local tectonic stress-field, to provide basic parameters for deep-buried tunnel design and construction, and by using the recently-developed hydraulic fracturing in-situ stress measurement instrument, a total of 10 valid in-situ stress data were obtained from the Guodashan tunnel horizontal borehole (maximum borehole depth: 508.10 m), creating a new record of hydraulic fracturing in-situ stress measurement in horizontal borehole. Our results show that at the borehole depth of 148.4 to 508.10 m, the maximum principal stress is 3.59-13.72 MPa, whilst the minimum principal stress is 3.28-8.36 MPa along the borehole section plane.According to the fracture impression results, the dip of the maximum principal stress along the borehole section plane is approximately horizontal in the deep part of the borehole, except for the shallow part of the borehole where the maximum principal stress is steep.According to the in-situ stress state of the horizontal borehole, we located the stress-releasing zone at 0 to 280 m depth, the stress-concentration zone at 280 to 330 m, and the undisturbed-stress zone at above 330 m depth. Based on the in-situ stress measurement results, wallrock stability of the Guodashan tunnel was analyzed. The analysis reveals that the wallrocks would experience slight to moderate rockburst at only 292.9 m and 508.10 m depth.

Key words: horizontal borehole, hydraulic fracturing, in-situ stress measurement, deep-buried tunnel, rockburst