Rockburst process and strength-weakening effect of the high-stress circular tunnel under internal unloading

Abstract

To investigate the influence of unloading effect of a circular tunnel face on rockburst process, by innovatively combining rock drilling unloading devices and triaxial systems, the strain rockburst simulation under the entire stress path of “high initial stress + internal unloading + stress adjustment” (HUS test) was realized for the intact cubic red sandstone samples (100 mm × 100 mm × 100 mm). Comparative tests were conducted on cubic red sandstone samples with prefabricated circular holes (φ 25 mm) under the stress path of “prefabricated circular hole + high initial stress + stress adjustment” (PHS test), thereby highlighting the influence of internal unloading on rockburst failure. The test results revealed that with an increase in vertical stress, the sidewalls in both the HUS and PHS tests suffered strain rockburst failure. Compared with the PHS test, the initial failure stress in the HUS test is lower, and it is easier to induce sidewall rockbursts. This indicates that the internal unloading influences the sidewall failure, causing an obvious strength-weakening effect, which becomes more significant with an increase in buried depth. The strain rockburst failure was more severe in the HUS test owing to the influence of internal unloading. V-shaped rockburst pits were formed in the HUS tests, whereas in the PHS test, arc-shaped rockburst pits were produced. It was also found that strain rockburst failure may occur only when the rock has a certain degree of rockburst proneness.

Keywords

• Rockburst
• Unloading
• Strength-weakening effect
• Deep rock
• V-shaped notch
• Circular tunnel