Quantitative estimation of potential rockburst pit depths during blasting excavation in deep tunnels

Accurate estimation of potential rockburst pit (PRP) depth contributes to assessing rockburst risks and developing prevention programs, while the existing empirical methods lack of reasonable consideration for the different damage distributions within surrounding rocks during blasting excavation. This study provides the PRP depth estimation formula matching two damage distributions, and subsequently establishes a quantitative estimation procedure. After obtaining the uniaxial compressive strength of the rock, the initial maximum principal stress, the geological strength index GSI, the disturbance factor Ds at tunnel profile and depths of high-damage zone (HDZ) and weak-damage zone (WDZ), the PRP depth can be determined by the given estimation formula. Acoustic wave testing and quantification of disturbance factors are utilized to obtain parameters Ds and depths of HDZ and WDZ. Taking two deep tunnels as examples, the accuracy of the proposed method is verified. The results show that the estimated PRP depth coincides well with the observed rockburst pit depth, and the estimation accuracy is obviously superior to existing empirical methods. Basis on this, the variation law of PRP depth during blasting excavation is analyzed. It is found that the formation and expansion of the PRP is attributed to the continuous reduction of rock mass strength during blasting excavation, and the PRP depth is positively correlated with Ds, HDZ and WDZ depths.