Abstract:Based on the existing empirical collapse distance formula,the influence coefficients of the ratio of the collapse distance and the tunnel span are considered;and a formula that is suitable for engineering calculation is then put forward. The numerical calculation results show that the critical collapse distance of peeling-off increases as the tunnel span extends,but there exists a limit value,which is related to rock quality and charge quantity. The limit value decreases with the increase of the rock quality;while on the other hand,the limit value increases with the decreasing of the charge quantity. If the tunnel span is given,the critical collapse distance increases with the augmentation of charge quantity. At the beginning of the increment,the increasing rate of the critical collapse distance is much higher than that of any later time. The distance is linear with the oblique angle and increases as the angle becomes larger. When the charge is placed in a vertical position to the target,the value of collapse distance is maximum based on the calculation result of the formula.