Relationship between cracked-zone radius and dominant frequency of vibration in tunnel blasting

Abstract

Most of the existing prediction equation of the dominant frequency of blasting vibration refer to the particle peak velocity to attribute the influence of blasting source factors to charge weight in general. In fact, the influence factors of dominant frequency are complicated. Although charge weight is the most convenient fitting parameter, it also has limitations in some cases. This study contributes to the understanding of the relationship between cracked-zone radii and the dominant frequency of vibrations during tunnel blasting. This relationship was studied using theoretical, numerical, and in-situ measurement approaches. It was found that the dominant frequency induced by blast vibrations is closely related to the cracked-zone radius, which is a more comprehensive parameter than the charge weight, as it also considers the type of structure, number and layout of blastholes, mechanical properties of rock, and conditions of the free surface. A prediction equation for the dominant frequency in tunnel blasting was derived from a combination of dimensional analysis and the theory of elastic–spherical wave propagation, whereafter validation is carried out for the proposed equation based on the measured dominant frequency from Pubugou hydropower station. The results showed that a favorable fitting correlation has been obtained in both zero-crossing dominant frequency and mean frequency. The charge weight and contour diameter of each delay were compared as fitting parameters for the dominant frequency. The latter performed better than the charge weight during tunnel blasting. The study is helpful to understand the attenuation characteristics of the dominant frequency induced by tunnel blasting, and has certain reference value for blasting vibration control and blasting design optimization.