In rock blasting, the blast of the former delay always creates new free surfaces for the latter. And the blast-generated free surfaces play a critical role in blasting vibration. A quantitative assessment of the blast-generated free surfaces on blasting vibration was carried out through experimental and numerical studies. Blasting vibration from the first and followed delays in the same row was compared and analysed in two field experiments. A coupled numerical approach with smooth particle hydrodynamics and dynamic finite-element methods was also conducted to simulate the fragmentation process and the blasting vibration from different delays in the same row. The results show that with the increasing number of free surfaces, the peak particle velocity decreases nonlinearly, and if the blasting geometry parameters and charge weight are the same in each blast delay in the same row, the explosive detonated in a first delay always produce higher vibration compared to those followed delays. The charge weight of the first delay in every row should be reduced by certain percentage if the same peak particle velocities are expected from followed delays in the same row.

After detonation of the explosive, the final blast-induced damage area around the blast-hole falls into three categories, namely crushed zone, fractured zone, and elastic deformation zone. This paper presents a modified model to calculate the size of crushed zone around a blast-hole in drill-and-blast, with the hoop compressive stress and cavity expansion effect taken into account. The material in the crushed zone was assumed to be a granular medium without cohesion, but with internal friction. On this basis, the formula for crushing zone radius was derived. The proposed approach was verified with tests reported in the literature and the simulated results from SPH-FEM coupled models. A full statistical analysis was also carried out, and the predicted values were found to be in better agreement with the test results compared with other models. A sensitivity analysis of the modified model showed that the size of the blast-induced damage area is mainly affected by the following factors: rock mass properties, in situ stress, and borehole pressure. In particular, the roles of borehole pressure and in situ stress are discussed. Finally, suggestions are made on how the size of the crushing zones can be decreased.