Abstract：Four groups of sonic wave tests have been performed in the bedrock blasting excavation at the Ling¢ao nuclear power station project of Guangdong Province，China. The changes of sonic wave speed before and after the detonation are obtained. Based on the relationship of sonic wave changing ratio and the critical damage parameter，the damage extention of each blast and sonic wave test is determined. It is found that surrounding rock in the depth of charging section is the most seriously damaged. In the area adjacent to the ground and beneath the bottom of the charge hole，the rock is less damaged under blasting. The damage parameters and depth under the bottom of charge holes increase clearly with the decreasing distance from the donation. It has also been observed that the horizontal damage distance of rock under explosion is approximate 3 times of the damage depth. The blast-induced damage extention distinctly increases with the single charge weight.
