As the main index to evaluate the blasting effect,the rock blasting fragmentation directly affects the subsequent construction objectives and construction costs of water conservancy and hydropower projects.In the process of quarry blasting,it is of great significance to improve the blasting efficiency and quality and meet the demand of good grading curve for the dam aggregates in the construction of water conservancy and hydropower projects.The influence of the number of free surfaces and the delay interval between holes on the rock blasting effect is studied by establishing a two-dimensional finite element numerical model.Firstly,the interaction of stress waves between holes and the reflection mechanism of explosion stress waves on free surfaces are explained theoretically.The conditions for the generation of blasting cracks are also analyzed.Then,with the help of ANSYS/LS-DYNA finite element software,RHT model is used to simulate the rock fracture process under different number of free surfaces and different delay times between holes,and WipFrag is used to analyze the rock grading under different blasting conditions.The numerical simulation results show that the influence of different number of free surfaces on blasting grading is obvious.Compared with no free surfaces,the maximum bulk yields of single free surface,two free surfaces and three free surfaces decreases by 25.9%,46.5% and 61.8%,respectively.It can be seen that the more the number of free surfaces,the more cracks produced in the rock,the better the blasting fragmentation effect.Compared with simultaneous initiation,delayed blasting is beneficial to improve the rock fragmentation effect,but the interaction between stress waves and holes is not obvious in short delayed blasting.