Comparison of dominant frequency attenuation of blasting vibration for different charge structures

Dominant frequency attenuation is a significant concern for frequency-based criteria of blasting vibration control.It is necessary to develop a concise and practical prediction equation describing dominant frequency attenuation.In this paper,a prediction equation of dominant frequency that accounts for primary parameters influencing the dominant frequency was proposed based on theoretical and dimensional analyses.Three blasting experiments were carried out in the Chiwan parking lot for collecting blasting vibration data used to conduct regression analysis of the proposed prediction equation.The fitting equations were further adopted to compare the reliability of three different types of dominant frequencies in the proposed equation and to explore the effects of different charge structures on the dominant frequency attenuation.The apparent frequency proved to be more reliable to express the attenuation law of the dominant frequency.The reliability and superiority of the proposed equation employing the apparent frequency were verified by comparison with the other five prediction equations.The smaller blasthole diameter or decoupling ratio leads to the higher initial value and corresponding faster attenuation of the dominant frequency.The blasthole diameter has a greater influence on the dominant frequency attenuation than the decoupling ratio does.Among the charge structures applied in the experiments,the charge structure with decoupling ratio of 1.5 and blasthole diameter of 48 mm results in the greatest initial value and corresponding fastest attenuation of the dominant frequency.

Modeling and Simulation of Dynamic Unloading of Prestressed Rockmass

During the excavation of deep rock,a sudden change in boundary conditions will cause the in-situ stress on the excavation surface to release instantaneously.This disturbance propagates in the form of an unloading stress wave,which will enlarge the damage field of surrounding rock.In this paper,the dynamic unloading problem of the insitu stress in deep rock excavation is studied using theoretical,numerical,and experimental methods.First,the dynamic unloading process of rock is analyzed through adopting the wave equation,and the equivalent viscous damping coefficient of the material is taken into consideration.Calculations show that there is significant tensile strain in the rock bar when the strain rate is above 10^-1 s^-1.With an increase in the length or damping coefficient,the wave state will change from an underdamped to an overdamped state.Second,implicit and explicit solvers of the finite element method are employed to simulate rock unloading processes,which can be used to verify the theoretical results from one-dimensional to three-dimensional stress states.Finally,the dynamic unloading experiment of a onedimensional bar is used to further verify the validity and accuracy of the theoretical analysis.