| Rock blasting excavation is widely used in many engineering fields,such as water conservancy and hydropower engineering,mining,transportation engineering,because of its economic and efficient construction advantages.In the process of blasting excavation,blasting vibration effect will inevitably be caused,and the safety and stability analysis of buildings caused by blasting seismic wave has always been a hot issue for engineering managers and scientific researchers.The acquisition of wave propagation parameters of rock mass,such as seismic wave propagation velocity,dynamic elastic modulus,dynamic Poisson's ratio and attenuation parameters,is one of the basic works in the field of rock mass engineering.It plays an important role in the study of failure process analysis,dynamic response calculation,impact evaluation and attenuation law of seismic wave propagation under explosion and other dynamic loads.Accurate acquisition of rock mechanics parameters is directly related to the accuracy of calculation and analysis results.Traditional methods for obtaining physical and mechanical parameters of rock mass media are mainly based on laboratory tests and the parameters obtained are usually static parameters,while the existing in-situ detection methods can only obtain local rock mass parameters.In addition,the different wave types are not taken into account in the determination of attenuation parameters of blasting seismic waves.In view of the convenience and economy of monitoring blasting vibration,the inversion study of wave propagation parameters of rock mass based on measured blasting vibration is carried out,and the difference of attenuation parameters of different types of waves is analyzed.It is helpful to enrich the means of in-situ detection of rock mass physical and mechanical parameters and also helpful to more accurately understand the propagation and attenuation law of blasting seismic waves,which has dual significance of theory and practice.The purpose of this paper is to study the inversion of wave propagation parameters based on measured blasting vibration time history curve by methods of theoretical analysis,numerical calculations combined with the experimental measure.The main research contents and achievements are described as follows:By analyzing the difference of energy,frequency and polarization properties between noise,P wave and S wave signals,an improved method for identifying P wave and S wave first arrival time of measured blasting vibration signal is proposed.On the foundation of STA/LTA method,the influence of noise to the detecting P wave first arrival results can be reduced to a minimum degree by means of introducing characteristic function of total energy time history curve.At the same time,by introducing a weight coefficient w,the characteristic curve of the recognition function is obtained,and the corresponding position of the maximum value in the curve is the first arrival time of P wave.Appling this improvement method,the influence of threshold selection on recognition results can be eliminated effectively.For S wave recognition,the identification characteristic function of S-wave is constructed by analyzing the changes of deflection angle,polarization degree,the ratio of the transversal to the total energy,and combining with the recognition weight coefficient.The S-wave first arrival point can be picked up by using this characteristic function.The results of numerical calculation and analysis of engineering examples show that its relative error is below 6% and that the method is effective,simple and suitable for phase identification on the engineering scale.Based on the elastic wave theory,the dynamic relationship between the propagation velocity of blasting seismic wave and the dynamic parameters of rock mass is deduced.On the basis of the identification of first arrival time of P and S wave,an inversion method of wave propagation parameters of rock mass based on the analysis of measured blasting vibration signals is proposed.Then,the method is applied to the determination of wave propagation parameters in two engineering examples.In this method mainly includes three big cores systems:(1)identification of the first arrival time of P and S waves in blasting vibration signal;(2)determination of seismic wave propagation velocity based on travel time difference of P and S waves;(3)inversion calculation of dynamic parameters based on seismic wave propagation velocity.This method not only enriches the method of in-situ detection of rock mass parameters,but also obtains the dynamic parameters of rock mass in a wide range compared with the traditional in-situ test.It can better evaluate the performance of rock mass in situ,and assist in identifying the location of geological defects such as fault fracture zone or weak structural plane in rock mass by using the obtained parameters.The analysis results of engineering examples show that the rock mass dynamic parameters obtained by this method are reasonable and reliable,which proves the validity of this method.Aiming at the characteristics of low frequency,low speed and carrying most of the vibration energy,a method of wave component separation based on R wave suppression is proposed and verified by numerical simulation.The key aspects of this method are:(1)converting the measured blasting vibration signal from time-space domain to time-frequency domain based on S-transform;(2)constructing R wave filter in time-frequency domain according to the characteristics of R-wave and implementing filtering processing;(3)converting the separated signal in time-frequency domain to time-space domain through inverse transform.The numerical simulation results show that the proposed wave component separation method can effectively suppress and extract R-wave without destroying low-frequency body wave signals.The attenuation parameters of different types of wave in blasting seismic wave are analyzed by using wave component separation method based on R wave suppression,with measured blasting vibration data from two engineering sites.Then,the discreteness of attenuation parameters of rock mass caused by wave type conversion is also discussed.For the quality factors of rock mass,there is a significant difference between the seismic wave without distinguishing the wave type and different types of waves.The quality factors of P wave in the two engineering sites are lower than those of R wave,which indicates that different types of waves have different loss and absorption rates in rock mass.For the attenuation coefficients of blasting vibration,the total attenuation coefficients(K& ?)without distinguishing the wave type and the attenuation coefficients of different wave types are also significantly different.The fitting results of measured blasting vibration data show that the attenuation velocity of R wave along the vertical direction is reduced by20?30%,compared to P wave,that is,the dominant wave type will change by the increase of spreading distance and transform from P wave to R wave.The fitting correlation coefficient and prediction accuracy of peak velocity of couple vibration are significantly lower than those of P wave or R wave,which should be attributed to the transformation of dominant wave type in blasting vibration at different distances. |
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