Rock Blasting Induced Seismic Components And Their Evolution Laws

Rock blasting has been widely used in a variety of engineering fields,such as water resources and hydropower engineering,mining,traffic construction,and civil engineering etc.The blast-induced seismic effect,as the most concerned blasting hazard,the prediction,evaluation and control of which is always the key research issue in rock blasting field.Hence abundant achievements could be witnessed in this field.However,the wave type is never be considered in the current prediction and control of blast vibration or in the available safety criteria.As different types of waves have their unique motion characteristics and mechanical mechanisms,they will subsequently cause different dynamic responses or failure patterns of structures.The ignorance of seismic components contained in blast vibration,on the one hand,will mislead the understanding of the failure mechanism of structures,and on the other hand,might cause the erroneous judgment of the safety of structures.Thus,it is of great theoretical and practical significance to investigate the seismic components and their evolution laws in rock blasting,so as to clarify the proportion of different waves and their mechanical mechanisms,and then carry out more targeted prediction and control of the hazard of blast vibration.This paper presents a series of investigations that focus on the topic of“Rock blasting induced seismic components and their evolution laws”via the combined approaches of theoretical analysis,numerical simulation and onsite blasting tests.The main contents and results are shown as follows:(1)The formation,classification,and characteristics of blast-induced seismic waves,as well as their source characteristics and the propagation effects were comprehensively illustrated and analyzed,under the basic theories of rock blasting mechanism,elastic dynamics,and stress wave propagation etc.At the same time,inspired by the thought of polarization analysis in seismology,a fast and effective method to discriminate the blast-induced seismic components was put forward under the prediction of polarization directions.(2)The generation mechanism of S-wave in rock blasting and its influence factors were analyzed overall.Meanwhile,the influence factors of S-wave were verified by the comparison of calculation results from three typical numerical models.Results indicate that the influence factors that cause the S-wave can be classified into the following three categories:Firstly,the primary S-wave that is radiated from the blasting source,and the inherent mechanism can be explained by the non-symmetric expansion of explosive,such as the finite detonation of the extended or cylindrical explosive charge;Secondly,the secondary S-wave that is induced by the wave mode conversion at the rock interface;Thirdly,the S-wave that is caused by the non-continuum shear deformation,cracking,or relative sliding etc.of rock mass near the blast-hole.In terms of the simulation of S-wave,it is suggested that the chosen models should be capable of comprehensively simulating the non-linear and non-continuum deformation or cracking behaviors of the near-field rock mass.The elastic-plastic damage model based on the coupling discontinuous-continuous calculation method is proved to be an appropriate model that can more fully reveal the influence factors of blast-induced S-wave.(3)The generation mechanism of Rayleigh wave(R-wave)in rock blasting and its growth and development characteristics on the free surface were comprehensively studied,from the perspectives of theoretical analysis,numerical simulation and onsite experiment.Results show that the R-wave is not immediately formed above the buried explosive,but gradually develops with the epicenter distance r.The R-wave is not formed until r reaches to 0.6h(where h is the buried depth of explosive),and it can be preliminarily identified if r exceeds 2.0h,then it is well developed and could be obviously identified when r approaches to 5.0h.For the buried spherical explosive charge,the ground blast vibration is consist of P-wave and R-wave.The horizontal vibration is mainly dominated by the P-wave,while the R-wave will dominate the vertical vibration with r increasing.For the buried cylindrical explosive charge,the ground blast vibration is consist of P-wave,S-wave and R-wave,but the S-wave component is negligible and easy to be covered by the R-wave,when the R-wave is well developed.The evolution of the proportion of P-wave and R-wave induced by the cylindrical explosive is similar to that induced by the spherical explosive.(4)According to three field experiments,the seismic components and their evolution laws in the vertical-hole blasting was studied.Then,after analyzing the proportion of various waves and the dominant wave type at different locations or in different directions,the influence area of each type of wave was partitioned.Finally,by using the FSWT(Frequency Slice Wavelet Transform)time-frequency analysis technique,the correlation relationship between the blast-induced seismic components and the frequency spectra was explored.Results indicate that,in the vertical-hole blasting,the ground blast vibration is mainly consist of P-wave,S-wave and R-wave,and the proportion of the three waves changes with their propagation.The P-wave is a significant component both in the near and far field,and its particle motion gradually tends to the horizontal direction with the epicenter distance r increasing,thus the horizontal vibration is mostly caused by the P-wave.The S-wave could be identified as a significant component only in the near field,and it serves as the dominant wave if r<2.3h from the view of the source pattern of cylindrical explosive.But its particle motion is ignorable and easy to be covered by the later-arriving R-wave,if the R-wave is well developed(i.e.in the far field).The R-wave grows gradually with r,and owing to its slower geometry spreading,the dominant wave type of the vertical vibration is converted from P-wave to R-wave when r exceeds(40?45)h.The multi-peak structure of the frequency spectrum of blast vibration has a dependence relationship with the seismic components.The frequency spectrum of blast vibration varying with the wave propagation could be attributed to the evolution of the proportion of different seismic waves in some extent.(5)The seismic components induced by a kind of horizontal smooth blast-holes and their attenuation characteristics were studied in an onsite blasting experiment and an onsite-based numerical simulation.Besides,the time-frequency spectrum of the corresponded waveforms was also analyzed.At last,the features of seismic waves induced by the general contour blasting were briefly discussed.Results show that,for the horizontal smooth blasting,only the S-wave and R-wave are included on the same plane of smooth blast-holes,while the P-wave component is ignorable.The horizontal vibration is mainly caused by the R-wave,while the S-wave mainly vibrates in the vertical direction and its vertical velocity in the near field is larger than the R-wave.However,the R-wave will dominate the vertical vibration if the horizontal SD(Scaled Distance)exceeds 22.5 m/kg^1/2(58?67 m),due to the faster geometry spreading of the S-wave.As for the seismic waves outside the same plane of smooth blast-holes,the influence of P-wave cannot be ignored and it might become the dominant wave type if the observation point is enough far from the smooth plane,i.e.the depth h is large enough.The seismic components induced by the horizontal smooth blasting also has an inherent correlation with the frequency spectra.The blast-induced seismic components is partly corresponded to the frequency content.