Study On Effect Of Blast-induced Seismic Based On Energy Theory

Blasting techniques have been widely used in the projects of water resource, mining, transport and city construction, etc. The negative effect of blast-induced seismic, especially the hazard to the surrounding buildings induced by blasting vibration, has been bringing the people to general attention and important regard. The effect of blast-induced seismic on buildings is a complex problem, which relates to geophysics, explosion mechanics and structure dynamics, etc. Therefore, to do further study on the problem is of both high theoretical and practical importance.Based on energy theory, a series of research have been done in the thesis, such as the characteristics of energy distribution and attenuation, the dynamic response of buildings induced by blasting vibration, and the safety assessment on blast-induced seismic, etc. The following achievements have been obtained:Firstly, characteristics of blast-induced seismic and damage mechanism of buildings under blasting vibration are analyzed. Considering the birth, transmition, and effect of blast-induced seismic as a transfering and transformating process of the energy, a model for studying effect of blast-induced seismic is established based on energy theory.An energy analysis method for blast-induced seismic based on power spectrum is put forward, after studying the physical meaning of power spectrum. Compared with the common analysis method based on wavelet transform, this method is not only simple in operation, but also quite clear in physical meaning. Based on moving average method, the power spectrum of blasting vibration is smoothed by the use of the window function, in order that the frequency band range and energy attribution of blasting vibration can be displayed intuitively.Based on a large number of measuring data, the energy distribution characteristics of seismic induced by different forms of blasting resource are studied. And difference of energy characteristic between blast-induced seismic and earthquake is compared and analyzed. The results show that the seismic induced by different types of drilling-and-blasting vary in energy distribution characteristics. As diameter and depth of the blasting hole increases, the frequency band of energy distribution becomes more focus and has the trend of moving to the lower frequency.Based on seismology theory, energy attenuation law of blast-induced seismic wave is studied. It turns out that the attenuation coefficient for the peak energy is of twice that for the peak particle velocity(PPV). During a same blasting, the total energy of blast-induced seismic is of direct proportion with square of the peak particle velocity. According to a great deal of measured data, some influence factors on attenuation law for the energy are analyzed. It shows that as limitative effect of free-face, hole-diameter, hole-depth and charging density increase, the initial energy value of blast-induced seismic will become greater. And such non-blasting factors as the characteristics of the rock mass and the condition of topography have notable influence on the energy attenuation coefficient.The response spectrum theory that is usually applied in earthquake engineering is employed to study the dynamic response characteristic of blast-induced seismic Based on the response spectrum theory of system with single degree of freedom, the response spectrum is calculated by using piecewise linear interpolation. Vibration acceleration is used as the loading parameter in response spectrum calculating, but blasting vibration velocity is the monitoring physical quantity in blasting engineering. To solve the problem, a method of de-noising by wavelet transform to obtain the accurate and clear acceleration curve from measured blasting vibration velocity data is proposed. Response spectrum analysis of blasting vibration induced by different types of drilling-and-blasting is performed with a vast amount of monitoring data. The result shows that response characteristics of vibration induced by different kinds of blasting have marked difference. Compared with the underground blasting, the response spectrum curve of the ground blasting vibration has peak points that are located in lower frequency. As the enlargement of diameter, depth of blasting holes and distance away from the explosion source, the probability of selective magnification in the structural response on blasting vibration will increase.According to free vibration frequency of common buildings, the dynamic response characteristics of buildings under the effect of different types of blast-induced seismic are analyzed. It shows that the dynamic response characteristics of buildings rely largely to the features of blasting vibration. Based on structure dynamic theory, the response characteristics of buildings to the different energy components of blast-induced seismic are studied with typical engineering example. The result shows that the amplification effect of the buildings to energy content with different frequency is obviously selective.Combining the energy damage mechanism, the different safety criterions for blast-induced seismic are analyzed. On the basis of"Equivalent Peak Energy"(EPE), a method of safety assessment on blast-induced seismic is proposed. The study suggests that it is feasible for the equivalent velocity of EPE to evaluate the damage induced by blasting vibration. The criterion based on EPE reflects the essence of blasting vibration damage more comprehensively than the safety criterion considering the effect of frequency. And it can be realized easily.