| With large-scale infrastructure construction in our country,more and more corresponding tunnel project construction will be opened.Because of the influence of the factors such as geological conditions,drilling and blasting method is commonly used in tunnel excavation.The harmful effect from blasting seriously affects the safety of tunnel construction and the construction efficiency.Generally speaking,the harmful effects of blasting are mainly refers to the blasting vibration.as the tunnel space is narrow and mostly in the underground tunnel,which is deep in hundreds of meters,it is unimaginable that once geological disasters caused by blasting construction.At the same time,the tunnel support structure and surrounding rock is very close to the explosive source during blasting construction,with improper working,the blasting vibration could not only damage the tunnel supporting structure but also cause the surrounding rock landslides,which threatening the safety of the workers and causing the lower construction efficiency.Moreover,the poor geological condition will lead to numbers of problems.Therefore,studying on the vibration effect of tunnel blasting is necessary and urgent.About safety criterion of blasting vibration,scholars have a lot of research work,developing from the initial velocity of single factor to the velocity-frequency double factor criterion,it is gradually evolving into multiple factors criterion,however,most of the project is still using the Blasting Safety Regulation(GB6722)as the basic guidance in practical application.In addition,although scholars put forward many kinds of target parameters as the basis to measure blasting vibration,most of the parameters of safety criterion still head from the blasting seismic wave characteristics,pay little consideration to the response of the structure itself under the blasting seismic wave not to speak of combination of the two factors.Especially to the tunnel engineering,blasting vibration distribution is more complex than other construction condition,the surrounding rock and supporting structure response to vibration should not be ignored.If still purely see from the perspective of characteristics of blasting seismic wave characteristics or structure itself,from which the safety criterion cannot comprehensively and accurately account for the actual harmful effect of blasting seismic waves engineering structure obviously.Therefore,safety criterion which consider to from the aspect of the energy input,transformation and dissipation is needed.Based on the field test in Xing-yan highway tunnel project,this paper reveals the blasting vibration characteristics in tunnel axial direction from the attenuation law,the goodness of fit,vibration intensity distribution law,respectively from the tunnel ground,vault,tunnel waist and the tunnel wall.Signal analysis method of structure dynamic response under the action of the blasting vibration to do in-depth research,based on the structural failure of two kinds of forms,from the tunnel blasting vibration characteristics and energy response of structure under the action of blasting vibration,explore the maximum instantaneous input energy and hysteretic energy dissipation dual index to evaluate the blasting vibration effect,combined with the engineering examples verify the feasibility of the indicators.Analysis based on the maximum instantaneous input energy and hysteretic energy dissipation index of blasting vibration active control of double guide,and combined with the actual engineering test.The main results are as follows:(1)There are obvious differences in the attenuation law of vibration velocity caused by different working holes,but the vibration amplitude of the different holes through Sadaovsk formula regression analysiscan get a good correlation,andwe can better guide the construction operations by using its optimized blasting design.Cutting vibration is the strongest,thus decreasing vibration technology focus on lowering the cut blasting vibration For this blasting design,it is possible to appropriately reduce the single bursting amount of the blasting blasting,or to stagger the peak of the blasting vibration,rather than simply limit the recursion.From the regression analysis of the measured vibration data,it can be seen that the K value of the cut hole blasting is much larger than that of the auxiliary holeand the peripheral hole.Therefore,theexplosivedosage of the auxiliary hole and the peripheral hole can be greater than that of the cut hole.(2)When the amount of explosives is large,the spectral curve peaks are less,the frequency bandwidth is narrow,and mainly concentrated in the low frequency region.When the amount of explosives is reduced,the spectral curve peaks increase,the multiple peaks appear,the frequency bandwidth is also increasing and high frequency components more.When the burst heart rate is small,the spectral curve peaks are more,and the band is wide,and mainly concentrated in the high frequency region.When the burst heart rate increases,the spectral curve peak decreases,the frequency bandwidth narrows,and mainly concentrated in the low frequency region.The low frequency band near the tunnel structure of the natural frequency,although the vibration velocity decays with the increase of the distance from the explosion center,but the dominant frequency band of the vibration signal is also close to the natural frequency,so the increase in bursting distance does not mean that the structure is more safer.(3)Frequency spectrum curve of tunnel waist focus on the low frequency area.Dominant frequency bands draw close to high frequency and band width will be wider from the tunnel waist to sidewall,tunnel waist to vault.At the same location,from the perspective of the main vibration frequency,tunnel waist is the most dangerous location of tunnel structure;As critical pitch increased at the same time,the velocity of arch,arch waist and sidewall in the same tunnel cross section change a little.At the frequency point of view,more shows that the arch position of the greatest risk of damage.Most of the tunnel blasting vibration signals with more than 90% of the energy distribution in the 200 Hz band,indicating that in the tunnel blasting process,millisecond delay detonator burst vibration signal although widely distributed in the frequency domain,the energy is mostly concentrated within 200 Hz.(4)The peak value of the input energy spectrum will increase with the increase of the acceleration peak value,and as the square relationship.Meanwhile,the peak value of the input energy spectrum will increase weakly with the increase of the main frequency of blasting seismic wave,from this point of view,the influence of main frequency is not significant to the input energy peak value.With the increase of vibration duration,the peak value of the input energy spectrum increases,mainly because of the energy input to the structure from outside.With the passage of time,the increase trend of the input energy will not be stopped until the vibration to be stopped.Duration that one of the blasting vibration elements can be reflected by the input energy spectrum,the input energy spectrum will contribute to synthesize effects of the three elements of vibration to the response law for structure,which will offer an important reference basis to the improvement of the safety criterion undoubtedly.(5)Under the influence of blasting vibration,when the engineering structure enters the elastic-plastic stage,the mode of the energy dissipation begins to change,which is mainly dominated by damping energy consumption and hysteresis energy consumption.Since the damping ratio is usually in the process of calculation,and the energy dissipated by the plastic deformation is the complete dissipation of the energy that is not involved in the energy conversion,it is of practical significance to evaluate the cumulative damage of the engineering structure and to measure the cumulative damage of the structure with hysteresis energy consumption.(6)The maximum instantaneousinput energy is used to measure the first-passage failure,and the cumulative damage is measured by the hysteretic energy dissipation.It is scientific and comprehensive to combine the two methods.The input-hysteresis energy criterion can be used as the criterion of structural failure to supplement and perfect the existing safety criteria.Different distances will have a great impact on the superimposed vibration waveforms,so the choice of the time difference between the holes must be taken into account. |
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