| As the process of blasting construction in urban subway, blasting vibration shall be strictly controlled because of the position of rock excavation is close to the Ground. The precise time delay technology become reality by using electronic detonators. The electronic detonator detonation technology is used in more and more metro tunnels. The electronic detonator has a huge advantage in improving rock breaking effect and decreasing blasting vibration intensity. The theoretical relationship between delay time interval, rock breaking and vibration control effects has not been established, the delay time of electronic detonator is determined by construction experience and multiple tests. Further research on blasting vibration controlling with precise time delay technology in metro tunnel is imperative.The paper is subsidized by national natural science funds “Research on characteristic of accumulative damage dynamical response of underground structure under blasting load effect based on confining pressure environment”(51374212), further research on blasting vibration controlling with precise time delay technology in metro tunnel by the engineering background of drilling and blasting method construction in Beijing and Shenzhen metro tunnel. Discussed the reasonable delay time between holes and segment from two aspects, namely improving rock breaking effect and decreasing blasting vibration intensity by using theoretical calculation, field testand numerical simulation, and research the influence of adjacent tunnel and ground building with tunnel blasting. The research content mainly included the following aspects:(1)The improvement measures were put forward because there is deficiency in existing HHT method on blasting signal analysis. We get the reasonable aggregate average numbers of CEEMD are 200-300 times by calculating decomposition time, excessive extreme with different iteration times and correlation coefficient between the original components and IMFs. The “transition section-stationary section” end extending method was put forward, the method included the determination of end extreme inside data, data expansion of from non-stationary signal to transition section and from transition section to stationary signal outside data. The decomposition results of simulation and practical signal show that the method kept extension trend of original signal ending, decreased the iteration times and overshoot and oweshoot of envelope caused by high-frequency periodic noise. The ending of original data change slightly by culling extension data.(2)The mode mixing and illusive component problems can be inhibited by using ending treatment put forward from the paper, decorrelation and CEEMD, The decomposition results of simulation signal show that the decomposing precision of the combined method is higher than the EMD and CEEMD, a better decomposition effect can be gotten by multi-iterations and a lower energy proportion of non-dominant frequency signal in each IMF in practical signal.(3)The results of field test had showed that the blasting dominant frequency is difficult to elevate when the tunnel is far from the ground. Because the high frequency wave is absorbed and the main frequency of signal is low, the amount of variable of the main frequency is little with distance change. The blasting vibration intensity can only be controlled by decreasing single hole and stage charge. Using three-row cut holes is better than double-row cut holes in damping effect and improving driving rates. Setting the delay time between holes should comprehensive consider decreasing blasting vibration and improving blasting effect. 2ms was chosen in cut hole delay time and 4ms with other types delay time, by the premise of blasting vibration velocity was no limit exceeding, improving rock breaking effect and decreasing the probability of secondary mechanical crushing rock. The safety judgment standard of velocity-frequency-energy was put forward, putted the energy proportion less than 20 Hz of the signal into the original safety judgment standard, the new safety standard is more comprehensive than the previous one.The vibration intensity of tunnel near the blasting side is much larger than that of the far from the blasting side. The blasting vibration velocity of lower bench is less than the upper bench from the global aspect because of the free face effect. The vibration velocity of tunnel face pre and post 1D range in tunnel near the blasting side is large, and the main frequency distributed from 30 Hz to 90 Hz, which would not be caused tunnel structure by resonance, structural damage is determined by vibration velocity primary.(4)Blasting vibration controlling and improving blasting effect between electronic detonators and common detonators were analyzed from blasting three factors and energy view. The electronic detonators are in achieving hole by hole blasting, increasing single time footage, the vibration intensity is less than the common detonators when the tunnel section area, blast-hole arrangement and blast holes numbers are roughly equal. Constructing the blasting superposition stress waveform under different delay time that using linear superposition method. The superposition waveform decreased obviously when the delay time is in range of waveform half-period, vibration frequency increased in different degree, the energy proportion of 0-20 Hz decreased in greater degree. The half-period superposition velocity may not be the minimum value, when t is in range from T/2 to T, the velocity appeared to increase. The total energy of millisecond blasting is less than that of simultaneous blasting, the total energy has a minimum value when time is in range of waveform half-period. The superposition energy is larger than single hole energy, which has proofed that using waveform half-period method to control blasting vibration is difficult.(5)The calculation formula of delay time between holes and sections were put forward based on the best rock breaking effect. The calculation method considered the single hole charge, charge length, angle between blast hole and tunnel face, decouple coefficient, rock behaviour, the quality and volume of throwing rock, explosive attribute and depth of footage comprehensively. The determined delay time that using electronic detonators to apply precise time delay technology must greater than the minimum time which a new free face is formed. According to calculation result, the delay time of cut hole is 3-4ms, auxiliary blastholes include inner ring hole and secondary ring hole is 3-5ms. The delay time of all kinds of explosive blasted per delay is 30 ms with the footage is 1.0m; The delay time of cut hole section is 45 ms, non-cut hole section is 40 ms with the footage is 1.5m; The delay time of cut hole section is 50 ms, non-cut hole section is 45 ms with the footage is 2.0m;(6)The numerical analysis of blasting vibration on closed-spaced tunnel shows that: when the blasting parameters is same, the blasting vibration influence on round tunnel is less, the shock resistance of horseshoe tunnel is poor. The vibration velocity between spandrel and side-walls of frontal wall is highest when the up-step blasting is used. The particle vibration velocity of frontal wall shows “fault” decay when the distance of tunnels increased. When the distance is 2D,the vibration intensity of frontal wall tends to uniform. The cut-hole with six can disperse blasting energy effectively and the blasting footage is reduced, the blasting vibration intensity is less than four cut hole when the segment explosive quantity is same. When the distance is 1.0D, the tunnel is easily damaged by blasting construction with 1.8kg and 2.6kg one-hole charge weight. The highest vibration velocity of three directions may not occur vertical planar which parallels the tunnel face, the vibration velocity oscillates between 5 meters longitudinally.(7)The calculation formula of delay time which considered adjacent blasthole space in tunnel near the blasting side were put forward. The reasonable delay time is determined by blast center distance, dynamite quantity per hole and distance difference between adjacent blasting hole. The distance difference between adjacent blasting hole is the greatest impact to determine delay time, followed by blast center distance and dynamite quantity per hole is the least at a certain distance. The best delay time between holes in tunnel near the blasting side is different when the position is not the same. The calculation results should also meet the requirements that the shortest time when a new free face is formed, namely not less than 3ms.The vibration waveforms with the same blasting parameters under different delay time in circular tunnel were analyzed. The results show there is a large proportion that the crest and trough can meet, decreased peak velocity and increased vibration frequency when the delay time is reasonable. The blasting waveforms which is in the same position g dispersed gradually with delay time increased. The meet probability of the crest with adjacent waveforms decreased, the peak energy can be controlled effectively. The result of numerical simulation and theoretical calculation is basically same, which confirmed the proposed calculation formula is feasible.The descending vibration effect of stress wave is not the same at different tunnel position. The vibration velocity of millisecond blasting is much less than that of simultaneous blasting in tunnel spandrel and side-walls near the blasting side. There is even appeared that the vibration velocity of small delay time blasting is larger than simultaneous blasting vibration velocity. According to calculation result, when there are 4 cut holes with charge 2.6kg in each hole, the reasonable delay time is 5-6ms; when dynamite quantity is 1.2kg per hole, the reasonable delay time is 3-5ms; when there are 6 cut holes with dynamite quantity is 1.8kg per hole, the reasonable delay time is 4-6ms after comprehensive considered adjacent blasthole space in tunnel, the shortest time when a new free face is formed, namely not less than 3ms and change of the largest velocity with different delay time in tunnel near the blasting side(8)We can get the results that the vibration intensity of input signal is the the greatest factor which influences response spectrum area after analyzed response spectrum and CEEMD of blasting waveforms with different delay time. The normalized response spectrum area is proportional to energy concentration degree, the more centralized energy is, the larger the normalized response spectrum area is, the more disperse energy is, the smaller the normalized response spectrum area is. The velocity response effect has the same trend to velocity response spectrum area, they have equivalence to evaluate construction safety. Comprehensive consideration vibration intensity of signal, energy distribution in different kinds of frequency band, velocity response spectrum area and velocity response effect to choose the reasonable delay time. Blasting vibration characteristic and comprehensive feature of building with external incentive response from the viewpoint of energy. |
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