| Drilling and blasting method is commonly used, when excavation and lining of mine shaft are in weathered zone and bedrock segment. With the progress of drilling technology and higher requirements of drilling construction speed, deep hole blasting technology has been widely used in shaft excavation. The hole depth reaching to 4~6m in deep hole blasting, both the charge weight of per blast hole and the total charge weight have greatly increased than before. With the increase of blasting dynamic load, direct and cumulative damage effects to the shaft lining will inevitably increase, resulting in lower structural durability of the shaft lining or even directly damage. Besides, borehole-blasting constructions and freezing sections have overlap areas, which increase the risk of direct damage to the frozen shaft lining or frozen pipe from blasting dynamic load, causing the perviousness of the shaft, and on the other hand, reduce the reaction rate of concrete wall under low water temperatures due to the influence of freezing temperature field, lower strength increase rate compared to room temperature, and weakened resistance to the blasting dynamic load.The “Blasting Safety Regulations”(GB6722-2014) conducted from July 1, 2015 depending on the different object of protection, the main vibration frequency and age gives the provisions of blasting vibration allow safety standards, according to field test, blasting under dynamic loading zone near the wall vibration faster than the new standard for mass concrete pouring velocity limits. Thus, based on the construction phase of shaft freezing method deep hole blasting in bedrock section(or weathered layer), large doses of blasting vibration effect of dynamic loading and dynamic response of a study wall, blasting well to reduce the dynamic load caused wall damage or cumulative damage, improve production efficiency, has important theoretical and practical significance. In addition, it also has significant reference value to our current related specifications and the revised standard.Relying on two subjects of the National Natural Science Foundation – “Rapid Excavation and Support in Large Section Roadway”(key projects, grant number: 51134025), “Mechanism of blasting dynamic load to frozen wall(tube) and support structure”( General program, grant number: 51274203), the paper has site monitoring of frozen shaft wall hole blasting dynamic response, vibration signal acquisition and analysis of spectral energy characteristics, and based on the results of site monitoring, through numerical simulation, laboratory tests inversion and other methods, shaft lining dynamic response and damage law is researched. The main results are as follows:(1) Field monitoring was used to test the blasting vibration of shaft lining at Yingpanhao coal mine belong to Ordos energy chemical industry co., LTD, and the lining vibration signal of different height away from blasting working space was obtained.(2) Blasting vibration signal analysis. To monitor the signal after denoising can effectively filter out high frequency components. The results show that: shaft blasting dimension value of fractal box is between 1.40-1.70, the fractal dimension has a significant difference in the direction, and with blasting distance increase showing obvious rule. The vertical component of the fractal dimension value is relatively small compared with the other two directions, indicating that the vertical component of signal frequency is lower, corresponding vibration amplitude is larger, cycle is longer. In the horizontal direction(radial and tangential) vibration signal on the fractal dimension greater value discrete does not appear, indicating that horizontal vibration intensity is substantially equal, high frequency occurs compared to the vertical. In terms of the structure of the wall, natural frequency at low frequency, due to its large degree of freedom in the horizontal direction, blasting vibration resistance to shear stress is much weaker than the vertical pull. Therefore, the damage to the wall structure mainly depends on the shear strength of the two horizontal directions, while the fractal dimension value on the horizontal direction is relatively large, frequency is high, shear capacity is weak, which is advantageous to the stability and integrity of the wall structure.(3)Blasting vibration waveform, in the range of 15 m near blasting source,is relatively complex, blasting vibration produces a very strong tensile stresses on the structure of the wall, which has the most obvious on the wall structure, since the distance between the concrete segment belonging to the initial setting and final setting stage, the larger structural damping can greatly reduce blasting vibration energy peak and duration of action. In the 15-27 m range, blasting vibration on the fractal dimension values stabilize, which belongs to the blasting vibration wave propagation stable stage. Wall structure is substantially the same extent in response to the distance within the segment, although somewhat attenuate the amplitude of the vibration, but the blasting vibration frequencies stabilized. The distance more than 27 m, blasting vibration frequency gradually to the development of low frequency, the fractal dimension value decreases, indicating a significant filtering effect of media wall, wave spectrum is relatively simple, relatively lower peak. This is the same to the actual monitoring conclusion. Therefore, we should focus on monitoring the intensity of vibration injury within 15-27 m.(4) According to the wavelet packet band energy distribution algorithm of blasting vibration signals, the energy distribution of blasting vibration signals can be accepted : frequency band energy that all vibration signals within 200 hz accounts for more than 90% of the total energy, with the increasing of blast center distance, blasting in low frequency band energy percentage trend decreases. Among them, the frequency range from 0 Hz to 60 Hz, with the increasing of blast center distance, the three-direction energy percentage in that frequency band range presents a parabola inverted bell. The percentage of energy measuring point from 2# to 4# whose corresponding blast center distance is 15 m-23 m on the whole is greater than 80% in monitoring, it proves that the period of the tensile stress in the apparent surge in distance which belongs to stress-strain relations in linear segment of elastic-plastic material from reinforced concrete wall. Within the period of the distance, the blasting vibration have a larger microscopic damage to the shaft lining, that harmful to overall stability of shaft lining. Within the frequency ranges of 60-100 Hz, the three-direction energy will decrease in a small amplitude, and then increase significantly, which behave obviously in vertical and horizontal tangential. This shows that with the increasing distance of the blast center distance, the energy distribution from low frequency band in a dominant place change into high frequency band has outstanding advantages. the three-direction energy of 100-200 Hz frequency band appear the vibration phenomenon which basically behaved as sinusoidal serrated, indicating in this frequency range, energy has a trend of multi energy band and blasting vibration energy discrete degree is relatively high, At the same time, the energy percentage changing degree compared to the other two vertical is small, almost meet the rule: vertical <radial <law. This order is identical with results of fractal box dimension; range from 200-1250 Hz of frequency band,the percentage of three-direction energy has an obvious decreasing trend, indicating that with distance increasing, high energy band of 200 Hz continue to decrease, but the high changes frequency band for the shaft lining has little effect, so do not consider as a major factor.(5) Weather the blasting vibration response of the shaft lining will result in an overall destruction of the shaft lining, depending on the natural vibration period of the shaft lining is within the spectrum accelerated sensitive area range of vibration wave accelerated response or not. The study found that the wider region of accelerated response spectrum will freeze more shaft lining in a rigid state, thus produce more intense vibration forces. correspondingly, if the response spectrum with the response cycle region is narrow, frozen shaft lining in response will be in a low level, With the increase in the height of buildings,the natural vibration period of the structure will be significantly longer, and with the natural vibration period of the shaft lining growth, it will reduce the extent of the response, but the response spectrum coverage area become larger, leading to more and more reaction of the wall structure in the sensitive areas speeding up, so the displacement of a large segment of the high shaft lining of the response will increases. Dynamic Response coefficients of standard response spectrum is consistent with accelerated response spectrum, and the frozen shaft lining Frozen wall which has the obvious magnification effect will get a comparatively narrow natural vibration period. Therefore, the acceleration of blasting vibration mainly affects the high-frequency, maximum blasting vibration velocity mainly affects the middle-frequency, and the low-frequency depends on the maximum displacement of blasting vibration.(6) Laboratory test results show that: there is a significant correlation between the dynamic load of concrete damage effect and the age of oscillation, Before the final set of concrete, vibration loads, have little impact on the ultimate compressive strength of concrete, After the final set to 1 d of age range, concrete vibration damage effect is more obvious, then, with the concrete strength increasing, the vibration damage effect gradually weakened, this consistent with The vibration signal spectrum analysis conclusion. The damage cumulative effect of concrete vibration is obvious in early stage, especially in the concrete which get multiple vibration. But the amplification of injury degree will decrease with the increased age. By scanning electron microscope specimen microstructure, and further confirms the macro test results. Concrete blocks that after 9h vibration have many micro-cracks, 3d vibration, the micro-cracks growth in the concrete blocks is not obvious, 5 times vibration test block micro deterioration is more obvious.(7) The numerical calculation results show that: the results of numerical simulation and experimental of the blasting vibration wave is consistent, the peak vibration curve measuring points agree well, indicating that the numerical simulation method used herein may be better to effectively predict blasting vibration velocity, to provide the basis for design of mine shaft excavation blasting. At the same time, extraction of each measuring point which frequency less than or equal to 60 Hz power ratio. Compare the results of numerical simulation and experiment, found that the simulation results in less than 60 Hz frequency energy accounted for 80% and 85% of the total energy, curve smaller shocks and have good consistency; In the vertical prediction of blasting vibration using the concept of equivalent elastic boundary, the vibration can effectively predict the effects of different explosive energy produced at the wall, while the energy of vibration will be predicted in advance. It is of great significance to effectively reduce the damaging effects of blasting vibration; for effective geological survey, obtain the accurate physical shaft layers of rock mechanical parameters can significantly improve the prediction of the energy distribution of blasting. |
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