Blasting Dynamic Response Characteristics And Vibration Reduction Technology In Shallow-buried Arch-tunnel

The problem of blast vibration damage caused by tunnel blasting has been a focus in underground engineering and blasting engineering. Due to the limitation of tunneling, this problem has become more annoying in arch tunnel, small-distance tunnel and cross tunnel,etc. Sometimes, for the aim of preventing the possible blast vibration damage,Non-Explosive method has to been used in tunneling, which lead to tunneling efficiency decrease. Therefore, making a thorough study on the dynamic response characteristics and vibration reduction blasting technology of new style tunnel is of momentous theoretic significance and engineering value.Taken the project of Yashan shallow buried arch-tunnel in the Urumchi expressway as background, through analyzing the field blasting vibration tests data, the free face and the burden was found play important role on the tunnel blasting vibration intensity. According to this conclusion, the tunnel blasting vibration velocity calculated formula (TBVF) was proposed based on the principle of dimensional analysis. Combined with this formula, the attenuation law of blast vibration was studied. The results of vibration tests and analyses showed that: Cut-hole did have smallest free face and largest burden than other blast-holes,therefore, the vibration intensity of cut-hole blast was up to 1.6 times larger than other blast-holes blast; Basting vibration intensity was inversely corelated with the area of free surface, but positively correlated with theburden of blast hole; In the same time, accorded to the regression analysis and comparison results of each blasting vibration velocity calculation formula, the tunnel blasting vibration velocity calculation formula could describe the vibration attenuation law more correctly.In order to restrain the side effect of noise on the decomposition efficiency and accuracy of blasting vibration signal with EMD, a decomposition method called SVD-EMD was proposed. Integrates the SVD-EMD with FFT and HHT transform, the time-frequency and energy distribution characteristics of blast vibration velocity signal were studied. The study results showed that: The intersection of difference spectrum effective value and curve was an effective way to determine the order choice of singular value, which ensure that the SVD-EMD could improve the resolution of HHT transformation results in both time domain and frequency domain. The vibration energy mainly distributed in the frequency band of 25?165 Hz,and there were three dominanting frequencies, including 43Hz,103Hz and 119 Hz, could be found in the frequency band. The peak instantaneous energy of cut-hole blast was largest, and it was up to 1.53?4.38 times larger than other blast-holes blast. Moreover, the PPV, dominating vibration frequency, instantaneous and total energy of superposition blast vibration waveform were discussed associate with linear superposition of waveform method, and get that the PPV, instantaneous and total energy could be at a relative low value range, however the dominating vibration frequency could be at a relative high value range when the time interval was among both 15?35 ms and 40?60 ms.The boundaries and the procedure of equivalent blasting load model of cut-blasting(EBLC) were discussed. And the EBLC was applied to calculate the dynamic characters of existing small-space tunnel and the middle-wall of arch-tunnel as the arch-tunnel was excavation with blasting quickly. The simulation results showed that: The PPV (peak partical velocity) ratio between outer and the inner face of existing tunnel lining was 1.15 to 1.34 and the PPV ratio between the surrounding rock and the inner face of existing tunnel lining was 1.54 to 2.09; For the existing tunnel lining, its peak dynamic tensile stress was 1.50?6.48 times larger than its static tensile stress, however for the middle-wall, its peak dynamic tensile stress was 11.90?15.38 times larger than its static tensile stress, this indicates that the dynamic effect was more obvious in near region than that in far region. In addition, associate with the maximum tensile stress criterion, crack growth stress criterion and Mohr-Coulomb stress criterion obtain that crack growth damage and tensile damage easy occurs to the lining of existing small-space tunnel and the middle-wall of arch-tunnel,respectively. Using the original blasting design, the safety factor of the existing small-space tunnel lining was only 1.08, which means that the risk of crack growth damage was very high.Combined with practical on site, stepped V-cut blasting technology was proposed to reduce blast vibration intensity. Based on the theory of millisecond blasting, Mohr-Coulomb criterion, Maximum tensile stress criterion, etc., the mechanisms of rock fragmention and the vibration reduction and the forming process of cut-cavity in the stepped V-cut blasting technique were deeply discussed. On this basis the calculation methods of main parameters,such as the horizontal angle of cut-blast holes, the depth of both outer and inner cut, the charge length of both outer and inner charged segment, the horizontal distance and the time interval between each charge segments, ect., were given in the paper. Meanwhile, through comparing and analyzing the numerical results of stepped-wedge cutting blasting and conventional cutting blasting process, obtained that the stepped-wedge cutting blasting technology can not only reduce the blasting vibration intensity effectively , but also can ensure a good blasting effect.In the deterministic FEM, the common analytic methods of single factor are usually used to determine the influence of each factor upon blasting effect. This method demands running a number of simulat calculation to get enough sample data, however, it usually cannot obtain the impact degree and the mutual relationship of every factor. Considering the process of stepped V-cut blasting is stochastic,therefore,a stochastic dynamic finite element analysis method based on the Response Surface Method (RSM) was utilized to study and determine the impact degree and the mutual relationship of every factor. The results of calculating and analysing show that: the horizontal distance of cut holes was the major parameter which do have significantly affect on both rock fractured area and vibration intensity, the angle of cut-hole was the secondary parameter, while the time interval is the secondary and the negligible parameter of rock fractured area and vibration intensity, separately.Finally, the research method and results of this thesis were synthetically applied to guiding the field blasting test in Yashan arch-tunnel. The advance per attack and the PPV were investigated and measured respectively. The results of statistical analysis indicated that the stepped V-cut blasting could achieve good vibration reduction effect, in the vibration decrease ratio in vertical and portrait and radial were 43.2%, 30.7% and 68.6% respectively.Meanwhile, on the premise of without any increase in the construction difficulty, the tunnel efficiency increase about 8.29%. The research results above has played a positive guiding role in similar programming and provide a new way to reduce blast vibration.