Study on angle arrangement of high-energy reduced-hole blasting in large section tunnel considering in-situ stress
To determine the optimal placement angle of blasting hollowing holes in large section tunnels under the effect of in-situ stress,based on the characteristics of blasting crack expansion,a theoretical calculation method of the optimal fracturing angle and hollowing angle under the effect of in-situ stress is proposed.Based on the Gonghe Village Tunnel of Ludian County to Qiaojia County Expressway in Yunnan Province,a comparative analysis of the effect of hollowing and blasting under different simulation conditions was carried out using ANSYS/LS-DYNA numerical simulation software.The optimal parameters were given,and field tests were carried out to verify the results.The results show that the optimum fracturing angle and hollowing angle for the study section of Gonghe Village Tunnel are 70° and 65°,respectively,and the theoretical calculations and numerical simulation results are basically in agreement with each other.By using the optimized high-energy reduced-hole blasting method,the number of drill holes per cycle of step blasting in the study section is reduced by about 15％,the drilling time is saved by an average of 14 min,and the control effect of over-undercutting is better.The results of the study can provide a reference for the design and construction of blasting parameters for similar large section tunnels.
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