Research On Safety Limit And Optimal Design Program Of Ming Great Wall Traversed Underneath By Tunnel Blasting Excavation

Cuiyan Tunnel in Chaoyang-Linghai High-Speed Railway TJ-3 section of Beijing-Shenyang High-speed Railway passes through the Ming Great Wall site section by blasting excavation.As the construction face continues to move forward,the influence of blasting vibration on the Ming Great Wall site at the top of the mountain ahead cannot be ignored.Therefore,this paper studies the safety clearance and optimal blasting design program for tunnel blasting excavation through the Ming Great Wall site.First of all,combined with the general situation of the project,a large number of relevant documents were consulted and on-site investigation was carried out on engineering geology and other conditions.The geological conditions,natural geographical environment and other basic data of the area where the project is located were obtained and the intersection point between the Ming Great Wall site and the tunnel strike were determined.Through the theoretical study of blasting vibration effect,the generation,propagation mode and propagation characteristics of blasting vibration wave and the safety criteria formulated by various countries on whether blasting vibration affects buildings(structures)were expounded.According to the actual situation on site and the research content in this paper,the safety criteria for determining whether blasting construction affects the Ming Great Wall site were determined.Secondly,according to the blasting vibration signals collected from the field monitoring test,HHT program was written by MATLAB software for Hilbert spectrum analysis on the vibration signals,and the propagation and attenuation law of blasting vibration intensity was analyzed from the perspective of energy.Based on the combination of the peak value of surface vibration velocity and the auxiliary frequency.What’s more,referring to the safety criteria determined in this paper,it is determined whether the current blasting construction program will affect the Ming Great Wall site.Then,based on dimensional analysis method,a prediction model of tunnel blasting vibration velocity peak value considering multiple influencing factors was established,and relevant parameters were obtained through nonlinear regression analysis.Compared with traditional Sadowski empirical prediction Equation,the results show that the new model is more accurate than traditional Sadowski Equation in prediction of vibration velocity.According to the safety criterion standard,the peak value of safety allowable vibration velocity for the protection of the Ming Great Wall site was determined to be 0.2 cm/s,and the threshold value of safety clearance for the protection of the Ming Great Wall site with the current blasting program was estimated to be 192 m by using the newly-built Equation.At the same time,based on theprinciple of reducing the intensity of blasting vibration,the blasting excavation construction program of the tunnel under the Ming Great Wall site was optimized to ensure that the blasting construction operation does not affect the Ming Great Wall site.Finally,the simulation software ANSYS/LS-DYNA and the field test were respectively used to evaluate whether the optimization program can be applied to the field construction work.Contrast analysis showed that the optimization program would not affect the construction of the Ming Great Wall site and can meet the requirements of all aspects.The feasibility of the optimization design program of blasting tunneling under the Ming Great Wall site was proved by integrating theory with practice.