Study On Damage Characteristics And Vibration Control Of Large Diameter Pipelines Affected By Blasting Construction Of Close Distance Tunnel

The research on damage characteristics,safety evaluation and vibration reduction control of pipeline under tunnel blasting vibration is a theoretical and technical problem and hot topic in tunnel construction.Due to unclear blasting vibration failure mechanism of pipeline and lack of effective blasting safety evaluation method and efficient vibration reduction technology,it is easy to cause pipeline vibration failure and then lead to major safety accidents and secondary disasters.The damage characteristics and safety evaluation method of tunnel blasting through underground pipeline are the basis of establishing safety control standard of pipeline blasting,which has important theoretical significance and research value.This research focuses on the damage characteristics and safety evaluation methods of large-diameter pipelines under tunnel blasting,with the construction of passing existing water pipelines through two typical long-span tunnels using drilling and blasting method as the engineering background.Multiple methods and technical means,such as on-site blasting vibration tests,numerical simulation,and theoretical analysis,were used to study the damage characteristics,safety evaluation methods,cumulative damage characteristics under multiple blasting batches and the vibration reduction mechanism and parameter optimization design of the damping hole in tunnel blasting.The main research contents and conclusions are as follows:(1)Research on damage characteristics and safety evaluation of large diameter pipelines under blasting action.The stress damage characteristics of three pipelines with different section shapes subjected to short range blast impact were studied.Based on the deformation theory,pipe-soil interaction,and considering the mechanical characteristics of the structure caused by different section shapes,the causes and mechanisms of pipeline damage failure are expounded.The results show that the failure points of the circular,square and horseshoe pipelines are different,which are located at the middle point of the side wall,the corner point under the side wall and the upper shoulder of the arch.Considering the influence of the path in the process of explosion wave propagation,a new safety evaluation and prediction method based on multi-parameter coupling of stressvibration velocity and propagation path is proposed.The prediction accuracy of this method is improved by about 8%～20% compared with the traditional method.This research provided safe construction parameters for similar projects where pipeline structures made of brittle materials such as concrete are subjected to close-range explosion effects.(2)Research on cumulative damage characteristics of large-diameter pipelines under multiple blasting.The key parameters of simulated explosion were determined by the calculation theory of loading stress wave,and the damage characteristics such as cumulative damage distribution range,damage degree,damage contribution of different types of holes and vibration response parameters such as vibration velocity,stress and displacement under the original blasting scheme and the improved blasting scheme were compared by numerical calculation.The improved blasting scheme can significantly reduce the damage degree and vibration response of blasting to the near nozzle line.The peak vibration velocity is reduced by about 60% and the peak tensile stress by about 50%.Finally,the safety evaluation of the improved blasting scheme is carried out from three aspects,including the current standard,cumulative damage amount and dynamic ultimate tensile strength index.(3)Research on damping mechanism and influencing factors of close blasting damping hole.Firstly,the analytical solution of the single-hole interference explosion wave was derived by using the wave function expansion method.Six key factors affecting the blasting damping rate were determined: the diameter of the damping hole,the spacing of the hole,the coverage area,and the arrangement form,row number and row spacing of the multi-row damping hole.Six groups of 30 models were designed for comparative analysis.The results reveal that it is necessary to increase the hole diameter and to reduce hole spacing and row spacing as much as possible.The reasonable coverage length of damping holes is 1.5 times coverage length of blasting holes.The blossom-form arrangement is recommended to adopted in the practical engineering.The rows number of damping holes is not more than 4 rows.Finally,it is applied in a typical adjacent tunnel project,which verified that the optimization design method of damping holes is reasonable and applicable.