Study On Deformation And Blasting Vibration Of Existing Structures Caused By Metro Construction

With the rapid development of infrastructure construction and blasting technology in China,blasting technology has been widely used in various engineering construction projects.However,blasting in the central urban area with dense population and complex existing structures will cause a series of negative effects,especially the damage caused by tunnel excavation blasting to adjacent existing structures have attracted much attention because of universality and civil disputes.To study the influence of tunnel excavation blasting on adjacent surface existing structures,the paper takes the tunnel blasting project of Xiamen Metro Line3 as the research background.On the basis of consulting and deeply studying the relevant literature,the principle of combining theoretical analysis,numerical calculation and on-site monitoring will be adopted to study the settlement,displacement and vibration speed of surface existing structures in the process of tunnel excavation and construction.The main research results include as follows:(1)In view of the generation mechanism,propagation characteristics of blasting seismic wave and the influencing factors of blasting seismic wave,the design principles of blasting for station foundation pit and tunnel excavation were determined according to the engineering geological conditions of Xiamen Metro Line 3 tunnel.Shallow hole multi-stage delay blasting and short-step smooth blasting were adopted for station foundation pit and tunnel excavation respectively.The blasting parameters of foundation pit and shallow buried tunnel were optimized by blasting vibration monitoring.The allowable maximum charging weight of different existing structures at different distances was obtained by using the Sodev's blasting vibration velocity calculation formula.(2)The three-dimensional numerical model was built by using Midas/GTS finite element software.The dynamic response of the tunnel excavation to the subsidence,horizontal displacement and vertical displacement of the existing surface structure was studied through the Yingxia railway,the frame bridge of Chenggong Avenue and the footbridge of the Pioneer Park.The results showed thatthe dynamic response indices of adjacent existing structures meet the relevant requirements,and the existing structures on the ground are safe.(3)According to filed monitoring blasting vibration,frequency spectrum of the measured blasting vibration signal was analyzed by using Fourier transform.The energy and frequency distribution of blasting seismic wave were studied,and then the influence of blasting vibration of adjacent existing structures was analyzed.The results showed that the vibration velocities of each measuring point of fender post of foundation pit were less than the peak particle vibration velocities of safy allowing;the vibration velocities of some measuring points of the frame bridge exceed the peak particle vibration velocities of safy allowing;the measures of combining full-section grouting to reinforce stratum in advance and advanced short pipe shed support should be adopted to strictly control the stratum settlement;the vibration velocities of each measuring point of adjacent existing structures were less than 10mm/s,which indicates that the design scheme of foundation pit and tunnel blasting was reasonable in the range of safe vibration velocity.The research results obtained in this paper can provide some guidance for the analysis of settlement,displacement and vibration velocity of adjacent existing structures caused by tunnel excavation.