| Due to the constraints of geographical and topographic features,tunnel construction often encounters the situation of high-voltage transmission tower above the tunnel.In the process of tunnel construction,accidents of tower tilt or collapse are easy to happen,which directly affects the operation of transmission lines,and poses a threat to national property and personal safety.At present,domestic and foreign scholars mainly focus on static analysis on the impact of tunnel construction on the high-voltage transmission tower,while the contents of blasting dynamic analysis are relatively few.In this paper,a shallow tunnel under high-voltage transmission tower of Le Guang expressway acts as the engineering background.Based on the theoretical summary of tunnel blasting vibration,the upper high-voltage tower is studied adopting the in-situ monitoring and numerical simulation analysis,obtaining the vibration regular pattern of blasting wave of high-voltage tower.The effects of different surrounding rock grades,different buried depth and different section area of tunnel on the upper high-voltage tower by blasting excavation are studied in detail.The major conclusions from this research are following:1.Through spot monitor of the blasting vibration velocity of tower foundation,and analysis and processing of the measured data,the variation of the peak vibration velocity of the tower foundation is obtained: With the increase of the burst center distance,the vibration velocity of X direction,Y direction and Z direction of the high-voltage tower is getting smaller and smaller.The degree of tower damage increases with the reduction in distance from explosion source.When the horizontal blast center distance is 20 m,the vibration speed of the tower foundation decays faster.In order to reduce the impact of blasting on high-voltage towers,blasting vibration control measures and methods for strengthening tower foundations are proposed.2.A three-dimensional numerical model for tunnel-tower is established by using finite element software Midas-NX.Through the analysis of transient dynamics,software simulate seven different burst center distance model of tunnel blasting construction under high-voltage tower.The results show the change regulation of the vibration velocity,ground settlement and tower foundation settlement.The three-way vibration velocity of tower foundation decrease along with the increase of explosive center distance.When the blasting center distance is 0m,the Z vibration speed of tower foundation D is 2.588cm/s,which is beyond the maximum allowable vibration speed 2.5cm/s,which may affect the tower.In order to ensure the safety of the tower's vibration,50 m can be used as a dividing line to adjust the blasting plan and reduce the risk.The research conclusions illustrate that the variation rule of vibration speed is consistent,indicating that the vibration response law of high-voltage tower is correct and reliable.3.The influence of tunnel blasting on the settlement of each tower foundation is very small.The settlement displacement of the tower base B point and the D point are greater than that of the base A point and the C point.The settlement difference of the tower is only about 0.1mm,and angle of inclination of the tower to the left line of the tunnel is only 0.84 degrees.According to the ? Technical code for building pile foundations ?(JGJ94-2008),the settlement displacement and tilt of the tower are within the control standard,and the tower is in a safe state.4.Research states clearly that: at the same condition of surrounding rock,the vertical and horizontal velocity of tower foundation decrease with burial depth of the tunnel increases;at the same condition of buried depth of the tunnel,the vibration velocity of tower foundation on soft rock is greater than that of tower base on hard rock.The vibration velocity of tower base on the single lithology is larger than multiple lithology interlacing situation.The law of the surface vibration velocity and surface settlement of the tunnel excavated by blasting show a single-peak form.The closer the blasting source is,the greater the surface velocity is,and the impact of blasting on the surface is more serious. |
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