Study On The Impact Of Shock Vibration And Excavation Unloading On Upper Span Railway Viaducts And Control Technology

Along with the rapid development of underground space,the construction of urban rail transit is in full swing,and there are more and more cross lines in the city,especially the cases of under construction projects penetrating the existing bridges occur from time to time.In the process of drilling piles for pit construction,due to the height limitation of the existing viaduct,the traditional rotary drilling rigs have limited working space,and the impact drilling rigs are generally used to form holes,and the vibration generated by the impact will inevitably have a greater impact on the bridge structure.In the current study,most of the focus on the excavation stage,while ignoring the impact of vibration in the hole-forming stage,which has a potential risk of uncertainty for subway viaducts with strict requirements on deformation and vibration.Therefore,this paper carries out the research on the impact and control technology of impact vibration and excavation unloading on the upper span rail transit viaduct,which can provide experience for similar engineering construction.On the basis of summarizing relevant research at home and abroad,this article relies on the foundation pit project of the subway station under construction in Jinan City to study the bridge structural response under the influence of impact vibration and excavation unloading through theoretical research,three-dimensional numerical simulation,and monitoring data analysis.The main content is as follows:(1)The impact load caused by impact vibration is described qualitatively and quantitatively,the impact physical model is established,and the mathematical expression of impact load is derived by solving the Equations of motion;Analyzed the propagation characteristics of shock type point vibration sources in rock and soil,and explored the relationship between reflected and refracted waves generated by vibration waves on different media surfaces;Summarized the calculation methods for surrounding surface settlement and bridge pile lateral displacement under excavation unloading.(2)A three-dimensional calculation model for impact vibration was established,and the impact process was simulated by establishing a time history load function to study the dynamic response of the surrounding soil,bridge piers,and bridge piles during the impact hole formation process.By analyzing the changes of soil stress,vibration velocity and displacement,the dynamic characteristics of surface soil under different Impact depth are obtained;Extract the stress vector cloud map,analyze the stress characteristics of bridge piers and piles,conduct research on the pier top with the highest vibration velocity and displacement,and analyze the changes in displacement and vibration velocity of the pier top during the impact drilling process;The dynamic response of the pier under different impact energy is explored by analyzing the impact hammer falling height and hammer weight variation parameters,which provides a reference for reducing the impact of impact hole forming on the adjacent Viaduct.(3)The three-dimensional calculation model of excavation unloading is established,and the displacement and deformation of support piles,surrounding ground and bridge piles during excavation are explored.The deformation laws of foundation pit and bridge under excavation unloading are obtained.Through the parametric analysis of support structure,the influence of support system on the deformation of adjacent Viaduct is explored,providing reference for relevant protection measures under the excavation of foundation pit,Extract on-site monitoring data and compare and analyze numerical simulation results to verify the accuracy of the excavation unloading calculation model.(4)Impact vibration and excavation unloading grouting reinforcement calculation models were established respectively to investigate the impact of grouting reinforcement on the bridge in the process of punching construction and pit excavation,and the protection effect of grouting reinforcement in the two phases of punching construction and pit excavation was obtained by comparing and analyzing the vibration speed and deformation before and after the grouting reinforcement,so as to provide reasonable suggestions for the similar construction of underpasses under the elevated bridges of the rail transit.