Study On Construction Safety Risk Assessment Of Tunnel Section Excavated Underneath An Existing Metro Line

With the acceleration of China's urban modernization and the rapid growth of urban population,traditional ground transportation has been difficult to support the high-speed operation of urban development,and the construction of urban rail transit has become in full swing.However,with the continuous intensive metro network,the excavation depth of urban subways has gradually increased,and subway lines under construction will inevitably penetrate existing subway lines from time to time,which puts higher technical and management requirements on construction and risks.The degree is also doubled accordingly.Therefore,it is particularly important and urgent to evaluate the construction risk of tunnel sections undercut through existing subway lines.This article is based on a typical engineering case of the Qingdao Metro Line 8 Qing Cang section undermining through the existing Qingdao Metro Line 3 Yong Qing section,which the arch bottom of Line 8 is only 0.445 m from the closest floor of Metro Line 3.It is expected to provide some reference and reference for the construction risk assessment and management of similar underground tunnels under the existing subway lines in the future.The main research contents and results of this article are as follows:(1)Based on the status quo and future development trend of construction risk management of domestically and internationally excavated tunnels,research and analysis of relevant literature and risk assessment methods for safety risk assessment of underground excavated tunnels.The questionnaire survey method was used to collect the possible construction risk factors and management risk factors,which based on the construction process of the Qingdao Metro Line 8 Qing Cang section undercutting through the Metro Line 3 Yong Qing section,and the risk assessment research and analysis of the construction of underground tunnels are carried out.(2)By analyzing and studying the geological and environmental background of the tunnel section engineering project of underground excavation under the existing subway line,the risk commonness of such projects is analyzed.The safety risk factors during the construction of the tunnel section of the underground tunnel under the existing subway line were analyzed,and in-depth research and analysis are carried out on the monitoring and management of the tunnel section of the underground tunnel undercut through the existing subway.(3)Through the establishment of a static risk assessment index assessment model,the initial risk level of the project is evaluated and analyzed,and the construction of the initial safety level risk assessment system for the tunnel section of the underground tunnel that is dug through the existing subway line is constructed.The degree of difficulty is evaluated from eight aspects: pre-construction preparation,tunnel excavation stage,initial shotcrete support,leading conduit and pipe shed,on-site concrete secondary lining,waterproofing operation stage,on-site monitoring situation and crossing special sections researched and established a four-level evaluation index system.(4)Through the establishment of a dynamic risk index evaluation model,which is applied to daily inspections and inspections,real-time evaluation of construction management risks.Build a construction safety inspection and evaluation system for the tunnel section of underground tunnels undercut through existing subway lines,which from the six aspects of personnel risk,mechanical risk,material risk,regulation and management risk,environmental risk,and measurement risk(5M1E),establish a safety inspection index management system for construction excavation underneath existing subway tunnels and adopt three levels.The evaluation standard has achieved the risk evaluation goal.