Research On Safety Control Technology Of Tianjin Metro Waixi Section Tunnel Close To Undercrossing Railway Bridge

In order to formulate the construction risk measures of subway tunnel undercrossing railway bridge,this paper relies on the Waixi section tunnel of Tianjin Metro Line 7 undercrossing Beijing-Tianjin Railway bridge project,through the method of numerical simulation and field monitoring,studies the transverse and longitudinal influence zoning of tunnel undercrossing bridge and the measures taken.The main conclusions are as follows:(1)All pile foundations of undercrossing Bridges are divided into class A,B and C.By changing the spatial position relationship between pile foundations and tunnels,72 working conditions of the three types of pile foundations are numerically simulated and analyzed,and the classification criteria of influence zones based on this project are proposed.The least square method was used to fit the allowable value,alarm value and warning value of displacement in the calculation results,and the boundary curves of the influence zones of the three kinds of pile foundations were derived.The influence zones were divided into strong influence zone,weak influence zone,extremely weak influence zone and no influence zone.(2)According to the settlement concentration area and settlement rate of pile foundation,the longitudinal influence zone of tunnel through pile foundation group was divided by three-dimensional numerical simulation,and the strengthening range of longitudinal influence zone was obtained: strong influence zone was 19.5m～28m,weak influence zone was 19m～30m,and very weak influence zone was 9m～31.5m.The influence zone reinforcement measures and grading countermeasures are put forward.According to the results of lateral and vertical effects,reinforcement measures in different areas are implemented for each pile of each type.There are five different working conditions: working condition one(no reinforcement measures),working condition two(isolation pile + full section grouting),working condition three(isolation pile + pipe shed grouting),working condition four(steel sheet pile + pipe shed grouting)and working condition five(steel sheet pile + lock anchor bolt).The settlement of pile foundation and the safety of tunnel under five working conditions were calculated respectively.Through comparative analysis,the optimal reinforcement measures were obtained as the second working condition(isolation pile + full section grouting).(3)According to the results of lateral and longitudinal influence zoning,pile No.7 in class C and pile No.3 and No.6 in class B are in strong influence zoning.Isolation pile and full section grouting reinforcement measures and super monitoring are adopted in the field;No.5 of class C piles and No.8 of class B piles are located in the weak impact zone.Full-section grouting reinforcement measures and super-strong monitoring are adopted on site.Pile No.2 and No.4 of class A piles are located in the extremely weak impact zone,and super strong monitoring measures are adopted on site.Pile No.1 in Class B is located in the no-impact zone,and ordinary monitoring measures are adopted on site.During construction,the settlement value of each pile is compared with the numerical simulation value,and the results show that;The field monitoring data are consistent with the calculated results.The construction safety of the measures that affect the zoning and grading strategy is verified.It provides reliable reference value for similar tunnel approaching underpass bridge engineering.