| With the development of urban rail construction,the subway network is more and more intensive.Because of the complexity of urban environment,the subway tunnel will inevitably pass through the existing buildings in the process of tunneling,which has a bad impact on the construction and building safety.It is of great practical significance to study the deformation law and control measures of the ground and pile foundation during the construction of shield tunnel under the building pile foundation.In this paper,based on the pile foundation project of the shield tunnel underpass frame structure building of Shenzhen Metro Line 6,the key technology of the construction of the shield underpass building pile foundation in the complex stratum is analyzed.Through the finite element modeling of MIDAS GTS,the deformation law of the ground surface and the building pile foundation caused by the shield underpass driving under the unreinforced condition is analyzed.In view of the large deformation of the direct construction surface and pile foundation,the soil reinforcement method of sleeve valve pipe and high-pressure jet grouting pile combination is proposed.Through the finite element simulation analysis of three reinforcement schemes,the optimal reinforcement scheme is determined and field construction is carried out.By comparing the monitoring results with the simulation results,the paper analyzes the settlement rules and control measures of the ground and the building in the process of the earth pressure balance shield passing through the pile foundation of the building.The main conclusions are as follows:(1)The influence of the pile foundation of the building under the shield on the ground settlement is mainly concentrated in the range of 20 m before and after the area under the shield,and the ground settlement of the area under the shield double line at the same time increases about 30%compared with the area under the single line.After the completion of double line shield tunneling,the settlement groove on the ground surface presents irregular "W" or "V" shape.(2)When the soil is not reinforced,the settlement of the ground and the pile foundation of the building caused by the construction of shield tunneling under the building pile foundation is large.The settlement of the existing pile foundation is to make up for the loss of the bearing capacity of the pile foundation.After the combination of high-pressure jet grouting pile and sleeve valve pipe is adopted for the soil,the settlement of the ground and the pile foundation of the building is reduced by about 70%.The method of soil consolidation for the underpass area can be effective Control the adverse effects of shield tunneling.(3)In the reinforcement of soil,the bearing capacity of pile foundation and the disturbance of cutterhead to surrounding strata should be considered simultaneously.Through comparative analysis,the reinforcement of the area below the neutral point around the pile has the best effect on improving the bearing capacity gain of the pile foundation of the building.(4)Different excavation methods of double line tunnel have great influence on stratum settlement,and the settlement of ground and pile foundation is the largest when double line tunnel is excavated at the same time.The construction of the left and right tunnel before and after can reduce the disturbance of shield construction,reduce the settlement of the stratum and pile foundation.The construction of the under tunnel is completed first,and the settlement of the ground and pile foundation caused by the side tunnel is the smallest.(5)The results of the numerical calculation and monitoring of the settlement of the ground and the pile foundation of the building are in good agreement with each other,and the variation law of the settlement is the same,and the numerical difference is small,which has a good reference value for the project. |
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