| Along with the development of metro,the subway line is constantly increasing,and the new line and the existing lines have been crossed to form a traffic network system.At present,the main problem about new line crossing seamlessly existing line is how to consider the subway deep foundation pit retaining structure deformation and foundation pit stability,the influence of the surrounding buildings,the structure of the existing railway station by unloading of soil and complex surroundings in the construction process of excavation.as a result,it is of great significance for reasonable design and safety construction of the foundation pit engineering to correctly grasp the deformation characteristics of retaining structure and surrounding buildings,the station structure in the process of excavation of the subway station.The paper is based on the deep foundation pit project of changsha metro line 3.The method of Numerical simulation(FLAC3D)combined with field monitoring data analysis was used to study the influence deep foundation pit excavation caused on the retaining structure,surrounding ground,surrounding buildings and existing cable stations,then the related deformation rules was summarized.The main results of this paper are as follows:(1)Through the analysis and study of the measured data,the variation curve of the horizontal displacement of retaining structure and settlement of the surrounding surface with the increase of excavation depth were obtained.at the beginning of the foundation pit excavation,Amplitude of oscillation of horizontal displacements of pile become larger;as the continue to dig under the foundation pit,soil pressure increasing,the direction of horizontal displacement of the pile moves toward the foundation pit and deformation curve tends to smooth,showing a clear "bow" type curve,however,the position of the maximum located in the pile depth of about 3m;The surface displacement of foundation pit had rapid uplift and rapid subsidence at the beginning of excavation,and as the excavation depth of foundation pit increases,it settled slowly.(2)By selecting a purlin of 12.5m of the north foundation pit's standard section as research object,the whole process of foundation pit excavation was reconstructed by numerical simulation method,and the deformation rules of retaining structure and surrounding soil were confirmed.The numerical simulation results and the monitoring results are compared and analyzed,and the general rule is the same and the values are similar.It is proved that the establishment of the model,the selection of parameters and the calculation process are correct,and it is also proved that the subsequent parameter effect analysis is feasible.(3)Through the establishment of the whole model including foundation pits and a building structure,the influence of deep foundation pit excavation on buildings is simulated,and the relative position of building and foundation pit(distance and direction),the depth of building foundation had a great influence on the absolute settlement of the building and the difference settlement and inclination rate: the absolute settlement of buildings,differential settlement and inclination rate decrease with the increase of the distance of the foundation pit;The absolute settlement and lateral movement of buildings decrease with the increase of the depth of building foundation,and the interaction between the superstructure and the foundation is explained.(4)The numerical simulation is carried out through the south foundation pit,no.2 railway station and the first and second paragraphs of the north foundation pit,and the following conclusions can be drawn: the maximum surface subsidence is always towards the excavation foundation pit,which eventually appears near the center of the station at the top of the station.three kinds of construction schemes have very nearly the same vertical displacement after the excavation of the foundation pit on both sides,and the deformation value is in a controllable range. |
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