At present

the development of urban underground space in soft soil area is prosperous in our country.The construction of deep foundations pits of high-rise buildings

subway stations and the tunnel brings a series of geotechnical engineering problems.Aiming at the problems in the construction

combining with a deep excavation subway station in soft soil area of Ningbo

considering construction steps

the land subsidence mechanism related to drawdown steps

excavation steps and support steps is studied.Computational model of deep pit of Ningbo subway station including construction steps is established using FLAC.Surface subsidence under different constructi

on steps is obtained.Research shows that the construction process has large influence on surface subsidence.The effect of drawdown enhances with the deepening of pit.The ground in the range of 20mout of the foundation pit subsides sharply in the process of deep foundation pit excavation

which should be taken more attention.The settlement difference of surface in the scope of 20

3

0mis large and easily causes engineering accident

which should not be ignored. Surface settlement can be effectively reduced by controlling the lateral horizontal displacement of soil in foundation pit

which can protect the surrounding buildings and municipal pipelines.