Study On Deformation Characteristic Of Deep Excavation With Large-span Foundation Pit In Deep Silty Stratum

With the rapid advancement of urbanization in China,the available space on the urban ground has become increasingly tense,the construction of the subway has been vigorously developed,and the underground subway parking lot has also increased.However,this status quo not only occupies urban land resources,but also has an impact on the surrounding environment.The research and development of underground parking lots is imminent.This paper relies on the deep foundation pit construction project of Yitian Car Park of Shenzhen Metro Line 10 to study the deformation characteristics of large-span deep foundation pits constructed in deep silt stratum.The main research contents are as follows:(1)Monitoring data analysis.By analyzing the field measured data,the law of deformation and deformation of deep foundation pit excavation in silty soil layer is revealed.The deformation of the underground continuous wall is in a "bow" shape,and the maximum deformation value appears at 1/3 of the top of the wall.At this point,this is basically consistent with the position of the maximum bending moment of the ground wall;the maximum position of the ground settlement appears in the range of 2H from the edge of the foundation pit,where H is the excavation depth of the foundation pit.(2)Comparative analysis of constitutive models.The ABAQUS finite element software is used to compare the two constitutive models of Moor Coulomb and Modified Cambridge.The calculation results show that the Moor Coulomb model will produce a slightly smaller simulation result than the actual data.This is because Moor Coulomb is an ideal elastoplastic model in the soil simulation.Uneven deformations are caused during deformation,and the results of the modified Cambridge model are very similar to the actual data.(3)Analysis of the deformation characteristics of the foundation pit.The ABAQUS finite element software was used to simulate the construction process of Yitian parking lot of Shenzhen Metro Line No.10.The variation of the retaining structure and the settlement of the ground surface after the wall were analyzed,and the bending moment,soil stress and support of the grounding wall were analyzed.Force characteristics.Comparing the simulated data with the monitoring data,the error is found within the requirements of the engineering construction,and the numerical simulation results are proved to be reliable.(4)Parameter sensitivity analysis.In the modified Cambridge model,the rebound curve slope k and Poisson's ratio v have the greatest influence on the deformation of the foundation pit.In the Moor Coulomb model,the cohesion force c has the greatest influence on the foundation pit deformation;at the same time,the parameters of the envelope structure are designed.And the design of the foundation pit span is also crucial for the deformation of the foundation pit.(5)Derivation of the surface settlement formula.From the point of view of elastic science and soil mechanics,according to Rankine's earth pressure theory,the stress calculation model of surrounding soil during excavation process under silt soil layer is analyzed.Then the relationship between stress and strain is used to find the soil.The vertical strain of the body is finally derived,and the prediction formula of surface deformation for deep foundation pit excavation in silty soil layer is derived.The reliability and rationality of the formula are verified by numerical simulation.(6)Surface impact area division.The surface subsidence curve is dimensionlessly optimized,and the ground settlement impact area caused by the excavation of large-span deep foundation pit under the muddy soil layer of Shenzhen Metro Line 10 is divided,and construction suggestions are proposed for each of the three areas.