| Most of the subway excavation layers in the coastal areas are saturated sand layers rich The subway excavation layer in the coastal area is mostly in the powdery clay layer rich in high water volume.Artificial freezing method is often used during construction.However,during the freezing construction process,it is easy to produce frost swelling phenomenon,resulting in damage to buildings and the surface.In response to the above problems,the subway tunnel of Tung Chung-Qingsheng Station on the Guangzhou Metro Line 4 was used as the engineering background,and the methods of physical mechanical properties analysis,numerical simulation and on-site monitoring were adopted.FLAC3D is used for numerical simulation,the variation of freezing temperature field with freezing time in artificial freezing construction is studied,and the optimization scheme of excavation is put forward,and the rationality of the optimization scheme is analyzed.The main research contents are as follows:(1)Taking into account the actual layout location,direction,thermal conductivity and latent heat coefficient of the freezing hole,a finite element model is established to simulate the development law of the temperature field during the active freezing period.(2)FLAC3D is used to simulate the freezing deformation of the soil during the active freezing period.(3)Under the condition that the wall thickness is 1.75 M,2.0 M,and 2.25 M,the temperature of the salt water is changed to simulate the change of the corresponding formation temperature field and the average temperature of the frozen wall over time.(4)The deformation of the surrounding soil during the excavation phase is simulated by FLAC3D.(5)Compare the results of three-dimensional numerical simulation with the monitoring results and draw a time temperature curve.Through the study,the results are as follows:(1)After freezing 10d,the zero isotherm meets,after 35d,a frozen column is formed,and after 50D,the frozen wall satisfies the design strength.(2)The soil from the freezing tube 6.0 m,10.0 m,15.0 m,and 17.5 M(surface)was significantly affected by the freezing of 15d,20d,30d,and 40d,respectively.(3)It takes 42 days to reach the design freeze wall at-25?,30 days to reach the design freeze wall at-30?,and 21 days to reach the design freeze wall at-35?.(4)The maximum surface settlement after excavation is 15.82 mm.(5)The prediction result curve is above the simulation result curve,and the trend is basically similar.The maximum prediction value is 15.82 mm,which is 0.97 mm larger than the measured result.As a result,it is concluded as follows:(1)The law of the temperature field of the entire active freezing period develops slowly first.(2)During the entire active freezing period,the law of soil freezing development is faster and slower.The closer the passage vault is to the freezing tube,the greater the displacement affected by the freezing.(3)The different freezing temperature makes the freezing wall reach the design strength at different times,and the higher the negative freezing temperature,the shorter the freezing wall formation time.(4)The main deformation feature of the surface after excavation is soil settlement.(5)The numerical simulation results and the engineering measurement results are drawn into a time temperature curve.The curve fitting is good,and the numerical simulation results are close to the engineering results. |
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