Study On Frost Heave Deformation Law Of Multi-ring Thin-wall Combined Cylinder Of Super Large Diameter Deep Foundation Pit

Under the environment where urban foundation pits are gradually becoming deeper and larger,the commonly used envelope structure of shallow foundation pits will face great challenges.Based on the large-scale application of the freezing method technology in the construction of deep shafts in coal mines,considering the introduction of the freezing method technology into the construction of the municipal deep large foundation pit envelope structure,the design concept of the application of multi-ring thin-wall combined cylinder of super large diameter deep foundation pit " was proposed.The problem of frost heaving and thawing in the application of the freezing method is also a hot issue of concern to various scholars,so it is necessary to study the frost heave deformation of the multi-ring thin-walled tubular combined frozen soil curtain structure formed by the multi-ring tube freezing.Frost heave deformation is the result of the interaction of the three fields of temperature field,moisture field and stress field.In the research and analysis,the coupling effect of temperature,moisture and stress must be considered.herefore,based on the coupling theory of water-heat-force,the frost heave deformation of the structure is analyzed.Firstly,based on the previous theories,the basic equations of temperature field,moisture field and stress field are obtained by reference and derivation,considering the dynamic changes of thermophysical parameters,hydraulic characteristic parameters and mechanical parameters caused by the interaction of the three fields.The value of is explained,and by introducing the concept of "solid-liquid ratio",a fully coupled water-heat equation is established;Considering the volume expansion caused by the ice-water phase transition and water migration,based on the moisture and ice content calculated by the total coupling of water and heat,the soil frost heave volume strain formula is deduced to realize the sequential coupling of the three fields of water,heat and force.Water-heat-force three-field coupling equation.Secondly,Use Comsol software for numerical calculation.Based on the three-field waterheat-force coupling equation,the PDE module in the Comsol software is used to carry out the secondary development of the water-heat-force coupling equation to realize the full coupling of water-heat and the one-way coupling of water-heat results and force.Parameter calculation to obtain the results of temperature field,moisture field and stress displacement field under the typical parameters;then carry out single-factor test calculation to study the initial water content,initial ground temperature,number of frozen tube turns,frozen tube row spacing,frozen tube spacing Frost heave deformation under five factors;finally,the effect of the factors on the frost heave deformation of the multi-cycle combined frozen soil curtain structure is analyzed by orthogonal test.Then,conduct an indoor physical model test.Based on the similarity theory,the actual engineering problems were modeled,and the prototype was scaled down indoors to obtain and analyze the temperature,stress,and displacement data during the process of freezing the multiloop tube to form a combined cylindrical frozen soil curtain structure.Finally,the numerical calculation results and the physical simulation test results are compared and analyzed to verify the consistency of the results under the two methods,so as to explain the correctness of the applied model in numerical calculation,and provide guidance and reference for subsequent research and engineering practice.There are 59 figures and 30 tables as well as 96 references in the paper.