Study On The Deformation Law Of Multi-cycle Frozen Thin-wall Combined Cylinder Of Deep Foundation Pit With Super Large Diameter

At present,the urban foundation pit is developing in large and deep areas.The traditional foundation pit enclosure method can no longer be satisfied.Try to use frozen soil curtain as the enclosure structure.However,when the conventional design theory of thick shaft cylinder freezing is used in deep foundation pits,The stress condition of the frozen wall will be very different from the actual situation,resulting in the design thickness of the frozen wall being too large.Therefore,this paper proposes a multi-ring thin-walled tube structure,and studies the deformation law of this structure during the excavation process.Firstly,the theoretical analysis is used to increase the force analysis of the unfrozen soil between the two circles of frozen soil on the basis of the conventional frozen soil constitutive relationship and the determination method of frozen wall thickness.Structural deformation law under external load.Secondly,the numerical simulation analysis method is used to perform typical parameter calculation,single factor test,orthogonal test and regression orthogonal analysis respectively.In the typical parameter calculation,the instantaneous stress and deformation of the composite structure during excavation and the creep after a period of construction are obtained.Deformation;study the effects of frozen soil thickness,frozen soil average temperature,unfrozen soil thickness,frozen soil circle number,excavation section height and exposure time on the stress field and displacement field of the combined structure during excavation in a single factor test;In the orthogonal test,the influence of various factors on the maximum creep deformation of the frozen soil in the exposed section of the inner ring is obtained;the center combination design of quadratic regression is used in the regression orthogonal analysis to obtain the maximum creep deformation of the frozen soil in the exposed section of the inner ring Quantitative relationship with various factors.Then,carry out physical simulation test research,carry out modeling design based on the similarity theory,carry out freezing large-scale deep foundation pit freezing model test,obtain and analyze the data of force field and displacement field during excavation.Finally,the theoretical analysis,numerical simulation and physical simulation test are compared and analyzed to analyze the error of the physical simulation test and the areas that need to be improved.The assumptions made by the theoretical analysis and the selection of parameters are improved to freeze the multi-ring thin-walled composite cylinder The calculation method of the wall is summarized to provide a reference for the design of similar projects in the future.There are 69 figures and 34 tables as well as 55 references in the paper.