| With the development and utilization of urban underground space in frozen soil areas in the cold and deep season,the number of deep and large foundation pits with large excavation depth and complex plane shapes continue to emerge.However,deep and large exposed foundation pits often face the problem of overwintering due to the long construction period.During the winter break,due to the frost heave of the soil,the failure or even destruction of the anchoring and supporting structure with the prestressed anchor cable as the main technical body has become increasingly prominent.However,domestic and foreign researches on the reliability of prestressed anchoring structures for deep foundation pits in freezing and thawing environments in the cold and deep seasons are almost blank,resulting in the lack of scientific and reasonable design methods and construction techniques for anchoring and supporting of deep foundation pits in frozen soil areas.In the passive dilemma of "experienced construction and dynamic design".In view of this,this paper takes the pre-stressed anchor support of a deep foundation pit during the winter in a subway station of Changchun City,Jilin Province as the research object.Through the field monitoring of the actual pre-stressed anchor structure,it reveals the pre-stressed anchor support of the deep foundation pit during the winter period.The force-deformation-displacement evolution law of the protective structure;the frozen soil water-heat coupling control equation is established based on the frozen soil water-heat coupling theory,and the coupling equation is solved by the COMSOL Multiphysic multi-field coupling numerical software,and the frost heave of the unearthed soil is further fitted The function relationship between coefficient and temperature.And with the help of the subprogram interface provided by the finite element numerical calculation software ABAQUS for the user,the FORTRAN program is written according to the frost heave coefficient formula to realize the secondary development of frozen soil materials;through the construction of a three-dimensional deep foundation pit prestressed anchor support numerical model,the freezing is realized The application of the expansion coefficient formula reveals the mechanics and displacement response characteristics of the prestressed anchor support structure under frost heave and temperature changes,and the deformation characteristics of the supporting pile.The main research content,methods and understanding are briefly described as follows:This article is based on the national key research and development plan:super-large landslide emergency treatment and rapid treatment technology research and development(2018YFC1505300).Combining three methods of on-site monitoring,theoretical analysis and numerical simulation,the frost heave mechanism of deep foundation pits overwintering and the force and deformation laws of anchoring and supporting structures are systematically studied.The main research work and results of this paper are as follows:Firstly,for the deep foundation pit of a subway station of Changchun Metro Line 6during the winter,the horizontal displacement of the pile top,the deformation and displacement of the retaining pile,the tension of the prestressed anchor cable,and the soil temperature of the sidewall of the foundation pit were monitored on site,and the monitoring data were sorted out.The analysis reveals the force-deformationdeformation evolution law of deep foundation pit prestressed anchor support structure under the combined action of three fields of water and heat in frozen soil area in the cold and deep season.Analyze the influence of frost heave and temperature change of deep foundation pit soil body in winter on prestressed anchor cable anchor support structure.Secondly,based on frozen soil theory,derive and establish frozen soil water-heat coupled control equations,use COMSOL to solve the coupled equations,and verify the change law of frozen soil temperature and moisture with related examples.The numerical simulation test of the frozen soil under the open system is designed to obtain the change law of ice content and total water content after the completion of the soil freezing,and then to fit the function relationship between the soil frost heave coefficient and the temperature.Thirdly,The numerical analysis software ABAQUS is used to establish a three-dimensional finite element model of the foundation pit supported by prestressed anchor cables for the actual deep foundation pit engineering.First,simulate the process of excavation layer by layer and add anchor cables,analyze the prestressed anchor cable tension,the horizontal displacement of the pile top,and the deformation of the pile body,and compare it with the on-site monitoring data of the foundation pit to verify the reliability of the model.On the basis of water-heat coupling,the FORTRAN program is written according to the frost heave coefficient formula to realize the secondary development of frozen soil materials,so that the soil is regarded as an elastic body for stress field analysis to realize the three fields of water field,temperature field and stress field coupling.According to the initial temperature field and surface temperature model of deep foundation pit soil before wintering,the simulation of the whole process of deep foundation pit wintering is completed,revealing the mechanical response characteristics of the pre-stressed anchor supporting structure of foundation pit under frost heave and temperature changes.Finally,the influence of anchor cable pre-stress,anchor cable vertical spacing,anchoring angle and anchoring section length on the effect of pre-stressed anchoring and supporting foundation pit is further studied,and the optimal pre-stressed anchor supporting plan is proposed and the pre-stressed anchor of the winter foundation pit is proposed.Optimized design of cable support scheme.In this paper,the simulation analysis of the prestressed anchor support structure of the winter foundation pit and the optimization design of the support scheme can provide a useful reference for the actual construction and design in the future. |
