Performances Of Highway Geosynthetic Encased Lime Columns Foundations In Degraded Permafrost Regions

Due to global warming,warm permafrost is dying.Take patchy permafrost in northeast China as an example,the dying of the permafrost causes differential settlement of infrastructures such as highway,railway,airports and buildings,which seriously affects the durability and stability of these infrastructures.A series of positive cooling methods such as thermosyphon,crushed rock embankment,insulated board subgrade,ventilated embankment are not applicable to degraded warm permafrost subgrades.Moreover,methods such as replacement filling,electricity or steam heating permafrost need large work quantity,are not conducive to guarantee the sustainable development of the permafrost environment.Based on the fact that the warm permafrost in northeast China is degraded seriously and the Mohe-bejicun highway,use geosynthetic encased lime columns to pre-melt permafrost foundation.In order to solve the problem of foundation settlement caused by warm permafrost dying,the finite element method is used to solve the coupled heat-moisture-stress numerical calculation model of composite foundation.The main research contents and conclusions are as follows:Firstly,Theoretical derivation was carried out for the calculation of temperature field and deformation field of geosynthetic encased lime columns composite foundation by using finite element method,and finite element verification models of temperature field and deformation field were established respectively by using finite element analysis software.Based on model test and field monitoring results to demonstrate the rationality of the calculation.Furthermore,Based on the finite element analysis software,a numerical model of the temperature field of the composite foundation was established to study the pre-melting effect and the evolution rule of the temperature field of the foundation during highway operation;By changing the design parameters of foundation,the influence of different heat release temperature of lime stone,pile spacing,pile diameter and initial mean ground temperature on the effect of pre-melting permafrost of lime columns is mainly compared,and the pattern of refreezing of foundation during highway operational period is analyzed.Finally,combining with the Darcy’s law and solid mechanics,building Coupled heat-moisture-stress geosynthetic encased lime pile composite foundation heat-moisture-stress coupling finite element calculation model,the analysis of the pile foundation in the process of construction and highway operation during the consolidation settlement of foundation,and compared with Mohe-beijicun highway permafrost foundation deformation to evaluate the treatment effect of foundation.