Analysis Of Uplift Bearing Capacity Of Column Pile Foundation Of Railway Catenary In Permafrost Area

In recee years, climale change and human acivtis have led to a series of changes in the temiperature and humidity of soil in cold ngions, which has caused changes in thephysical and mecanical properies of the soil, caused changes in the bearing capacity of thefoumdat?on in the soil and afeted the safe use of the foundation. Al present, there is not acomplete study on the bearing cnpacity and deformation response of the foundation under thecondin of the change of soil parameters. Fisly the paper studies the change of temperatureand hungidity in the Qinghai Tibet Placa, designs a series of indoor tests sccording to thechange?f soil moisture, and determines the change rule of mechanical parumeters of the soilaround the pile and the contact surface betwcen the pile and the soilTben the temperaturefield anglysis model is cstablished to calculale the permafrost upper limit of pilesoil system.Finally, the bearing capa?city and deformation response of pile foundution under uplih load areanalyzed by esablishing the mechanical model, which can peovide referene for evaluatingthe long-erm bearing capacity of pile foundation.In view of the dynamie change ol the pile envionment, this paper mainly studies thechange of environmental temperature and humidiy. Firstly, through literature teview, thepecipiaion data and surface temperature diula of the Qinghai Tibet Plateau in the past 60 years and 30 years are abtained. Then, the change rule of precipitation and surfacetemperature with time is amalyred by mathematical satisis. The results show that thetemperalure and humidity of the Qinghai Tibet Plateua will inerase with time, In the next 50 years, the pemafrost humidity will incrtase by 6%, and the temperalure will imcrease by 1?,which can provide basic reference for determining the emvitonrment of lrozen soil at any time.In view of the change of physical and meheanieal parameter of pl-ol system withsoil tempentur and humidiy, a sries of indor tests inludig soil physial poperiese test,triaxial shear test and pile-soil interface direct shear test are designed.By setting different gradient moisture content and different freeze-thaw cycles,the change rule of mechanical parameters of soil and pile-soil interface with time and moisture content of soil is obtained.The results show that with the increase of water content,the cohesion and internal friction angle of the soil around the pile will decrease,the cohesion of the pile-soil interface will increase,and the internal friction angle will decrease,which provides the basis for determining the parameters of the soil and the contact surface at different times.In view of the change of temperature field of pile-soil system with time,the temperature field calculation model of pile-soil system is established by FLAC3 D numerical simulation software,and the temperature fields of pile-soil system in 2019-2069 are simulated respectively.Through the distribution of temperature field,the location of permafrost upper limit is determined,the change trend of soil upper limit near and far end of pile is analyzed,and the uplift bearing capacity of pile under the change of temperature field is calculated.The results show that in the next 50 years,the upper limit of frozen soil around the pile will rise first and then fall,the upper limit of frozen soil at the far end of the soil will gradually decline,and the uplift bearing capacity of pile foundation will gradually decrease.This can provide the initial condition for the calculation of the uplift bearing capacity of pile foundation under the condition of the change of soil parameters.In view of the dynamic change of bearing capacity of pile foundation,the mechanical calculation model of pile-soil system is established by numerical simulation software,and the basic parameters and initial conditions of the mechanical model are determined by using the above research conclusions.The stress and deformation response of pile at different times and states are calculated respectively,and the failure mechanism of pile-soil system under different states is discussed.The results show that the uplift bearing capacity of the pile after50 years is about 40% of the current value when the active layer is melted,and about 50%when the active layer is frozen.If the dynamic changes of the physical and mechanical parameters of the pile-soil interface and the soil around the pile are not considered in the design,the uplift bearing capacity will be lower than the design value 20-30 years after the completion of the pile construction.