Research On Frost-Drawing Resistance Of Photovoltaic Bracket With Expanded Bottom Pile In Seasonal Freezing Zone

Photovoltaic power generation project as one of the strategies of sustainable development strategy adhering to the development concept of economic and social development,resources and environment coordination,has been widely used in many regions.However,in areas with seasonal frozen soil,photovoltaic support foundation is seriously affected by freezing and pilling during wintering projects,which causes a lot of engineering problems,which need to be solved by further research.In this paper,the photovoltaic engineering project in Changchun,a typical seasonal freezing area,is taken as the background,and the research work is carried out by combining theoretical analysis and numerical simulation for the photovoltaic bracket base expanding pile foundation.The distribution of temperature field in soil during freezing period and melting period is studied,and the stress and pull displacement characteristics of the expanding pile of photovoltaic bracket foundation during freezing period and melting period are analyzed.And the influence factors such as different pile type parameters in the process of using the expanded bottom pile are deeply studied and analyzed.The main research results are as follows:1.Through the simulation analysis of soil temperature field in this region,it is shown that the freezing depth of soil in the freezing period(November～February)expands downward with the decrease of external temperature;The maximum freezing depth is about 1.75 m at the lowest temperature in January.The ice crystals in the soil melted in early March,and the melting lasted until the end of May.2.Through the numerical simulation analysis of the straight pile and the expanded bottom pile in normal temperature,freezing period and melting period,the change law of pile foundation displacement,soil displacement and stress,tangential stress and normal stress of pile under the action of normal temperature,freezing period and melting period are compared and analyzed.The comparative analysis results of freezedrawn displacement show that the freeze-drawn displacement of enlarged bottom pile foundation is reduced by about 30% compared with that of straight round pile foundation with the same parameters.3.Under the conditions of maximum freezing action,vertical load and horizontal load,the freeze-drawing resistance characteristics of photovoltaic bracket expanded bottom pile with different pile type parameters are analyzed.The influences of pile length,diameter expansion ration and height of bottom expansion on the freeze-pulling characteristics of bottom expansion pile are mainly analyzed.The results show that with the increase of pile length,diameter expansion ratio and height of bottom expansion,the freeze-pulling displacement of pile foundation gradually decreases,the extruded stress between pile and soil increase continuously,the freeze-pulling resistance of pile foundation also increase,and the relative displacement between pile and soil decreases correspondingly.And through the analysis of the influencing factors,the optimal scheme of pile type parameters for expanding bottom is given.