| The permafrost of the Qinghai-Tibet Plateau has been degraded and the grade of road engineering has been improved continuously.Pile foundation engineering has been widely used.In the process of freezing and thawing during the operation period,the frost heave and thawing settlement of the frozen soil around the bridge foundation induces the bridge engineering disease,which is one of the major problem to be solved urgently in the permafrost engineering.In view of the above problems,this paper studies the change of frost heave and thawing settlement of pile-soil system during the service of pile foundation.Based on the pile foundation engineering of Chalabing Bridge,the indoor model test and numerical simulation were used to analyze the formation mechanism of frost heave and thawing settlement characteristics of pile-soil system.The calculation model of frost heave and thawing settlement of pile-soil system during freezing and thawing was established,and the variation of frost heave and thawing settlement of pile-soil system in the future years was studied.The research results can provide reference for the construction of pile foundation in permafrost regions,structural design optimization and prevention of engineering freeze damage.The main works were as follows:(1)In view of the formation mechanism of frost heave and thawing settlement of pile-soil system during freezing and thawing process,the indoor model test was used to simulate the geological conditions of the pile foundation of Chalabing Bridge,and the thawing-freezing process was carried out.The temperature of soil around the pile,the unfrozen water content of soil around the pile,displacement of pile and soil were monitored during the freezing and thawing process.Based on the experimental data,the temperature field and moisture field variation principle of the pile-soil system were analyzed.Combined with the variation principle of temperature field and moisture field,the formation mechanism of frost heave and thawing settlement of pile-soil system was obtained.(2)In view of the of frost heave and thawing settlement model of pile-soil system,based on the heat transfer equation considering the phase transition,the water migration equation and the stress-strain equation,the coefficient type partial differential equation module(PDE)in COMSOL Multiphysics finite element software was used to perform secondary development to obtain the mathematical model of frost heave and thawing settlement of pile-soil system,and simulated the indoor model test to obtain the change of temperature,moisture,frost heave and thawing settlement,compared the numerical simulation results with the model test data,and the reliability of the numerical model of frost heave and thawing settlement of the pile-soil system was proved.(3)In view of the problem of frost heave and thawing settlement of pile-soil system in the future,the geological conditions of pile foundation engineering was simulated by using the model of frost heave and thawing settlement of the pile-soil system.Considering the increase of atmospheric temperature in the future,the temperature field,moisture field and frost heave and thawing settlement of the pile-soil system after 1 year,10 years,30 years,50 years was studied.By analyzing the temperature field change of the soil around the pile,the temperature field distribution of the soil around the pile and the upper and lower limits of the frozen soil are obtained.The change of moisture field in the soil around the pile was analyzed,and the changes of unfrozen water content,ice content and water migration in the soil around the pile were obtained.Finally,the variation of the displacement field of the pile-soil system was analyzed,and the displacement variation of the pile and the soil around the pile in the future years were obtained.It was concluded that the influence of the settlement of the pile-soil system on the stability of the pile foundation in the next 50 years is much greater than that of frost heave. |
PDF Full Text Request