Numerical Simulation Of Pile Foundation Thermal Regime And Its Control Effect In Permafrost Regions

Frozen soil is a kind of extremely unsteady geologic body sensitive to climate and environment change. Besides of mineral composition, density and moisture content of soil particle, its physical and chemical features and engineering properties are closely related to the ice content and thermal state of frozen soil. Climate change and human disturbance could also bring about the temperature change within a certain zone of frozen soil. Caused by thermal disturbance, the phase change of water may also lead to frost heaving and thaw deposit problems, and afterward impacting on the stability of engineering structures in frost regions. Thus research on temperature change of frozen soil region pile foundation was conducted in this paper, which in on the basis of the influence to building properties caused by frozen soil thermal state. The paper also proposed temperature control measures during construction period and subsequently maintenance period, and simulations on their controlling effect and influence factors were conducted.The correctness of numerical simulations of earth temperature in natural state was firstly verified in this paper and then the temperature field of soil varying with time in natural state was obtained. Based on this point, research was conducted at following aspects:refrigerating fluid measure is emphasized to realize the quick refreezing of pile soil while analyzing the effect of construction disturbance and simulating the hydration heat process of pile foundation. In consideration of the influence to temperature field of frozen soil pile foundation caused by climate heating, the sensitivities to the maximum thaw depth and earth thermal state were discussed and analyzed for different frozen soil types, soil conditions and heating rates. On the basis of the degradation of frozen soil due to climate change, this paper also proposed the hot pin technology and artificial freezing technology for the purpose of temperature control, and simulation on their effects were conducted through finite element analysis. In the end, the conductivity factor, which is an important parameter in temperature field computation, was analyzed by optimized inversion computation through the optimization module of finite element analysis.Main results obtained through numerical simulation of frozen soil pile foundation under the influence of construction disturbance and climate change are as follows:the finite element analysis of natural foundation by using regression temperature via measured temperatures and boundary layer theory is feasible. For cold fluid control measures, freezing effects varies with different arrangements under the condition of same sectional area and the more pipes, the better the effect will be. The feasibilities of hot pin and artificial cold technology were verified and the option should be determined by construction conditions and environmental factors due to their different controlling effects. The inversion computation method of the conductivity of foundation soils was proposed and its feasibility and practicability were verified, which is significant in some degree for constructions in frozen soil region theoretically and practically.