Numerical And Experimental Study On Frost Heave Characteristics Of Frozen Soils At Pore Scale

Frozen soil regions accounts for approximately 70% of the earth's total land area.The area of frozen soil regions in China,where highways,high-speed railways and other transportation infrastructure will be built in the near future,ranks 3rd in the world,taking up 75% of national territory.The periodic change of climate may cause frost heave,thawing settlement and other diseases of subgrade soil of highways and high-speed railways.Therefore,the research of frost heave characteristic and the regularity of heat and moisture transfer of frozen soil during freeze-thaw process is of great significance to the construction of infrastructure in frozen soil regions.Some research of frost heave characteristic of frozen soil during freeze-thaw process is more concerned with macro-scale experimental study at present stage;besides,the existing numerical model is incapable of dealing with the influence of transient pore structure on frost heave characteristic.Based on thermo-solid coupling numerical method,the frost heave process of frozen soil was separated into heat conduction and pore water expansion.The mathematical model of frost heave governed by transient heat conduction differential equations and basic motion equations of transient dynamics was proposed.According to the gradation and porosity of soil tested,the geometric model of spherical soil particle and pore water was established.The frost heave of frozen soil was studied by numerical method from two aspects,soil temperature distribution and soil particle displacement,aimed at the influence of different counts of freeze-thaw cycles,the gradation of soil particles and the freezing temperature.The results of numerical simulation indicated that the freezing rate of coarse soil particles was slower than that of fine soil particles.In addition,the freezing rate decreased with the increase of temperature of upper surface of the geometry model.The displacement of fine soil particles was larger than that of coarse soil particles during freezing process;besides,the displacement of soil particles distributed gradedly was significantly larger than that of particles distributed evenly.The displacement of soil particles decreased gradually with the increase of freezethaw cycles during freezing process.The variation regularities of parameters against time and the influence of the freeze-thaw cycles on frost heave and heat and moisture transfer during freezing process was analyzed by the acquisition of temperature,water content inside the soil and displacement on the upper surface of soil based on the indoor frost heave experiment platform.The experimental results showed that the sudden change of water content and water potential of soil occurred during the process of state transition of freezing and thawing.The difference of state transition temperatures during freezing process and thawing process was discovered by analyzing the variation regularity of water content against temperature of soil.Frost heaving amount,mainly coming from the top layer of soil in this study,decreased with the increase of freeze-thaw cycles.Comparing the variation of frost heaving rate against the count of freeze-thaw cycles obtained from numerical method and experimental method,the variation trends of both above fit well,hence the accuracy of the numerical model in this study was verified.