Study On The Influence Of Soil Particle Size Distribution For Frost Heave Level Of Frost Soil

The area of permafrost and seasonal frozen soils in China accounts for about 75% of the country's land area.Frost heave and thaw settlement in the soil are the causes of the frozen disasters in the frozen regions.In order to prevent frost heave and thaw settlement of traffic roads,buildings and other facilities,it is necessary to study the mechanism of the disease during soil freeze-thaw.At present,the research on the microscopic characteristics of soil frost heave is not sufficient.The related mathematical models mostly adopt the continuous medium model based on the discrete macroscopic continuous equations,and it is difficult to deal with the influence of the non-steady state microstructure on the degree of frost heave.Therefore,in this paper,the thermo-mechanical coupling method is used to study the influence of soil particle for frost heaving level,mainly including the following work:An indoor experimental platform of frozen soil for frost heaving was set up,and parameters such as temperature,displacement,and moisture content during freezing of frozen soil were collected.The surface temperature of the frozen soil was changed,and the variation of each parameter under different surface temperature conditions was studied and analyzed,and then the influence of the change of the upper surface temperature on the degree of frost heaving of the frozen soil was obtained.Experimental results show: during the freezing process,the water content and water potential in the freezing zone have dropped significantly,dropping by 68.9% and 136.1k Pa,respectively.The lower the upper surface temperature,the faster the water content and water potential changed in the frozen soil.When the upper soil was in a frozen state,the soil moisture content in the unfrozen areas has decreased very slightly,and the water migrated to the frozen edges.The amount of frost heave mainly comes from the phase change of the pore water in the surface soil.The lower the surface temperature of the frozen soil,the faster the freezing rate and the more obvious the change in frost heave,but when the surface soil is completely frozen,the maximum amount of frost heave was the same.It was 2.19 mm and the frost-heave rate was 1.83%.Coupling method analysis the problem emphasizes that a complete single field problem does not exist,and there are various interrelated effects between various physical phenomena.Therefore,based on the experimental results,the indirect coupling method was used to divide the soil frost heaving process into heat conduction and pore water expansion.The soil frost heaving mathematical model controlled by the non-steady-state conduction differential equations and transient kinetic basic equations of motion was established.The soil particle geometry model was established using the Matlab program of soil structure reforming.Model verification results show: The variation of the internal temperature during the freezing process of the soil model was consistent with the unsteady heat conduction process.The maximum amount of frost heave was 1.74 10-2mm and the frost heaving rate was 2.12%.The relative error between the simulated frost heaving rate and the experimental results is small(about 15.8%),which verified the validity of the numerical model.The numerical simulation study of the changes of soil internal temperature and particle displacement in freezing process was carried out,and the effects of particle radius,particle size distribution and soil surface temperature on frost heave of frozen soil were analyzed.Simulation results show:Soil with larger particle radius or smaller gradations had a larger volume fraction.During the freezing process,due to the small change in the overall temperature of the particles,the increase in the volume fraction of the soil caused the cooling rate of the soil to slow down and the internal temperature gradient was large.When the volume fraction decreases,the soil porosity increased,and when all the pore waters undergo phase transition condensation,the soil frost heave increased and the particle displacement increased.During the freezing process,when the soil surface temperature decreased,the soil freezing rate increased and the temperature gradient decreased.Therefore,increasing the radius of the soil particles,the temperature of the upper surface or reducing the size of the soil particle grading can help delay the occurrence of frost heave and reduce the degree of frost heave.