Research On Translocation Of Moisture-heat-salt Mechanism Of Roadbed In Seasonal Freezing Area

Seasonal freezing soil lies on the northward area of north latitude 30°in our country and it occupies about 53.5 percent of the acreage of whole country. Seasonal freezing soil is a kind of special soil-water system in which there is ice crystal, and it is geology object composed of soil grain, ice, pore water, and gas. Freezing in soil makes water transfer to frozen area, and it plays a very important role in the research of agriculture,water resources,environment and engineering. Seasonal frozen damage is a very important problem in building road in the north of our country. The problems of swelling,salt expansion and road mudding all come of moisture,heat and salt translocation. With the development of resource,engineering construction,environmental protection in freezing and polar areas, the research of moisture,heat and salt transfer in roadbed soil is causing more concern. Accurately understanding the mechanism of salt expansion is the demand of the constructing and development of the saline soil area engineering. The sulfuric acid saline soil is a typical saline soil which is harmful to the engineering structure. Based on the mechanism of moisture,heat and salt transfer, this article do the following work in order to grasp and control the dynamics and process of moisture,heat and salt transfer.(1)On principle of simplifying model and having not any effect on the rule of transfer, basing on conservation of energy, the author set up basic partial differential equation of moisture movement,heat transfer partial differential equation and solute migration basic equation. Moisture movement equation: Heat transfer equation:Salt movement equation:(2)Through the analysis of the dynamic variation law of moisture,heat and salt at different freezing time in the system of freezing soil, it finds that: The moisture content increased within the scope of the upper soil layers mainly concentrated in less than 1m, the frozen section is not greater than the temperature gradient above permafrost, and as the moisture and the heat transfer, the salt changes in the performance of increased-decreased- increased. With the contrast of calculated result and actual measurement, it finds that the couple model is reasonable.(3)The stress-strain equation is solved by the finite element method in time step of finite difference method, it finds that: the settlement of surface displacement in the center of roadbed is bigger than on the hard shoulder which is symmetrical. Through the comparison between the fourth and fifth cross-section of displacement in roadbed, it demonstrates that the insulating layer can effectively improve the stability of roadbed in the seasonal freezing soil of sulfuric acid.