Study On The Influence Mechanism Of Frost Heave Characteristics Of Saturated Graded Soils

Frost heave mainly occurs in the frozen fine soil with sufficient water supply in the cold area projects.The soil is often affected by the content of fine particles in the soil,and the frost heave will cause obvious damage to the highway,building foundation,pipeline and other infrastructure in the seasonal frozen area.Therefore,it is of great significance for engineering construction in cold regions to understand the variation law of freeze-thaw process of saturated graded soil,build a comprehensive model that can be used to simulate the freezing process of saturated graded soil,and carry out research on the effect of fine grain content on frost heave characteristics of graded soil under the open system.In this thesis,two kinds of quartz sand and powder with definite particle size were used as test materials,and the basic physical properties of the samples were tested by mixing the soil with different fine grain contents.Then,by building an indoor soil freezing experiment platform,controlling the soil sample gradation,cold boundary temperature and water supplement method,the unilateral saturated gradation soil frost heaving experiment was carried out.Experimental studies have shown that with the increase of the content of small particles and temperature gradient,the freezing area deepens,the freezing rate of graded soil increases significantly,the temperature stability time in the soil sample prolongs,and the water supply and frost heaving amount also increase significantly,the ice lens and the freezing front move steadily towards the lower end of the soil sample.At the same time,the water supply has a direct effect on the continuous frost heave and the thickness of ice lens in the later freezing period of soil sample,and the frost heaving caused by supplementary water is the main part of the total frost heave,and the water supply time has a certain delay.In addition,based on saturated soil seepage theory,heat conduction theory and force balance,a water-thermal-mechanical coupling model of saturated graded soil freezing was established considering particle level pairing.The PDE module in COMSOL is used for coupling solution of the model,and the correctness and reliability of the model are verified by comparing the results of experiments and references.The concept of geometric mean grain size was introduced,and the corresponding hydraulic and thermal parameters were obtained according to the grain grading scheme.The effects of fine grain content,temperature gradient and initial water content on the frost heave characteristics of saturated graded soil were studied,and the influence mechanism was analyzed.The potential relationship between the thickness of ice lens and temperature and stress was explained.The results show that both fine particle content and initial water content in soil samples affect the freezing depth of soil,and then affect the freezing front and the ice lens position,but the influence of temperature gradient is more significant.With the increase of the content of small particles,the more bound water content on the surface of fine particles,the more air enters the soil sample during the freezing process,the more water replenishment,and the more obvious frost heaving.The frost resistance of saturated graded soil is affected not only by fine grain content and temperature gradient,but also by initial water content.When the initial water content grows up,the amount of frost heave of graded soil also increases.The formation of ice lens is greatly affected by soil permeability coefficient and temperature gradient.The number and thickness of ice lens soar up with the increase of fine grain content as well as temperature gradient.The negative pore water pressure gradient appears near the freezing front and increases with the expansion of frost layer.The existence of negative pore water pressure gradient is the main driving force of water migration in saturated soil,which directly affects the external water migration above the freezing front.The influence mechanism of frost heave characteristics of gradated soil is discussed,which provides much reference for engineering construction and application of gradated soil in cold region.