The Modification And Application Of Salt-Frost Heave Deformation Theory Of Sulphate Salty Soil Subgrade

With the reciprocal influence of moisture, salt, heat and stress, sulphate salty soil can cause pavement salt expansion crack, aggravate frost heave, boil and pavement erosion. For the lack of four-field coupling theory during salt expansion and numerical analysis of salt-frost heave deformation of sulphate salty soil, it is necessary to research on the mechanism and rule of salt-frost heave deformation of sulphate salty soil, to provide the basis for road construction and road disease prevention.To precisely calculate the salt-frost heave deformation of sulphate salty soil, the paper improves the four-field coupling theory according to the mechanism of salt-frost heave deformation primarily. In the next section of this paper, the theory is applied to Comsol Multiphysics finite element software, to calculate the salt-frost heave deformation of the road subgrade test section of sulphate salty soil of Xinjiang agricultural21th-24th group. In the third part of this paper, the result of calculated value and simulation value of displacement are compared. The main research contents and results are as follows:(1) Based on hydrodynamic model and the law of conservation of mass, the equivalent salt content and equivalent moisture content are established in the equations of moisture field and salt field, which simplified the coupling dynamic model of moisture-salt-heat-stress during salt expansion processes of saline soil as the coupling factors. Two important effects which include the effect of solute diffusion and hydrodynamic dispersion and the effect of phase change of salt crystals-salt solution on salt transfer have been taken into consideration. According to the conservation of energy, the effect of saline soil’s phase change latent heat is added which makes the equation of temperature field more fitted for the practical situation of engineering.(2) In order to implement the calculation of salt-frost heave deformation, the reaction rate of glauber’s salt is added and the frost heaving and salt expansion is taken into unified consideration.(3) The field test section of the ulphate salty soil subgrade was selected in Xinjiang and the local subgrade temperature, distribution of moisture and salt, salt-frost heave deformation law of subgrade were monitored long-termly. The data of temperature, salt and salt-frost heave deformation has been analyzed. From these values, the law of salt-frost heave deformation is obtained.(4) The modified theory is applied to Comsol Multiphysics finite element software, and the improved parts include:the physics of transport of diluted species in porous media including reaction which is added into the salt transfer; the temperature field useing the physics of heat transfer in porous media, setting three different solid including soil, ice and glauber’s salt, and adding the effect of saline soil’s phase change latent heat. In the physics of solid mechanics, both the elasticity of material and the volume increase of ice, especially glauber’s salt, are considered.(5) The model is verified by contrasting the result of calculated value and simulation value which combines the data from the field samples of Xinjiang.The study of this paper can give a reference to the calculation of salt-frost heave deformation of sulphate salty soil subgrade.