Study On The Calculation Method And Application Of Salt Expansion Of Subgrade In Sulfate Soil Area

Saline soils are mainly distributed in the arid regions of northwest China,of which Xinjiang is the province with the largest area and the widest distribution of saline soils in China.In recent years,the demand for developing transportation in sulfate-stained land areas has become more and more prominent.Due to the unique solubility of sulfate,the salt expansion of roadbed has become one of the many problems that plague engineering practice.Therefore,it is necessary to deeply research the water-salt migration law and the development process of salt swelling deformation of roadbed in sulfate-soiled soil areas,so as to provide a theoretical basis for road construction and maintenance in sulfatedsalted soil areas in Xinjiang.The research takes the sulfate soil subgrade in the Yanqi reclamation area of The Second Division of Xinjiang Production and Construction Corps as the main research object,and uses COMSOL Multiphysics 5.5 to establish the subgrade finite element model in order to study the migration law of moisture and salt in the subgrade.Moreover,by applying the deduced salt expansion calculation method,the model is able to predict the development of roadbed salt expansion.The main work and corresponding results are summarized as follows:(1)By establishing the calculation model of subgrade water-salt-heat,the migration and distribution law of moisture and salt in subgrade under the influence of temperature and evaporation intensity within one year is analyzed.The changes of water content and salt content of subgrade with time at different locations were studied.(2)Analyze the migration and distribution law of moisture and salt in the roadbed within four years.(3)According to solubility and the type of precipitated crystals,the crystallization process of sodium sulfate in the soil under ideal conditions is divided into three stages.Based on the above premise,The theoretical amount of sodium sulfate crystallization in different stages and the theoretical salt expansion ratio of sulfate saline soil are deduced and amended,and the calculation method is verified。(4)Apply the derived salt expansion calculation method to predict the salt expansion deformation of the subgrade under actual working conditions,and analyze the variation law of the salt expansion amount at different positions on the top surface of the subgrade with time.