The study of water vapour transfer in unsaturated expansive soil

On the basis of the gas state equation, fluid mechanics, soil mechanics theory and characteristics of unsaturated expansive soil. The water vapour flow per unit area method of calculating is geted. It revealed that the water vapour flow is co-decision by temperature, soil and water situation. and it is directly proportional to the suction gradient. and it has non-linear relationship between soil porosity, water saturation, the absolute temperature and suction. According to the calculating of test data to illustrate the feasibility of the method of calculation, in order to further study lay the foundation for migration of water vapour.