Based on the theory of soil seepage and evaporation

the interaction model of atmosphere-unsaturated soil is established.With the field observations of climate as the boundary conditions

numerical simulation of soil water migration in foundation is investigated to obtain the dynamic distribution of moisture content in foundation soil under atmospheric influence.The results show that the changes of soil water content in foundation decrease with the increase of the depth

and they are not affected by atmosphere below the depth of 3.5 m.So the depth of atmospheric influence on expansive soil foundation in Nanning is 3.5 m.On this basis

a method for deformation of expansive-soil foundation is proposed to consider the wetting-drying effect and the change of water contents at 1.0 m depth based on the research results of wetting-drying effect on shrink and expansion of expansive soil.By the aid of an engineering example

a comparison is made with the traditional method to illustrate that this new method is more suitable for engineering practice.