Swelling deformation of expansive soil due to moisture absorption often leads to safety problems of engineering. Taking Nanyang mid-expansive soil as research object

the triaxial expansive experiment has been realized by improving the water inlet control system and the measurement of external volumetric strain. And the relationship between the volume expansion rate after sufficient moisture absorption

the final water content and the initial water content

the average principal stress has been obtained through the triaxial expansive test. Experimental results show that the volume expansion rate and final water content in different stress states decrease while the cover load or the average principal stress increases

which has a good linear relationship in semi-logarithmic coordinates. Through theoretical derivation

the unified relationship and expression of expansion models in different stress states are established. And applying the expansion model in the numerical calculation

law of stress field distribution of expansive soil slope considering swelling deformation is analyzed; plastic zone developing character of expansive soil slope with different expansion grades in the condition of sufficient moisture absorption is compared; effect of replacement measures with different treatment thicknesses is proved. Operation of this expansive experiment is simple

and the expression of this model is relatively concise

whose parameters are easily obtained. This model can be used in numerical calculation and simplified calculation

which has good practical value.