In order to study the relationship between the initial dry density, water content and free swell ratio, the indoor test on free swell ratio of expansive soil in the subgrade of Louyi expressway was carried out. The results show that when the initial water content is constant, the free swell ratio of expansive soil will increase with the increase of dry density; when the dry density is constant, the free swell ratio diminishes with the increase of water content. The free swell model and time function model were established for the expansive soil in the subgrade of Louyi...