Through the indoor free load swelling rate test，Yichang City，a section of a highway reconstruction project of expansive soil were studied. Key analysis free load swelling rate of a non-load time，the proportion of mixed sand，the relationship between the initial dry density， experimental studies have shown that：Free load swelling rate is mainly divided into rapid expansion，slow expansion and eventually stabilize in three stages；during the initial dry density is constant，weathered sand soil free load swelling rate will increase the proportion of sand mixed with the rapid decrease slowly after the first lower，weathered sand soil modified free load swelling rate is not sensitive to the amount of sand mixed；in the same mixed sand ratio， weathered sand soil free load swelling rate increases with increasing initial dry density increases rapidly between them have a good linear correlation，expansive soil subgrade construction in progress when control of the initial dry density，to help reduce its swelling deformation，ensuring the stability of embankment.