Abstract: With regard to the problems in the free swell experiments and the evaluation of stabilized expansive soils,the free swell ratio method was introduced to evaluate the swelling capacity of lime and fly ash treated expansive soils.Based on the test results,the good linear relationships among the free swell ratio and the physical property parameters and the commonly used swell-shrinkage property parameters were identified.The possibility of using the free swell ratio in evaluating the swelling capacity of lime or fly ash stabilized expansive soils was shown,and its practicality had been approved through the utilization of the proposed method in practical engineering projects.