In the cold region, frost heave damage in water conveyance channels constructed on expansive soil poses a significant threat to project sustainability. This study aims to investigate the evolution and physical mechanisms of frost heave inhibition by soilbags for expansive soils with varying water contents and dry densities. Standard calibration tests for sample preparation and frost heave deformation tests were conducted on expansive soils with and without soilbag constraints. The test results demonstrate a direct correlation between the compaction height of the sample and its dry density, enabling precise control of the dry density by adjusting the compaction height. Regardless of the presence of soilbag constraints, the relationship between frost heave deformation and time can be divided into three stages: cold shrinkage, rapid freezing and freezing stability. The frost heave of the expansive soil was significantly reduced under the restraint of the bag for samples with the same initial state, indicating that the soilbag can effectively inhibit the frost heave of the expansive soil. Moreover, as water content and dry density increased, the frost heave rate of the samples exhibited a significant increase. The frost heave inhibition rate of the soilbag increased significantly with the increase of dry density, but it did not increase notably with increasing water content. The intrinsic mechanism of soilbag inhibiting frost heave of expansive soil is revealed using the theory of segregation potential and the principle of reinforcement constraint. A conceptual model of the skeleton structure of frozen expansive soil under the influence of soilbag constraints is proposed, based on the pore diameter distribution curve obtained through mercury intrusion porosimetry. This model better explains the variations in the evolution of frost heave inhibition rates of soilbags under different water contents and dry densities.
