Investigation on frost heave of saturated-unsaturated soils

Frost heave is a process of coupled heat-water-mechanics, which refers to heat transfer, water migration, water-ice phase change, deformation, etc. The mechanism of the frost heave for saturated-unsaturated soils was investigated to establish a frost heave model. As the freezing continues, for saturated soils, because all pores are filled with pore water, the total increased volume due to water migration and water crystallization will separate soil particles and induce frost heave. For unsaturated soils, because of the existence of unsaturated pores, volume expansion generates by water and vapor migration and water-ice transition will firstly fill into the unsaturated pores until a critical state is reached. After that, further increased volume will separate soil particles and induce frost heave. Therefore, effective strain ratio was introduced to establish the relationship between frost heave strain of unsaturated soils and the fields of moisture and temperature. Tests were carried out for silty soil. Then, based on the inverse theory, a simplified criterion was proposed to determine the effective strain ratio, and the effective strain ratio was back-calculated according to the test results. Finally, an innovative universal frost heave model for saturated-unsaturated soils was proposed.