Laboratory observation and analysis of frost heave progression in clay from the Qinghai-Tibet Plateau

Frost heave has great impacts on the thermal and mechanical stability of structural foundations in cold regions. To account for these impacts, it is necessary to evaluate the soil frost heave process induced by water migration and ice segregation under different temperature gradients. By using the digital image processing Technology (DIPT), a series of laboratory one-dimensional freezing experiments were taken to investigate the ice lens formation, water migration and their distribution characteristics in the Qinghai-Tibet clay. The obtained results showed that the freezing front reached a stable state when a certain temperature gradient has been applied to the soil column for about 24 h. After that, the frozen parts in soil columns could be divided into three main zones along their longitudinal direction according to their morphological characteristics, change patterns and the contributions to sample deformations. There were the zone A in which very thin ice lenses were developed, the zone B in which thin ice lenses were developed, and the zone C in which a thick ice lens was developed. It was found that the ice segregating in the zone B had a significant influence on the soil frost heave, while ice segregating in the zone C caused consolidation in unfrozen zone. Generally, the segregating temperature happened in the zone B and zone C was between −0.31 °C and −3.53 °C. By analyzed the Computed Tomography (CT) pictures obtained from tested samples, we had reasons to believe that the inner cracks and gaps between irregular polygons had provided pathways for water migrating from unfrozen zone to frozen zone, especially to the zone B and zone C and resulted in sample's frost heave and consolidation finally.