Abstract: In the process of unidirectional freezing, the generation and development of segregating ice is an important factor affecting the structural characteristics of frozen and thawed soil. Three unidirectional freezing boundary conditions were selected, i.e., cooling rate (from 0.5 ℃/s to 0.005 ℃/s), cold temperature (from –30 ℃ to –70 ℃), and water replenishment (no water replenishment, constant pressure water replenishment) to explore their influence on the development of segregating ice. To facilitate the measurement of segregating ice, an independent meso-measurement system has been developed using optical microscope digital photography. This system enables in-situ and non-contact measurement of segregating ice cracks. The experimental results demonstrate the following findings: (i) The distribution of segregating ice is not only influenced by temperature gradients and warm end replenishment conditions, but also by the cooling rate at the cold end of the unidirectional freezing process. (ii) The width of the segregating ice in the frozen area is more significantly affected by the movement rate of the frozen front than by the temperature gradient. (iii) During the freezing process, the width of the frozen ice exhibits an exponential relationship with the movement rate of the 0 ℃ line. Based on this characteristic, an empirical formula is proposed to predict the crack width of segregating ice in the frozen zone. This formula can be used as a reference for evaluating unilateral frost heave failure in practical engineering construction, particularly under conditions of varying cooling rates.

Key words: unilateral frost heaving, cooling rate, clay, segregating ice cracks, ultra low temperature