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Abstract The offshore and seabed silty clays are typical chloride saline soils since they are soaked in seawater. This paper aims at characterizing the frost heave mechanism of chloride silty clay. A series of open-system one-dimensional frost heave tests were conducted on chloride silty clay to investigate the frost heave and water-salt migration during freezing. The Nuclear Magnetic Resonance(NMR) relaxometry tests were performed to obtain the pore-size distribution of specimens at a specific time of interest during freezing. The internal relationship between microstructure change and frost heave was discussed. The results of open-system one-dimensional frost heave tests indicated that the propagations of freezing front，water-salt migration and frost heave were dependent on the salt content. The freezing front quickly developed，moved at a high rate and then gradually stabilized. The location of the freezing front at the thermal equilibrium was farther away from the cold end in a lower-salt content specimen. The water potential gradient was higher in lower-salt content specimen，driving more water-salt migration. The frost heave decreased with increasing the salt content and the solution intake induced frost heave dominated in the total frost heave. At the end of freezing process，the frost heave ratio increased and then decreased with increasing the salt content. It was found out that a threshold(i.e.，1% salt content) existed，at which the minimal frost heave ratio could be identified. The NMR results indicated that mesopores account for the main part of specimen voids and mesopores transformed into macro- and micropores during freezing. The lower the salt content，the greater the transformation ratio of the pore volume. For that more amount of water-ice phase change can be identified in low-salt content specimen，leading to more significant microstructure change. Consequently，the specimen with lower salt content experienced a larger amount of frost heave.
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