Experimental study on deformation characteristics of chloride silty clay during freeze-thaw in an open system

Abstract

Artificial ground freezing (AGF) is widely applied in coastal urban areas for underground transportation infrastructure construction. It is vital to understand deformation characteristics and the mechanisms of chloride soils during freeze-thaw (F-T) for the safe application of AGF. A series of unidirectional open-system F-t-tests were conducted to investigate the deformation characteristics of saturated clay with various NaCl content. Continuous measurements were performed on important parameters such as temperature, solution intake volume, frost heave, and thaw settlement during F-T. Besides, the pore size distributions were obtained via the Nuclear Magnetic Resonance relaxometry to help reveal the deformation mechanism. The results indicated that the freezing front propagated rapidly (Phase I) and then reached a plateau at the thermal equilibrium stage (Phase II). The location of the freezing front in Phase II was dependent on salt content. The amount of solution intake decreased with increased salt content. The rate of solution intake in two phases was also found to be salt content-dependent, while for a certain specimen the order of the rates in two phases varied with increasing salt content. The total frost heave for the same freeze time decreased with increasing salt content and the solution intake induced frost heave mainly contributed to the total frost heave. Total thaw settlement was relatively insensitive to the salt content of higher values. At the end of freezing and thawing processes, minimal frost heave ratio and thaw settlement coefficient were both identified in the specimen with 1% salt content. Moreover, the evolution of pore structure was found to be more prominent in specimens with lower salt content due to more water-ice phase change during freezing, which caused more significant frost heave.