This study investigates the rapid freezing behavior of saturated clays under large thermal gradients. Although the freezing characteristics of soils under natural/low thermal gradients such as ice lens formation and water migration have been extensively studied, the freezing of a saturated soil under a large thermal gradient is not understood. This study presents rapid freezing tests to examine the freezing behavior of saturated fine-grained soils in a closed system under large thermal gradients using liquid nitrogen (LN). Temperatures are measured inside specimens during freezing and micro-CT visualized internally after freezing. Results show that large thermal gradients develop near the surfaces of specimens upon their submersion in LN. The specimens freeze homogeneously, and no visible ice lenses form, owing to the insufficient time for water migration and ice segregation under rapid freezing. The specimens fracture and split into major pieces, under no confining stresses in this study; freezing first occurs near the boundaries, and the freezing front propagates inward, creating temporal, differential volume changes between the outer and inner parts of the specimens, which leads to fractures in the unconfined state. The fractures affect subsequent temperature propagation and thermal gradients.

中文翻译：

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大温度梯度下饱和粘土的快速冷冻

本研究调查了饱和粘土在大温度梯度下的快速冻结行为。尽管已经广泛研究了自然/低热梯度下土壤的冻结特性，例如冰透镜形成和水迁移，但尚未了解饱和土壤在大热梯度下的冻结。本研究提出了快速冷冻试验，以检查使用液氮 (LN) 在大热梯度下封闭系统中饱和细粒土壤的冷冻行为。在冷冻过程中测量内部标本的温度，冷冻后在内部可视化显微 CT。结果表明，当样品浸入 LN 时，在样品表面附近会产生大的热梯度。标本冻结均匀，没有可见的冰晶形成，由于在快速冷冻条件下水分迁移和冰分离的时间不足。在本研究中，试样在没有围压的情况下断裂并分裂成大块；冻结首先发生在边界附近，冻结前沿向内传播，在试样的外部和内部之间产生时间上的差异体积变化，从而导致无侧限状态下的断裂。裂缝影响随后的温度传播和热梯度。这会导致无约束状态下的断裂。裂缝影响随后的温度传播和热梯度。这会导致无约束状态下的断裂。裂缝影响随后的温度传播和热梯度。