(1. Schoool of Civil Engineering，Southwest Jiaotong University，Chengdu，Sichuan 610031，China；2. China Construction First Group Construction and Developwent Co.，Ltd.，Beijing 100102，China；3. China Communications Construction Company
Fourth Harbor Engineering Institute Co.，Ltd.，Guangzhou，Guangdong 510230，China)
Abstract：A novel apparatus，based on the ultrasonic-induced nucleation and solid refrigeration technology，was designed for the freezing point test of soils to solve the problems of“size effect”and“hypercooling”. The freezing temperature of NaCl solution measured by the apparatus was in good agreement with the relevant test results，which indicated that it had reliable accuracy and stable performance. On this basis，freezing point tests with different test methods and soil densities were carried out. Results shows that the soil sample could not be frozen uniformly under constant temperature condition，resulting in the different freezing state of soil samples and inducing the“size effect”. This problem can be overcome by the linear freezing mode. In order to analyze the influence of microscopic geometry characteristics of the soil sample on freezing temperature under different densities，the Fourier-Voronoi(FV) algorithm was used for the numerical reconstruction of the accumulation pattern of soil particles. The Pores and Cracks Analysis System(PCAS) was adopted to quantitatively analyze the pore characteristics of soil. It indicated that the most probable pore width had the strongest correlation with freezing temperature. The confinement effect of capillary porosity is more obvious when the dry density of soil increases and the pore between soil particles narrows，resulting that the formation of condensation nuclei is more difficult and the supercooling phenomenon is more outstanding. The ultrasonic pulse excitation can promote the random movement of water molecules，which increases the probability of condensation nucleus generation and eliminates the influence of supercooling on the freezing point test results. Therefore，the combination of the linear freezing mode and the ultrasonic excitation has a good application prospect in the freezing point test of soils.
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2021, Vol. 40 
