Application of PIV in model tests on frozen unsaturated soils and grayscale correlation analysis

PIV is a velocity-measuring technique commonly used in the field of experimental fluid mechanics and geotechnical tests, but few previous reports are found on the use of this technique in frozen silty clay (especially unsaturated condition) due to the lack of surface texture. The self-made model test apparatus for frozen soil, Canon Eos camera and GeoPIV software, are used to analyze the movement of soil particles. The experiment results demonstrate that: (1) The constant light area is needed to be built in studio which significantly affects the PIV results. (2) Due to the insufficient surface texture of clayey soils, PIV cannot be used. Therefore, to allow the analysis, some materials are used to make the artificial texture of silty clay and the silica particles with a diameter 0.3 mm are the best tracking particles. (3) Change of ice-water phase during freezing will cause the grayscale variation of silty clay images inevitably. The minimum acceptable correlation coefficient tolerance for seed is 0.85 and the minimum correlation coefficient tolerance is 0.69 according to the statistical results.