Compaction mechanics of unsintered snow layers based on particle image velocimetry techniques

The knowledge of snow response under applied loads, particularly the deformation process during compaction, is important for avalanche modeling and cold region engineering. This paper is devoted to analyzing the deformation process of unsintered snow layers under compaction loads. An experiment framework that allows the observation of the unsintered snow deformation process on the symmetric plane of indentation is utilized along with the particle image velocimetry (PIV) technique. The experiment results show that during deformation, the snow particle velocity field can be categorized into four types: Type A, initial velocity field; Type B, vertical velocity field; Type C, shear band velocity field; and Type D, irregular velocity field. The shear band in loose snow beneath the compacted zone in Type C is the main difference between the deformation processes of snow samples with small and large initial depths, and it is also the key driver of the “egg shell” compaction effects in snow samples with large initial depths. The 150 mm depth sample exhibited the most regular compaction zone, with the Type B velocity field dominating for over 90 % of the duration. In contrast, the 300 mm depth sample displayed the most pronounced “egg shell” structure, with a 21.6 % density decrease between the surface and underlying layer. The findings in this study provide guidelines for developing construction methods and procedures for snow runways and roads, and can be utilized as a database for the validation of snow compaction numerical models.