Experimental study of the dynamic characteristics of Songhua River silt with fine grains under freeze-thaw cycles using asymmetric hysteresis

The contact and bonding of soil particles are affected by the fine particle content of silty sand and the freeze-thaw cycle effects in the seasonal frozen zone, which are reflected as the dynamic characteristics of silty sand from the macroscopic point of view. The dynamic stress, dynamic shear modulus, dynamic shear modulus ratio, and damping ratio of Songhua River silt with different contents of fine soil particle (less than 0.075 mm) after repeated freeze-thaw cycles were studied respectively using a low-temperature dynamic triaxial test system and were compared with those of quartz sand. In order to approach the real test results, a piecewise equation was used to solve for the dynamic parameters. The results show that repeated freeze-thaw cycles have a great influence on reducing the dynamic stress, the dynamic shear modulus, and the dynamic shear modulus ratio, while they increase the damping ratio. For a given fine particle content and number of freeze-thaw cycles, the dynamic stress, dynamic shear modulus, and damping ratio of the Songhua River silt with fine particles are larger than those of quartz sand when the dynamic strain reaches 0.2%, and the difference gradually decreases as the number of freeze-thaw cycles increases. The dynamic shear modulus of the Songhua River silt with fine grains decreases more slowly with increasing dynamic strain than that of quartz sand. Therefore, a normalized empirical model was established to describe the relationship between the dynamic shear modulus ratio, the damping ratio, and the dynamic strain. This model is suitable for Songhua River silt with different fine particle contents and numbers of freeze-thaw cycles, and it provides good prediction results. Furthermore, the evolution of the model parameters with the experimental conditions was analyzed, and the limit value of the fine particle content was determined to be 10%. After repeated freezing and thawing, the influence of the fine particle content on parameters a and c weakened. The regression relationship between the model parameters and the test conditions can be described by a binary quadratic equation. It is suggested that the soil parameters should be used for the dynamic response analysis of Songhua River silt with fine grains after five freeze-thaw cycles.