Dynamic behavior of coarse-grained materials with different fines contents after freeze-thaw cycles under multi-stage dynamic loading: Experimental study and empirical model

The effect of freeze-thaw (F-T) cycles on dynamic behavior of coarse-grained materials (CGMs) (i.e., coarse-grained materials used in railway subgrade named as base course materials) is critical to ensure the service status of railway subgrade in seasonally frozen regions. In this study, a series of stress-controlled dynamic triaxial tests were conducted on CGMs with various fines contents (FCs) exposed to F-T cycles. Typical test results were then analysed and discussed, highlighting the environmental effect on the dynamic properties. The results demonstrated that the dynamic shear modulus decreased with the increase of FC or the number of freeze-thaw cycles (N_FT), but the damping ratio (D) results indicated just the reverse characteristic. In this regard, a modified empirical model was determined to describe the relationship between dynamic shear modulus (G_d) and dynamic shear strain amplitude (γ¯_d). Meanwhile, a unified mathematical formula was proposed to characterize D. Furthermore, the two proposed empirical equations were found to be severely inconsistent with the previous ranges suit for seismic loading. The study provides a useful reference for preliminary evaluation of the response to train loading for CGMs subjected to F-T cycles.