Dynamic characteristics of carbonate saline soil under freeze-thaw cycles in the seaonal frozen soil region

The occurrence of road damage, such as frost heave and thaw settlement, is highly likely in saline soil subgrades in seasonally frozen areas due to traffic loads and freeze-thaw cycles (FTC). In this regard, a low-temperature dynamic cyclic triaxial test was conducted to investigate the dynamic characteristics of carbonate saline soil under traffic load. The study explores the impact of salt content (SC) and the number of FTC on the backbone curves, the dynamic shear modulus (TDSM), and the damping ratio (TDR) characteristics of saline soil. An improved H-D model was employed to derive the dynamic backbone curve, and TDSM and TDR empirical formulas were established.The study's results show that the backbone curves of saline soil exhibit typical nonlinear and strain-hardening characteristics. Additionally, a higher salt content or more FTC result in a smaller TDSM and a larger TDR of the remodeled saline soil. TDSM shows an inverted "S" shape with an increase in cyclic shear strain, and the decay rate of TDSM increases when the cyclic shear strain is greater than 10-4 and less than 10-3. The decay rate of TDSM decreases and approaches a constant value after the cyclic shear strain exceeds 10-3. The decay of TDSM of low-salt soils (salt content less than 0.5%) mainly occurs in the first six freeze-thaw cycles. In contrast, the decay of TDSM of high-salt soils (salt content more than 0.5%) remains highly dependent on the number of FTC. Furthermore, TDR show an flat "S" shape with an increase of cyclic shear strain. The rate of increase in TDR of low-salt soil decelerates after six FTC, while the rate of increase in TDR of high-salt soil decelerates after nine FTC. Finally, empirical formulas for TDSM and TDR were established by varying the fitting parameters. The results of this study provide a useful reference for engineering projects in regions that encounter seasonal freezing. These findings will assist engineers in the design and construction of structures that can withstand the detrimental effects of traffic loads and FTC.