Climate change and human action significantly impact the state of soil, particularly saline and loess soils in China's arid and semi-arid regions. Infrastructure is continuously built on these problematic soil areas, making it crucial to study the impact of external factors on the engineering properties of subgrade soil. This paper proposes a test device by which a few physical conditions (salt content and temperature) can be controlled and the mechanics parameters (deformation and resilient modulus) of soil samples can be dynamically investigated. Using the proposed device, the resilient moduli of the samples collected from an in-situ highway project on different wetting–drying and salt washing–supplying paths were measured and analyzed. The results indicate that, for the same final moisture content, the modulus value of a soil sample subjected to the drying → wetting path is larger than that of a soil sample subjected to the wetting → drying path. Further, the resilient modulus of soil samples is weakened after multiple wetting–drying cycles, while the stiffness of soil samples obtained from high soluble salt content is lower than that of soil samples with the same initial soluble salt content. Finally, the proposed device is simple and convenient to use and provides a reliable method for exploring the mechanism of mechanical behavior degradation of saline and loess soils and the subgrade settlement in problematical soil areas.