Abstract: Determining the long-term mechanical properties of red mudstone under the influence of moisture is crucial for evaluating the long-term stability of geotechnical structures. Firstly, laboratory tests were first conducted to determine the clay mineral content, water absorption, expansibility, and peak strength of triaxial tests under different immersion conditions. Subsequently, graded loading creep tests were performed on samples with different immersion times, and the effects of different load levels and immersion times on creep characteristics were systematically compared. Finally, the moisture damage factor was introduced to establish an improved Burgers creep model, whose accuracy was verified through parameter inversion and numerical analysis. The results show that the stress-strain curve of red mudstone under the action of water changes from strain softening to strain hardening. The creep characteristics of red mudstone under external load are significant and affected by the damage effect caused by water content. As the stress level and moisture content increase, both the stable creep rate and the ratio of creep strain to instantaneous strain increase. Under the influence of moisture, the long-term strength of red mudstone is lower than its instantaneous strength, with a strength loss rate of 19.8% after 30 days of immersion. The modified Burgers model improved by introducing damage factors has high fitting accuracy and can provide a reference for the long-term stability of structures such as slopes, tunnels, and dams in red mudstone areas.

Key words: red mudstone, creep, creep deformation, constitutive model, Burgers model