<p>The Mesri constitutive model is extensively employed for characterizing the creep behavior of sliding zone soils in landslides, given its capacity to accurately forecast the creep behavior of diverse clay types. Utilizing the sliding zone soil from the Tongqu Village landslide in Nanyang City as a case study, this research performed conventional triaxial tests and triaxial creep tests with a coarse-grained soil triaxial creep apparatus, as the soil predominantly comprises silty clay interspersed with a minor quantity of gravel. The cohesion, internal friction angle, and the changes in shear strength under various confining pressures were determined for both the natural water content and saturated conditions. Mesri creep models were formulated for distinct water contents and confining pressures.The results provide clear evidence that the accumulated creep strain from time-dependent effects shows a significant 10–39% increase compared to instantaneous deformation.The Mesri model developed in this study accurately characterizes the creep behavior of the landslide slip zone soil, as evidenced by a root mean square error (RMSE) below 0.15% and a coefficient of determination (R²) generally surpassing 0.95. Furthermore, a significant reduction in shear strength—ranging from 28 to 44%—was observed under saturated conditions compared to the natural state, underscoring the profound influence of moisture content on long-term strength. The model proves particularly effective in describing the steady-state creep rate and accurately captures long-term creep characteristics, independent of variations in stress level. Consequently, this research establishes a theoretical foundation for assessing the long-term stability of landslides.</p>