Abstract: Rockfill is the primary load-bearing material in earth-rock dams, crucial for withstanding water pressure. Developing a constitutive model that accurately describes its mechanical properties is essential for predicting the stress and deformation in high earth-rock dam bodies. Based on triaxial drained test results, stress expressions describing the strength and dilatancy characteristics of rockfill are established. By analyzing the outcomes of rheological and wetting tests, flow rules for rheological and wetting deformations are formulated, and expressions for rheological and wetting moduli are constructed. This framework leads to a unified method for calculating rockfill loading, rheological, and wetting deformations within the generalized plasticity theory framework. The method’s validity is confirmed through simulations of triaxial drained, rheological, wetting, and combined triaxial rheological-wetting tests on rockfill.