Hydro-mechanical interactions govern the deformation of granite soil-rock mixtures (GS-RM) under cyclic drying and wetting. However, a limited understanding of the underlying mechanisms restricts their reliable application as engineering fillers. This study performed a series of conventional triaxial compression tests on GS-RM subjected to drying-wetting cycles, with cycle numbers \(\:{N}_{DW}\:\) = 0, 1, and 5 and confining pressures \(\:{\sigma\:}_{c}=\:\) 100, 200, and 300 kPa. Based on the experimental analysis, a corresponding critical-state elastoplastic constitutive model for the GS-RM was established. The results indicate that the drying-wetting cycles deteriorate the mechanical properties of the mixtures. After five drying-wetting cycles, reductions of 15.6%~20.1% in shear strength and 41.7%~57.5% in shear modulus were observed, respectively, within the investigated confining pressures. Additionally, volumetric strain increases with the number of cycles, although higher confining pressure partially alleviates the degradation. Based on the experimental analysis, an empirical relationship between state parameters and the cycle number was established, yielding a modified state-dependent constitutive model. Validation results on GS-RM confirm that the proposed model accurately captures its mechanical response and degradation trends, including strain hardening and volumetric contraction during loading. Additional verification against comparable data indicated that the model also effectively captures the primary mechanical response and degradation trends of other water-softening soil-rock mixtures (SRMs), particularly the transition from volumetric contraction to dilation during loading. This research provides a theoretical reference for the design and evaluation of SRM filling structures.
