Mechanical experimental characteristics and constitutive model of cemented sand and gravel (CSG) material under cyclic loading with varying amplitudes

Abstract Triaxial cyclic loading–unloading tests were conducted on cemented sand and gravel (CSG) specimens with cementitious contents of 20, 40, 80, and 100 kg/m ³ to elucidate their mechanical response under realistic engineering conditions. As the cementitious content increased, the hysteresis loops in both the stress-strain and volumetric strain-axial strain spaces evolved from near-elliptical to crescent-shaped, reflecting a progressive reduction in energy dissipation. During loading, the tangent modulus was formulated as a function of the volumetric stress ratio, whereas the nearly linear unloading–reloading paths enabled the use of their slopes to represent this ratio directly. Within the generalized plasticity framework, these findings yielded explicit expressions for the loading direction, shear-dilation relationship, and plastic modulus valid for both loading and unloading stages. On this basis, a twelve-parameter elastoplastic constitutive model was constructed, treating each stage as a coupled elastic–plastic process without invoking an explicit yield surface. Parameters were calibrated against the cyclic test data obtained at multiple amplitudes. Numerical simulations reproduced the observed stress-strain behaviour with high fidelity, demonstrating the model’s capability to capture the unloading-reloading characteristics of CSG and underscoring its applicability to engineering analyses involving cyclic loading.