Curing- and confinement-dependent mechanical behavior of loess–slag backfill: A fractal-informed constitutive interpretation

• Curing enhances backfill stiffness through fractal refinement of pore topology. • The pore fractal dimension D f 0 shows a strong non-linear link with stiffness K . • Confinement regulates damage scaling via AE b min and fractional order α . • Distributed damage under confinement promotes ductile deformation stability. • Post-peak softening correlates with damage-induced fractal degradation Δ D f . The mechanical performance of cemented backfill in deep engineering environments is jointly governed by curing-induced microstructural evolution and confinement-controlled deformation processes, yet their respective roles and interactions remain insufficiently understood. In this study, the curing- and confinement-dependent mechanical behavior of loess–slag backfill was investigated through triaxial compression tests, acoustic emission (AE) monitoring, mercury intrusion porosimetry (MIP), and a fractional-order constitutive interpretation focused on the stable hardening regime. Results indicate that curing primarily enhances intrinsic stiffness by refining pore network topology. This effect is quantitatively captured by the monotonic increase in the intact-state pore fractal dimension ( D f 0 ) and its strong non-linear correlation with the generalized stiffness coefficient ( K ). In contrast, confinement regulates the damage evolution pathway. The minimum AE b-value ( b min ) correlates strongly with the fractional order ( α ), revealing a fundamental transition from localized brittle cracking to distributed ductile deformation. Furthermore, post-peak softening behavior is shown to be closely linked to damage-induced fractal reorganization, with a strong monotonic relationship between the softening index B and the fractal-dimension increment Δ D f , highlighting the role of fractal preservation in maintaining post-peak stability. Overall, this study provides a fractal-informed constitutive interpretation that clarifies how curing and confinement jointly control stiffness development, deformation mode, and failure stability of loess–slag backfill, offering insights for the design and optimization of cemented backfill systems under high-stress conditions.