"A Physics-Informed Unified Constitutive Framework for Sands and Clays: Critical State Consistency, Fabric Evolution, and Predictive Multi-Scale Seismic Response"

A long-standing limitation in constitutive modeling of geomaterials is the entrenched dichotomy between sands and clays, which has hindered the development of frameworks that remain predictive across the full spectrum of soil types, densities, plasticities, and saturation conditions. This study introduces a physics-informed, unified constitutive framework for granular–cohesive geomaterials that integrates the principles of Critical State Soil Mechanics with advanced multi-scale formulations to capture both static and dynamic behavior, from small-strain cyclic response to large-deformation failure and liquefaction phenomena. The proposed model achieves critical state consistency while systematically addressing deficiencies in existing formulations—most notably the fabric evolution inconsistencies observed in established approaches such as Dafalias–Manzari (2004). The framework employs a generalized state parameter that intrinsically couples stress, strain, density, plasticity index, and degree of saturation, thereby eliminating the need for excessive empirical calibration. A novel tensorial description of fabric evolution is incorporated, enabling accurate prediction of anisotropic hardening, cyclic mobility, and pore pressure build-up under complex loading paths. Furthermore, the model preserves objectivity and stability across monotonic, cyclic, and irregular seismic loading scenarios, with predictive robustness validated against a broad suite of laboratory element tests and numerical simulations. Results demonstrate that the unified formulation not only reproduces the characteristic signatures of both sands and clays at critical state, but also delivers accurate forecasts of strain accumulation and pore pressure evolution in transitional soils. This work establishes a pathway toward next-generation constitutive theories that reconcile the physics of granular and cohesive behavior, offering a versatile and implementable tool for advanced geotechnical earthquake engineering applications.