Consistent dilatancy-based constitutive model of rock salt for geo-energy storage applications: An open-source numerical implementation

Accurate numerical simulation of salt cavern performance in underground geo-energy storage of hydrogen, natural gas, compressed air, and CO 2 requires the integration of precise design criteria into a rigorous mechanical constitutive framework. This framework should be consistent with the design criteria, describing all mechanical loading (either short or long-term) deformations with a single parameter set. Due to methodological disconnects between the experimental derivation of design criteria and constitutive laws, only a limited number of consistent constitutive models exist in the literature. The RTL2020 model exemplifies such a mechanical constitutive law by incorporating dilatancy both as a feature in the mechanical constitutive model and as a design criterion, enabling accurate prediction of either short- or long-term mechanical deformations, including volumetric strain, with a single parameter set. This study presents a novel numerical implementation strategy for the RTL2020 model within an open-source simulator. The approach employs a stress–strain update algorithm using Newton–Raphson iterations with an adaptation of the classical implicit integration scheme (elastic predictor-inelastic corrector). This formulation ensures unconditional stability, rapid convergence, high numerical accuracy and low computational cost at the constitutive level. Validation against experimental data confirms the model’s capacity to reproduce key mechanical behaviours of rock salt, including the negligible influence of mean pressure on axial and deviatoric strains and the strong sensitivity of volumetric strain to mean pressure. These results underscore the robustness of our implementation. Application of the model to numerical triaxial cyclic-loading simulations further reveals a profound dependence of deformation rate and mechanism on loading frequency and stress amplitude, which has important implications for the long-term performance of hydrogen storage caverns in rock-salt formations. The model is open-source, making it readily accessible to the geomechanics community as a reliable tool for salt cavern design in geo-energy storage.