Wrapper-based integration of a thermo-hydro-mechanical hypoplastic bentonite model in OpenGeoSys via MFront

This paper presents the implementation of a hypoplastic thermo-hydro-mechanical constitutive model for bentonite into the OpenGeoSys (OGS) simulation platform using a wrapper-based interface with the MFront code generation tool. The model, originally developed as a stand-alone model in the Triax platform, features a double-structure formulation that captures micro- and macroscale interactions, as well as suction and temperature-dependent mechanical responses of bentonite relevant to engineered barrier systems in deep geological repositories (DGR). The integration strategy preserves the validated legacy implementation of the model while enabling its use within modern multiphysics simulations through a modular MFront wrapper. Verification is performed using single-element benchmarks in Triax and MTest , demonstrating numerical consistency. The implementation is validated by simulating two laboratory experiments on Czech bentonite (BCV), showing good agreement with experimental measurements and with reference results from the Sifel code. The developed interface provides a robust and flexible framework for coupling advanced bentonite models with large-scale geotechnical simulations for application in the integrity and performance assessments of bentonite barriers in the scope of safety assessment of DGR.