Reliable prediction of geomaterial behaviour is essential for risk informed design of resilient geosystems. This requirement is becoming increasingly important not only for terrestrial geo-disaster reduction, but also for future extraterrestrial surface engineering. Lunar regolith is a highly irregular granular material formed by long term impact and space weathering processes. Its mechanical behaviour differs markedly from that of terrestrial soils because of low stress levels, ultra high vacuum, interparticle adhesion, and angular particle morphology. These features lead to nonlinear strength behaviour, strain softening, and pronounced dilatancy, which pose challenges for conventional constitutive models.
This study develops a hypoplastic constitutive model named Simhypo-Luna for lunar regolith. The model is established based on the simhypo-sand framework and extended by incorporating particle morphology and vacuum induced interparticle adhesion. Particle sphericity is introduced to describe the influence of grain shape on the critical stress ratio and critical void ratio. A surface energy related adhesion parameter is further adopted to represent apparent cohesion and enhanced dilatancy under vacuum conditions. Through these modifications, the model links particle scale characteristics with macroscopic stress strain and volumetric responses while retaining a concise parameter structure.
The predictive capability of Simhypo-Luna is examined through triaxial compression simulations under different particle shapes, confining pressures, density states, and adhesion conditions. The results show that the model can reproduce the main mechanical features of lunar regolith, including morphology dependent shear strength, post peak strain softening, state dependent response, and adhesion enhanced dilatancy under low stress conditions. The proposed model provides a practical constitutive framework for evaluating the mechanical stability of lunar regolith in future surface exploration and construction, and extends geotechnical constitutive modelling toward extreme environments beyond Earth.