Constitutive Modeling and Model Comparison of Temperature Effects on the Mechanical Behavior and Wetting-Induced Swelling of Expansive Mudstone

Temperature-dependent mechanical behavior and wetting-induced swelling affect the stability of underground structures in expansive mudstone. Three modified constitutive models were evaluated against temperature-controlled triaxial compression and laterally constrained swelling tests. The Mohr–Coulomb strain-softening and Hoek–Brown-based unified hardening–softening models incorporated temperature effects and equivalent swelling strains. The unsaturated unified hardening model was extended through equivalent temperature–stress mapping. Mechanical calibration used data from 12 triaxial conditions, supplemented by evaluation at 40 °C after recalibration at 20 and 60 °C. Swelling parameters calibrated at 20 °C were held constant at higher temperatures. For the 12 calibration conditions, the Mohr–Coulomb model yielded the lowest errors in peak deviatoric stress and deviatoric stress at 5% axial strain. The hardening–softening model improved pre-peak response and peak-strain estimates relative to Mohr–Coulomb. The unsaturated model achieved the lowest pre-peak normalized root-mean-square error of 10.10% and a swelling mean absolute error of 0.22 percentage points across 40–80 °C, but overestimated deviatoric stress at 5% axial strain. The sensitivity results support a staged calibration procedure involving initial parameter estimation followed by joint refinement using the designated calibration data. These findings provide a basis for model selection and parameter calibration in analyses of temperature-dependent mechanical and swelling responses of expansive mudstone.