In order to explore the effect of the foaming agent type on the properties of foamed mixture lightweight soil mixed with bauxite tailings (FMLSB), low-density (437.5 kg/m³ and 670 kg/m³) and high-density (902.5 kg/m³ and 1170 kg/m³) FMLSB were prepared using protein-based and synthetic-based foaming agents (AF and SF, respectively). The foam stability, micro characteristics, compressive strength, fluidity, and volume of water absorption of the FMLSB were investigated. The results showed that the foam made from AF had better strength and stability compared to SF. The internal pore sizes of both AF- and SF-FMLSB at low density were large, but at high density the internal pore sizes and area porosity of AF-FMLSB were smaller than those of SF-FMLSB. In terms of compressive strength, the compressive strength of AF-FMLSB was improved by 17.5% to 43.2% compared to SF-FMLSB. At low density, the fluidity of AF- and SF-FMLSB is similar, while at high density the fluidity of AF-FMLSB is much higher than that of SF-FMLSB. In addition, the stable volume of water absorption of SF-FMLSB is smaller than that of AF-FMLSB at low density, and the corresponding water resistance is better, but the situation is reversed at high density.

To investigate the pitting evolution behavior of carbon steel in industrial–coastal atmospheric environments, a multiphysics numerical model was established by coupling tertiary current distribution, mass transport, and deforming geometry based on electrochemical corrosion mechanisms. Based on this framework, the effects of pH, salt concentration, and relative humidity (RH) on the pitting corrosion rate were systematically analyzed, and a predictive model for the pitting rate was subsequently developed. The results indicate that the pitting morphology gradually evolves from an initial conical shape to a hemispherical morphology and eventually develops into a quasi-cylindrical form. When the pH value increases from 6.0 to 7.0, the pitting rate decreases significantly, with a maximum reduction of 23.96%. Within the salt concentration range of 0.5%–1% (mass fraction), increasing salt concentration markedly accelerates the pitting process, resulting in a maximum increase in the pitting rate of 10%. In addition, the pitting rate exhibits a pronounced peak within the RH range of 72%–77%. The corrosion rates predicted by the proposed model are in good agreement with the experimental results, with relative errors within 5%. These results indicate that the numerical model and prediction formula established in the present study can reasonably predict the pitting evolution behavior and corrosion rate of carbon steel.

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.