The main problem in expansive soil treatment with steel slag (SS) is the relatively slow hydration reaction that occurs during the initial period. To circumvent this, SS-treated expansive soil activated by metakaolin (MK) under an alkaline environment was investigated in this study. Based on a series of tests on the engineering properties of the treated soil, it can be reported that SS could enhance the strength and compressibility of expansive soil, with strength increasing by approximately 108 % for SS contents exceeding 10 % compared to 3 % lime-treated soil, and the compression index reducing by 20 %. Further addition of MK plays a dual role, enhancing strength for higher SS content while excessive MK leads to strength reduction due to insufficient pozzolanic reactions and hydration product transformation. Expansive and shrinkage behaviors are notably improved, with a 5 % increase in SS content reducing the free swelling ratio by 0.66 %-5.9 %, and the combination of 15 % SS and 6 % MK achieving a nearly 300 % reduction in the linear shrinkage ratio. Microstructural analysis confirms the formation of hydration gels, densification of the soil structure, and reduced macropores, validating the enhanced mechanical and shrinkage resistance properties of the SS-MK-treated expansive soil. Additionally, to develop predictive models for mechanical and the content of hardening agents (SS and MK), the experimental data are processed utilizing a backpropagation neural network (BPNN). The results of BPNN modeling predict the mechanical properties perfectly, and the correlation coefficient (R) approaches up to 0.98.

Compacted loess is widely used in construction and road engineering in the Loess Plateau region. It inevitably undergoes vertical deformation and desiccation-induced cracking due to environmental effects. This study investigates the deformation and cracking characteristics of compacted loess under vertical pressure during desiccation. Samples with initial water contents ranging from 5% to saturation are prepared for desiccation under vertical stresses of 0-100 kPa. Changes in resistivity are simultaneously monitored during desiccation. After desiccation, the microstructural characteristics of the soil are examined using X-ray computed tomography (CT), mercury intrusion porosimetry (MIP), and scanning electron microscopy (SEM) techniques. The effects of initial water content and vertical pressure on vertical strain, drying cracks, and electrical resistivity of compacted loess are analyzed. The results indicated that high vertical pressure and water content lead to significant compressive and desiccated deformation of compacted loess, which is reflected in the microstructure by a smaller pore size distribution (PSD). Lower initial water content and higher vertical load are more effective in suppressing cracking during the desiccation of compacted loess. The surface crack ratio (Rsc) of compacted loess is reduced by 99.54% as pressure increases from 0 to 100 kPa and water content decreases from saturation to 5%. The directions of cracks in loess during desiccation and the microstructural changes caused by deformation are effectively characterized by resistivity measurements. This study explores the variations in mechanical properties during desiccation of compacted loess and provides a theoretical foundation to use resistivity for characterization.