Thermally induced transition from expansive clay to a frictional granular state: An experimental investigation

Thermally induced volumetric response of natural clays: effects of OCR, plasticity, and recent stress history.

Understanding the thermally induced volumetric response of fine-grained soils is important for geo-energy systems, underground storage facilities, and radioactive waste repositories. This study examines the thermo-mechanical response of two natural silty clays from Budapest, Hungary, with different plasticity levels and stress histories. Slow-heating tests under drainage-promoting boundary conditions and heating-cooling cycle tests were performed using a temperature-controlled oedometer on low-plasticity (LP) and high-plasticity (HP) samples. The specimens were heated from [Formula: see text] to [Formula: see text] under different over-consolidation ratios, ranging from OCR = 1 to 22. The results show that normally consolidated samples contract during slow heating. Overconsolidated samples show a more variable response, indicating that OCR alone is not sufficient to describe the thermal volumetric behaviour. The HP samples generally developed larger thermal volumetric strains than the LP samples, showing the influence of plasticity on the magnitude of thermal deformation. The low-stress naturally overconsolidated specimens, LP12 and HP22, showed mainly contractive behaviour, although their response should be interpreted with caution because their OCR values were inferred from apparent preconsolidation pressures obtained from separate room-temperature oedometer tests. During repeated heating-cooling cycles, most irreversible volumetric strain developed during the first cycle, while later cycles showed smaller strain increments and a trend towards more recoverable behaviour. The tests were not independently verified as fully drained by pore-pressure measurements; therefore, the results are interpreted as laboratory-scale evidence under drainage-promoting conditions rather than as proof of a unique drained mechanism.

MECHANICAL AND MICROSTRUCTURAL PERFORMANCE OF EXPANSIVE SOILS STABILIZED WITH FLY ASH–DESULPHOGYPSUM BLENDS

Expansive soils pose significant challenges to civil engineering infrastructure due to their high plasticity, excessive swelling, and shrinkage behavior under fluctuating moisture conditions. These characteristics often lead to structural distress, including pavement cracking, foundation settlement, and loss of bearing capacity, particularly in regions such as the Niger Delta where seasonal moisture variation is pronounced . This study investigated the effectiveness of industrial waste materials, specifically fly ash and desulphogypsum, as sustainable stabilizing agents for improving the geotechnical properties of expansive soils. Laboratory experiments were conducted on untreated and treated soil samples with varying proportions of fly ash (5–15%) and desulphogypsum (5–15%), including their combined application. The natural soil was classified as highly plastic clay (CH) with a liquid limit of 92% and plasticity index of 71%, indicating high swelling potential. The addition of stabilizers significantly modified the soil behavior. The plasticity index decreased progressively with increasing stabilizer content, reaching a minimum value of 24% for the combined mix of 10% fly ash and 15% desulphogypsum. Compaction characteristics improved, with maximum dry density increasing from 1.485 g/cm³ to 1.556 g/cm³, while optimum moisture content reduced from 24.8% to 19.6%. Unconfined compressive strength (UCS) results demonstrated substantial improvement in strength due to stabilization. The untreated soil exhibited a UCS value of 89.2 kPa, which increased to 456.3 kPa after 28 days of curing for the combined stabilizer mix, representing a 411% increase. Regression models developed for predicting UCS and plasticity index reduction yielded strong correlations with coefficients of determination (R²) of 0.887 and 0.862, respectively, and mean absolute error below 8%. Sensitivity analysis revealed that incremental increases in fly ash and desulphogypsum content contributed positively to strength development, with fly ash having a slightly higher influence. Optimization analysis identified an optimal stabilizer combination of 16.1% fly ash and 10.9% desulphogypsum, corresponding to a predicted UCS of 468.3 kPa and a minimum plasticity index of 22.1%. Economic evaluation showed that the combined stabilization method cost approximately ₦3,600/m³ compared to ₦11,700/m³ for conventional lime stabilization, resulting in a cost reduction of about 69%. The results demonstrated that the combined use of fly ash and desulphogypsum significantly improved the engineering performance of expansive soils by reducing plasticity, enhancing strength, and improving compaction characteristics. The study established that these industrial by-products offer a cost-effective and environmentally sustainable alternative for ground improvement in the Niger Delta, with strong potential for application in road construction and foundation engineering.

Strength enhancement of expansive and non-expansive clays using colloidal silica

Expansive and soft clays pose major challenges in infrastructure development due to their high compressibility, low shear strength, and significant volume changes upon wetting and drying. Conventional cement-based stabilisers are effective but carbon-intensive, motivating the search for sustainable alternatives. Colloidal silica (CS) has emerged as a sustainable, low-carbon alternative to traditional cementitious binders for stabilising problematic soft soils. This study investigates the potential of CS to improve the unconfined compressive strength of both expansive (Bentonite) and non-expansive (Kaolinite) clay samples. The gelling time results show that increasing CS concentration and the presence of NaCl significantly reduce gelation time, while bentonite–CS mixtures gel faster than kaolinite–CS mixtures due to higher surface activity and cation-exchange capacity. Laboratory experiments were conducted at 30% CS and 15% NaCl concentrations with two curing periods of 7 and 14 days to evaluate changes in unconfined compressive strength (UCS). Kaolinite exhibited approximately 50–55% increase in peak strength between 7 and 14 days of curing, while bentonite showed about 20–25% higher UCS than kaolinite under identical treatment conditions. The findings demonstrate that CS is an effective and environmentally friendly stabiliser that can improve both expansive and non-expansive clays, making it a promising alternative for sustainable ground improvement applications.

Micromechanical mechanisms of microstructural evolution governing mechanical response of frozen sandy clay under true triaxial stress conditions

Compaction, CBR, and microstructural performance of lateritic soil stabilized with recycled concrete aggregate

Assessment of Geotechnical and Microstructural Properties of Expansive Clay amended with Bauxite Residue using Sodium Silicate