Studies on chemically stabilised soils have shown that the effectiveness of treatment is largely dependent on the soil’s natural environment. This type of soil can be categorised as problematic due to its weak properties. At the preliminary stage, soft clay soil does not meet the requirements necessary for construction purposes because the entire load from the top of the building will be transferred to the underlying soil. This research considers the soil stabilisation of a soft clay soil (Kaolin S300) stabilised with various percentages of lime and 4% silica fume. The percentages of lime vary at 3, 5, 7 and 9%, while the percentage of silica fume is fixed at 4%. The main objective in this research is to improve the undrained shear strength of soft clay soil mixed with various percentages of lime (L) and 4% silica fume (SF). The properties of the soils were compared for kaolin only and for different percentages of lime mixed with 4% silica fume. The results showed that the optimum percentages of lime and silica fume with respect to the maximum shear strength occurred at 5 and 6%, respectively. The soil–L–SF mix increased the shear strength and angle of internal friction compared to soil–lime and soil–SF mixes because the pozzolanic reaction between lime and SF was more effective with soil particles. The optimum percentage for enhancing the shear strength and the angle of friction was 7–4% L–SF.

Soil stabilization, as a cost-effective and environmentally friendly method, is used in the building of systems such as roads, dams, and river levels. Chemical stabilization of soil is carried out by adding binder or by-products such as lime (L) and silica fume (SF) to the soil, thereby modifying the geotechnical performance of the soil. This type of soil can be categorized as problematic due to its weak properties. At the preliminary stage, soft clay soil does not meet the requirements necessary for construction purposes because the entire load from the top of the building will be transferred to the underlying soil. This research considered the soil stabilization of a soft clay soil (Kaolin S300) stabilized with various percentages of lime and 4% SF. The percentage of lime varied at 3%, 5%, 7%, and 9%, while the percentage of SF was fixed at 4%. The main objective in this research was to improve the undrained shear strength of soft clay soil mixed with various percentages of lime and also 4% SF. The focus of the study was on determining the physical properties of the soils tested and the consolidation of kaolin mixed with 4% SF and different percentages of lime. The results showed that the optimum L-SF percentage with respect to the maximum shear strength occurred at 5%. The soil-L-SF mix increased the shear strength and angle of internal friction compared to the soil-L and soil-SF mixes because the pozzolanic reaction between lime and SF was more effective with soil particles. The optimum percentages for enhancing the shear strength and the angle of friction were 7% and 4% for lime and SF, respectively. Microstructural development took place in the stabilized soil due to an increase in the lime content of tertiary clay stabilized with the L-SF mix.

Soft soil problems and increased production of fuel waste have emerged due to world population growth. These two problems are prompting engineers to introduce new methods of using waste fuel to stabilize the soil. Previous research has shown clear sustained improvements in soil properties using palm oil fuel ash (POFA) when mixed with a calcium-based binder such as NaCl, lime or cement. The use of such a stabilizing agent can reduce the economic problems associated with reducing the cost of waste disposal and create a sustainable ecological system. It is an alternative method of replacing part of the soil to ensure a balance between economic growth and ecological privilege, leading to the achievement of green technology goals. However, this research is aimed at improving the properties of processed soft kaolin clay with a combination of POFA and gypsum. The physical and mechanical properties of all samples were tested. The results showed a decrease in the specific gravity with the addition of POFA and an increase with gypsum alone, as well as a decrease with a mixture of POFA and gypsum and a decrease in the soil plasticity index due to a better increase in the plasticity limit compared to the liquid limit. This is considered a sign of improved geotechnical properties and reduced linear shrinkage. It was also shown that the treated clay showed an increase in the optimal water content and a drop in the maximum dry density. Nevertheless, it can be concluded that the initial properties of the processed soft kaolin clay with the addition of POFA can be significantly improved.

The application of chemical stabilizer in soil stabilization can effectively reduce the negative environmental impact in the construction industry. However, the stabilization of soft clay remains a challenge due to the costly and non-eco-friendly materials such as cement and lime. This research demonstrates the combination of SF and ESA in stabilizing the kaolin soils, based on the basic engineering properties and undrained shear strength (USS). Its effect was studied via the inclusion as cement replacement material in kaolin soil at 2, 4 and 6% (by weight of dry soft kaolin clay soil) of SF and ESA substitutions of 3, 6 and 9% (by weight of dry soft kaolin clay and SF content). The result shows a considerably lower specific gravity (4.9% reduction), reduced plasticity index (PI)(48.4% reduction), decreased maximum dry density (MDD) (5.5% reduction), increased optimum moisture content (OMC)(8.7% increment), and higher USS (68.8%). In conclusion, the combinations of SF and ESA as soil stabilization agents successfully enhance the soil strength of the kaolin opening a route to the low cost and eco-friendly materials in soil stabilization.