Novel Capping Layer for Foundations in Expansive Soils Using Sustainable Materials
Creators: name: Karami, Hadi
Publisher: name: RMIT University
Year: 2025
Subjects: classificationCode: 400502
subject: Civil geotechnical engineering

description: Expansive soils are found all over the world. These soils are highly plastic and can cause damage to infrastructure, building foundations, and roads due to their low strength, high compressibility, and volumetric changes. The behaviour of expansive soils is sensitive to moisture changes, which can lead to significant problems for structures built on them. Building on weak expansive soils is challenging because of their low bearing capacity and susceptibility to volume changes under moisture fluctuations. Expansive soil uplift pressure can cause significant swelling pressure on foundations, while clay shrinkage can lead to substantial foundation settlement during dry seasons. These differential movements can cause damage to the building's superstructure, leading to service and ultimate limit state failures. To mitigate such adverse behaviour on structures, the underlying clay needs improvement before supporting the structural foundations. This research focuses on improving the bearing capacity and volumetric response of expansive soils using sustainable additives.
The traditional method of treating expansive soils with calcium-based additives has been associated with concerns over cost and environmental impact. However, this study proposes the use of recycled materials like glass and fly ash as secondary additives to improve the properties of expansive soils in subgrades and foundations. Several mechanical tests, including the Standard Compaction Test, Unconfined Compressive Strength (UCS) test, and Direct Shear Test, were conducted to assess the behaviour of various additives, along with microscopic tests like SEM, XRD, FTIR, TGA, and porosity, and a hydraulic conductivity test (permeability). The study also explored the impact of secondary additives like Class F fly ash, lime, CSA cement, enzyme, recycled concrete, and polymers on improving the expansive soil behaviour.
Through advanced microscopical analysis techniques, we were able to evaluate the effectiveness of chemical additives, glass aggregate, and powder in soil stabilisation. The combination of secondary additives with clay showed promising results in terms of mechanical behaviour, but the addition of glass waste further improved the density, UCS, and frictional characteristics of the stabilised soil mix. While changes in the chemical composition were detected in soil mixed with secondary additives, the addition of glass had little effect. These findings provide insight into how standard stabilisers can be utilised with waste glass to enhance the hydro-mechanical characteristics of expansive soils. Specifically, this research shows that the stabilised soil-glass matrix, derived from secondary additives, increases the bearing capacity of expansive weak clays and offers a sustainable solution for managing glass waste.
The results of the optimum stabilisation mix were verified by conducting proto-type model tests simulating foundational loads in order to propose a new method for improving the stability and moisture control of foundations. A capping layer was added underneath the foundation using a recycled glass-based stabilisation approach. A prototype foundation was constructed, and its performance was monitored in the laboratory under various moisture and load conditions over one year. The results showed that the capping layered foundation outperformed the traditional foundation in terms of stability and moisture control, even during seasonal fluctuations. The outcome of this research proposes a sustainable foundation construction process using recycled glass wastes, which could significantly improve the performance of foundations in expansive soils.