: Investigation into an adopted design procedure for raft foundations of light structures on expansive soils located in the Free State region of South Africa

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4. : Investigation into an adopted design procedure for raft foundations of light structures on expansive soils located in the Free State region of South Africa

Raft foundations are characterized by their ability to distribute building loads and minimize differential movement. Raft foundation construction has become very popular in areas affected by expansive clay soils in South Africa. Expansive clays can cause heave when the suction potential exceeds the foundation's pressure, leading to visible cracks, jammed doors, damaged floors, and compromised structural integrity. Large parts of South Africa are affected by expansive soils, including the Karoo Supergroup and the Beaufort Group, found in South Africa's Gauteng Province, Free State Province, parts of the Western Cape Province, and certain areas in the Eastern Cape Province. These geological formations are associated with expansive clays, posing challenges for construction and engineering projects. The study highlights the critical importance of custom-made foundation solutions for the unique challenges expansive soils pose. This paper draws inspiration from Pidgeon's universal method (1988) and Bester et al.'s (2016) work on moisture variation underneath a raft foundation. Pidgeon's design approach provides a valuable outline for designing raft foundations on expansive clays based on edge heave and mound-shaped that will develop. However, the assumption of a centre-located dome-shape underneath a raft foundation is unrealistic since the previous studies did not consider the shadow cast by the structure. By applying this design approach to expansive soil conditions, this study suggests an improved approach and design to mitigate heave damages and ensure the long-term stability of structures built on expansive clay soils. This research explores raft foundation design in South Africa and suggests a new approach to mitigate structural damages of the challenges of expansive clays. By adopting this new approach, designers can enhance the service life of light-structured housing, ultimately contributing to the long-term sustainability of South African housing projects.

18th African Regional Conference on Soil Mechanics and Geotechnical Engineering (ARCSMGE2024)

Foundation Engineering