Abstract:
Over the past decade, there have been 45 tailings storage facility (TSF) disasters worldwide,
resulting in fatalities, serious environmental damage, and the destruction of entire
ecosystems. These failures often stem from substandard design or operational practices.
Many TSFs are constructed in regions associated with intrusive mafic rocks such as gabbro,
norite, pyroxenite, and anorthosite, which are commonly found alongside platinum group
metals in areas like the Bushveld Igneous Complex in South Africa and the Great Dyke in
Zimbabwe. The stability of these structures can be significantly influenced by the residual
soils present at the construction sites. Residual soils, both cohesive and non-cohesive,
contain varying quantities of different minerals, which can impact the compaction
characteristics and, consequently, the stability of the TSF foundations. Cohesive soils rich
in clay minerals, such as kaolinite and smectite, exhibit properties that can hinder effective
soil compaction. The expansive nature of smectite due to its ability to absorb large amounts
of water and host free exchangeable cations, counteracts the compaction process, reducing
soil stability. Soil compaction is a complex process influenced by several factors, including
compaction effort, method, water content, particle size distribution, and mineralogy. This
study aimed to analyse these factors using a series of laboratory tests, including foundation
indicators, MOD AASHTO compaction testing, and X-ray diffraction analysis, on residual
soils from two TSF construction sites. The findings revealed that soils with high clay content
tend to retain more water and have a higher optimum water content, adversely affecting
their compaction properties. This study highlights the critical need to consider the
mineralogical composition and weathering effects of residual soils in the design and
construction of TSFs. By improving our understanding of these factors, we can enhance the
stability of TSF foundations, reducing the likelihood of future failures. The insights gained
from this research highlight the importance of thorough geotechnical assessments in the
successful design and maintenance of TSF’s.
