Thulisile Kunjwa

Nelson Mandela University

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Lucian Bezuidenhout

Karolinska Institutet

Gerrit Olivier

University of Tasmania

Philasande Mambalu

Nelson Mandela University

Barry Morkel

Nelson Mandela University

Fabien Génin

Nelson Mandela University

Sameera Musa

Nelson Mandela University

Divan Stroebel

Nelson Mandela University

Gaathier Mahed

Nelson Mandela University

Thakane Ntholi

Nelson Mandela University

Taufeeq Dhansay

Nelson Mandela University

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Nelson Mandela University

Council for Geoscience

Centre National de la Recherche Scientifique

South African Environmental Observation Network

Institute of Seismology

Institut des Sciences de la Terre

Université Grenoble Alpes

Université Joseph Fourier

Université Gustave Eiffel

University of Cape Town

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Ambient noise Love wave tomography at a gold mine tailings storage facility

Géotechnique Letters (2018)

Gerrit Olivier Tjaart de Wit Florent Brenguier Lucian Bezuidenhout Thulisile Kunjwa

Tailings storage facilities (TSFs) are some of the most challenging structures to operate in the mining industry. Some of these structures are susceptible to liquefaction and piping failure, and need to be monitored carefully. In this study, ambient seismic noise interferometry is applied to image the internal structure of a tailings storage facility (TSF) that showed signs of increased seepage. Twenty geophones were deployed along a roughly 100 m section of the TSF and recorded continuous seismic data. The ambient noise was used to create Love wave dispersion curves between sensor pairs, which were in turn inverted to estimate the shear wave velocity of the dam wall as a function of depth. The velocity profile indicated the phreatic surface roughly 10 m below the surface, with regions near the centre of the array showing the phreatic surface as close as 3 m below the surface. These areas are spatially well correlated with the area where increased seepage was identified and the results were comparable with cone penetration tests that were performed in the area. The study showed that the analysis of ambient seismic noise can be a cost-effective, fast and non-invasive method to image the internal structure of TSFs.

Ambient noise level

Geophone

Geophysical Imaging

10.1680/jgele.18.00016

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Earth Stewardship Science—Transdisciplinary Contributions to Quantifying Natural and Cultural Heritage of Southernmost Africa

Remote Sensing (2020)

Bastien Linol Warren Miller Cheryl Rensburg Renée P. Schoeman Lucian Bezuidenhout

Evaluating anthropogenic changes to natural systems demand greater quantification through innovative transdisciplinary research focused on adaptation and mitigation across a wide range of thematic sciences. Southernmost Africa is a unique field laboratory to conduct such research linked to earth stewardship, with ‘earth’ as in our Commons. One main focus of the AEON’s Earth Stewardship Science Research Institute (ESSRI) is to quantify the region’s natural and cultural heritage at various scales across land and its flanking oceans, as well as its time-scales ranging from the early Phanerozoic (some 540 million years) to the evolution of the Anthropocene (changes) following the emergence of the first human-culture on the planet some 200 thousand years ago. Here we illustrate the value of this linked research through a number of examples, including: (i) geological field mapping with the aid of drone, satellite and geophysical methods, and geochemical fingerprinting; (ii) regional ground and surface water interaction studies; (iii) monitoring soil erosion, mine tailing dam stability and farming practices linked to food security and development; (iv) ecosystem services through specific biodiversity changes based on spatial logging of marine (oysters and whales) and terrestrial (termites, frogs and monkeys) animals. We find that the history of this margin is highly episodic and complex by, for example, the successful application of ambient noise and groundwater monitoring to assess human-impacted ecosystems. This is also being explored with local Khoisan representatives and rural communities through Citizen Science. Our goal is to publicly share and disseminate the scientific and cultural data, through initiatives like the Africa Alive Corridor 10: ‘Homo Sapiens’ that embraces storytelling along the entire southern coast. It is envisioned that this approach will begin to develop the requisite integrated technological and societal practices that can contribute toward the needs of an ever-evolving and changing global ‘village’.

Anthropocene

Stewardship

Earth system science

Citizen Science

10.3390/rs12030420

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Ambient seismic noise imaging of a tailings dam internal structure

South African Journal of Science (2024)

Thulisile Kunjwa Moctar Doucouré

Several tailings dam failures have been reported over the past few decades, raising questions about the stability of these structures. Over the past 30 years, there have been more severe failures of tailings dams, which have resulted in damage to the environment, fatalities and severe socio-economic issues. It is often impossible to predict when tailings dams could fail, so there is an urgent need to develop cost-effective methods for monitoring their stability and preventing such catastrophic events. Recent advancements in techniques related to ambient seismic noise have the potential to introduce new approaches to subsurface imaging and monitoring. In this study, we investigated the potential of using ambient seismic noise to monitor the interior wall of a tailings dam. We used 20 3C short-period geophones to record ambient noise over 3 days continuously. We set up the geophones at the Harmony Gold Mine tailings dam in Welkom, South Africa, along a survey profile approximately 100 m long. Seismic interferometry was used from the recorded data to retrieve empirical Green’s functions. We computed the dispersion curves’ inversion to determine the dam wall’s shear wave velocity at different depths. The calculated shear wave velocity cross-sections revealed a region of reduced velocity within the dam wall, situated between 2 m and 10 m beneath the surface. This zone of low velocity can be a sign of water-saturated material or other subsurface anomalies, which might jeopardise the dam’s structure.

Geophone

Tailings dam

Seismic Noise

Ambient noise level

Passive seismic

10.17159/sajs.2024/16366

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