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Abstract

A fiber optic distributed sensing system focuses on monitoring parameters that are useful for determining the short- and long-term behavior of the structure in response to external actions, including seismic activities and long-term phenomena such as seepage, tunneling, sinkholes, and other geo-structural movements. Monitoring large retaining structures with such a system provides direct strain, deformation, and temperature measurements across the broad interior area, enabling early detection, localization, and assessment of subsurface damages. Measurements are provided every metre along the entire sensing cable; this is particularly important in cases where the location of defects cannot be predicted, rendering localized geotechnical instrumentation ineffective. Fibre optic distributed sensing cables are relatively easy to deploy and are generally available for retrofit installation inside the dam structure, using trenches on the downstream face or laid during construction beneath the geomembrane liner within the bedding sand layer. Mapping the cable route enables an exact correlation between a linear coordinate on the cable length and a position within the dam. The installation of the cable is expected to be carried out during the further raising of the embankment; additional cable sections will be connected to the previously installed cables and measured with the existing measurement system, requiring only an update of the mapping. The measurement system is located remotely from the sensing area, allowing a section of sensing cable to connect to the sensing area at the storage facility several kilometres away without any performance degradation. The system provides online, 24/7, real-time operational data management. Such fibre optic distributed sensing systems enable the monitoring of storage facilities with long, accurate, continuous, and precise data for geotechnical diagnostic purposes. This paper will introduce the principles and benefits while presenting a relevant application example of use in the Mareesburg Tailings Storage Facility, which is part of the Mototolo Mine owned by Anglo American and located in Limpopo province, South Africa.