1184 known zone of historical seepage distress. Source: Wagner et al 2023 Strategically placed at dam embankment downstream, fibre optic cable through DTS detects realtime changes over large areas and distances. Seepage alters soil temperature, and fibre optic distributed sensing systems detect these changes precisely and frequently, providing continuous, real-time monitoring and providing a quantitative assessment on early signs of seepage occurring within the dam. 3.3 DSS/DAS strain-based deformation monitoring Rayliegh (DAS) and/or Brillouin (DSS) distributed sensing is used to detect spatial patterns of deformation including localised strain gradients associated with settlement, shear deformation, or crack initiation at lift interfaces, Figure 5. Unlike point sensors, distributed sensing along fiber optics provides a full spatial profile of strain over time, available in real-time, and allows for early detection of developing issues. A single fiber replaces hundreds of discrete sensors, reducing installation complexity and costs. [15][7][6]. Figure 5 – Strain preceding slope failure detected on fiber optic cable over 1-day period, Source: Ouellet et al, 2024 For strain measurements, Fibers are trenched, embedded, or attached to dam structures (e.g., embankments, spillways, foundations) to detect localized or widespread strain changes. The system detects anomalies like cracks, seepage, subsidence, or deformation caused by dam loading, settlement, seismic deformation and aging. Distributed strain monitoring is increasingly recognized in geotechnical research as an effective method for detecting subtle physical changes. This makes it an essential dataset for supporting TARP triggers in TSF applications. 3.4 DAS for far-field acoustic imaging and monitoring DAS complements DTS/DSS, often on the same fiber optics cable installed in the infrastructure, by providing dense measurements of strain-rate (i.e., deformation rate) along the fibre, enabling the TSF to be monitored as a spatially continuous seismic array. Two passive approaches are commonly cited for earthworks: (i) ambient noise interferometry (ANI), Figure 6, where cross‑correlation of ambient wavefields is used to estimate seismic velocities and their changes over time; and (ii) potentially detection of acoustic emissions associated with flowing water or evolving internal state. Applied programs in embankment dams show the application of extracting seismic velocities from DAS data. Comparing seismic velocities against a previous measurement or baseline can detect changes potentially associated with seepage/internal erosion. [2][3].
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