Abstract Description: Identifying and evaluating zones of seepage flow in embankment dams is a challenging issue for dam performance evaluation because there are few methods to directly measure seepage rates within a dam. Seepage is a critical condition to understand for overall dam safety since seepage is the trigger for many failure modes in embankment dams. Active Fiber Optic Distributed Temperature Sensing (A-DTS) is an emerging technological application by which heat transfer around a fiber optic cable can be measured and correlated to material properties or conditions. The A-DTS system consists of (1) an interrogator using laser pulses to measure temperature continuously along the length of a fiber optic cable and (2) a heating cable to provide thermal power along the cable. The heat transfer measured by the A-DTS in subaqueous conditions can then be directly related to the flow rate of water over the cable. When applied within fully-screened piezometers through an embankment dam, including its foundation or abutments, the principles of the operation allow for profiling of the seepage flow regime.
This study deployed an A-DTS system to fully-screened piezometers at two tailings storage facility embankment dams to investigate seepage for design of a cutoff wall and toe drain performance, respectively. Some investigated zones exhibited no- or low-flow conditions, while other zones had very high flow conditions based on the local geologic stratigraphy and/or position within the dam configuration. Investigations using other technologies, including tracer testing, packer testing, and/or borehole geophysics, were also completed at select locations, and those results are compared with the A-DTS results herein. This paper highlights the dam safety and performance insights gained from deploying the A-DTS system and evaluating its results, as well as identifying logistical considerations and lessons-learned for practical implementation of this technology in comparison to other methods of evaluating seepage flow in embankment dams.
Learning Objectives:
Describe the challenges of measuring seepage flow rates through dams, dam foundations, and abutments; and why assessment of seepage is so critical to dam safety.
Describe A-DTS technology, how it was applied to piezometers in two tailings dams, and the pertinent aspects of these dams to the anticipated seepage in-situ.
Show the results of the seepage assessment and how the results compare to other methods of assessing seepage at the same dams (e.g., tracer tests, geophysics).
