Abstract
Abstract. Internal erosion is the cause of a significant percentage of failure and incidents involving both dams and river embankments in many countries. In the past 20 years the use of fibre-optic Distributed Temperature Sensing (DTS) in dams has proved to be an effective tool for the detection of leakages and internal erosion. This work investigates the effectiveness of DTS for dike monitoring, focusing on the early detection of backward erosion piping, a mechanism that affects the foundation layer of structures resting on permeable, sandy soils. The paper presents data from a piping test performed on a large-scale experimental dike equipped with a DTS system together with a large number of accompanying sensors. The effect of seepage and piping on the temperature field is analysed, eventually identifying the processes that cause the onset of thermal anomalies around piping channels and thus enable their early detection. Making use of dimensional analysis, the factors that influence this thermal response of a dike foundation are identified. Finally some tools are provided that can be helpful for the design of monitoring systems and for the interpretation of temperature data.
Highlights
Backward erosion piping is a specific kind of internal erosion mostly occurring under water-retaining structures that are founded on fine to medium sand (ICOLD, 2015)
Interpretative schemes devised for temperature measurements performed in earth dams assume that heat transfer occurs mostly by advection in the zones affected by internal erosion and by conduction in the rest of the soil (Johansson and Hellström, 2001; Johansson and Sjödal, 2009)
The experimental results confirmed that the optimal location of a Distributed Temperature Sensing (DTS) sensor for the detection of backward erosion piping is close to the landside toe of the embankment
Summary
Backward erosion piping is a specific kind of internal erosion mostly occurring under water-retaining structures that are founded on fine to medium sand (ICOLD, 2015). The erosion process typically starts at the downstream side of the structure, where the flow lines converge at an unfiltered exit (Fig. 1). The erosion channels, or pipes, grow backwards and when they reach the upstream side a pressure surge can cause an excessive enlargement, often followed by the failure of the embankment. Backward erosion piping can occur, less frequently, under revetments (Galiana, 2005) or in riverbanks and dike bodies with sandy inclusions (Hagerty, 1991). Backward erosion piping represents a significant problem for the safety of river and sea dikes located in delta areas, including, for example, the Po Plain in Italy and a large part of the Netherlands. Many other experimental and theoretical studies followed across the years
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