No abstract

A method to assess the suffusion susceptibility of core soils in compacted dams based on construction dataSuffusion, as one of the main internal erosion processes in earth structures and their foundations, may increase their failure risks. The paper aims at presenting a general method to assess the suffusion susceptibility of core soil samples belonging to zoned hydraulic embankment dams. On one hand, the suffusion susceptibility of the soil samples is evaluated by an erosion resistance index. Thanks to existing statistical analyses, the erosion resistance index is estimated from several soil parameters that can be easily measured in-situ or in laboratory during the construction of a dam. On the other hand, the saturated hydraulic conductivity of the soil samples is evaluated based on the amount of fines content and on available construction data. Moreover, the power dissipated by the flow is inferred based on the saturated hydraulic conductivity and simplified fluid boundary conditions. The combined consideration of the erosion resistant index and of the power dissipated by the flow permits to identify zones characterized with a relatively larger suffusion potential (lower erosion resistance index and larger power than their respective average). Throughout, the method is applied to a particular zoned dam with a till core, from Northern Quebec, as a proof of concept.

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Heat carried by the seepage water along hydraulic flow lines can serve as a natural tracer to help detect contrasting hydraulic conductivities in embankment dams. Thermal monitoring was realized on the 94.5 m high QA-01 embankment dam in northern Quebec to characterize the temperature distribution across its entire section. The analysis of the annual thermal response of the dam clearly showed a zone of higher seepage velocities in the compacted till core. Approximations concerning the increased hydraulic conductivity were made using a simple thermal model. Complementary numerical modelling provided a more rigorous quantitative assessment of the seepage patterns. The calculations have shown hydraulic conductivities that are 20 times larger than the expected values. Thermal monitoring can detect zones of increased seepage, which can be related to internal erosion or other factors, such as the variability of the soil properties due to construction practices. Temperature measurements alone are not adequate to determine the cause of a permeable zone in a dam or to predict its possible evolution.