Thermal conductivity measurements for cable burial in the intertidal zone

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Landfalls of offshore people cables are often planned in areas where sediment transport may influence the burial of the cable over time. The cable should retain sufficient cover throughout its operational lifetime to prevent it from becoming exposed. Measuring the depth of burial with conventional methods requires periodic surveys with amphibious survey vessels but changes in the sediment cover may be sudden due intense erosion (e.g. during storms). During the storms, the survey vessels cannot collect data in a safe manner.

Measuring the temperature change of the optical fiber in the cable allows for the depth of burial of the cable to be derived using a 2D plane strain thermal model of the cable and the soil if the thermal conductivity of the soil is known. However, in the intertidal zone, seepage flows may occur between high and low tide which will lead to convective heat transport. This convective heat transport will lead to a more rapid lowering of the temperature of the cable.

In this contribution, thermal laboratory measurements are reported which quantify the influence of seepage flow on the heat transport around a model cable. The measurements are used to determine an equivalent thermal conductivity for seepage flow conditions. Even though the heat transport will have a convective component, determining a representative equivalent thermal conductivity allows the 2D heat transport models to be used in the intertidal zone. Burial depths at the landfall locations can thus be determined, even during periods with adverse weather.

21st International Conference on Soil Mechanics and Geotechnical Engineering (Vienna)

TC209