Geotechnical Characterization of Marine Unconsolidated Sediments for Cable Routing between the Islands of Madeira and Porto Santo

Abstract

Pombo, J.; Rodrigues, A., and Lapa, N., 2020. Geotechnical characterization of marine unconsolidated sediments for cable routing between the islands of Madeira and Porto Santo. In: Malvárez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1245–1251. Coconut Creek (Florida), ISSN 0749-0208.The national economic sustainability strategy encourages the use of oceanic territory and resources for the reduction of dependency on fossil fuels. Submarine cables are subject to several risks, especially those associated with the seafloor stability processes, which are not described by the normal characterization of the marine sedimentary layer. As such, to ensure the safety and economic success of any new project it is essential to know the properties of the seabed, in particular, the geotechnical ones. Only in this way it will be possible to estimate and mitigate the natural hazards effects (e.g. submarine movements and landslides) or excessive burial of the electric power cable that could compromise the integrity of the infrastructure. If unavoidable, protection actions and measures should be taken, when submarine cables cross any rocky area, or highest slope area. In this paper, we will present the results of the geotechnical characterization of the marine soils along a corridor between Madeira and Porto Santo Islands. Unconsolidated sediments were collected in both islands and results of laboratory analysis (grain size, water content, carbonate content, Atterberg limits and triaxial tests) indicate the occurrence of frequent downslope mass movements in both islands.