Investigating the Geological Processes Controlling the Geotechnical Behaviour of Carbonate Sediments

The seabed of Australia’s offshore wind areas comprises a significant proportion of carbonate sediments, likely in excess of 50 to 90% depending on the region. Carbonate sediments have long been considered problematic for geotechnical engineering applications as their properties are typically outside the ranges defined for silica sediments. This knowledge gap limits the ability to accurately characterise offshore wind sites with only limited geotechnical data – i.e. significant volumes of site-specific testing is required – which affects project schedule and cost.

This study integrates a database of more than 1200 individual CPTs and nearly 1500 individual boreholes from the North West Shelf of Australia, one of the largest carbonate shelves in the world, to better understand the effect of geological processes on the geotechnical properties of carbonate sediments. The results show that cementation, water depth and sediment source have the strongest influence on their geotechnical properties. Post-depositional reworking of the sediments, including through mass transport deposits, could also be an important contributor to sediment variability. The study demonstrates that the geotechnical behaviour of carbonate sediments can be spatially related to the geological processes that affected them during and after deposition and can therefore be estimated from regional geological data.