Experimental study of the shear strength behaviour of carbonate sands from the northeastern coast of Brazil

The development of wind energy in offshore areas has to deal with carbonate soils in coastal regions. In Brazil, offshore wind farm projects with prospects for implementation on the northeastern coast require further research, as detailed geotechnical studies of carbonate soils in this region are scarce. Therefore, this paper presents a comparative study of a quartz sand and two carbonate sands from the coast of Ceará in northeastern Brazil. The samples were characterized, analyzed with XRF, SEM, grain breakage analysis, and tested with direct shear tests and drained triaxial tests. The offshore carbonate sand specimens exhibited higher shear strength parameters in most tests, with friction angle increases of 23.5% and 22.5% from the loose to the dense state in direct shear and triaxial tests, respectively. Conversely, the quartz sand mostly displayed intermediate values in these parameters, suggesting that there is no direct correlation between calcium carbonate content and shear strength.