Interface friction angle of glauconitic sands for pile design

The soil-to-steel residual interface friction angle (δres) is an important parameter for designing monopiles. The δres is usually obtained using the ring shear or the interface direct shear box test. To date, there is a limited body of knowledge on interface behaviour of glauconitic soil, and no database or guidelines are available on how to obtain reliable estimates of δres in glauconitic soil Obtaining res can be challenging as the glauconitic soil may behave sand- or clay-like dependent on the degree of particle crushing taking place either in advance of the test as part of the specimen preparation procedure or during the test itself. This can result in under- or overestimation of δres depending on how tests are performed in the laboratory. The current research presents a preliminary database of Bishop-NGI ring shear tests results on glauconitic sands. Effects of grain crushing, time, vertical effective stress, glauconite and fines content, were investigated. This database is meant to aid the offshore industry in the estimation of δres for design practice.