Assessment of friction properties at geotextile encapsulated-sand systems' interfaces used for coastal protection

Friction properties at geotextile interfaces play an important role in the stability of geotextile encapsulated-sand systems in coastal protection. The stabilising action of the frictional force is important to oppose sliding along the contact surface and to prevent deformations, which may lead to structural failures. This paper presents a set of experiments, based on large-scale direct shear tests performed under both cyclic loading and cyclic displacement conditions, examining friction at interfaces between geotextile specimens, sand-filled geosystem elements, and between a sand layer and a sand-filled geosystem element. The results presented here indicate that the friction parameters (i.e., shear strength and friction angle) derived from geotextile specimens are below those obtained for sand-filled elements, which suggests that using the former for the stability analysis is conservative. The tests carried out with a sand layer surface showed that a modification to the shear plane slope is likely to occur – for the sand-filled geosystem element buries into the sand layer. This deformation can result in toe instability, ultimately leading to progressive damage or even collapse of the entire structure.