Understanding rock–steel interface properties for use in offshore applications

The properties of unbonded rock–steel interfaces and the characteristics that control this behaviour seem to be an under-researched area in terms of geotechnical application, for example in the design of gravity-based foundation systems or dead weight anchors and the interaction of pipelines on rock. Although basic guidance does exist for rock–rock interfaces or pipeline behaviour, this focuses on macro roughness, with little consideration of micro roughness, relative roughness of the surfaces or their strengths and hardness. Therefore, in order for design and understanding to develop in these areas, there is a need for basic interface friction parameters and understanding of the interface characteristics that control the strength of the interface, such that correct values can be used, but also so that the interface properties can be best manipulated to improve interface interaction. This paper presents interface friction angles for four types of rock sheared against steel interfaces of different roughness at a variety of normal stresses. The rocks themselves have a range of surface roughness, strength and hardness. The results of the testing programme are used to improve a simple analytical approach for predicting the shear strength of rock–steel interfaces that allows input of key controlling parameters.