Up-lift resistance of pipelines within a rock berm

Abstract

Recently, it has become more economically viable to protect and stabilise shallow water pipelines by creating rock berms on the sea-bed rather than using conventional trench and burial techniques. Quantifying both the magnitude of the vertical resistance to buckling and the pipeline movement to mobilise the resistance through the rock berm remains critical to both the pipeline and rock berm design. This paper summarises the results from previous R&D physical test programmes conducted by University of Western Australia and Oxford University, on behalf of TechnipFMC, to quantify the vertical resistance and mobilisation of the resistance through rock berms. Further the results of these physical tests have then been used three-fold. First to review and assess the empirical methods that are currently presented in literature and in code to estimate the vertical up-lift resistance of a rock berm. Second to provide recommendations on up-lift factors, Af, which improve on current up-lift resistance estimates using the standard empirical approach presented in code. Thirdly to calibrate and validate numerical rock berm models, in particular to define appropriate FEA parameters, which can be used with confidence to undertake future parametric studies to assess the impact of berm width and berm side slope angle on the ultimate vertical resistance provided by a rock berm.