Evaluating the use of HaSPro for predicting deformation of small rock gradings under opposing waves and currents

When designing loose rock scour protection for jacket foundations, it is common practice to idealise each jacket leg as an equivalent monopile diameter to sup-port the analysis. It is also typically assumed that scour development around a jacket leg is self-similar to that of a monopile, although this may not always be the case. Jacket foundations are generally installed in deeper water, where near-bed hydrodynamic con-ditions can be less severe; this can allow designs with smaller rock grades (e.g. CP32/90, CP45/125, CP45/180). As part of a wider study, HR Wallingford assessed the performance of scour protection at large jacket foun-dations typical of offshore substations and compared the results with those for an equivalent monopile. The study had several objectives, including evaluating whether scour processes at these more complex jacket foundations are self-similar to those at monopiles, and assessing the applicability of recent industry guidance (Handbook of Scour Protection, Deltares, 2023; and DNV Recommended Practice for rock scour protection for monopiles, 2022). This paper fo-cuses on the results of the monopile tests conducted with waves and opposing currents compared against the design approach outlined in Deltares (2023).