In order to reasonably determine the scour protection measures and engineering quantities
it is necessary to accurately estimate the local scour range and volume of the pile foundations. Based on the analysis of concepts such as internal friction angle of sediment particles
underwater angle of repose
and slope angle of scour pits
this article uses effective data from 240 sets of unprotected pile foundation scour monitoring at an offshore wind farm in Yancheng
Jiangsu and 96 sets at an offshore wind farm in Zhanjiang
Guangdong. Local scour pits are generalized as annular circular cones
and the empirical relationship between local scour pit slope angle and scour depth is statistically analyzed. A new method for calculating the local scour volume and range of pile foundations under the combined action of waves and current is proposed. The verification using the reserved 60 sets of scour monitoring data showed that the local scour range and volume of the pile foundation calculated according to the formula based on internal friction angle in the current specifications were significantly smaller
while the scour volume calculated by the method in this paper was quite close to the measured volume as a whole. The local scour pit of the pile foundation is located below the bed surface
and the sediment particles on the slope do not need to be in a critical incipient-motion. The slope angle is smaller than the underwater angle of repose and internal friction angle. The calculation formula for local scour range in current standards should be revised accordingly. This method provides a basis for adopting targeted scour protection measures and developing reliable scour protection devices. However
in the future
it is still necessary to continue accumulating local scour monitoring data of offshore pile foundations to continuously improve the calculation accuracy of scour volume and range.