An experimental study on pile scour mitigating measures under waves and currents

Abstract

An experimental study has been carried out to investigate effects of four flow-altering scour countermeasures placed around a foundation pile under currents only as well as under coexisting waves and currents. The countermeasures are sacrificial piles, downstream bed sill, sleeve and slot in the pile. Their arrangements follow the suggested optimal configurations, with some of them slightly modified. In terms of the evolution of scour depth and bed topography around the pile, the scour countermeasures are evaluated, subjected to steady currents with or without irregular waves. A comparison between maximum scour depth with the countermeasures and one without the countermeasures demonstrates the efficiency of countermeasures. All the tested scour measures reduce the scour depth by 17.6%-42.6% under the action of currents only and 5.8%-24.0% under the combined action of both currents and waves. The results also show that it takes a shorter time for the scour depth to reach its equilibrium with the measures under either coexisting currents and waves or currents only than ones without the measures.

A Review and Design Principle of Fixed-Bottom Foundation Scour Protection Schemes for Offshore Wind Energy

“…Flow-altering protection schemes can be introduced in the following four major categories, namely: (1) openings through piers, as shown in Table 1; (2) structure attachment, as shown in Table 2; (3) bed attachment, as shown in Table 3; (4) pile alteration schemes, as shown in Table 3. [45] 2012 Kumar et al [43] 1999 Tang et al [15] 2022 Tang et al [51] 2023 Liang et al [44] 2015 Jahangirzadeh et al [52] 2014…”

“…It is generally believed that the larger the diameter of the hole, the stronger its scouring protection [15,21,[41][42][43]. Liang et al [44] adjusted the hole size and arrangement position in the experiment, the scour depth reduction rate was always below 26.1% under the unidirectional flow and wave-current coupling conditions, thus the scour protection effect was considered less than ideal. In other experiments, the single slotting scheme only has a scour depth reduction rate less than 35%, such as the experiments of Tafarojnoruz et al [45].…”

“…Therefore, when considering the horizontal plate protection scheme, we should first consider the layout position in the horizontal plane or the area below it. For the effect of horizontal plate diameter on scour protection ability, Liang et al [44] experimentally concluded that diameters of three times the pile diameter have better scour protection ability than those that are two times the pile diameter. Vertical plates and vanes are another major category of structural attachments.…”

“…The maximum scour depth reduction rate of the group with the best effect in their experiments was 50%. Liang et al [44] found that the extended foundation with three times the pile diameter has better scour protection effect compared with the extended foundation with two times the pile diameter, and the maximum scour depth is reduced by 89.4% and 61%, respectively. Yao et al [65] found that, unlike the scour development pattern under an unprotected foundation, scour development under an extended foundation starts from behind the pile and extends to the front of the pile.…”

A Numerical Model for the Scour Effect on the Bearing Capacity of an Offshore Wind Turbine with a Five-Bucket Jacket Foundation

“…Scouring can lead to a decrease in bearing capacity, which can threaten the response and stability of the overall structure of offshore wind power. Therefore, the prediction and prevention of scouring have also garnered attention from related scholars [37]. Kishore et al [38] conducted experiments on two different stiffness monopile foundations in soft clay with and without scouring under different eccentric lateral loading conditions.…”