Scour Protection Design Methodology

For details of the code implementation, please see Scour Protection Design API.

Scour Protection Design

This module calculates the required scour protection material for a fixed substructure to avoid seabed erosion around the installation. It is based on a DNV GL standard and geometric calculations.

The potential depth of the a free forming scour pit is calculated using a simplified version of the relationship presented in the DNV GL report (equation J.5):

\(\frac{S}{D} = 1.3\)

where \(S\) is the calculated depth of the scour pit and \(D\) is the overall diameter of the substructure. The default value (1.3) is a conservative assumption and may be overridden by the user as follows:

config = {
    ...

    "scour_protection_design": {
        "scour_depth_equilibrium": 1.2
    }

    ...
}

The radius of the scour pit is then calculated using the soil friction angle (\(\phi\)) and a simple geometric relationship:

\(r = \frac{D}{2} + \frac{S}{tan(\phi)}\)

The default value for \(\phi\) is 33.5deg, representing the soil friction angle for medium density sand. The total volume of scour protection material is then calculated as follows,

\(V = \pi * t * r^2\)

where \(t\) represents the depth of the scour protection material. This value defaults to 1m in the code, which represents an appropriate initial assumption and not a complete design. For sites that exhibit greater seafloor currents, the scour protection layer may be as thick as 2m, whereas calmer sites may only need 0.3-0.5m of material. In the abscense of a geotechnical study, this value is difficult to calculate and is instead presented to user as a configurable input so the cost impacts of different thicknesses can be investigated.

Terms:
  • \(S =\) Scour depth

  • \(D =\) Monopile diameter

  • \(r =\) Radius of scour protection from the center of the monopile

  • \(\phi =\) Soil friction angle

Default Assumptions:
  • \(\frac{S}{D} = 1.3\)

  • \(\phi = 33.5\) * Angle for medium density sand

References