This paper addresses the phenomenon of seafloor scouring generated by mass gravity flows in deepwater settings, focusing on the influence of a surficial crust on seafloor scour characteristics. Clay sediments within the crust zone are characterized by undrained shear strengths greater than the undrained shear strength of clay sediments immediately below the crust. Finite-element analysis is used to investigate the influence of a surficial crust extending within the upper 1.5 m below seafloor on mass gravity flow induced near-seafloor sediment deformation pattern for a flow in the far-field and at the location of a mudmat supported subsea structure. Analysis results corresponding to a flow in the far-field revealed that for the same flow thickness the presence of a seafloor crust would result in a near-seafloor failure wedge of smaller lateral extent compared to the failure wedge mobilized for a seafloor with no crust. Additionally, minimum flow thickness required to initiate seafloor scouring increases with increasing crust strength. For a flow at the edge of the mudmat, a greater crust strength would translate into a greater flow thickness required to mobilize sediments underneath and adjacent to the mudmat and cause seafloor instability at the mudmat location. It was also found that for a flow of specific thickness in contact with the subsea structure, the ultimate horizontal load required to trigger instability of the mudmat-subsea equipment system increases with increasing crust strength.
Aurelian C. Trandafir
Keywords: mass gravity flow, seafloor scour, surficial crust, mudmat, finite-element modeling
Publisher: DFI