Surficial Crust Effects on Mass Gravity Flow Induced Seafloor Scour Characteristics-Paper

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The study uses finite-element analysis to examine how a stronger surficial clay crust affects seafloor scouring caused by mass gravity flows and the stability of mudmat-supported subsea equipment. The crust, extending up to 1.5 m below the seafloor, has greater undrained shear strength than the underlying clay. Analyses modelled flows in the far field, at the mudmat edge, and in contact with the equipment.<br /><br />In the far field, a crust reduces the lateral extent of the sediment failure wedge but has little effect on its maximum depth. It also raises the minimum flow thickness needed to initiate scouring. For crust strengths 2.5–5.5 times the intact seafloor strength, this threshold is 2.2–3 times that for an uncrusted seafloor.<br /><br />Near the mudmat, stronger crust likewise increases the flow thickness required to trigger seafloor instability. A flow at the mudmat edge requires 1.2–2.4 times the minimum thickness needed for a comparable far-field failure, partly because the structure buttresses the sediments. With a crust, failure surfaces extend below the mudmat skirts and become increasingly rotational as crust strength rises.<br /><br />When a flow contacts the equipment, the crust increases the ultimate horizontal load required to destabilize the mudmat–equipment system, expanding its failure envelope. It also shifts some failure mechanisms—such as inverted-scoop and planar sliding—from the skirt region into weaker clay beneath the crust.<br /><br />Overall, a surficial crust can delay scour and improve resistance to flow-induced instability, but it changes where and how failure develops. The findings are based on two-dimensional numerical analyses; three-dimensional effects require further study.

Keywords

finite-element analysis

surficial clay crust

seafloor scouring

mass gravity flows

undrained shear strength

mudmat stability

subsea equipment

sediment failure wedge

flow-induced instability

scour resistance