Seabed trenches, as a geological hazard, have an adverse influence on the adjacent anchors. Seabed trenches mainly appear in the Gulf of Guinea, where the seabed soils have some features, e.g., high plasticity, high water content and low shear strength. However, the marine engineering geology where seabed trenches appear is still unrevealed, as well as the trenching process related to soil erosion. In this paper, the information about seabed trenches was summarized, and marine engineering geology where seabed trenches appear was analyzed. Then, penetration tests of a chain-bar penetrometer were conducted to investigate the soil deformation and erosion near the surface. Experimental observations reveal that the normalized soil resistances from both penetrometers exhibited similar trends, although the soil deformation mechanisms were different. In the cyclic tests, the soil resistance was degraded significantly in the first 20 cycles, and water flow induced by chain motion eroded the soil particles near the chain links. This paper provides some insights into the marine engineering geology and development process of seabed trenches.

clay, erosion, subsea structure, shear strength, deformation