In-situ strength testing of deep-sea superficial sediments using a high-resolution ball penetrometer

Deep-sea engineering requires precise evaluation of seabed sediments properties. However, traditional in-situ testing instruments struggle to identify low-strength sediment and cannot operate effectively beyond 6000 m. This study introduced a high-resolution ball penetrometer designed to assess in-situ undrained shear strength of deep-sea sediments. Firstly, the penetrometer integrated optical fibers as core sensing components with a pressure differential structure. Subsequently, the resolution and pressure resistance of the penetrometer were thoroughly examined. The penetrometer's performance was evaluated through the laboratory, harbor basin, and deep-sea tests. Finally, the penetrometer was utilized to investigate sediment properties in a deep-sea mining area. The results demonstrate that: (a) the penetrometer's design allows sensors to perform under pressure up to 120 MPa; (b) the pore water pressure and penetration resistance sensors maintain resolutions 0.1 kPa and 0.5 N, respectively; (c) it detects subtle changes in sediment properties more effectively than conventional T-bar and CPTu; (d) it is especially suited for testing ultra-soft sediments; (e) the sediment in the Western Pacific mining area exhibits variability, including stratified structures and weak layers. © 2024 Elsevier Ltd