Mechanism of low-disturbance and high-pressure-retaining sampling of seafloor sediments at 10000-meter depth and its laboratory experiment and on-site sea trials

Abstract

Obtaining high-quality 10000-meter-deep seafloor sediment samples is the prerequisite and foundation for conducting deep-sea geological and environmental scientific research. The bottom structure of the deep seafloor is complex, and the physical and mechanical properties and disturbance resistance of sediments of different lithologies vary greatly, so the sediment sampler inevitably disturbs the sediments during the sampling process and affects the quality of the sediment samples. A new type of deep-sea sediment pressure retaining sampler is introduced, the force state and elastic–plastic state of the sampler destroying sediments are analyzed, the radial disturbance model of sediment coring based on the spherical cavity expansion theory is established, and the radius of sediments undergoing plastic deformation around the spherical holes is used as an index for evaluating the radial disturbance of sediments. The distribution of stress and strain fields in the sediments during the expansion of the spherical cavity and the influencing factors of the radius of the radially disturbed region (plastic region) are analyzed using an arithmetic example, and the influence law is analyzed. A sediment disturbance experimental platform was built indoors to simulate the sediment coring process. The radial stress field and pore water pressure of the sediment during the coring process were monitored by sensors arranged inside the sediment, and the results of indoor tests verified the correctness of the perturbation theory model. The sampler was carried aboard the deep-sea manned submersible FENDOUZHE and conducted on-site tests at depths of 9298.4 and 9142.8 m in the Kuril-Kamchatka Trench. Pressure-preserved sediment samples were retrieved, with preservation rates of 94.21% and 92.02%, respectively, which are much higher than the current technical indicator of 80% of pressure-holding ratio for deep-sea sediments. The retrieved sediments have obvious stratification characteristics and little disturbance.