IN SITU OBSERVATION OF SUBMARINE SLOPE DEFORMATION AND SLIDING

Tidal channels are widely distributed in the Zhoushan islands, and submarine slope instability events are widely developed. Frequent submarine landslides pose a great threat to offshore facilities such as submarine optical cables, sea reclamation projects, ports and wharfs. The investigation and research on its occurrence mechanism has attracted more and more attention. Based on the self-developed seabed deformation observation system, combined with the pore water pressure observation system and hydrodynamic observation system, this paper has carried out 75 day deformation observation on the typical seabed slope in the southwest of Zhujiajian island in Zhoushan since August 29, 2019. The results show that the sediment deformation in the observation range is divided into three parts. The cumulative deformation of the sediment on the potential sliding surface at the bottom of the seabed slope(12~13.5m under the seabed) is about 0.75mm. The lateral deformation process presents the characteristics of step change, and the deformation direction is consistent with the slope tendency, and the top deformation is consistent with the tidal direction. It is found that the change of tide level will change the change of sediment excess pore water pressure, and the change of excess pore pressure difference between deep and shallow sediments is the main trigger factor for the lateral deformation of potential sliding surface of submarine slope in the observation area. There are many tidal channels in the sea area of Zhoushan islands, and the instability of submarine slopes is widely developed.