Observation and evaluation of soil stratum deformation in reclamation area under ocean tides

Reclamation areas in coastal regions serve as primary human settlements, where groundwater undergoes fluctuations due to changes in ocean tides, resulting in deformation variations within the soil stratum. In this paper, the UWFBGs (ultra-weak fiber Bragg grating arrays) technique with micro strain accuracy and meter-scale resolution was used to investigate the soil stratum strain under ocean tidal effects. Through observations made at a borehole in Yushan Island, Zhoushan, China, semi-diurnal and spring-neap cycles of soil stratum deformation were identified, and the main influencing factor for soil tidal intensity within borehole depth was further analyzed. The concept of "soil stratum tidal strain energy density" was proposed to quantify the extent of soil deformation influenced by ocean tidal effects and four levels were divided to evaluate the borehole stratum. The results were of great importance for precise monitoring of soil deformation, and analysis of subsidence characteristics in reclamation areas.