Static and seismic responses of pile-supported marine structures under scoured conditions

• Main Author: Jiang, Wenyu
• Other Authors: Lin, Cheng
• Format: Others
• Language: English; en
• Published: 2021
• Subjects: Local scour; Pile tension capacity; Vertical effective stress; Scour-hole dimensions; Sand; Offshore wind turbine; monopile; Earthquake; Liquefaction; Soft clay; Soil stress history; Pile group; Lateral capacity
• Online Access: http://hdl.handle.net/1828/13557; Jiang, W., Lin, C., 2021. Scour effects on vertical effective stresses and lateral responses of pile groups in sands. Ocean Eng. 229, 109017. https://doi.org/10.1016/j.oceaneng.2021.109017; Jiang, W., Lin, C., Sun, M., 2021. Seismic responses of monopile-supported offshore wind turbines in soft clays under scoured conditions. Soil Dyn. Earthq. Eng. 142, 106549. https://doi.org/10.1016/j.soildyn.2020.106549; Lin, C., Jiang, W., 2019. Evaluation of vertical effective stress and pile tension capacity in sands considering scour-hole dimensions. Comput. Geotech. 105, 94–98. https://doi.org/10.1016/j.compgeo.2018.09.013

Scour is a process of removing soils around foundations by currents and waves. For the pile-supported marine structures such as the monopile-supported offshore wind turbines (OWTs) and the pile-supported bridges, scour can decrease the pile capacities and alter the dynamic responses of the structures. At present, there is not a widely accepted method to estimate pile axial or lateral capacity under scoured conditions. For example, different recommendations are used among the existing design standards for estimation of the vertical effective stress and the resulting capacities for single piles under different scour conditions. None of the existing standards or design practice has even considered the scour effects on the behavior of pile groups. Furthermore, the investigation into the responses of piles under multiple hazards of scour and earthquakes is rarely reported. To address the foregoing limitations, this study first introduces an analytical solution to determining the vertical effective stress of soils around single isolated piles under scoured conditions and uses it to examine the limitations of the existing standards in estimation of pile tensile capacity (Chapter 1). The effect of soil-pile interface friction is highlighted. Next, the study proposes new approaches to investigating the combined effects of scour and earthquakes on the lateral responses of the monopile-supported OWTs in sand (Chapter 2) and soft clay (Chapter 3). Lastly, simple and practical methods are developed based on the p-y curve framework for analyzing the lateral responses of pile groups in sand (Chapter 4) and soft clay (Chapter 5) subjected to static lateral loading. The proposed methods in this study were encoded into a series of open-source computer scripts for engineering practice. They were verified with the 3D continuum finite element (FE) analyses. Using the proposed methods, standard methods, and 3D FE method, parametric analyses were conducted to investigate the scour effects on the lateral behavior of the monopile-supported OWTs under crustal earthquakes and that of the pile groups under static loading. The factors considered in the parametric study included effects of scour-hole dimensions, soil stress history, soil density, soil-pile interface behavior, soil liquefaction potential, pile group configurations, etc. Through the parametric analyses, the standard methods were critically assessed by comparing the results to those calculated by the proposed methods and 3D FE methods, and some design-related issues were also discussed. === Graduate