Bearing capacity of helical pile group foundation in clay over silty sand

Recognized as a growing priority in offshore foundation engineering, helical piles demonstrate exceptional operational stability and lifecycle cost advantages, solidifying their role in modern marine infrastructure development. However, limited knowledge regarding the bearing capacity and failure mechanisms of helical pile group foundations under multi-directional loads in layered soils poses significant challenges for design and optimization of offshore wind platforms and other marine structures. This paper investigates the bearing capacity and failure mechanisms of the helical pile group foundation embedded in layered clay-over-silty-sand soil profiles using numerical simulation. The numerical model is validated against previously exhibiting published data before conducting a parameterized study. Key findings demonstrate that group configurations significantly enhance horizontal capacity compared to single piles, while clay-over-silty-sand stratification induces distinct delamination-type failure mechanisms of the soil around helical pile, contrasting with the global plastic flow observed in uniform clay. The study establishes the normalized bearing capacity envelopes for vertical-horizontal-moment (VHM) loading cases and provides algebraic equations to facilitate conservative design practices. These results offer valuable insights into optimizing the design of the helical pile group foundations for offshore wind platforms and other marine applications.