Stiffened sand compaction piles for coastal applications: A numerical assessment

Forming a stiffened sand compaction pile (SSCP) by placing a small-diameter pile as a core inside a sand compaction pile (SCP) can theoretically offer several advantages in marine sediments. However, SSCPs have only been validated for accelerating consolidation and facilitating rapid embankment construction; their effectiveness as a foundation system for marine infrastructure under seismic and environmental loads in multi-layered soils (soft clay and liquefiable sand) has not yet been assessed. To address this, numerical simulations were validated against three full-scale observations and one centrifuge test. Subsequently, the responses of a single SSCP under vertical and lateral loading were compared with those of a pile having identical core dimensions. The same comparative approach was then adopted to evaluate the efficiency of the SSCP as a foundation system for three types of coastal infrastructure. Results indicate that placing a pile inside an SCP can increase vertical and lateral capacity by up to 3 and 1.8 times, respectively, reduce seismic-induced maximum axial forces and bending moments, and decrease settlement and tilt. Finally, to assess the trade-off between performance gain and environmental cost, the carbon footprint (CF) of the SSCP relative to a same-geometry pile was quantified and used to normalize the observed improvements.