Diameter and pile-sand stiffness effects on laterally loaded piles in centrifuge modelling

Offshore wind turbine demands have led to diverse and increasingly larger foundation pile diameters over the years. Although the effect of scaling pile diameter (D) on lateral loading capacity (H) has been studied, its relationship with pile–soil relative stiffness (E_e/G*) remains under-explored. This study presents centrifuge experiments on nine steel tubular piles subjected to monotonic loading with unload–reload cycles in drained sand. All piles share the same diameter-embedded depth ratio and load eccentricity but vary in wall thickness and are tested under different centrifuge accelerations, resulting in nine prototype diameters and three distinct E_e/G* values. This controlled setting allows for examining the applicability of the generalised scaling law (GSL) for modelling diameters beyond small centrifuge limits. Results indicate a power-law relationship between H and D, described by parameters that vary with E_e/G*. The effects of E_e/G* are insignificant until the relative loading displacement (Y/D) reaches 10%. For low E_e/G*, better lateral response normalisation can be achieved by considering structural non-linearity. The re-loading stiffness (E) also approximates a power-law relation with D, and the higher relative stiffness (E_e/G* = 417) case shows the largest drop in E. GSL shows acceptable accuracy at small Y/D and lower E_e/G* before the pile enters non-linearity.