As the global transition to renewable energy accelerates, ensuring the reliability of foundations in offshore structures is increasingly important. In the context of floating wind structures, pile foundations can be used as anchor points for station keeping against significant cyclic loading. Tubular piles have proven reliable while offering a high tensile load capacity, but accurate predictions of pile tensile capacity and stability without extensive testing are essential to avoid overconservative design. This paper presents findings from the Tubular Pile Pull-out Testing (TPPT) Joint Industry Project, which involved field testing on tubular steel piles under monotonic and multi-stage cyclic loading at the Port of Rotterdam. This paper primarily discusses the comparison between predicted and measured pile capacity and stability under cyclic loading. The predictions were based on interaction charts recommended in the literature for piles under tensile loading. Pile responses in interaction charts are classified as stable, metastable, or unstable based on their displacement responses to the applied cyclic loading in relation to the static capacity. The results observed in the field tests are compared with the stability response previously defined in the literature. In particular, the TPPT testing programme included tests near the chart zone where stable and metastable curves converge towards the unstable zone, where the proximity between curves leads to uncertainties in determining pile stability.

The tunnels located in the shallow depths of loose saturated sand are significantly prone to liquefaction-induced uplift. Research works are, therefore, in progress to propose efficient techniques for mitigating uplift. In this study, 1 g physical modeling was used to assess the performance of helical piles for decreasing liquefaction-induced uplift. The effects of pile length, number of pile helixes, and the pile spacing in plan view were investigated. The uplift mechanism of the tunnel and helical pile system was also analyzed. The results demonstrate that the penetration of the helical piles into the dense layer underlying the superficial liquefiable sand has decreased tunnel uplift significantly. However, excessive close pile spacing along the tunnel resulted in shear surface interference, and the efficiency of the excessive number of helical piles decreased significantly. The detailed view of the uplift mechanism showed that utilization of the piles extended the transition phase of uplift during shaking. Helical piles can efficiently restrict the possibility of rapid uplift of the tunnel and shorten the duration of the primary uplift phase.

This paper presents a new empirical model to predict the mean period (T_m) as a frequency-content parameter of earthquake record using the strong ground motions recorded in Iran during 1975–2019. An updated earthquake databank containing 2281 horizontal acceleration records was employed to develop the empirical model through a systematic fitting procedure. A simple functional form for the model was found as a function of epicentral distance (R), moment magnitude (M_w), and the shear wave velocity averaged at the top 30 m of the recording sites (V_s30). The proposed model is compared with three existing predictive models and the results are discussed in terms of magnitude, source-to-site, and site dependencies.