A suction pile is a promising option when floating offshore structures are deployed at deep and distant locations. A suction pile is typically used for the foundation system of a mooring system subjected to horizontal loading with a load inclination. In this study, the effects of installation method, loading position, and load inclination on the behavior of a suction pile under monotonic horizontal loading were evaluated via large-scale soil chamber testing. A series of horizontal load tests were performed by varying the loading position at pile embedded lengths of 1/4, 1/2, 2/3, and 3/4. A horizontal load test with a load inclination of 20° was conducted and compared with that of a load inclination of 0°. The failure mechanism of the suction piles under monotonic horizontal loading was assessed via particle image velocimetry (PIV) analysis. The movement of the suction pile during monotonic horizontal loading was elucidated in terms of the horizontal displacement, vertical displacement, and rotation angle. The results of this study show apparent differences between jacking and suction-installed piles and piles under different loading conditions. The PIV analysis shows that the rotational behavior under monotonic horizontal loading can be a critical point to affect the horizontal resistance of the suction pile.

This paper presents the reliability-based resistance factor calibration of driven steel pipe piles and the implementation of Load and Resistance Factor Design (LRFD) on practical design cases. Resistance factors of driven steel pipe piles were calibrated in the framework based on reliability theory using static pile load test results. The results of fifty seven load tests conducted to failure were compiled and these 57 data were divided into three different groups based on their data quality. For the three groups, reliability analyses were performed for two static bearing capacity equations and for different target reliability indices (2.0 and 2.33 for group piles and 2.5 for single piles) following the First-Order Reliability Method (FORM) and using the Monte Carlo Simulation (MCS). It is noted that the resistance factors were highly dependent on the quality of load test data. To implement the calibrated resistance factors, a case study on an actual bridge foundation design was performed. The case study result showed that, for the given target reliability index, the developed LRFD method using the resistance factors calibrated in this study could contribute to cost savings when it is compared with Allowable Stress Design (ASD) case using a safety factor of 3.0.

A monopile is the most conventional structure foundation for offshore wind turbines (OWTs) in the world. However, the Korean offshore wind industry has mostly been using the jacket type of foundation. The main reason for the current situation in Korea is that most of the marine soil consists of weak layers of sand and clay. Thus, the monopile foundation depth has to be deep enough to satisfy the intended serviceability design requirement of the monopile and the rotation limit at the seabed; a conventional monopile design concept alone might be insufficient in Korean offshore conditions, or otherwise could be very expensive, e.g., resulting in a rock socket installation at the tip of the monopile. The main objective of this paper is to introduce a novel hybrid monopile that is composed of a monopile and a supplemental support with three buckets, followed by assessing the lateral resistance of the hybrid system through physical experiments and finite element (FE) simulations. Namely, 1/64.5 small-scaled monopile and hybrid physical models with a monopile diameter of 7 m for a 5.5 MW OWT were loaded monotonically. The results show that the hybrid monopile improves the lateral bearing capacity regarding the initial lateral stiffness and ultimate load. The FE analyses of the corresponding physical models were also implemented to support the results from the physical model test. The numerical results, such as the structural member forces and soil deformation, were analyzed in detail. Additionally, a case study using FE analysis was conducted for the 5.5 MW OWT hybrid monopile support installed in a representative Korean weak soil area. The results show that the hybrid monopile foundation has a larger lateral resistance and stiffness than the monopile.

Large-diameter monopiles that can safely support the lateral loads caused by wind and waves have been widely used for the foundations of offshore wind turbines. However, when the penetration depth is insufficient as a result of the presence of thick soft ground or it is difficult to penetrate rock, the lateral load capacity of the monopiles may be insufficient, leading to structural instability of the wind turbine system. To address this problem, hybrid monopiles have been proposed, which include appendages such as suction buckets attached around the monopiles installed on the seabed. Such suction buckets are arranged in the form of a tripod at 120° intervals with respect to the center of the monopile. These increase the bending resistance of the monopile by sharing the lateral load applied to it. Although the proposed monopiles were presented as conceptual foundation types, their actual support mechanisms and bearing capacity improvement effects must be verified experimentally. In this study, a centrifuge model test was conducted to identify the support mechanism of hybrid monopiles and the degree of improvement in their bearing capacity compared to the existing large-diameter monopiles. The experiment results showed that an appendage composed of suction buckets dispersed the load acting on the monopile, thereby significantly increasing its bearing capacity.

In this study, a new type of suction pile foundation for floating structures, namely group suction piles, was proposed to improve the shortcomings of conventional single suction piles. Small-scale model tests were performed to estimate the horizontal behavior of single suction piles and group suction piles with different pile spacing (2, 3 and 4 times the pile diameter) under various loading conditions in terms of loading locations and inclinations. The horizontal behavior of group suction piles with different pile spacing was analyzed for various loading locations and load inclinations based on the model tests. For the given group pile configurations (a group pile having 9 component piles with a pile formation of 3 × 3), the horizontal resistance increased with increasing pile spacing. The maximum ultimate horizontal resistances were found at the loading locations of 50% of the embedded depth. Unlikely in the single suction pile case, the significantly maintained residual resistances were found for group suction piles. The residual resistances of group suction piles were at least higher than 40% of the corresponding ultimate horizontal resistances.

This study presents an integrated framework that couples three-dimensional geotechnical ground modeling with a HAZUS-based urban seismic vulnerability assessment for Seoul, Korea. Over 63,000 boreholes, in situ seismic tests, and building inventory records were compiled into a unified relational database following rigorous multi-stage quality control. A multi-parameter N–Vs regression model was calibrated to supplement missing shear-wave velocity (Vs) data, reducing prediction errors by more than 20% relative to conventional empirical equations. Based on the quality-controlled Vs dataset, a high-resolution three-dimensional Vs–ground model was constructed to represent subsurface heterogeneity and associated uncertainty across the metropolitan area. The building inventory, comprising approximately 700,000 structures, was standardized according to the HAZUS structural taxonomy and mapped to Korean seismic design eras, enabling a Seoul-adapted vulnerability assessment in which exposure characterization and seismic demand are localized. Site-specific ground-motion amplification and response spectra derived from the 3D ground model were used to modify the spectral acceleration input to the HAZUS fragility functions. Results reveal pronounced spatial variability in site conditions, with northern mountainous zones corresponding primarily to NEHRP Site Class B, central districts to Class C, and southern alluvial basins to Classes D–E, producing amplification differences of up to 1.7 under identical input spectral accelerations. High-risk zones such as Gangnam, Songpa, and Yeouido exhibit concentrated expected damage where thick alluvial deposits coincide with dense stocks of mid-rise reinforced-concrete buildings. Overall, the study demonstrates that integrating high-resolution 3D geotechnical ground models with HAZUS-based fragility analysis provides a physically consistent and data-driven basis for urban-scale seismic risk assessment and resilience planning.