## 1 Introduction
Numerical and analytical studies have also contributed to the body of research on the lateral behavior of monopile foundations. In this regard, the pile-soil interaction has commonly been investigated using solid elements for numerical methods [24; 25; 26; 27; 28] as well as discrete spring elements for both analytical and numerical methods [8; 29; 30; 31]. The PISA project is one of the most comprehensive studies in this realm, intending to improve the conventional p-y method by incorporating supplementary soil resistance components that are significant for monopiles with a low L/D ratio [32]. Termed as diameter effect, pile tip resistance and interface frictional resistance along the pile surface--as shown in Figure 1--become considerable for large-diameter monopiles with a low L/D ratio [10; 33; 34; 35]. Therefore, the PISA project accounted for the large diameter effect by considering four soil reaction components along the pile, namely, the lateral soil reaction along the shaft (p), the distributed moment reaction due to the vertical shear distribution along the pile (m), the shear force reaction at the pile base (\(H_{B}\)) and the moment reaction due to the normal stress distribution at the pile base (\(M_{B}\)) [8]. The latest revisions of the DNVGL-ST-0126 guideline suggest that the p-y curves utilized in monopile design should undergo validation via finite element (FE) analysis. Nevertheless, there is currently no consensus on the best method to achieve this in practice [26]. Although previous research has presented different methodologies to conduct such analysis for a wide range of monopile dimensions in homogenous and layered soils, their assumptions should be tested in different offshore site conditions. A literature review reveals that while studies on monopiles in sandy soils or rock-socketed foundations are abundant--reflecting the predominant site conditions in South Korea--few have focused on clay soil profiles in the region. Rigorously validated numerical studies based on large-scale monopile load tests in clay provide a valuable insight into monopile foundation performance, though such studies are limited in the literature. Therefore, more studies are required to develop a comprehensive understanding of the subject and to enrich the database needed to adapt the new design methods. Moreover, simplified one-dimensional methods, as proposed by API and DNV, are still used at the tender design stage and optimization of an entire wind farm, due to their analytical convenience when performing all the necessary design iterations. In the present study, the lateral response of monopile foundations in clay has been investigated using 3D numerical modeling and the 1D standard p-y method proposed by common standards. The numerical model has been verified against the results of a large-diameter monopile test conducted by the PISA team at the Cowden site. The 1D standard p-y method, henceforth termed as the 1D DNV p-y method, has been conducted using a commercial finite difference software equipped with the p-y curve formulations suggested by [PERSON] (1970) and [PERSON] (1975) for soft and stiff clay, respectively [11; 36]. The difference between the predicted lateral response of the monopiles of various geometries using the above-mentioned methods has been evaluated for both small (service) and large (ultimate) displacements. Furthermore, the contribution of different resisting soil components on the lateral capacity of monopiles has been identified for various slenderness  
Figure 1: Schematics of an OWT support structure, loads acting on it, and resisting components in the foundation system. ratios, and some design aspects such as the minimum embedment length criteria have been investigated. Finally, several conclusions are drawn, providing factual insights into the shortcomings of the current practice in monopile design, merits offered by numerical modeling, and possible recommendations for improving the current standard p-y method.