###### Abstract  
Offshore wind energy development is driven by ongoing research and development to determine technological issues connected with offshore wind turbines. A fundamental design difficulty is the offshore wind turbine foundations. By far, one of the most commonly practiced foundation systems is mono helical pile foundations because of their simplicity and resilience. Most of the studies on mono helical piles were focused on granular soils and few studies were on clayey soils. However, mono helical piles in clayey soils under combined loading remain to be examined. Hence, a series of three-dimensional finite element analyses were carried out to predict the uplift and lateral capacity of the helical pile embedded in soft clay. The numerical model is verified using the results from the analytical results and a small-scale laboratory test. The verified model is used to simulate the helical pile behavior under the combined uplift and lateral loading condition considering the pile with a different number of helical plates. The results of the combined loading analyses reveal that the lateral capacity decreased when the pile was subjected to uplift load, and a maximum reduction of 12% is observed in mono helical piles provided with a single plate for an applied 50% of the ultimate uplift load. The influence of uplift load also increased the bending moment of the helical pile. Finally, it is suggested that the helical piles should be designed considering the aspects for combined loading conditions. mono helical pile; combined loading; offshore foundations; earth anchors; deep foundations 202212682720222022202202202220220222022202220222202  
anchoring, and bridges. The usage of this pile offshore declined in the period of the 1890s and 1990s, among other developments of various foundation techniques such as bored piles, ground anchors, and driven piles where the application is more predominantly for onshore construction [4; 5]. Helical pile anchors also used as a tension-resistant foundation technique and effectively control the heave or uplift of footing on expansive clay beds [6]. Nowadays, helical piles are well recognized in abundant uses such as offshore mooring systems, underpinning, pedestrian bridges, guy wire anchors, tie-backs while excavating, house foundations, transmission and wind energy towers, and solar panel installations [5]. It is included as deep foundations in the International Building Code 2015 (IBC 2015) (Chapter 18, Section 1810) [7] where geotechnical and structural design specifications are given for tensile and compressive loading conditions. Much research has been carried out to examine the helical pile behavior under pure compressive, uplift, and lateral loads. [PERSON] et al. [8] and [PERSON] et al. [9] proposed the first method for evaluating the axial capacity of helical piles in order to design multi-helix helical piles in cohesive soils. The \"individual bearing method\" and the \"cylindrical shear method\" are the two most often used methods for estimating the load capacity of multi-helix piles. The results of [PERSON] et al. [8] show that the transition from cylindrical shear failure to individual plate bearing failure occurs at a particular spacing ratio S/D, where S is the inter-helix spacing and D is the diameter of the helical plate, and it is found as greater than 1.5. However, [PERSON] [4] discovered that this transition is mostly reliant on the stiffness and type of the soil, with no discernible S/D between the two modes. In terms of embedment depth (H), [PERSON] and [PERSON] [10], [PERSON] et al. [11], [PERSON] [4], and [PERSON] [5] investigated the deep and shallow failure modes in detail. [PERSON] et al. [11] carried out an experimental investigation in remolded soft marine clays by placing the model helical anchors at different embedment depths and found that when the embedment depth ratio (H/D) is kept at less than two, it governs the shallow failure mode. They identified deep failure modes as those that govern when the H/D is greater than four.