## 3 Results and Discussions
### Results of Combined Loading
#### 3.3.1 Uplift Loading Effect on Lateral Capacity of Helical Pile  
A series of numerical analyses were done on a fully embedded single helical pile in order to study the influence of uplift load on the lateral capacity of the helical piles. The spacing ratio and the number of helices are varied and the embedment depth ratio is kept constant. The numerical analysis is carried out by applying a simultaneous lateral load and uplift load on the helical pile. Figure 15 shows the effect on lateral capacity when the helical pile is subjected to uplift loading as Q = 0, 0.25 Q\({}_{\text{u,ult}}\), and 0.5 Q\({}_{\text{u,ult}}\). It is evident that the lateral capacity decreases when the helical pile is subjected to uplift load. [PERSON] et al. [19] reported the same for multi-plate helical piles embedded in cohesionless soil subjected to combined loads.  
The ultimate lateral capacity of the helical pile constructed as per IBC [7] for the analyzed piles under different loading conditions and the measured values are presented in Table 4. It is seen from the table that the greater the magnitude of uplift load applied,  
Figure 14: Capacity ratio vs. Embedment depth ratio.  
Figure 15: Effect of uplift loading on lateral capacity of helical pile.  
the greater the percentage decrease. When the pile SHP-1 having a lateral capacity of 0.0928 kN is subjected to 25% and 50% uplift loads, there is a nearly 8% and 12% reduction in lateral capacity, which is 0.0854 kN and 0.0814 kN, respectively. Furthermore, increasing the number of helical plates from SHP-1 to SHP-4, the percentage decrease almost equals zero. Thus, designing a helical pile and choosing the number of helical plates possesses a vital role in the reduction of lateral capacity. As seen from Figure 15, it is clear that the reduction in lateral capacity is recovered as the number of helical plates is increased. From a design viewpoint, this recommends that the inclusion of more helical plates is essential whenever the pile needs to withstand lateral forces with tension loads. The reason for the recovery in lateral capacity due to a further increase in tensile load is explained by [PERSON] et al. [19] as the upward movement of a helical pile tends to increase the radial stress with depth.  
Figure 16 shows the variation of bending moment with depth for a helical pile subjected to pure lateral, and then under combined lateral and uplift loading. The arrow in the figure represents the direction of loading. It is seen from the result that the uplift capacity induces more bending moment at the core of the shaft. The plastic moment capacity of the pile considered here is M\({}_{\text{p}}\) = 0.190 kNm (\(D\) = 14 mm and steel yield strength, \(\sigma_{y}\) = 415 MPa). The maximum bending moment caused by the combine loading is significantly less compared to plastic moment capacity; hence no plastic hinge is formed in this case. It is important to keep in mind that screw piles that are designed to resist lateral movement may need to have bigger cross-sections to be able to withstand more weight. Moment capacity, on the other hand, may be a factor that cannot be ignored when designing screw piles.