## 3 Numerical Simulation of Uplift Capacity in Composite-Anchor Piles
### Parameter Study Results Based on Finite Element Method
Particularly when considering the logistics and transportation of materials, smaller diameter piles are more manageable and easier to transport. Therefore, a thorough assessment of site conditions, load requirements, and cost implications is necessary to make an informed decision regarding the pile diameter. The composite-anchor cable is the main reinforcement structure of the composite-anchor pile. To assist construction professionals in selecting suitable uplift pile configurations based on varying real-world project conditions, finite element simulations were conducted using three, four, and five composite-anchor cables. Figure 6 illustrates the changing trend of the pile top load-displacement curve in the three sets of simulations. It is evident from the figure that when comparing three composite-anchor cables to four composite-anchor cables, the pile top displacement decreases by 2 mm, and the bearing capacity increases by 10%. However, if the number of anchor cables is further increased to five, the pile top displacement only decreases by an additional 0.5 mm, and the bearing capacity only increases by 2%. In general, under these conditions, increasing the number of anchor cables effectively enhances the bearing capacity of the composite-anchor pile when the number of cables is less than four. However, when the number of anchor cables is four or more, having too many cables can lead to a wasted partial bearing capacity and increased cost burden. Furthermore, the composite-anchor pile is a more intricate structural component compared to the overall foundation, and having an excessive number of anchor cables may increase manufacturing difficulty and labor costs. Additionally, the fixed cross-section of the pile results in a higher reinforcement ratio when the number of cables is increased, which can lead to brittle failure under extreme loading conditions and compromise the overall stability of the structure. Therefore, conducting a comprehensive  
Figure 5: Load–displacement curves with different pile diameters. analysis and cost-benefit assessment to determine the optimal number of anchor cables for a specific project is crucial. The primary load-bearing component in the composite-anchor pile under investigation is the steel strand. The larger the diameter of the steel strand, the larger its cross-sectional area, resulting in lower section pressure under the same uplift load. With the material strength of the steel strand guaranteed, larger-diameter strands are less prone to deformation and can withstand higher uplift loads. Consequently, composite-anchor piles using larger-diameter steel strands experience smaller displacements at the pile top. But to optimize the structural design of composite-anchor piles, calculations were performed using two commonly used steel strand diameters: 15.2 mm and 21.8 mm. Figure 7 illustrates the numerical results of Type-C for varying strand diameters. The figure reveals that the bearing capacities of the pile with the two different steel strand diameters are comparable when the load is below level 6. Moreover, the displacement difference at the pile top during this stage is minimal, ranging from 0 to 1 mm. However, as the load progresses, the displacement difference between the two diameter steel strands at the pile top increases to a range of 1.5 to 3.0 mm. Therefore, in practical applications, trade-offs need to be made based on the structural load-bearing capacity. When the load conditions exceed 3840 kN, larger-diameter steel strands should be chosen. However, larger-diameter steel strands are usually more expensive and may impact the project's cost. Additionally, the installation of larger-diameter steel strands is more challenging and requires specialized equipment, which may increase labor costs and construction time. Therefore, when the load-bearing capacity requirements of the project are relatively low, smaller-diameter steel strands should be used.