## 3 Numerical Simulation of Uplift Capacity in Composite-Anchor Piles
### Numerical Simulation Based on Finite Element Method  
Based on previous research findings, it has been determined that the influence range of composite-anchor piles on the surrounding soil during vertical uplift bearing capacity tests is approximately twice the pile diameter. The load at the top of the pile has negligible effects on the deformation and stress of the soil beyond this range. Therefore, in order to minimize the number of elements and simplify the computational process, the finite element model was created by extending the pile body 20 times the pile diameter outward. ABAQUS 2020 software was used for modeling, and Figure 2 illustrates the three-dimensional numerical model of the composite-anchor pile. The modeling depth was set at 30 m, with an extension of 8 m below the pile base. The three-dimensional finite element model represents a cylinder with a diameter of 16 m and a height of 30 m. The uplift pile has a diameter of 0.8 m and a height of 22.0 m, located at the center of the model. The composite-anchor cable within the uplift pile consists of steel strands, grout, and steel pipes, each with a length of 22.0 m. These elements are distributed around the pile body, with a concrete protective layer thickness of 70 mm, in accordance with the actual field conditions. A detailed modeling approach was employed based on the structural characteristics of the composite-anchor pile. The model comprises a total of 78,716 elements, with 41,180 elements specifically dedicated to simulating the uplift pile. To accurately represent the structural design while ensuring mesh convergence [26; 27], the internal composite-anchor cable was subdivided into 34,020 elements, accounting for approximately 82.6% of the overall uplift pile model. After establishing the solid model, vertical and lateral displacement constraints were applied at the bottom of the model, normal horizontal constraints were imposed around the model, and gravity load was applied. During the modeling process, the material property parameters are chosen based on the actual parameters of the materials used in the field load tests. These parameter values align with the experimental study mentioned in reference [22] and can be found in Tables 3 and 4 of the study. By utilizing these specific material property parameters, the model can more accurately replicate the behavior of the composite piles observed in the experimental study. Figure 2: Three-dimensional numerical model: (**a**) overall model; (**b**) cross-section of uplift pile; (**c**) section of main reinforcement of composite-anchor cable [20]. In the analysis of the bearing capacity of composite piles, several parameters were selected for investigation. Firstly, four different pile sizes were chosen, namely 800 mm, 900 mm, 1100 mm, and 1200 mm. These sizes are commonly used in large-diameter pile foundation projects and are suitable for various soil types and load requirements. The selection of pile size in civil engineering depends on factors such as soil properties, load requirements, and specific project conditions. By considering these common pile sizes, the research results can be more widely applicable to different engineering scenarios. Secondly, the number of anchor cables was considered as an important parameter affecting the bearing capacity and stability of composite piles. In practical engineering, the selection of the number of anchor cables is based on design requirements, soil conditions, seismic requirements, and other factors. In the field load tests, four anchor cables were chosen as the primary configuration, and additional configurations with three and five anchor cables were included as control groups. This allows for a broader range of working conditions to be studied and analyzed. Lastly, the diameter of the steel strand was investigated as another significant factor influencing the bearing capacity and stability of the pile. Different diameters of steel strands exhibit different strength and stiffness characteristics, which directly impact the pile's bearing capacity.