Analysis of the Influence of Bearing Plate Position on the Uplift Bearing Capacity of Low-Header CEP Single-Pile Foundations
Abstract
1. Introduction
2. Construction of the Simulation Analysis Model
2.1. Determination of Model Dimensions
2.2. Material Parameters
2.3. Finite Element Model Construction
2.3.1. Pile–Soil Model Construction
2.3.2. Mesh Division and Pile–Soil Contact
2.4. Boundary Constraints and Loading Method
3. Finite Element Simulation Result Analysis
3.1. Load–Displacement Result Analysis
3.1.1. Analysis of Load–Displacement Curve Trends
- During the initial loading stage, from 0 to 700 kN, the load–displacement curves for each group are linear and nearly coincide. This suggests that, within this range, the displacement increases only slightly as the load is applied, and the structure remains in the elastic phase. The curves are almost identical, indicating that the performance of the low-capacity pile foundation, regardless of pile cap position, is similar during this stage;
- During the mid-loading stage, from 700 to 1400 kN, the pile head displacement for each group continues to increase linearly; however, distinct trends begin to emerge. This behavior can be attributed to the activation of the bearing plate, which signifies that the pile foundations with different pile cap positions begin to exhibit divergent mechanical behaviors during this stage;
- When the load exceeds 1400 kN, the loading enters the later stage. At this point, the bearing plate has fully engaged. Due to factors such as variations in the bearing plate positions among the model groups, the trends of the curves diverge significantly. Specifically, for the M1 to M6 groups, as the position of the bearing plate is moved one pile cap overhang radius closer to the pile tip, the pile’s pullout capacity increases notably. Among these, the pullout capacity improvement is most efficient in the M4 to M5 groups. However, for the M6 group and beyond, although the pullout capacity continues to increase, the rate of improvement becomes significantly limited. This phenomenon clearly demonstrates that the bearing plate position has a substantial effect on the pile’s pullout capacity. Once the bearing plate is fully engaged, this effect becomes more pronounced and is clearly reflected in the load–displacement curve trends.
3.1.2. In-Depth Comparison and Analysis of Load–Displacement Curves
- During the initial loading stage, from 0 to 1500 kN, the slopes of the curves for all groups are relatively small, indicating that, at this stage, displacement increases only slightly as the load is applied, and the structure remains in the elastic phase. The trends of the W0 and W1 groups are similar, while the trends of the W2 to W9 groups exhibit a similar pattern. This suggests that, in the early loading stage, differences in load–displacement responses start to emerge between the different groups;
- During the mid-loading stage, from 1500 to 2500 kN, as the load increases, the slopes of the curves for all groups gradually become steeper, indicating that the rate of displacement increase begins to accelerate. The load–displacement curves for the W0 and W1 groups exhibit a sharp downward trend, with the pile head displacement increasing significantly until it no longer converges. For the W2 to W9 groups, the trend reveals that, due to the varying positions of the bearing plate, displacement differences become progressively more pronounced. This indicates that, in the mid-loading stage, the pile head displacement of the W0 and W1 groups undergoes more significant changes, while displacement differences among the W2 to W9 groups increase as a result of the differing bearing plate positions;
- After 2500 kN, the loading enters the later stage. The slopes of the curves for all groups become steeper, and the rate of displacement increase accelerates as the structure transitions into the plastic stage. The pile head displacement differences for the W2 to W9 groups increase sharply. For the W2 to W6 groups, as the position of the bearing plate moves one pile cap overhang radius away from the pile head, the pullout capacity increases significantly. However, when the bearing plate is moved a certain distance away from the pile head, the efficiency of pullout capacity improvement diminishes. This indicates that, in the later loading stage, the pile head displacement differences for the W2 to W9 groups increase notably, and the pullout capacity for the W2 to W6 groups is influenced by the position of the bearing plate, with an optimal distance range existing.
3.1.3. Comparison and Analysis of Pullout Displacement Contour Maps of Low-Capacity Bored Cast-in-Place Pile Foundation and Low-Capacity CEP Single-Pile Foundation
- During the initial loading stage, from 0 to 1500 kN, the pile body of the W0 group low-capacity bored cast-in-place pile foundation undergoes significant displacement, and the soil above the pile cap experiences considerable sliding, as shown in Figure 9b. In contrast, for the W5 group low-capacity CEP pile foundation, the pile body exhibits relatively small displacement, the sliding range of the soil above the pile cap is smaller, and the bearing plate has not yet started to function, as shown in Figure 9b’;
- As the load increases from 1500 kN to 2500 kN, entering the mid-loading stage, the pile body displacement of the W0 group pile foundation increases dramatically, and the sliding of the soil above the pile cap expands rapidly, eventually forming a “fan-shaped” sliding zone. The ANSYS simulation fails to converge, and loading is terminated, as shown in Figure 9c. In contrast, for the W5 group pile foundation, the soil above the bearing plate gradually starts to slide and continues to increase, with the bearing plate beginning to function. The soil above the pile cap also begins to bulge, as shown in Figure 9c’;
- When the load reaches 2500 kN, entering the later loading stage, the sliding of the soil above the bearing plate and pile cap for the W5 group pile foundation gradually expands, eventually forming a “fan-shaped” sliding zone, as shown in Figure 9d’.
3.1.4. Displacement Contour Map Analysis Under Vertical Tensile Force
- The pullout capacity of the low-capacity CEP single-pile foundation increases as the distance between the bearing plate and the pile head grows. However, once the bearing plate moves a certain distance away, the rate of increase in pullout capacity slows significantly. This phenomenon occurs because, during the pullout process, the interaction between the soil above the bearing plate and the soil above the pile cap becomes increasingly significant. When the bearing plate reaches a critical distance from the pile head, the effect of this mutual interaction diminishes, and the bearing plate and pile cap begin to resist the pullout load independently. As a result, increasing the distance between the bearing plate and the pile head beyond this point does not substantially enhance the pullout capacity;
- In the W1 group, the bearing plate is positioned too close to the pile head, which leads to sliding failure of the soil above the bearing plate during the pullout process, causing a loss of pullout capacity. Additionally, the presence of the bearing plate reduces the side friction of the pile body compared to the W0 group. Consequently, the pullout capacity of the low-capacity bored cast-in-place pile foundation in the W0 group exceeds that of the low-capacity CEP single-pile foundation in the W1 group.
3.2. Comparison and Analysis of Shear Stress Contour Maps Under Vertical Tensile Force
- When subjected to vertical tensile force, the load tension gradually transfers from the upper structure (e.g., column) to the pile cap. In the case of the bored cast-in-place pile foundation, the stress on the pile cap spreads outward and is also transmitted downward through various parts of the pile body. In contrast, for the CEP pile foundation, the stress on the pile cap primarily spreads outward but is mainly transmitted downward to the upper portion of the pile body at the bearing plate. The stress on the lower part of the pile body beneath the bearing plate is minimal, with most of the stress concentrated in the upper central region of the bearing plate;
- Under vertical tensile force, analysis of the stress distribution on the pile cap reveals that the stress is highly concentrated in the central region, while it is relatively low at the edges. This suggests that the pile cap does not fully utilize its capacity during load-bearing. In other words, simply increasing the pile cap size does not lead to a proportional increase in load-bearing capacity. Once the pile cap reaches a certain size, its load-bearing capacity will plateau. Therefore, in practical engineering applications, it is sufficient to ensure the pile cap size meets the requirements specified in the engineering code, effectively preventing the unnecessary waste of concrete due to oversized pile caps, thus achieving both economic efficiency and rational design.
4. Conclusions
- The inclusion of a low-capacity pile cap also enhances the pullout capacity of the pile foundation. Therefore, it is important to consider the pile cap’s role in bearing the pullout load in order to reduce the number of piles required. However, the size of the pile cap does not lead to a proportional increase in pullout capacity. The load is distributed over a limited area of the pile cap before being transferred to the pile body. Thus, the pile cap size should only meet the requirements specified in the engineering design standards and need not be excessively large, thereby preventing unnecessary waste of concrete;
- Compared to the low-capacity bored cast-in-place pile foundation, the low-capacity CEP single-pile foundation exhibits notable differences in the distribution pattern of pullout displacement, the magnitude of displacement, and its impact on the foundation’s stability. It is clear that the introduction of the bearing plate significantly enhances the pullout capacity of the low-capacity pile foundation;
- The pullout capacity of the CEP single-pile foundation varies significantly with the position of the bearing plate. As the bearing plate is placed further from the pile cap, the pullout capacity increases. However, once the bearing plate reaches a certain distance, the pullout capacity levels off. Additionally, when the bearing plate is positioned too close to the pile head, the soil above the bearing plate experiences overall sliding failure, resulting in a sharp decrease in pullout capacity. Therefore, the bearing plate should not be positioned too close to the pile head;
- The placement of the bearing plate should be determined by considering factors such as the pullout capacity of the low-capacity CEP single-pile foundation, the distance at which the bearing plate influences the soil beneath the pile cap, and the point at which the bearing plate begins to function. Based on these considerations, it is recommended that the bearing plate be positioned at a distance of d1 = 4R0 to 5R0 from the pile head;
- Given that stress concentrations are relatively high at the junction between the bearing plate and the pile body, it is advisable to design this region with a curved shape. This approach effectively mitigates stress concentration, thereby reducing the risk of failure.
Author Contributions
Funding
Data Availability Statement
Conflicts of Interest
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Group | W1 | W2 | W3 | W4 | W5 | W6 | W7 | W8 | W9 |
---|---|---|---|---|---|---|---|---|---|
Pile length d1 (mm) | 500 (1R0) | 1000 (2R0) | 1500 (3R0) | 2000 (4R0) | 2500 (5R0) | 3000 (6R0) | 3500 (7R0) | 4000 (8R0) | 4500 (9R0) |
Material | Density (t/mm3) | Elastic Modulus (MPa) | Elastic Modulus | Cohesion (MPa) | Friction Angle (°) | Friction Coefficient |
---|---|---|---|---|---|---|
Clay | 1.688 × 10−9 | 40 | 0.35 | 0.04355 | 10.7 | 0.3 |
Concrete | 2.25 × 10−9 | 3.0 × 104 | 0.2 | -- | -- |
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Qian, Y.; Qi, D.; Mou, Y.; Wang, X.; Wang, Z.; Sun, L.; Ma, Z. Analysis of the Influence of Bearing Plate Position on the Uplift Bearing Capacity of Low-Header CEP Single-Pile Foundations. Buildings 2025, 15, 1353. https://doi.org/10.3390/buildings15081353
Qian Y, Qi D, Mou Y, Wang X, Wang Z, Sun L, Ma Z. Analysis of the Influence of Bearing Plate Position on the Uplift Bearing Capacity of Low-Header CEP Single-Pile Foundations. Buildings. 2025; 15(8):1353. https://doi.org/10.3390/buildings15081353
Chicago/Turabian StyleQian, Yongmei, Deshun Qi, Yu Mou, Xihui Wang, Ziyu Wang, Lin Sun, and Zhongwei Ma. 2025. "Analysis of the Influence of Bearing Plate Position on the Uplift Bearing Capacity of Low-Header CEP Single-Pile Foundations" Buildings 15, no. 8: 1353. https://doi.org/10.3390/buildings15081353
APA StyleQian, Y., Qi, D., Mou, Y., Wang, X., Wang, Z., Sun, L., & Ma, Z. (2025). Analysis of the Influence of Bearing Plate Position on the Uplift Bearing Capacity of Low-Header CEP Single-Pile Foundations. Buildings, 15(8), 1353. https://doi.org/10.3390/buildings15081353