Horizontal and Uplift Bearing Characteristics of a Cast-In-Place Micropile Group Foundation in a Plateau Mountainous Area
Abstract
:1. Introduction
2. Field Testing of Micropile Group Foundations
2.1. Experimental Overview
2.2. Experimental Loading Process and Result Analysis
3. Numerical Simulation Study of the Micropile Foundation
3.1. Establishment of Numerical Model
3.2. Comparison and Analysis of Experimental and Inversion Results
4. Study on Horizontal Uplift Combined Loads
4.1. Pile Strain Response
4.2. Distribution of Average Lateral Frictional Resistance
4.3. Bearing Characteristics under Uplift–Horizontal Load Interaction
5. Conclusions
- (1)
- During the field uplift loading test of micropile group foundations in the plateau mountainous area, the load distribution among individual piles is relatively uniform. The load is transmitted from top to bottom until it reaches the ultimate limit state. The lateral friction resistance of the pile body in the micro pile group foundation follows the order: Part 3 > Part 1 > Part 2.
- (2)
- The micropile group foundation has an ultimate uplift bearing capacity of 1200 kN with a steep load–uplift displacement curve. Its horizontal bearing capacity is 620 kN with a gradual load–horizontal displacement curve. The numerical inversion results are in good agreement with the experimental data, confirming the feasibility of numerically studying the bearing behavior of micro pile group foundations.
- (3)
- Under the combined load–coupling effect, the additional moment M1 generated by the unbalanced lateral friction resistance on both sides of the pile cross-section is greater than the additional moment M2 generated by the P–Δ effect. As a result, the relative displacements and lateral friction resistance on the left and right sides of the upper part of the foundation are different from those under individual uplift loading conditions, and the piles located farther from the soil under compression exhibit larger net bending moments.
- (4)
- Compared to the condition of applying uplift load alone, the flexural deformation of the pile caused by the application of combined loads results in an increase in lateral friction resistance on the Part 2 side, while the lateral friction resistance on both the Part 1 and Part 3 sides decrease. As a result, the overall lateral friction resistance of the pile decreases, leading to a reduction in the ultimate uplift bearing capacity of the foundation. Moreover, the larger the horizontal load, the more significant the reduction effect.
- (5)
- The bearing performance of the micropile group foundation under U–H combined loading is related to the load ratio parameter, n. As n decreases, the uplift bearing capacity of the micropile group foundation continues to weaken, while the horizontal ultimate bearing capacity gradually increases. When n = 0.76, the horizontal bearing capacity of the foundation becomes equivalent to the horizontal bearing capacity under the action of a single horizontal load.
- (6)
- Based on regression analysis of experimental data, the horizontal bearing capacity follows a fourth-order function relationship with the reciprocal of the load ratio, while the uplift bearing capacity exhibits a second-order function relationship with the reciprocal of the load ratio. These bearing characteristics differ from those observed under single-direction loading. The enclosed area between the yield envelope and the plumb line of unidirectional ultimate bearing capacity under the combined load is divided into the “failure zone” and “safety zone.” The reduction in uplift capacity within the “failure zone” should be considered during the pile foundation design.
Author Contributions
Funding
Institutional Review Board Statement
Informed Consent Statement
Data Availability Statement
Acknowledgments
Conflicts of Interest
References
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Sample ID | Sampling Depth/m | Water Content/% | Plasticity Index | Compression Modulus /MPa | Poisson Ratio | Cohesion /kPa | Internal Friction Angle/(°) |
---|---|---|---|---|---|---|---|
1 | 0~1.6 | 22.94 | 12.5 | 14.9 | 0.33 | 12.50 | 25.60 |
2 | 1.6~3.0 | 20.12 | 13.0 | 15.3 | 0.32 | 14.89 | 28.45 |
3 | 3.0~3.9 | 19.89 | 11.6 | 18.8 | 0.30 | 20.47 | 15.05 |
4 | 5.2~5.8 | 22.18 | 14.5 | 19.4 | 0.29 | 23.08 | 17.39 |
5 | 5.8~6.2 | 21.86 | 14.8 | 21.5 | 0.30 | 23.61 | 17.87 |
6 | 8.0~9.0 | 24.43 | 15.1 | 15.4 | 0.32 | 17.18 | 30.49 |
Type of Load | Field Test (kN) | Simplified Standard Calculation Method (kN) | Deviation Rate |
---|---|---|---|
Uplift Load | 1200 | 1109 | 7.6% |
Lateral Load | 620 | 596 | 3.9% |
Name | Depth /m | Density /(g/cm3) | Elastic Modulus /MPa | Poisson Ratio | Cohesion /kPa | Internal Friction Angle/(°) |
---|---|---|---|---|---|---|
Silty gravel | 0~3 | 2.09 | 4.9 | 0.32 | 13.70 | 27.03 |
Silty sand | >3 | 2.13 | 8.2 | 0.30 | 21.39 | 16.77 |
Pile body | \ | 2.50 | 31,500.0 | 0.20 | \ | \ |
Pile cap | \ | 2.50 | 31,500.0 | 0.20 | \ | \ |
Upper columns | \ | 2.50 | 31,500.0 | 0.20 | \ | \ |
Name | Shear Stiffness | Normal Stiffness | Cohesion/kPa | Internal Friction Angle/(°) |
---|---|---|---|---|
Interface 1 | 7 × 109 | 7 × 109 | 10.96 | 21.62 |
Interface 2 | 7 × 109 | 7 × 109 | 17.11 | 13.42 |
Ratio of Uplift to Horizontal Load | 10:1 | 5:1 | 4:1 | 3:1 | 2:1 | 1:1 | 2:3 | 1:2 | |
---|---|---|---|---|---|---|---|---|---|
failure load /kN | uplift | 1030 * | 1020 * | 996 * | 950 * | 840 | 560 | 395 | 304 |
horizontal | 105 | 204 | 249 | 316 | 420 * | 560 * | 592 * | 608 * |
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Li, H.; Ren, G. Horizontal and Uplift Bearing Characteristics of a Cast-In-Place Micropile Group Foundation in a Plateau Mountainous Area. Sustainability 2023, 15, 13554. https://doi.org/10.3390/su151813554
Li H, Ren G. Horizontal and Uplift Bearing Characteristics of a Cast-In-Place Micropile Group Foundation in a Plateau Mountainous Area. Sustainability. 2023; 15(18):13554. https://doi.org/10.3390/su151813554
Chicago/Turabian StyleLi, Haitao, and Guangming Ren. 2023. "Horizontal and Uplift Bearing Characteristics of a Cast-In-Place Micropile Group Foundation in a Plateau Mountainous Area" Sustainability 15, no. 18: 13554. https://doi.org/10.3390/su151813554