doi:10.1007/s13344-020-0056-y

Performance of X-Section Concrete Pile Group in Coral Sand Under Vertical Loading

doi: 10.1007/s13344-020-0056-y

PENG Yu^{1, 2},
LIU Jia-yi³,
DING Xuan-ming^{1, 2
, ,},
FANG Hua-qiang^{1, 2},
JIANG Chun-yong^{1, 2}

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Corresponding author: DING Xuan-ming, E-mail: dxmhhu@163.com

摘要

Abstract: To reveal the bearing capacity of the X-section pile group in coral sand, a series of model load tests are conducted. The testing results are presented as load−settlement curves, pile−soil stress ratios, distributions of side friction and axial force, and load-sharing ratio between side and tip resistances. The reliability and accuracy of the numerical simulation model are veriﬁed by comparing the results of the model test. Comparative analysis between X-section and circular section piles with the same cross-sectional area indicates that the bearing capacity of the X-section pile group is much larger than that of the circular pile group. The axial force of X-section piles is smaller while the peak skin friction is larger than that of circular piles at the same depth. The skin friction of the core pile is the largest, followed by the side pile and the corner pile is the smallest when the load is relatively small; however, it is converse when the load is larger than 10 kN. Compared with piles in silica sand, the pile in coral sand has a lower bearing capacity, and the sand breakage leads to the steep drop failure of pile foundation. Moreover, pile positions under the raft have less effect on the load-share differences among corner, side and core piles in coral sand. This study provides a reference for the construction of pile foundations in coral sand.
- X-section pile group /
- coral sand /
- model test /
- numerical analysis /
- pile−soil stress ratio

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Figure 1. Layout of piles and apparatus in model test.

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Figure 2. Fabrication of the X-section model pile.

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Figure 3. Contrast of P−S curves between circular and X-section piles.

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Figure 4. Distributions of axial forces.

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Figure 5. Comparison of distribution of axial forces under different loads.

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Figure 6. Distribution of skin friction.

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Figure 7. Comparison of distribution of skin friction under different loads.

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Figure 8. Load-sharing ratio of side resistance and tip resistance.

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Figure 9. Distributions of (a) axial force and (b) side friction along depth of piles.

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Figure 10. Load-sharing ratio of side resistance and tip resistance in the 4-pile group.

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Figure 11. Comparison of load-displacement curves between numerical simulation and model test.

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Figure 12. Distributions of (a) axial force, (b) side friction between numerical simulation and model test.

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Figure 13. Comparative axial forces of (a) corner pile, (b) side pile, and (c) core pile under the raft.

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Figure 14. Relationships between axial force and vertical load in stimulation of corner, side, and core piles under several typical depths.

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Figure 15. Comparative side frictions of (a) corner pile, (b) side pile, and (c) core pile under the raft.

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Figure 16. Relationships between skin friction and settlement of (a) corner pile, (b) side pile, and (c) core pile.

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Figure 17. Relationship between load sharing and vertical load of piles under different locations under the raft.

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Table 1. Basic parameters of coral sand used in this test

Ground soil	Coral sand	Silica sand
Proportion, G_s	2.74	2.65
Maximum dry density, $ {\textit{ρ}}_{\rm{max}}$ (g/cm³)	1.70	1.68
Minimum dry density, $ {\textit{ρ}}_{\rm{min}}$ (g/cm³)	1.08	1.42
Depth, z (cm)	70	70
Cohesion, C_cu (kPa)	0	0
Friction angle, w_cu (°)	35	34
Uniformity coefficient, C_u	2.42	1.22
Curvature coefficient, C_c	1.02	0.97
Moisture content, v (%)	0	0
Relative density	0.68	0.71

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Table 2. Parameters used in numerical simulation models

Materials	Constitutive model	Modulus, E (MPa)	Poisson’s ratio, $ {\textit{ʋ}}$	Cohesion, c_cu (kPa)	Friction angle, $ {\textit{φ}}_{\rm{cu}}$ (º)	Unit weight, $ {\textit{γ}}$ (kN/m³)	Lateral coefﬁcient, K₀
Pile	Elastic	30000	0.20	−	−	24.50	1
Pile raft	Elastic	206000	0.25	−	−	76.44	1
Soil	Mohr-Coulomb	40	0.30	0	34	16.17	0.48
Contact surface	Coulomb sliding	−	−	0	28	−	−

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