Centrifuge Test on Bearing Capacity of Energy Piles in Sand Affected by Thermal-Cool Cycles
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摘要:
为研究砂土中能源桩在热冷循环温度作用下的承载能力，开展不同密实度奉浦砂土中细长能源桩的离心机模型试验. 试验中进行20次热-冷温度循环作用，获得能源桩轴力、侧摩阻力、单桩承载力等的变化规律，并进行对比研究. 试验结果表明：随着温度循环次数增加，能源桩桩身轴力均逐渐衰减并趋于稳定，且中密砂中能源桩最大轴力衰减值远高于密砂中能源桩；在热冷温度循环过程中，中密砂中能源桩桩身中下部存在中性点，在冷循环过程中中性点以上存在正的附加侧摩阻力，下部存在负的附加侧摩阻力，而在热循环过程中中性点以上存在负的附加侧摩阻力，下部存在正的附加侧摩阻力；密砂对能源桩下部存在明显的约束作用，使其在冷循环过程中全桩身相对桩周土体存在向下的位移趋势，产生全桩身正的附加侧摩阻力，而热循环过程中产生负的附加侧摩阻力；长期循环荷载作用使得能源桩的桩基承载力发生折减，与相应原型桩相比，埋设于中密砂和密砂中的能源桩承载力分别减小了7.3%和15.6%；密砂中的原型桩及能源桩承载力均高于中密砂中原型桩约11%；当实际工程中能源桩处于不同密实度的砂土层中时，需采取合理的措施，以满足能源桩的承载要求.
Abstract:To study the bearing capacity of energy piles in sand affected by thermal-cool cycles, a centrifuge model test on slender energy piles buried in Fengpu sand with different compactions was carried out. The change rules of the axial force, side friction, and individual bearing capacity of energy piles were obtained and compared under 20 thermal-cool cycles in the test. The test results show that the axial force of the energy pile decays gradually and tends to be stable with increasing thermal-cool cycles. The maximum axial force attenuation value of the energy pile buried in the sand with medium compaction is much larger than that buried in the dense sand. During thermal-cool cycles, for energy piles buried in the sand with medium compaction, a neutral point is located at the bottom half of the pile. Positive additional side friction is generated above the neutral point during cool cycles, and negative additional side friction is generated underneath the neutral point. Oppositely, during thermal cycles, negative additional side friction appears above the neutral point, and positive additional side friction is underneath the neutral point. The dense sand has an obvious constraint effect on the lower part of energy piles. Positive additional side friction is distributed along the pile during cool cycles because the pile moves downward relative to the surrounding soil. During thermal cycles, the additional side friction is negative. The bearing capacity of the energy piles will be reduced because of the long-term temperature cycles. The bearing capacity of the energy piles buried in the dense sand and sand with medium compaction is reduced by 7.3% and 15.6%, compared with the prototype pile. The bearing capacity of the prototype pile and energy piles buried in the dense sand is 11% larger than that of the prototype pile buried in the sand with medium compaction. Therefore, reasonable measures should be taken to meet the bearing requirements of energy piles when buried in sandy layers with different compactions in actual engineering.
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Key words:
- energy pile /
- centrifuge test /
- bearing capacity /
- temperature cycle /
- compaction
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图 6 不同循环次数下能源桩桩身轴力衰减曲线
Figure 6. Axial force attenuation curves of energy pile under different temperature cycles
图 7 末次热循环过程不同温度下桩身轴力
Figure 7. Axial force of energy pile at different temperatures during last thermal cycle
图 8 末次热循环过程中不同温度下桩身附加轴力
Figure 8. Additional axial force of energy pile at different temperatures during last thermal cycle
图 9 末次冷循环过程中不同温度下桩身轴力
Figure 9. Axial force of energy pile at different temperatures during last cool cycle
图 10 末次冷循环过程中不同温度下桩身附加轴力
Figure 10. Additional axial force of energy pile at different temperatures during last cool cycle
图 11 循环温度荷载作用下桩侧摩阻力变化
Figure 11. Side friction variation of energy pile with temperature cycle
图 12 末次热循环过程中不同温度下桩身附加侧摩阻力
Figure 12. Additional side friction of energy pile at different temperatures during last thermal cycle
图 13 末次冷循环过程中不同温度下桩身附加侧摩阻力
Figure 13. Additional side friction of energy pile at different temperatures during last cool cycle
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