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摘要: 基于多年冻土区桩基混凝土的设计与施工, 研究了多年冻土区大直径钻孔灌注桩的早期回冻规律, 通过桩基现场试验并结合数值仿真模型分析了桩周混凝土水化热和桩周冻土回冻规律。分析结果表明: 在灌注完成后25 d内桩侧温度在1℃以上, 在灌注完成45 d后桩侧温度逐渐恢复到0℃; 数值模拟结果显示在灌注完成60 d后桩身温度下降至0℃, 在灌注完成200 d后桩周土体回冻至天然状态; 入模温度每提高2℃, 桩侧峰值温度提高1℃左右, 而2倍桩径处峰值温度提高0.5℃左右。可见, 在大直径桩基条件下桩基混凝土中可以不添加或少添加早强剂, 也没有必要刻意降低拌合物入模温度; 桩基的施工时间最好安排在暖季, 为混凝土的养生提供较好的外部条件。Abstract: Based on the design and construction of pile foundation concrete in permafrost regions, the early refreezing law of large-diameter cast-in-place pile in permafrost regions was studied. Through pile filed test and numerical simulation model, the hydrate heat of concrete and the permafrost refreezing law around pile were analyzed. Analysis result shows that pile side temperature is above 1 ℃ within 25 d after finishing pouring, and gradually recovers to 0 ℃ in 45 d after finishing pouring. Numerical simulation result shows that the pile temperature decreases to 0 ℃in 60 d after finishing pouring. The soil mass around pile is refrozen to natural state in 200 d after finishing pouring. Every 2 ℃ increase of molding temperature results in 1 ℃ increase of peak temperature at pile side and 0.5 ℃ increase of peak temperature at two times of pile diameters away. For large-diameter pile foundation, the addition of hardening accelerator to pile foundation concrete can be avoided or decreased. It is not necessary to sedulously decrease the molding temperature of mixture. The best construction time of pile foundation is in warm seasons, which can provide a good external condition for concrete curing.
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图 2 桩基地温监测剖面
Figure 2. Monitoring sections of ground temperatures for pile foundations
图 7 计算温度与监测温度的对比
Figure 7. Comparison of calculated temperature and monitored temperature
图 8 桩身温度与天然地温的对比
Figure 8. Comparison of pile temperature and natural ground temperature
图 10 不同入模温度下桩侧温度随时间的变化
Figure 10. Variation of temperature at pile side with time under different molding temperatures
图 11 灌注完成5 d后桩侧温度随深度的变化
Figure 11. Variation of temperature at pile side with depth in 5 d after finishing pouring
图 12 灌注完成30 d后桩侧温度随深度的变化
Figure 12. Variation of temperature at pile side with depth in 30 d after finishing pouring
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