During pile-driving operation using a hollow stem auger (CFA-pile), the lowering of the reinforcement cage into the concrete over the last several meters is greatly affected by the rheological properties of the concrete. Concrete is cast without applying vibration requiring a highly fluid consistency. The concrete rest phase inside the boring cavity begins once concreting has been completed; this phase lasts 30 min or longer in some specific cases, extending until the reinforcement cage has been completely lowered, during this time the paste in concrete becomes restructured. No current test or recommendation serves to guarantee an appropriate casting process for successful lowering the reinforcement cage in a pile. A device has been developed to assess the capability of introducing reinforcement cages into plastic concrete. Tests were carried out both in the laboratory and on site. The restructuring of the concrete at rest due to its thixotropy or loss of workability has been evaluated with a rheometer and correlated to the reinforcement embedment capacity. A structural build-up threshold value and a critical static yield stress have been identified. Analysis of the results demonstrated the potential of the research results to improve the concrete mix design criteria for deep foundations produced with the CFA-piles technique.

中文翻译：

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混凝土地基流变特性对连续飞行螺旋（CFA）桩施工的影响

在使用空心钻杆 (CFA-pile) 打桩过程中，钢筋笼在最后几米内下降到混凝土中的过程受混凝土流变特性的影响很大。混凝土浇筑时不施加振动，需要高度流动的稠度。混凝土浇筑完成后，钻孔内的混凝土静止阶段开始；在某些特定情况下，此阶段会持续 30 分钟或更长时间，直至钢筋笼完全降下，在此期间，混凝土中的糊状物会重新构造。目前没有任何测试或建议可以保证采用合适的铸造工艺来成功降低桩中的钢筋笼。已经开发出一种装置来评估将钢筋笼引入塑性混凝土的能力。测试在实验室和现场进行。由于其触变性或和易性损失，静止混凝土的重组已使用流变仪进行评估，并与钢筋嵌入能力相关。已经确定了结构堆积阈值和临界静态屈服应力。结果分析表明，研究结果具有改善使用 CFA 桩技术生产的深地基的混凝土配合比设计标准的潜力。