Influence of rheological properties of concrete foundation on the implementation of continuous flight auger (CFA) piles

摘要

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.