Influence of rheological properties of concrete foundation on the implementation of continuous flight auger (CFA) piles
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ORIGINAL ARTICLE
Influence of rheological properties of concrete foundation on the implementation of continuous flight auger (CFA) piles Y. Vanhove
. C. Djelal
Received: 5 May 2020 / Accepted: 14 September 2020 Ó RILEM 2020
Abstract 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
Y. Vanhove (&) C. Djelal ULR 4515, Laboratoire de Ge´nie Civil et ge´o-Environnement (LGCgE), Univ.artois, Be´thune 62400, France e-mail: [email protected] C. Djelal e-mail: [email protected]
results demonstrated the potential of the research results to improve the concrete mix design criteria for deep foundations produced with the CFA-piles technique. Keywords Rheology Yield stress Structural build-up Deep foundation CFA-pile
1 Introduction When shallow foundations are not feasible due to the presence of compressible soils, deep foundations serve to transfer the structural loads of engineering facilities into higher quality layers found at greater depths. These processes are integrated into applications covering all building types (housing construction, industrial, commercial, engineering structures, wind turbines, etc.). Pile-driving using a hollow stem auger, with or without reinforcement has undergone continuous development over the years and it is extensively applied for building foundations [1–3]. This technique offers a quick and economical solution, with reduced noise and vibration nuisances. It is adapted for boring below the water level and moreover, avoids the use of tubing, regardless of the type of ground traversed. Piles driven with a hollow stem auger are considered as both bored piles (extraction of a very small soil volume) and screw piles (lateral soil displacement due
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the ease of reinforcement cage placement. This behavior was observed by using a simple test d
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