Q. Free- fall concrete placement in bored piles?
Based on the research by STS Consultants Ltd it was found that concrete placed by free falling below 120 feet will not suffer from the problem of segregation and strength of concrete won't be detrimentally impaired provided that piles' bore and base are dry and free of debris. Furthermore it's assumed in the past that during free falling of fresh concrete into the pile bores the hitting of falling concrete in the reinforcement cage causes segregation. Though in accordance with experimental results of STS Consultants Ltd, striking of reinforcement cage by fresh concrete doesn't have significant effect on the strength of concrete.
Additionally for long bored piles, it's impractical to conduct vibration to concrete. For concrete placed by free falling method, impact action arising from free falling is presumed to induce adequate vibration. Alternatively concrete placed by tremie method appears to be lack of vibration and this can affect the integrity and strength of concrete. The research results showed that strength of vibrated concrete was slightly higher than unvibrated concrete. Vibration proved to have added benefit to concrete strength however not essential to achieve the design pile strength.