Research for Updated Guide to Support Fluids for Deep Foundations DFI previously highlighted the work that the EFFC and DFI undertook to reduce the quality issues encountered by using tremie concrete in drilled shafts and diaphragm walls, which led to the publication of the second edition of the EFFC/DFI Guide to Tremie Concrete for Deep Foundations. Given the clear linkage between tremie concrete and support fluid in both foundation elements, the EFFC and DFI Concrete Task Group identified the need for a greater review of the characteristics, testing and management of support fluids. This focus subsequently resulted in the publication of the first edition of the Guide to Support Fluids for Deep Foundations in March 2019. This guide was groundbreaking in many ways, and will serve as a valuable reference in the future. It was the first time that the collective knowledge pool of good practice from around the world was brought together into a single authoritative publication. A second edition is already planned, which will be based on an extensive field research study that is being funded by EFFC, DFI, contractors, consultants and suppliers. It is also hoped that the study will forge links with academics working on support fluids, which already includes numerical modelling, polymer fluids testing, trench stability investigations, influence of fluid type on side friction, and the influence of a support fluid on the bond strength between a reinforcement and concrete cast in a support fluid. The research to develop the upcoming edition has been divided into two parts. The first is focused on obtaining con- tractors’ standard fluid test data from sites in North America and Europe; second, other data is being obtained from the study, which is being led by two independent specialists. These specialists are spending three to four days each on a total of 20 different project sites that were proposed for inclusion by contractors in the U.S. and Europe. The study involves a series of nonstandard tests, new procedures and test equipment to improve support fluid man- agement and develop a better compre- hension of support fluid behaviour. The study will run until mid-2021 and has the following primary objectives: • Record properties of fresh, excavation and recycled/cleaned fluid • Establish a property/depth profile for the excavation fluid • Compare excavation base hardness methods and tools • Compare commonly used f luid samplers • Investigate the accuracy of concrete depth indicators • Record concrete levels during casting inside and outside the cage • Obtain and test fresh and hardened samples from the interface layer • Test fresh concrete properties The project stakeholders are grateful to the contractors that have so far volunteered to give access to their projects, so that independent specialists can implement the study. This has been designed specifically to limit possible production time losses on site. Before access onto a site, a detailed planning discussion is held with the site team and any necessary inductions are carried out. All information obtained during site visits is treated as strictly confidential by the specialists and is only disclosed to members of the Task Group who have signed a detailed confidentiality/ nondisclosure agreement. Contractors who have allowed testing on their site will be allowed to check and approve the draft of the second edition before publication. The site testing involves performing standard tests on the fluid at different stages (fresh, during excavation, after cleaning and prior to concreting). Alternative procedures to measure the fluid density will be evaluated, as the Task Group identified a limitation in the accuracy of the standard mud balance for measuring fluid density (especially polymer-based support fluid); the target is to increase the measurement accuracy from 0.01 g/ml to 0.005 g/ml. Other nonstandard tests will be carried out that are aimed at measuring the fluid rheological parameters such as apparent viscosity, gel strength and fine content in polymer support fluids. Data acquired to date is proving invaluable and the Task Group is optimistic that, as more sites are visited, the quality and volume of data will enable good practice and procedures to be ‘fine-tuned’ in the second edition. Of course, more sites are required, and DFI would be interested in hearing from anyone that may wish to contribute to the study and ultimately to the findings that will define the content of the latest edition of the EFFC/DFI Guide to Support Fluids for Deep Foundations. For more information, contact Peter Faust at [email protected] or Mary Ellen Bruce Large, DFI director of technical activities, at [email protected] . If all goes according to plan, the second edition of the Guide to Support Fluids for Deep Foundations will be published in 2021/2022. But in the meantime, the first edition is available for free download at www.dfi.org www.effc.org or . This article was written by Peter Faust, vice presi- dent of business development, Malcom Drilling. DEEP FOUNDATIONS • MAY/JUNE 2020 • 55
