Polymer fluid effect on Bored Pile Performance
Bored piles are a popular foundation solution in urban areas where minimal vibration is a prerequisite during construction.
Given that 96% of the carbon footprint generated during the construction of a bored pile is associated with the material consumption, the geotechnical industry is in search of an alternative installation solution.
Keller, Balfour Beatty and KB International LLC, supported by Geoinstruments, funded large-scale tests in NBIF to investigate an innovative technique using different supporting fluids (polymer and bentonite) during pile construction to determine their impact on the pile performance. Polymer support fluids, which offer a smaller site footprint, ease of fluid mixing, and better concrete-sand interface resistance were compared against traditionally used bentonite slurry.
Eight bored reinforced concrete piles, 300mm in diameter and 4.5m in length, were installed in compacted sand at NBIF, four with polymer and four with bentonite slurry as the supporting fluid. The piles were instrumented with strain gauges and distributed fibre optic sensors (DFOS) along the reinforcement bar along their length. Other sensors included linear variable differential transformer (LVDTs), pressure cells and geophones. The piles were pulled out using NBIF’s 250kN dynamic actuator at a speed of 0.01mm/s while monitoring the pull-out force. The piles were exhumed, and the shape and size validated with the use of a 3D scanner.
Initial findings suggest that longer resting times for polymer fluids in the hole could improve pile performance and that polymer piles produce thinner filter cake than bentonite piles. Further investigation is needed to confirm these findings and determine the full impact of polymer fluids on pile performance as compared to bentonite slurry.
The work and collaboration have been recognised by the team winning the ICE West Midlands Awards 2024 in the Studies and Research category.
Piling equipment drilling into concrete and sub-strata
ICE West Midlands Piling Group photo with their award
References
Faroqy, A., Zhai, W., Jefferson, I., Metje, N., Hansard, K., Luo, S., De Weale, J., Spinks, H., Pennington, M. & Konieczny, P. (2023). The Effect of a Supporting Fluid on a Pile’s Shaft Shear Resistance. Investigation at NBIF Facility. 18th Conference of the Associated Research Centers for the Urban Underground Space and 2nd International Conference on Exploration and Utilization of Underground Space, W. Wu et al. (eds.), ACUUS Singapore 2023, Nov. 2023. 1071 - 1076.