The Effect of a Supporting Fluid on a Pile's Shaft Resistance. Experimental Study at NBIF Facility

Bored piles are a popular foundation solution in urban areas where minimal vibration is a prerequisite during construction. Traditionally, bentonite slurry is used to keep a hole open during pile construction. More recently, a synthetic polymer is gradually gaining popularity to replace bentonite support fluid. Compared to the bentonite, polymer fluids can offer a smaller site footprint, ease of mixing, and lower fluid disposal cost. Although some of the field trials suggest that the polymer piles could outperform the bentonite pile under the maximum proof load, to date, no large-scale controlled tests have been conducted which provide an in-depth comparison between piles constructed using polymer or bentonite slurry. This paper describes a set-up of well-controlled large-scale tests on 300 mm diameter, 4.5 m long bored piles, instrumented with strain gauges and distributed fibre optic sensors (DFOS), and constructed in compacted sand at the National Buried Infrastructure Facility (NBIF) using both polymer and bentonite slurry as the supporting fluid.