Zen and the Art of Drilled Shaft Construction: The Pursuit of Quality

Construction of Large Drilled Shafts (The 2nd Annual Mike O’Neill Lecture)

“…In a similar [ FIg. 9] Loss of Concrete into Cavity during Extraction (Brown 2004) manner to the tremie discussed previously (the temporary casing might be thought of as a very large diameter tremie), a drop in head of concrete within the casing can lead to a breach of the seal below the casing or tremie, if a tremie is used inside the temporary casing.…”

“…10. The inability of the concrete to flow laterally can lead to entrapment of laitance (the contaminated concrete on the top of the rising column of concrete) and encapsulation of pockets of low strength as described by Brown (2004). Yao and Gerwick (2004) describe the desirability of underwater concrete to flow laterally in a "bulged" flow pattern with a relatively flat, smooth top surface rather than as a "layered" flow pattern which can result in steeply sloped and rugged top surface that increase the exposure of concrete surfaces to water.…”

Construction techniques for bored piling in sand using polymer fluids

“…Uncontrolled reuse of the fluid can lead to depletion of the active polymers (Lam et al, 2014b). Previous experience has also shown that the use of these fluids can increase the risk of 'soft toe' and concrete contamination due to the settling of suspended soil particles (Brown, 2004;Fleming et al, 2009). Unlike a gelling bentonite slurry which may perhaps suspend soil particles up to coarse sand size, polymer fluids have a lower particle-holding ability owing to their different rheological properties.…”

“…The potential problems of 'soft toe' and concrete contamination are therefore the most significant for ground conditions consisting mainly of coarse silts and sands, as these are the particle sizes that are most likely to settle out of suspension after the completion of an excavation and prior to concreting. Brown (2004) reported that there have been numerous cases of projects with polymer fluids where removal of silts and fine sands from the fluid has been difficult. On one project near the Atlantic coast in the USA, the contractor had to overpour the concrete by over 2 m in order to remove concrete contaminated with silt.…”

“…6 m of fluid to be heavily laden with silt so that it appeared as a gel. Based on these and other anecdotal experiences with polymer fluids in silty fine sands, Brown (2004) urges engineers and contractors to exercise caution in the use of polymers in these ground conditions. The authors agree that care is necessary and this paper sets out the basic issues.…”