Construction techniques for bored piling in sand using polymer fluids

Abstract

This paper is concerned with the use of polymer fluids for the construction of bored piles in silty fine sand, a situation which has been found to significantly increase the risk of ‘soft toes' and concrete contamination due to the settling of the suspended soil particles in the fluid. To illustrate how these problems can be avoided by adopting a simple fluid-testing regime and improved construction practice, this paper presents a case history of polymer use at a site in Glasgow where the ground conditions consist of silty fine sand. Fluid testing showed that the used polymer fluid was heavily laden with soil particles and that cleaning using chemical additives alone was not sufficient to reduce the amount of suspended solids to an acceptable level. The pile bores were therefore left open overnight to allow the particles to settle out of suspension, the effect of which was confirmed by further fluid testing. The settled solids were removed with a base cleaning bucket. Structural integrity tests conducted on over 50 working piles constructed using this method showed no sign of defects. High-strain dynamic loading tests on two completed piles also confirmed their performance despite the extended pile bore open period.