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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.

This is the accepted version of the paper.This version of the publication may differ from the final published version. Permanent repository link Number of words in main text and tables:5138 words Number of figures: figures AbstractThis paper describes the concept and field testing of a 1200mm diameter x 30m deep hollow cast in situ rotary bored pile foundation. The aim of the foundation is to allow large diameter piles to be constructed using less concrete than in an equivalent conventional solid pile and with a view to allowing reuse at a later date. Reuse is made possible because the hollow core of the pile allows access for inspection after demolition of an existing structure. The new piles may also allow modification to enhance load capacity by augering through the base and extending their length. In addition, the piles are better suited than conventional piles for use as 'energy piles' to allow environmentally friendly heating and cooling. The geotechnical performance of the hollow test pile was comparable with a conventional solid pile constructed during the same trial. Details of construction are given including lessons learned.• A list of notations, defining all of the symbols used.•

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