Recent Developments of Drilling Techniques for Construction of Foundation Works

The sinking of a drillhole into the ground (or overburden drilling) for installation of pipe piles for shoring works and cased excavation for construction of pile foundations is an important type of geotechnical works. The Odex system, which was the dominant technique for overburden drilling in Hong Kong some 20 years ago and notorious for causing problems such as ground subsidence and sinkhole formation, is seldom used nowadays. There have been significant developments in the technology of overburden drilling since the introduction of the Odex system. In this paper, the problems associated with the traditional techniques of overburden drilling are discussed. Two pieces of recently introduced equipment which can mitigate or eliminate the problems caused by conventional equipment are described. They include the Spiral Flush pilot bit which can reduce the likelihood of air leakage and an entirely different system named the Airless Flushing system which uses water instead of compressed air as the flushing medium for removal of cuttings. A case study which demonstrates the benefits of the Spiral Flush drillbit will also be described.