ABSTRACT
In 1976-1977 the Commonwealth Department of Housing and Construction built a major extension to Haymarket Telephone Exchange in Sydney. After discovery of the dyke on the site, a study was made of reported dyke exposures in an endeavour to predict the likely engineering properties of the Haymarket dyke. Contact metamorphic effects on Hawkesbury Sandstone have sometimes been absent but in other instances the sandstone has been well indurated and vitrified for many metres on either side of the intrusion, and has sometimes been quarried for road pavement material. Geophysical techniques are of no use in locating dykes in the central city area due to high background noise and interference from buried services and other structures. The detection capability of Bison seismic equipment was evaluated at Haymarket after the dyke's position had been accurately established by drilling and site excavation. Site specific information was needed before development of a foundation and excavation strategy could proceed.
