During rock cutter dredging for the trench for the Sydney Harbour Tunnel, partially cut in rock of the Hawkesbury Sandstone, tool consumption data were obtained and compared with the wear value F developed by Schimazek, and with the cutting and abrasive wear rates as determined by the Newcastle-upon-Tyne cuttability tests. It appears that while the F-values correlate well with actual tool consumption, correlations with laboratory cutting and abrasion tests are not always significant.

The F-value is obtained from a number of easily measured rock parameters (Brazilian tensile strength, mineralogical composition and grain size.) Use of the F-value is considered advantageous compared to laboratory tests which measure the abrasivity of rock directly because it is difficult to perform sufficient abrasivity tests to cover the variability inherent in a rock mass and it is impossible to perform laboratory tests that are truly representative of the actual cutting and abrasion mechanisms operating. Site investigations for rock dredging projects would be improved if systematic determinations of the F-values were carried out. This would help to improve the ‘educated guesses’ of tool consumption currently practised during the tendering stages of a dredging project. Accurate prediction, however, will always necessitate a trial dredge excavation to calibrate and to check the appropriateness of the abrasivity parameters chosen.

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