this report presents data on the particle-size distributions of debris and the amounts of energy expended while cutting chalk with drag picks and disc cutters during the tunnelling trials at chinnor, oxfordshire. samples of debris were sieved and generalised relations were found between the coarseness index and the specific energy values. however there was considerable scatter in the results much of it attributable to variations in rock strength. because of this only primary trends could consistently be distinguished and it was concluded that a debris-size distribution approach is unlikely to provide a useful method of assessing tunnel boring machine performance.(a)

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