Mechanical excavation of hard rocks

In the case of hard rocks the problems arising with the use of mechanical tools consist chiefly in a slow advance rate accompanied by an intensive wear due to the toughness and abrasiveness of the rock. In order to allow the further extension of mechanical excavation beyond the limits of presently available technology two possible ways can be followed: using special tips made of polycrystalline diamond for longer duration; availing of the assistance of waterjet for better performance. Both solutions are being developed in the case of picks or disks applied to roadheaders and full-facers. The paper illustrates the results obtained at the DIGITA laboratories of the University of Cagliari on a mediumhard rock using a carrousel-type testing machine capable of reproducing the conditions of rock-tool interaction encountered in the industrial practice and discusses the prospects of the technological advances under development. 1 FOREWORD Interest is growing today regarding the development of a suitable technology for the excavation of hard rocks as an alternative to the use of explosive. In fact, although blasting can be applied successfully for winning a great variety of rocks and geologic situations, a number of drawbacks are often encountered such as overbreak, noise, airblast, flyrock and vibration. Moreover, the lack of accuracy in tunnelling may render the support and concrete finishing more expensive, thus upsetting the economic advantage of a cheaper excavation. Finally the DB Volume removed per unit time; Specific energy. Correlations linking these parameters to the operational variables have also been sought, aiming at finding the optimum conditions.