ABSTRACT
In tunnelling, mine development and production, and shaft construction speed of excavation and rate of penetration are major economic factors. In many cases, high productivity, higher safety, and lower costs can be achieved by mechanical excavation systems, and as a result, these systems have been gaining more acceptance and wider area of application in mining and tunnelling activities. Yet the use of these systems, especially in very hard rocks is very challenging. In such conditions cutting tools require high cutting forces, wear very fast, experience reduced tool life, and machines require high maintenance. This results in low machine utilization, and reduced productivity, and increased product cost. This paper presents innovative concepts for improving the cuttability of hard and abrasive rocks by using pre-conditioning systems through introduction of micro-fractures in the rock mass. The concepts include high-power microwave irradiation which leads to fracturing and weakening of the rock. The initial results of laboratory experiments using a 24 kW microwave and observed crack networks will be discussed. The result of experimental program has confirmed changes to rock mechanical properties due to initiation of micro-cracks in the rock which will reduce rock strength and thus leads to easier excavation and higher production rates. An outlook will be provided especially with respect to possible hybrid systems aiding the centre and gage cutters of the Tunnel Boring Machines (TBM) by pre-damaging the rock.
