Abstract

Drilling and blasting is one of the most commonly used and convenient method for many mining and civil applications to break rocks, especially hard rocks. Because of many environmental, safety and productivity issues (i.e. Cycle time), the industry and contractors are looking for an alternative system of breaking of rocks. In underground rock breakage applications such as tunneling, continuous mechanical excavation method, normally with tunnel boring machines (TBMs) or road headers is becoming more popular and commonly used by contractors. One of the main disadvantages of such system is that, it cannot handle very hard rocks and uneconomical major disc or bit wear takes place. Today, novel explosive free rock breaking technologies (thermal, electrical, nuclear energy and microwave) are available and could be used on their own or assist mechanical conventional machines to be able to break harder rock material. This is possible because it is hoped that the microwave will reduce the strength of the rock prior to the impact of mechanical device. Three main mechanical parameters of rocks such as compressive strength, tensile strength and abrasivity index value were used to highlight the influence of microwave on to the mechanical properties of rocks. Seven different rock types were prepared and tested. Each individual specimen was exposed to the microwave energy in three power levels 800, 1250 and 3000 watts, within 0, 15, 30, 60, 120 and 240 seconds time of exposure. Different rocks due to their mineralogy behave differently when exposed to microwave energy. CERCHAR abrasivity index value of almost all samples shows reduction of about 30% as the power level of exposure increases. The tensile strength of certain samples reduces significantly as in basalt reduces of up to 80%. The unconfined compressive strength value of almost all samples reduces about 30% as well. The reduction of the strength and abrasivity of hard rock cause the penetration rate and the life time of cutter tools of a TBM to be increased by combining the microwave energy to the cutter head of the mechanical excavator.