Technical-Economic Comparison Between Excavation by D&B and by Roadheader in Two Underground Gypsum Quarries

The goal of the research is to evaluate the most suitable exploitation technique in two underground gypsum quarries, both of them located in Piedmont (Italy). The methods currently adopted pertain to the “Rooms and Pillars” category, but the techniques employed in the two quarries are different, i.e. mechanical (by roadheader) and conventional (by Drill & Blast) respectively. The choice of an excavation technique results from a study which takes into account a number of parameters, such as morphology of the orebody, productivity, depreciation, workforce, plant engineering and consumptions. First of all, a thorough knowledge of the geological characteristics of the area is necessary, and geomechanical properties of gypsum must be known: a wide, bedded and regular orebody favors the use of the mechanical exploitation, whereas inhomogeneous, non-linear and small orebodies often require the great versatility of the explosive. The technical comparison has highlighted that the productivities obtained by the two excavation techniques are almost equivalent: gypsum allows minimal tools wear, optimizing production times of the cutter head, whereas its plasticity can require specific consumptions of explosive higher than in rocks of comparable hardness. As to the economical aspect, the total costs of excavation with Drill & Blast are 25% higher than those with roadheader: indeed, even if the mechanical excavation will lead to higher investment costs for machinery and to large consumptions of electricity, it involves a very important saving on diesel fuel and explosives, which has a fundamental impact, i.e. a third of the costs of consumption, more than one sixth of the total costs of extraction, as well as an increase in labor costs. Another important aspect is the environmental sustainability of the mechanical excavation, with a diesel consumption much lower than the conventional method, and the possibility of an almost total abatement, if conveyor belts are employed instead of truck dumpers for muck transportation.