Making economically viable the exploitation by D&B in a quarry within sensitive, highly populated area

The paper presents the results of an experimental campaign carried out at the Sasso Poiano quarry close to Varese, northern Italy. The area is near a historic site, inhabited villages and a well-known lake, so that the use of explosive is subject to severe restrictions imposed by Italian standards. The exploitation is therefore carried out by blasting with low specific charge (PF=50 g/m3) to obtain pre-fracturing of the rock, which is followed by mechanical excavation through backhoe excavators. The goal of the study was to test new techniques for the expansion of the mine, to reduce the production costs and increase the efficiency of the site, maintaining the same level of production as previously achieved by standard bench blasting. The hypothesis to be tested was that of introducing new equipment able to ensure the productivity of the plant with lower operating costs and maintenance. 28 blast tests have been performed, with the aim of obtaining a site law suitable to describe the behavior blast-induced vibrations within the marlstone and therefore predict the maximum allowable charge per delay (CPD) to respect legal limits of peak particle velocity (PPV). Afterwards, 9 blasts were selected to evaluate two options: varying the CPD and/or the geometry of the drilling mesh. The grain size distribution of the blasted material was analyzed through a photogrammetric technique, to evaluate the best solution. The results determined the best blasting configuration, together with the purchase of a single backhoe excavator, smaller than those currently adopted. This choice reduces the fuel cost by about 40% and lowers overall costs of the equipment maintenance.