Indagini sperimentali per l'ottimizzazione di scavi a cielo aperto in prossimità di un'area sensibile e densamente popolata

The paper presents the results of an experimental campaign carried out at the Sasso Poiano mine, close toVarese, 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) in order 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, in order 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 behaviour blast-induced vibrations within the marlstone and therefore allow to predict the maximum allowable CPD to respect legal limits of PPV.Afterwards, 9 blasts were selected, carried out by to evaluate two options:varying the charge per delay (CPD) and/or the geometry of the drilling mesh.The grain size distribution of the blasted material was analysed through a photogrammetric technique, in order to evaluate the best solution to be taken.The results allowed to determine the best blasting configuration, together with the purchase of a single backhoe excavator, smaller than those currently adopted: this choice allows to reduce the fuel cost by about 40%, in addition to lower costs of the equipment maintenance..