AbstractThe research presented in this paper deals with technical and economical evaluations of tunnelling jobs; it has been carried out in collaboration with Scandinava Macchine S.p.A. of Genoa, a company that for 35 years has constructed, sold and serviced tunnelling equipment. By now, the choice of machinery for constructing tunnels is more or less empirically based on the experience gathered over the years. Owing to the high cost of the equipment it is necessary to limit the possibility of making incorrect evaluations as far as machinery choice and foreseeable employment time are concerned. With this objective, the research we have carried out is aimed towards supplying the means for evaluating the technical/economical implications of the possible alternatives whwn constructing tunnells. The research team deemed that the construction of a stochastic, discrete, at-event simulator could fully satisfy the above requirements.Owing to the complexity and vastness of the considered problem, two independent but interfaceable calculation programs have been set up: the first one is represented by the simulator, and supplies the technical characteristics of the tunnel; the second program, utilizing the first one's outputs, exploits the choices taken into consideration. In the experimental phase hierarchic factorial designs have been employed for the economic evaluation of the alternatives, considering characteristic parameters of the subsurface works.