Factors influencing overbreak volumes in drill-and-blast tunnel excavation. A statistical analysis applied to the case study of the Brenner Base Tunnel – BBT
This paper deals with the analysis of overbreak in tunnels excavated with the drill-and-blast method. The overbreak phenomenon has many negative impacts on tunnelling organisation and economy and its precise assessment plays a fundamental role in the process of construction optimisation. The study proposes an operative methodology to estimate overbreak volumes and to distinguish so-called technical overbreak, mainly related to drill-and-blast design and execution, from geological overbreak, typically influenced by rock-mass characteristics.