Reduction of Q-Barton Uncertainty: Proposal of a New Methodology Based on a Factual Geological–Geotechnical Database to Apply in Tunnels

The main goal of this study is to analyse and quantify errors, doubts, and uncertainties associated with the use of Q-Barton system parameters. This study also analyses how related factors influence the observer in tunnel openings. Data from six penstock tunnels of an underground hydraulic circuit at a hydroelectric power plant were used to study the application of the Q-Barton index. Records of values adopted at tunnel opening faces were compared with values calculated and quantified objectively. The values adopted by a geologist at the tunnel opening (Q-Barton-geologist) were compared with statistical values of the Q-Barton (Q-Barton-GGDB) generated from a factual database. This comparison enables the evaluation of the accuracy and influence of the Q-Barton system in tunnel openings, as well as the consequences on labour days and geotechnical support costs associated with a structure represented by the sample used. Using Q-Barton-GGDB, savings of 17.5% on geotechnical supports and 12.9% on labour days will be achieved. Final results highlight the need to explore the issues discussed here further.