Quantitative Assessment of Structural Controls on Drill-and-Blast Overbreak: Sector-Based Prediction of Over-Excavation Depth and Volume via the Universal Discontinuity Index

Accurate overbreak prediction is critical for cost control, stability, and support optimization in drill-and-blast tunnels. Traditional empirical models, typically applied during early design, rely on global rock-mass descriptors that under-represent local structural variability and anisotropic discontinuity controls. This study examines the practical usefulness of the Universal Discontinuity Index (UDi), a quantitative metric combining physical damage, effective stress intensity, fracture active ratio, and kinematic block potential, by comparing it with seven widely used empirical predictors at the New Mine Level project (El Teniente, Chile). UDi was computed from 3D photogrammetry-derived discontinuity data and an in-situ stress model for seven representative advances/sectors, and its results were compared with laser-scanned overbreak volume and depth. In this dataset, UDi shows strong linear association with measured overbreak (Pearson r values corresponding to ∼73–97% of variance in selected comparisons), whereas classical empirical models exhibit weak or inconsistent associations. Component analyses indicate that the Effective Stress Intensity Factor (ESIF) and volumetric fracture intensity (P32) are the most informative contributors, and a correlation-informed weighting strategy highlights sector-dependent sensitivities that are relevant for localized support design. Given the limited sample size, the reported correlations should be interpreted as evidence of promising signal and transferability potential, motivating validation on larger datasets and under varied blasting and geological conditions. UDi can capture rock mass anisotropy and heterogeneity, offering a high-resolution, practical tool for tunnel risk management. Its integration into mapping workflows could reduce over-supporting and enhance advance-rate forecasting in complex geological conditions. • UDi enables spatially resolved overbreak prediction in complex rock masses. • Quantitative comparison shows UDi outperforms seven empirical models. • Integration of photogrammetry and stress data supports operational use of UDi. • ESIF and fracture intensity (P32) drive localized support optimization.