Tunnel overbreak and underbreak prediction using measurement-while-drilling and reconstructed blasthole geometry

Overbreak and underbreak along the excavation profile were predicted at the peripheral-hole scale in drill-and-blast tunnelling. A data set of 537 peripheral holes from 12 consecutive blasting cycles in a tunnel was compiled, including measurement-while-drilling logs, charge-structure records, reconstructed blasthole geometry and post-blast point-cloud profiles. For each hole, 50 depth points were sampled from 1 m below the hole top to the hole bottom. Geometric and charging descriptors derived from blasting theory were computed along depth, including local hole spacing, burden to a reconstructed free surface, concentration factors and charge presence. Summary statistics (mean, quartiles and interquartile range) were computed to represent each hole. A gradient-boosting decision-tree model was trained to predict the blasthole-deviation-corrected overbreak/underbreak value at sampling points and evaluated using cross-validation. The model achieved a root mean square error of 0.137 m, a mean absolute error of 0.096 m and a coefficient of determination of 0.773. Interpretation using Shapley additive explanations quantified the contributions of geometric, charging and drilling-response features.