Integrated Evaluation of Block Geometry and Blast-Induced Fragmentation in the Jointed Rock Mass: Empirical and Numerical Approach

Abstract

Quantitative characterisation of muck pile shape and size analysis, along with the natural block geometry is crucial for cost optimisation in large tunnelling operations, especially in complex geological terrain such as the Nepal Himalaya. In this study, 15 controlled-blast rounds were analysed very closely, and the empirical block-volume estimation, image-based fragment analysis, Zingg and Sneed–Folk shape classification, and three-dimensional distinct-element numerical analysis methods were used to identify the behaviour of the muck pile as well as the natural block. From the field, 853 rock fragments were measured along three orthogonal axes to calculate fragment size and volume. For the distinct-element analysis, the measurement of joint spacing, orientation, and persistence are incorporated. The analysis demonstrated that natural rock blocks predominantly have cubic geometries. On the other hand, blast-induced fragments are dominated by bladed and elongated shapes, indicating the rock mass’s strong anisotropy. The statistical validation results demonstrate the strong linear correlations between field-measured and image-based fragment volumes (R² = 0.786, RMSE = 0.056, p < 0.001), and the relationship between empirically estimated and DEM-based block volumes (R² = 0.831, RMSE = 0.07, p < 0.001) is more reliable, with a high R-square, Low RMSE, and p-value. The results reveal the strong relation between field observations, image-based analysis, numerical simulations, and empirical predictions, which confirms the applicability of the proposed integrated fragmentation framework for optimising tunnel blasting performance in the drill-and-blast tunnel.