Destress Blasting and Destress Drilling in Deep Hardrock Mining : Stress Management and Rockburst Mitigation

Deep underground hardrock mines face escalating rockburst risk as depth and stress increase. This thesis develops and demonstrates an integrated framework for stress management and rockburst mitigation that combines literature study based destress blasting findings and field trial based destress drilling findings with energy‐based indices observed from literature study, monitoring (specifically high-resolution 3D laser scanning and Cloud to Cloud analysis), and a conceptual geostatistics study, tailored to Swedish deep mining conditions. Four objectives structure the work: (i) based on literature study, derive a design framework for destress blasting from six decades of international and Swedish practice; (ii) based on the literature study, construct a quantitative evaluation methodology (Edestress concept contributed by this thesis work) that integrates the strain energy storage coefficient (F), brittle shear ratio (BSR) and burst potential index (BPI) with fracture and seismic observations; (iii) execute and analyse a controlled field trial of destress drilling at Zinkgruvan mine; and (iv) develop a geostatistical concept (semi-variograms and kriging) to predict destress efficiency at unsampled locations with quantified uncertainty. The methodology adopted for the thesis study integrates structured literature and case-history analysis, numerical and energy-based reasoning, and field experimentation with high-resolution 3D laser scanning of the drift and cloud-to-cloud (C2C) analysis. Based on literature study, the destress blasting component organises key rockmass, stress, and explosive parameters into a conceptual decision framework and design guidance; the evaluation framework developed from literature study specifies how F, BSR and BPI are computed and interpreted alongside monitored fracture and seismic responses; the Zinkgruvan mine practical field trial isolates the mechanical effect of uncharged inclined boreholes by keeping production-blast variables constant and quantifying geometric outcomes through C2C and volume-added metrics; and the geostatistical study shows how semi-variogram modelling and ordinary kriging can map performance indicators and their uncertainty to support risk-aware planning. Across case histories and supporting analyses, destress blasting is shown to be effective but highly localised and transient: stress relief typically extends only a few metres from the blast, and benefits decay rapidly as faces advance, necessitating continuous inclusion of destress features in each round within burst-prone zones. Mechanistic interpretation links reductions in boundary tangential stress and strain energy density to blast-induced fracture networks whose extent depends on rockmass brittleness and charging/timing choices; highly brittle rocks are both more burst-prone and more responsive when patterns and charge intensities are matched to site conditions. The practical Zinkgruvan mine field trial (depth of 1285 m) provides quantitative evidence that destress drilling stabilises development drifts. Rounds with 46 mm, 4 m destress drilling holes inclined at 20° (roof and shoulders) exhibited up to 2.5 m3 less scaled ‘volume added’ per metre of advance and a 20 – 30 % reduction in C2C profile standard deviation relative to non-destressed rounds, indicating lower overbreak and improved excavation profile control. It was observed that the first two rounds after a destressed round also performed comparably well, evidencing a short-range residual benefit that dissipates by the third non-destressed round, an operationally important finding for sequencing and cost-risk optimisation. The thesis study advances practice by: (i) organising destress blasting design considerations into a transferable, Swedish-context-aware framework; (ii) unifying energy indices (F, BSR, BPI) with fracture/deformation and seismic monitoring for quantitative evaluation at excavation scale; (iii) providing a high-fidelity, field-validated C2C/volume-based assessment of destress drilling in a deep, burst-prone Swedish mine; and (iv) introducing a geostatistical prediction concept that generates mine-wide efficiency maps with confidence bounds to reduce hazardous measurement campaigns and guide targeted data acquisition. The main conclusions and recommendations are that destress measures must be engineered and applied continuously in high-risk zones; design should be matched to rockmass brittleness and in situ stress; evaluation should jointly track energy indices, deformation/fracture, and seismicity; soft-scaling (where appropriate) practices should be integrated to minimise added volume; and geostatistical mapping and digital tools (3D scanning/C2C, IIoT) should underpin adaptive, feedback-driven planning.