In mining, tunneling, and other blasting applications, excessive rock fracturing can compromise stability and deteriorate environmental and economic outcomes. Predicting the extent of blast-induced cracks is critical to accurately assess structural damage and optimize blast design. Seven blast tests were performed on 150 × 300 mm cylinders with a central blasthole of 280 mm length. PETN cord (5 g/m) was used, and the decoupling ratios (f) of 2.5, 4.2, and 5.0 were achieved by varying the blasthole diameters. In this study, qualitative and quantitative aspects of the induced cracks (number, type, velocities, propagation patterns, etc.) were examined using ultra-high-speed (UHS) photography and 2D Digital Image Correlation (DIC) method. Numerical modeling with LS-DYNA was conducted to simulate the experiments, to expand the analysis from 2D to 3D. The experimental results showed that crack initiation, gas ejection, and damage level decreased when increasing the decoupling ratio; notably, no damage occurred when f = 5. Crack propagation velocity using the DIC results showed V_c = (839.40 ± 46.57) m/s. A model for V_c from the experimental results was established through curve fitting with a R² > 97%. The DIC analysis enabled the distinction of the fracture process zone and the crack tip location. The numerical modeling results provided a realistic estimation of the cracks and damage compared to the experiments. The experimental and numerical results show that increasing the decoupling ratio reduces qualitative and quantitatively the blast-induced cracks, demonstrating how blast-induced damage could be limited.

As mining progresses to greater depths, the challenges of high stress become more pronounced, often resulting in rockbursts that significantly impact deep underground mining operations. To address these challenges, Zinkgruvan mine in Sweden is testing destress drilling as a proactive measure to reduce the propensity for rockbursts and enhance the long-term stability of the mining drift, particularly in the roof and shoulders. Destress drilling holes, in this study, were drilled at 20° inclination on the periphery of the exploration drift and strategically placed ahead of development blasts. Laser scans of the drift were conducted before and after scaling, and the point cloud data was analysed using Cloud Compare software, with the Cloud-to-Cloud (C2C) algorithm employed to detect profile changes. This allowed for a comparison between blast rounds with and without destress drilling to assess the technique’s effectiveness. Results demonstrated that destress drilling reduced stress concentrations in the surrounding rockmass, as evidenced by reduced profile change. Blast rounds with destress drilling had up to 2.5 m3 less volume added per metre. C2C analysis showed 20 % to 30 % lower standard deviation and consistently lower mean deviation, indicating improved profile uniformity. These findings highlight the technical and operational benefits of destress drilling. 

Mining at deep-seated deposits is associated with high stresses, which upon redistribution during mining, may cause induced seismic events. This mining-induced seismicity can lead to rockbursts that pose a threat to mining activities. Rockburst failures are classified based on the location of their occurrences, sources, and severity. Rockbursts have been recorded in deep and hard rock mines in various countries around the world. In Sweden, rockburst failures have been prominent since the year 2000, attracting researchers to study Swedish deep mines experiencing these failures. An investigation and mapping of failures during seismic events at the Kiirunavaara mine in Sweden from 2014 to 2017 evaluated seismicity parameters but did not focus on the failures and performance of rock supports. This paper analyzes failures mapped and investigated during seismic events in four blocks at the Kirunavaara mine, focusing on the failure mechanisms of the rock and rock supports. It considers geological factors, rock support, and provides remedial suggestions. It was found that most damages were either directly or indirectly influenced by stress changes due to seismic events. This analysis can provide insights for designing rock supports to mitigate rockburst occurrences.

In Sweden, drilling and blasting is generally regarded as the predominant excavation method for tunnel construction. While many studies focus on the blast performance within the tunnel perimeter, few studies have examined the effects of the induced cracks behavior in these designs (where the charge is decoupled). This work aims to improve the understanding of crack initiation and development during contour blasting. The investigation consists of a small–scale blast test to study the crack development around a blasthole using the Digital Image Correlation (DIC) technique. The experimental setup involved a cylindrical rock–like sample with a central blasthole and a decoupled PETN cord (Pentaerythritol tetranitrate) explosive charge by 3.9. The data was collected with an ultra–highspeed camera (UHSC) and processed using image engineering. Based on the experiment, numerical modelling was carried out to compare and investigate the behavior of the cracks. The analysis approach included tracking crack development using the strain values for both experiment and numerical modelling. These results emphasize the importance of combining the strain analysis in different directions to find the crack development sequence. The experimental and numerical results show good consistency, providing valuable information on crack development behavior around a blasthole. 

Rock support can be divided into surface and reinforcement support. Surface support contain failing rocks and collects applied loads, while reinforcement support transfers collected load from the surface to competent rock away from the surface. The perfomance of rock supports is affected by several factors, such as stress regime in the sorroundings and the geology of rock. Geological structures affect the propagation of dynamic stress waves and therefore, rock support. The movement of joints by either expansion or contraction affects the propagation of stress waves and rock bolt crossing the joint. This article focuses on modeling the impact of joint mechanical and spatial properties on rock support when subjected to dynamic loading induced during blasting tests. The model used a coupling of LS-DYNA and UDEC, where LS-DYNA simulated the blasting and UDEC simulated the rock mass and rock suppports. Changes in joint parameters were studied in relations to rock support response. These changes in joint parameters affect the propagation of waves and therefore, the loading and displacement of the rock supports. Results show that rock bolts absorb large load and large deformation/displacement at joints near the surface. This study provides insight how uncertainity in geological structures can affect rock support performance. 

The numerical analysis results from an improved design of large-scale dynamic test of rock support (Test 6) is presented in this paper. The improved field test was designed based on the results obtained from field tests and the numerical analysis of the earlier tests (Tests 1 – 5) conducted at LKAB Kiirunavaara mine. The performed numerical analysis investigates how the improvements including minimizing the expansion of blasting gases into the burden, avoiding the complete damage of the burden, and creating sub-planar waves were achieved under the improved design of the test. Furthermore, the response of supported and unsupported excavations as well as the complex interaction of stress waves and rock support was numerically studied. The numerical analysis comprised of two stages (i) the explosion stage modelled with the finite element code LS-DYNA and (ii) the wave propagation stage which was modelled using UDEC with the results from LS-DYNA as input. The accuracy of the developed models was investigated by comparison of the UDEC models results to the data obtained from the field test. The numerical analysis results confirmed that the improved designed burden has assisted in reducing the areas of tensile yielding in the burden and as a result, the gas expansion and complete damage of the burden was avoided. The simulation results showed that the used support system (Swellex Mn 24 and reinforced shotcrete) has effectively limited the displacement of the test wall and prevented ejection during the dynamic loading. The combined numerical technique has shown its advantage when simulating blasting as well as interaction between waves and opening and it can thus be used as a tool for evaluating rock support performance.

The numerical analysis of four dynamic large-scale field tests conducted at LKABKiirunavaara mine are presented in this paper. The aim was to numerically studythe behavior and response of the burden and the tested walls in field Tests 1, 2, 4and 5. For this purpose, two numerical methods were combined, i.e. the finiteelement code LS-DYNA and the distinct element code UDEC. The LS-DYNA wasused to calculate the blast load, and the UDEC was used to propagate the calculatedload in the model where the geological conditions of the test site and the installedrock support in the field tests were modelled. The model was calibrated bycomparing the velocity and displacement calculated on the surface of the opening,and the zones yielded in tension were used to study the failure mechanismdeveloped in the burden. The numerical models were able to mimic the behavior ofthe jointed rock mass and the rock support fairly well. It is concluded that thenumber of major joint sets was the main reason to the difference between the failuredevelopment in Tests 1 and 2 and Tests 4 and 5. The numerical analysis of Tests 1and 2 confirmed that the gas pressure in the vicinity of the test wall in those testswas minimum. In Tests 4 and 5, it was observed that, the generated fractures in theburden combined with the natural joint condition of the burden, increased thepossibility for blocks to rotate and move within the burden. The complete burdendamage in Tests 4 and 5 was concluded to be the be due to the ejection of rockblocks in the vicinity of the test wall upon the arrival of stress wave, and ejection ofthe remaining portion of the rock blocks in the burden by the gas expansion. 

Mining in deep underground mines continues to face the challenges of rockburst caused by high mining-induced stresses during excavation. Destress blasting technique has been reported in many practices as an active rockburst mitigation measure with various degrees of success. Rockburst is becoming significant in the Kiirunavaara Mine, Sweden when it continues to reach deeper deposits. Based on the in-situ stress situation in a footwall drift of the Kiirunavaara Mine, a destress blasting pattern was proposed, and the numerical modelling was conducted to evaluate the effectiveness of the proposed destress blasting pattern. The entire modelling process including applying in-situ stresses, excavating drift, drilling blastholes, and blasting was carried out with the LS-DYNA code. Blast-induced damage was evaluated. The principal stress redistribution with and without destress blasting was compared to evaluate the performance of the destress blasting. Numerical modelling results indicate that destress blasting with emulsion explosives induces more damage to the rock mass compared to ANFO explosive; moreover, the principal stress redistribution after destress blasting is more complex compared to the case without destress blasting but stress reduction around the blastholes is observed.