Drilling and blasting remain central to tunneling in Sweden, where high standards for minimal overbreak and damage drive the research towards a deeper understanding of blast-induced cracks. Recent research rethinks the approach of examining the effects of explosive detonation and its interaction with the surrounding rock. This paper synthesizes advances from small-scale studies on crack initiation, development, and coalescence during blasting. Key parameters, such as decoupling ratio, specific charge, and the strategic use of empty guideholes significantly influence the extent and direction of blast-induced cracks. High-speed imaging offers valuable information about crack propagation behavior. The results enhance the understanding of how these blast design parameters govern crack propagation, enabling the tailoring of the blast designs that promote desired cutting cracks while minimizing the unwanted or damaging ones. The emphasis of this work refers to tunnel contour stability and efficient rock cutting, contributing to crack propagation control. The findings provide a foundation for evaluating blast damage, supporting a more precise, sustainable, and safer tunneling while identifying gaps for future research. 

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. 

The propagation of cracks is a critical factor in the efficiency, stability, and safety of the blast in mining and tunneling operations. Understanding and controlling blast−induced cracks helps achieving goals such as reducing overbreak and minimizing damage zones. Despite interest in minimizing blast damage, few experimental studies have examined the effects of empty holes (guideholes) on blast−induced cracks. This work explores the influences of different blast designs on crack propagation patterns using an ultra−high−speed camera (UHSC) and the digital image correlation (DIC) method in small−scale blast experiments. Four samples of rock−like material with a 2.5 decoupling ratio and empty guideholes were blasted with PETN cord (3.6 and 5 g/m). The configurations included: two samples with a central blasthole with two and four guideholes, a sample with two blastholes with an empty guidehole, and a sample with four blastholes and a central guidehole. The experimental setup consisted of the samples and a DIC system with one UHSC to capture in 2D how the detonation of the different blast designs affects the material behavior. The configuration had a spatial resolution of 0.6 mm per pixel and a time resolution of 4.83 μs. DIC analysis revealed the exact location of the areas of cracks in the strain development, and the development velocity of several points along the cracks was calculated using the displacement results. The findings indicate that the use of guideholes has a greater influence than the specific charge on the number and the type of propagated cracks. There was no evidence that the crack development velocity (up to 1354.6 m/s) was more influenced by the specific charge than the propagation paths or the blasthole configuration. Cracks were classified considering their final role (cut cracks or damaging cracks) and shown to have a direct relationship with the blast design. The present research highlights the importance of combining qualitative and DIC analysis, which overall enhanced the understanding of crack propagation patterns and serves to improve explosive design strategies and optimize underground excavation processes.

Careful blasting is a controlled blasting technique that is often used to minimise theoverbreak and damage to the remaining rock mass. Although decoupled charges in blastholes arecommon, the influence of empty guideholes in directing crack propagation has been less investigated.This study presents small-scale experiments using magnetite mortar cylinders with two and four emptyguideholes around a central blasthole, charged with 0.28 kg/m3 of PETN with a 2.5 decoupling ratio. Thiswork investigates the influence of the different guidehole configurations on crack development throughultra high-speed (UHS) photography and digital image correlation (DIC). The results indicate that theguideholes significantly influence the trajectories of the cracks, attracting their development and thusreducing the development of unwanted cracks. These findings provide insight into blast-induced cracksand contribute to knowledge for designing blasts where precise control of the cracks is critical. 

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.