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.

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. 

Seven large scale dynamic tests of rock support were conducted at LKAB’s KiirunavaaraMine in order to develop a methodology for the design of dynamic load resistant rocksupports. The tests were performed to increase the understanding of the response of rocksupport installed on the walls and roof in a tunnel and subjected to strong dynamicloading. The tests were originally numerically simulated by using two numerical tools,LS-DYNA and UDEC, in a former PhD Project at Luleå University of Technology, LTU(Shirzadegan, 2020), to investigate the performance of the test set up, the response ofsupported and unsupported excavations during the field tests as well as the complexinteraction of stress waves and rock support. The comparison of the numerical results andthe results obtained from field tests showed that the combination of LS-DYNA and UDECcould satisfactorily simulate the field tests. This work is the continuation of the LTUproject with LS-DYNA and UDEC.Since the analyses were previously conducted with 2D models, while in reality thestructural geology, ground motion measurements, fracture investigations and supportmotion, as well as the deformation measurements, occur in a 3D space, in the presentproject three-dimensional analysis are carried out using 3DEC that can assist in studyingthe interaction of the dynamic load with rock joints, rock blocks, tunnel wall and installedrock support. In this project the analyses are carried out in two stages: (i) the explosionstage is modelled in 3D with the finite element code LS-DYNA and (ii) the wavepropagation stage is modelled in 3D with the program 3DEC, where the results from LS-DYNA are used as input.The numerical simulations in this project can be used to analyse the behaviour of rockmasses and rock support systems under dynamic loading conditions. These simulationsprovide valuable information about the response of the rock mass to dynamic loading andcan be used to optimize the design of rock support systems. The numerical results evaluatedifferent rock support performance (Swellex Mn24 bolt and D -bolt) under dynamicloading conditions.3DEC modelling in the present study shows that: a) numerically calculated velocitypatterns match well those observed in the field for Test No. 6, b) larger displacementsoccurred for certain rock blocks in the unsupported crosscut and, c) the patterns of themost displaced rock blocks in the model very much resemble the positions where falloutswere observed in the field close to the footwall drift in the unsupported crosscut. (PDF) Dynamic modelling of rock bolts at Kiirunavaara mine. 

Rock masses are far from being continuum and consist essentially of intact rock and discontinuities such as joints. Presences of discontinuities affects the propagation of the stress wave in rock mass. In this paper the impact of joints properties and features on the dynamic response of underground cross-cuts to seismic loading induced during dynamic large-scale field test in Kiirunavaara mine, was numerically investigated. The numerical methods used comprise the finite element code LS-DYNA and the 2D Universal Distinct Element Code (UDEC). The LS-DYNA model simulated the blasting and acquired the crushed zone and the vibration velocities around the crushed boundary. The vibration velocities from LS-DYNA were then used as an input velocity in the UDEC model. The studies of parameters such as joint normal and shear stiffness, joint spacing and joint orientation were conducted. The vibration responses at the wall of the underground cross-cut from UDEC were analyzedand compared to observed field test results. The results show that the normal stiffness has large effects on the peak particle velocity (PPV) while the shear stiffness contributes less influence. However, changes on joint space and orientation affect the PPV at the wall of the cross-cut. The joint stiffness explains the quality of the joint to transmit the stress wave while the joint spacing, joint orientation describe the blocky in burden which explain number of times the stress wave will be reflected before reaching cross-cut wall. The analysis can be useful during designing of the blast, burden as well as cross-cut support.

Ground support systems are commonly used to mitigate the potential consequences of rockburst in burst prone mines. To assess the capacity of ground support systems when subjected to dynamic loading, simulated rockburst tests using blasting were conducted at the Kiruna Mine. In this study, a numerical simulation for one of the field tests was conducted using the LS-DYNA code to investigate the dynamic response of the ground support systems including shotcrete and rockbolts. The numerical results showed a similar particle vibration pattern and a crack pattern to those of the field measurements. The effects of the detonator position and the charge configuration on the dynamic response of ground support systems are also discussed. Numerical results indicated that the peak particle vibrations on the tested panel increase along the direction of detonation propagation. It is difficult to use different charge concentrations in one borehole to investigate the effect of different dynamic loads on the dynamic response of support systems. Numerical results also indicated that 2D numerical modeling for simulated rockburst experiments could overestimate the dynamic response of ground support systems.

In this thesis, numerical analyses of two types of laboratory test with the three dimensional Distinct Element Code, 3DEC have been carried out. The laboratory experiments simulated were the punching tests of the shotcrete by Holmgren (1979) and the direct shear tests by Malmgren et al (2005). The analysis of the punching tests comprised plain shotcrete and shotcrete reinforced by bolts. Two different approaches were used to model the shotcrete behavior: (i) liner structural elements and (ii) zoned block material. The liner structural elements only allows for separation at the interface while the shotcrete material is linear elastic. The zoned block material was assigned linear elastic material as well as linear elastic- perfectly plastic properties. Numerical model geometry of punch and direct shear tests which are the same as physical problems constructed by numerical codes. For both punch and direct shear test the shotcrete layer has smaller zone size than the rock block zones size. From the punch test the results indicate that, the interaction between shotcrete and rock for both elastic and linear elastic perfectly plastic material is governed by interfaces properties. For all tests in punch the interface breaks when tensile strength of the interface reached, the strength drops to zero while in the laboratory experiment the strength drops to two third In direct shear test, the result in both elastic and linear elastic perfectly plastic material gives the values which are less than the laboratory experiment result. Since laboratory tests are expensive and time consuming, there advantages of using numerical methods in analyzing the interaction of rock and shotcrete. This thesis suggest that the 3DEC can be used to study the interaction between shotcrete and rock if more study of interfaces properties are well understood.