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.

The increasing mining depth in the Luossavaara-Kiirunavaara Aktiebolag (LKAB) mine located in the northern part of Sweden leads to higher stress magnitudes, resulting in increased seismic activity and more seismically-induced damage. The effectiveness of various ground support systems under dynamic loading conditions has therefore become of prime interest to LKAB for successful and safe mining at deep levels. The problems of mining-induced seismicity have necessitated the use of ground support systems which are capable of withstanding strong dynamic loads. Within this respect, a series of seven large-scale dynamic tests of rock support were conducted at LKAB Kiirunavaara mine. Explosives were detonated in boreholes in the pillar between two cross-cuts in order to generate dynamic loads on the rock support system installed on the cross-cut wall. This was done to evaluate the response of rock support subjected to strong dynamic loading. The tests included ground motion measurements, fracture investigation, ground and support motion imaging, as well as the deformation measurements. The design and the results of field Tests 1 to 7 and their associated numerical analysis are presented in this thesis. Field Tests 3 and 7 are excluded from detailed analysis in this study since the burden condition in these tests were different from the rest of the tests. The performance and energy absorption by the support system comprising Swellex Mn 24, 100 mm fibre reinforced shotcrete (40 kg/m3 steel fibre) and 75 mm * 75 mm weld mesh with 5.5 mm diameter is estimated and compared to the large-scale and laboratory test results conducted in different countries. The field tests results indicated that the relation between the burden and the used amount of explosive material and number of blastholes has a vital role in either reducing or involving the effect of detonation gases in test results. Results from field Tests 1, 2, 4 and 5 (considered in this study) showed that in Tests 1 and 2 minimum damage was created on the surface of the wall despite high PPVs were measured on the test wall. In Tests 4 and 5 complete damage of the burden was occurred despite the burden was in the range of Tests 1 and 2. Results from Tests 1 – 5 were used to design an improved burden in Test 6. The evidence of the damage to the test wall in Test 6 showed that the design in Test 6 was successful in terms of minimising the effect of gas in the burden and generating a sub-planar stress wave. The large amount of data recorded during these tests was used to develop the numerical models, and to study the field tests in more detail. The aim was to study the behaviour and response of the burden, free surface of the opening, and the installed rock support to the dynamic loading generated by a nearby blast numerically. A combination of two numerical methods, including the Finite Element code LS-DYNA and the Discrete Element code UDEC was used in the numerical analyses. The LS-DYNA model was used to calculate the dynamic input for the UDEC analysis. This was done by identifying the crushed zone boundary (CZB) developed around the blasthole. The velocity at the CZB (at the moment when it was fully developed) was applied as an internal boundary condition in the UDEC model. The geological conditions of the test site and the installed rock support were modelled in UDEC. The peak particle velocities, the velocity – time graphs, the maximum displacement generated on the surface of the wall, and the ejected thickness of the rock from the wall computed in the UDEC models were studied, and compared to the data obtained from field tests. This was done to identify the models that well represent the field tests behaviour. The identified models were used to study the failure mechanism in the burden and the rock support response to dynamic loading. Results indicated that, the numerical models were able to mimic the behaviour of the jointed rock mass and the rock support fairly well. The difference in behaviour between the numerical models and the field Tests 1 – 5, appeared to be caused by the gas expansion in the field tests, especially Tests 4 and 5. The numerical analysis results confirmed that the design of the burden in Test 6 limited the development of tensile yielded zones and as a result, complete failure of the burden was avoided. Furthermore, the ejection experienced from the wall was similar to that in actual seismic event. Numerical analysis results indicated that the geological structure of the burden and in particular the formed wedges near the opening have a significant role on the damage developed on the surface of the test wall. The presented testing method has the potential to be used in all similar large-scale testing of the rock support. Performing numerical analysis can significantly save time and energy while searching for an optimum design of the burden. By using a calibrated numerical model, it is possible to test the performance of different support systems using the same boundary conditions, in future studies.

A series of large scale dynamic tests were conducted at the LKAB Kiirunavaara mine using explosives to generate the dynamic load on the support system. This was done with the aim of developing a testing methodology for in-situ testing of ground support. Furthermore, the response of the installed rock support system to strong dynamic loading was evaluated. The results of the Tests 1, 2, 3, 4 and 5 indicated that the relation between the burden and the used amount of explosive had a vital role in either reducing or involving the effect of the detonation gases in the test results. Higher peak particle velocities were measured compared to those of similar large scale tests carried out in other countries. However, the level of induced damage in Tests 1 and 2 was limited to a fractured zone behind the support system while in Tests 4 and 5 the burden was unexpectedly destroyed. Based on the test results and preliminary numerical analysis, a modified test (Test 6) was designed at the same mine. The aim was to avoid the unexpected damage of burden as was observed in earlier tests, and to modify the dynamic loading leading to increase the depth of fractured zone and if possible pushing the support system beyond its limit. Results indicated that a larger fractured zone compare to earlier tests was developed behind the support system while the installed support system was still functional. Evidence from the damage to the tested cross-cuts in Test 6 indicated a reduction of radial cracks that provide access for the gas expansion. The results indicated that the installed support system, designed for dynamic conditions, performed well under the loading conditions which can cause ejection

Based on the test results and preliminary numerical analysis of four large scale dynamic testing of rock support (Tests 1, 2, 4, and 5), a modified test (Test 6) was designed at LKAB Kiirunavaara underground mine. The aim of the modified design was to avoid the unexpected damage of burden as was observed in earlier tests, and to modify the dynamic loading leading to increase the depth of fractured zone and if possible pushing the support system beyond its limit. In this test, ground motion measurements were conducted using accelerometers, fracture investigations were made using an inspection borehole camera, and ground motion imaging and laser scanning were performed before and after blast. In Test 6, the columns of explosive were located in the middle of a pillar between two cross-cuts one supported by a rock support for seismic conditions, and the other supported by only plain shotcrete. Results indicated that a larger fractured zone compare to earlier tests was developed behind the support system while the installed support system was still functional. In cross-cut without support system, the ejection of blocks of rock from the test wall was observed. Evidence from two cross-cuts indicated a reduction of radial cracks that provide access for the gas expansion. Furthermore, the performance of the rock support was investigated by comparing with the results from the unsupported cross-cut. The results indicated that the installed support system, designed for dynamic conditions, performed well under the loading conditions which can cause ejection.

A series of five large scale dynamic tests were conducted at the LKAB Kiirunavaara mine using explosives to generate the dynamic load on the support system. This was done with the aim of developing a testing methodology for in situ testing of ground support. Furthermore, the response of the installed rock support system to strong dynamic loading was evaluated. The tests included ground motion measurements, fracture investigation, ground and support motion imaging, as well as deformation measurements. The results indicated that the relation between the burden and the used amount of explosive had a vital role in either reducing or involving the effect of the detonation gases in the test results. In addition, the type of explosive which was used in the tests had a great impact on minimising the gas expansion effects. Higher peak particle velocities were measured compared to those of similar large scale tests carried out in other countries. However, the level of induced damage was limited to a fractured zone behind the support system and propagation of cracks in the shotcrete. Measured peak particle velocities were used to calculate the kinetic energy transmitted to the fractured zone of the test wall. The energy absorption by the Swellex, reinforced shotcrete and weld mesh was estimated by measuring the elongation/deflection of the support elements and relating these measurements to previously conducted laboratory tests. The comparison of maximum estimated energy absorbed by support system with the maximum estimated kinetic energy indicated that as the support system is still functional, the energy is partly reflected back to the surrounding rock. The results of the measurements in Tests 1, 2, 4 and 5 are presented in this paper and the methodology used to design the tests is discussed.

In order to assess the capacity of ground support systems when subjected to dynamic loading, simulated rockburst tests by using blasting have been conducted at LKAB Kiirunavaara underground mine. In this paper, a numerical simulation for one of the field tests is conducted using LS-DYNA code to numerically investigate the effect of the different aspects of the charge design including the initiation point and the geometry on the test results. In the simulation, an explosive material model is used to model the detonation of explosive used in field tests and the Riedel-Hiermaier -Thoma (RHT) material model is used to model the dynamic response of the rock mass. The decoupling effect between the explosive and the wall of borehole is also taken into account in the model. The numerical results show a similar particle vibration pattern and a crack pattern to those of the field measurment. The effects of the position of the initiation point and the charge structure on the dynamic response of rock mass are also discussed. The results can be a reference for blast design for future field tests.

A series of seven large scale dynamic tests were conducted at LKAB Kiruna mine using explosives in the vicinity of cross-cuts to generate dynamic load on the support system. The aim was to develop an in-situ testing method for rock support, i.e., to determine the dynamic load that causes failure to the test wall and/or support system. The methodology used to design Tests 1 to 7 is discussed in this paper and the level of damage to the test wall and support system in each test is described. Comparison of results in different test designs indicated that increasing burden and number of blasthole at the same time, increases the possibilities of obtaining more planar waves and decreases the destructive effect of detonation gases.

The increasing mining depth leads to higher stress magnitudes, resulting in increased seismic activity and more seismically-induced damage. The effectiveness of the ground support system under dynamic loading conditions has therefore become of prime interest to the mining companies in order to provide safe mining conditions with a minimum of production disturbances caused by unstable infrastructure. The problems of mining-induced seismicity have necessitated the use of ground support systems which are capable of withstanding strong dynamic loads. Although there are large amounts of measurement data from the site-installed seismic systems, they cannot be used directly to design and select the appropriate support systems due to lack of control over the location and nature of the seismic source and the effect of the rock mass on the seismic waves. Large-scale tests using explosives as the seismic source have therefore become a useful method to evaluate the performance of rock support systems for seismic conditions. A series of seven large scale dynamic tests of rock support was conducted in the Kiirunavaara mine. Explosives were detonated in boreholes in the pillar between two cross-cuts in order to generate a dynamic load on the rock support system installed on the cross-cut wall. This was done with the aim to develop a testing methodology for in-situ testing of ground support. Furthermore, the response of the installed support system to strong dynamic loading was also evaluated. The tests included ground motion measurements, fracture investigation, ground and support motion imaging, as well as the deformation measurements. The results of the measurements in Tests 1 to 7 are presented and the methodology used to design the tests is discussed. The results indicated that the relation between the burden distance and the used amount of explosive material and number of blastholes has a vital role in either reducing or involving the effect of detonation gases in test results. The large amount of data recorded during these tests will be useful for the calibration of more advanced numerical models. The energy absorption by the Swellex Mn24, 100 mm fibre reinforced shotcrete (40 kg/m3 steel fibre) and 75 mm x 75 mm weld mesh with 5.5 mm diameter was estimated and compared to that obtained from the large scale in-situ tests and laboratory tests conducted in different countries. The comprehensive ground motion data provided for the whole test wall was used to estimate the kinetic energy transmitted to the fractured zone where the support system was installed.