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  • 1.
    Edelbro, Catrin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Sjöberg, Jonny
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Dahner-Lindqvist, Christina
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Malmgren, Lars
    Prediction and follow-up of failure and fallouts in footwall drifts in the Kiirunavaara mine2012In: Canadian geotechnical journal (Print), ISSN 0008-3674, E-ISSN 1208-6010, Vol. 49, no 5, p. 546-559Article in journal (Refereed)
    Abstract [en]

    A likely result of changes in rock stresses due to progressing mining is an increased number of compressive stress–induced failures. This paper presents the results from numerical analysis and observations of stress-induced fallouts infootwall drifts in the Kiirunavaara underground mine. A brittle-plastic cohesion-softening friction-hardening (CSFH) material model was used for simulating brittle fallouts. To account for mining-induced stress changes, the local model stress boundary conditions were extracted from a global model. The rock mass properties were based on field observations in the footwall drifts as well as on results from laboratory testing. A multi-stage analysis was carried out to gradually change the stresses to simulate mining progress. A parametric study was conducted in which strength properties, location, and shape of the footwall drift were varied. Yielded elements and maximum shear strain were used as damage and fallout indicators. The modelling results were sensitive to the shape of the drift. The location of the predicted fallouts was in good agreement with the location of observed fallouts for the case in which the drift roof was simulated flatter than the theoretical cross section. The results indicate that the true shape of the drift is different from the planned one

  • 2. Malmgren, Lars
    Interaction between shotcrete and rock: experimental and numerical study2005Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    At LKAB’s underground mines in Malmberget and Kiruna in northern Sweden shotcrete and rock bolts are the main rock support elements. A safe working environment for the miners and high accessibility to the mine are important issues. To address these issues and to improve the use of the support, LKAB initiated a doctoral thesis study on the interaction between its rock support system and the rock. The objectives of this thesis were: to identify important parameters involved in the interaction between shotcrete and rock and if necessary investigate important quantities of these parameters, to improve the understanding of the interaction of shotcrete and rock. To achieve the first objective a number of laboratory and field tests were carried out. The second objective was achived by numerical analyses. The main conclusions are: The analyses showed that the rock strength and the unevenness of the surface had a large impact on the number of failures at the interface and in the lining. Furthermore, the behaviour of the lining was sensitive to small amplitudes of the surface roughness. A high bond strength was favourable according to the analyses. The results from the field tests showed the importance of the bond at the interface. If bond failure occurs the ability to distribute and control the crack width ceases. Failure mapping in the mine showed that that a thin shotcrete layer (<20 mm) did not perform well. It is therefore, important that the designed thickness is achieved when shotcreting. The extent of the excavated damage zone had a minor effect on the behaviour of the shotcrete lining if the surface was uneven. For an even surface, the influence of the extent of the EDZ on shotcrete was obvious but not serious. The rock support is generally designed for static loading conditions. In many cases, however, the openings are also subjected to dynamic loads. By field tests, vibration measurements and analyses the influence from blasting induced stress waves on the performance of shotcrete was investigated. The main conclusions are: Failure mapping showed that the fibre reinforced shotcrete has the ability to give stable conditions close to the drawpoint. The non-linear analyses showed fair agreement with the failure mapping. The single-degree-of-freedom (SDOF) model, though it is relatively simple, can be used to predict the response of an arbitrarily shaped rock wedge supported by shotcrete.

  • 3. Malmgren, Lars
    Shear strength of fibre reinforced beams: a literature review2005Report (Other academic)
    Abstract [en]

    The literature review summarises results from shear strength tests of fibre reinforced concrete beams. In addition results from shear strength test of push-off specimens are reported. Fibre reinforced beams without steel bars are not normally susceptible to failure arising from shear stress, tensile or flexural stress are usually the key causes of failure. Design criteria which are usable in practical design are presented. The various design criteria for shear strength based on beam tests showed small differences in predicted shear capacity of concrete reinforced with 40 to 60 kg/m3 steel fibres. The shear capacity of push-off specimens was much higher than the shear capacity of beams.

  • 4. Malmgren, Lars
    Shotcrete rock support exposed to varying load conditions2001Licentiate thesis, monograph (Other academic)
    Abstract [en]

    Field and laboratory tests and analyses This Licentiate thesis deals with the function of shotcrete as rock support. An extensive failure mapping of shotcrete in the Kiirunavaara mine has been conducted to improve the understanding of the performance of shotcrete. Furthermore, the adhesion strength obtained for different types of scaling/cleaning methods and the relationship between adhesion and compressive strength were investigated in field tests in the mine. The failure mapping showed that most of the observed failures of shotcrete are in areas with a thin shotcrete layer (

  • 5. Malmgren, Lars
    Strength, ductility and stiffness of fibre-reinforced shotcrete2007In: Magazine of Concrete Research, ISSN 0024-9831, E-ISSN 1751-763X, Vol. 59, no 4, p. 287-296Article in journal (Refereed)
    Abstract [en]

    In mining flexible linings are preferred because large displacements of underground openings are often allowed. This often results in extensive cracking of the shotcrete. Therefore, ductility of shotcrete is very important. In an investigation comprising 45 beam tests and 33 panel tests, Young's modulus, residual flexural strength and absorbed energy were determined for shotcrete reinforced by polypropylene fibres, steel fibres and steel mesh. The residual flexural strength was determined as the average strength over the displacement range 0-4 mm. Beams reinforced with steel fibres had higher residual flexural strength than beams reinforced with polypropylene fibres or steel mesh. The shotcrete reinforced with steel fibres and the best polypropylene fibres had almost the same energy absorption in the panel tests (0-25 mm displacement range) as well as in the beam tests (0-20 mm displacement range). Young's modulus of reinforced shotcrete determined by beam tests was lower than that derived from compression tests of cast concrete

  • 6. Malmgren, Lars
    et al.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Behaviour of shotcrete supported rock wedges subjected to blast-induced vibrations2006In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 43, no 4, p. 593-615Article in journal (Refereed)
    Abstract [en]

    The static state of stress at the brow in a sub-level caving mine is, due to stress re-distribution, almost uniaxial (major principal stress perpendicular to the cross cut). Since large amounts of explosives are detonated in each production round, the impact of stress waves on the brow can be significant. An extensive failure mapping programme in the Kiirunavaara mine showed that many of the failures close to the brow were structurally controlled. Furthermore, the area of damaged shotcrete was extensive when plain shotcrete was used. At brows supported by fibre reinforced shotcrete, damage in the roof was observed within a horizontal distance of about 3 m from the drawpoint. To study the behaviour of roof wedges supported by shotcrete and subjected to blast-induced vibrations a single-degree-of-freedom (SDOF) model was developed. The model consists of a shotcrete layer and a rock wedge. Vibration measurements showed that maximum particle velocity was approximately 1.2 m/s. The acceleration record showing the largest magnitude was used as the load in the dynamic analyses. The analyses showed that a wedge can be ejected by a dynamic load even if the static safety factor was >10. Furthermore, the non-linear response of the wedges was in most of the cases greater when the wedge was supported both by the joints and the shotcrete layer compared to the case when the wedge was only supported by shotcrete. A conclusion from the analyses is that it is difficult to predict the dynamic response from static calculations. To provide a safe working environment close to the drawpoint, the rock support must sustain the impact of stress waves from production blasting. To support rock wedges subjected to dynamic load the support must be able to consume the energy imposed on the wedges from blasting. The non-linear numerical analyses showed that reinforced shotcrete has the necessary bearing capacity to support the wedges formed in the roof of the cross cut close to the brow. This was in fair agreement with the failure mapping. The single-degree-of-freedom (SDOF) model can be used to study the response of an arbitrarily shaped rock wedge supported by shotcrete as long as the movement of the wedge can be idealised by a pure translation and the dimensions of the wedge are small compared to the length of the incident wave. Analyses showed that 2D wedges can be used to judge whether symmetric or non-symmetric 3D wedges in a uniaxial stress field (which occurs close to the brow) are stable or not when they are subjected to waves induced by blasting.

  • 7. Malmgren, Lars
    et al.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Interaction of shotcrete with rock and rock bolts: a numerical study2008In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 45, no 4, p. 538-553Article in journal (Refereed)
    Abstract [en]

    The shotcrete-rock interaction is very complex and is influenced by a number of factors. The influence of the following factors was investigated by a series of numerical analyses: the surface roughness of the opening, the rock strength and Young's modulus, the discontinuities, the extent and properties of the excavated disturbed zone, the mechanical properties of the interface between shotcrete and rock, and the thickness of the shotcrete lining and the rock bolts. The study was carried out as a sensitivity analysis. The results showed that the rock strength and the surface roughness had significant impact on the number of failures at the rock-shotcrete interface and in the shotcrete lining. Furthermore, the behaviour of the lining is sensitive to small amplitudes of the surface roughness. In all the cases investigated, a high interface strength was favourable. The results indicate that if a thick shotcrete lining is dependent on the bond strength. The benefit of using a thicker lining can be doubtful. The analyses showed that for an uneven surface the extent of the EDZ had a minor effect on the behaviour of the shotcrete lining. Furthermore, if rock bolts were installed at the apex of the protrusion instead of at the depression, the number of failures decreased both at the interface and in the lining

  • 8. Malmgren, Lars
    et al.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Rolund, S.
    WSP, Malmberget.
    Adhesion strength and shrinkage of shotcrete2005In: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 20, no 1, p. 33-48Article in journal (Refereed)
    Abstract [en]

    Shotcrete is widely used as rock support in mines and in civil engineering projects. In many cases the adhesion between the shotcrete and the rock is one of the most important properties. The objective of this study was to: (i) identify typical failures of shotcrete in a mining environment, (ii) measure the growth of the adhesion strength of shotcrete with respect to age, (iii) investigate the influence of surface treatment (scaling and cleaning) on the adhesion strength of shotcrete and (iv) investigate the occurrence of shrinkage cracks in the shotcrete and failures in the interface between the shotcrete and the rock. The failure mapping showed that most of the observed failures of shotcrete are in areas with a thin shotcrete layer ( less than or equal 20 mm) together with a low adhesion strength. Furthermore, the measured average thickness of shotcrete (40 mm) was almost the same as the ordered thickness, the problem is the wide scatter. In 18% of the thickness measurements, the shotcrete thickness was less than or equal to 20 mm. If the shotcrete lining in the mine has the same thickness distribution as during the tests, the supporting ability of as much as 18% of the shotcrete lining can be considered as more or less negligible. No differences in free shrinkage were observed between plain and steel fibre reinforced shotcrete. Relatively large areas with lack of contact between shotcrete and wall were observed in the shrinkage tests. This indicates that restrained shrinkage can destroy the bond between the shotcrete and rock. The results from the restrained shrinkage tests show the importance of the bond at the interface. If bond failure occurs, the ability to distribute and control the crack width ceases. The growth of the adhesion strength on a sandblasted concrete wall and the growth of the compressive strength showed a correlation. However, the scatter in the results indicates that further investigations have to be done in order to establish a reliable relation between the growth in adhesion and compressive strength with age. The results from the field tests showed that the adhesion strength was significantly higher on rock surfaces that had been water jet-scaled (with 22 MPa water pressure) than those treated by mechanical scaling followed by cleaning of the rock surface (water pressure 0.7 MPa).

  • 9.
    Malmgren, Lars
    et al.
    Mining Technology R and D, LKAB Kiruna Mine.
    Saiang, David
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Töyrä, Jimmy
    Bodare, A.
    Division of Soil and Rock Mechanics, Royal Institute of Technology, Stockholm.
    The excavation disturbed zone (EDZ) at Kiirunavaara mine, Sweden: by seismic measurements2007In: Journal of Applied Geophysics, ISSN 0926-9851, E-ISSN 1879-1859, Vol. 61, no 1, p. 1-15Article in journal (Refereed)
    Abstract [en]

    The presence of an excavation disturbed zone (EDZ) around an excavation boundary can significantly affect the overall performance of the excavation and the general safety of men and equipment. Hence, it has been an important subject of research in various rock excavation projects. The EDZ is generally defined as the rock zone beyond the excavation boundary where the physical, mechanical and hydraulic properties of the rock have been significantly affected due to the excavation and redistribution of stresses. For LKAB's Kiirunavaara underground iron ore mine in Sweden, the understanding of the EDZ is essential for optimal design of rock support. With this main objective an EDZ investigation was conducted at the mine using seismic measurement techniques. Cross-hole seismics and spectral analyses of surfaces waves (SASW) were the main techniques used. Borehole Image Processing Systems (BIPS) complemented the seismic measurements. The results show that an EDZ with a thickness of 0.5–1. 0 m existed behind the boundaries of the mining drifts being investigated. The magnitude of the Young's modulus of this zone was 50% to 90% of that of the undisturbed rock.

  • 10. Malmgren, Lars
    et al.
    Svensson, T,
    Kiruna grus och stenförädling AB.
    Investigation of important parameters for unreinforced shotcrete as rock support in the Kiirunavaara Mine, Sweden1999In: Rock mechanics for industry: proceedings of the 37th US Rock Mechanics Symposium, Vail, Colorado, USA, 6-9 June 1999 / [ed] Bernard Amadei, Balkema: Balkema Publishers, A.A. / Taylor & Francis The Netherlands , 1999, Vol. Vol. 2, p. 629-635Conference paper (Refereed)
    Abstract [en]

    The results from an extensive shotcrete failure mapping together with initial adhesion strength tests showed that there were a number of parameters for unreinforced shotcrete as rock support that needed to be further investigated. A more extensive adhesion strength test program was carried out which included studying the effects of accelerator concentration, time and the surface treatment method. The results from these investigations are presented in this paper. It is shown that water-jet scaling and sufficient thickness of the shotcrete give favourable conditions for the use of unreinforced shotcrete as rock support. The result of the tests carried out in Kiirunavaara shows that the adhesion strength has a wide range of variation.

  • 11.
    Nordlund, Erling
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nyberg, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Saiang, David
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Shirzadegan, Shahin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Westblom, Magnus
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Zhang, Ping
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Marklund, P-I
    Boliden Mineral AB.
    Sandström, D.
    Boliden Mineral AB.
    Malmgren, Lars
    Samverkan mellan bergförstärkningssystem och bergmassa2011In: Bergmekanikdag 2011: Föredrag, Stiftelsen bergteknisk forskning - Befo , 2011, p. 19-28Conference paper (Other academic)
  • 12.
    Nordlund, Erling
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Saiang, David
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Zhang, Ping
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Basarir, Hakan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nyberg, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Shirzaegan, S.
    Luleå tekniska universitet.
    Westblom, Magnus
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Malmgren, Lars
    Marklund, P-I
    Boliden Mineral AB.
    Nordqvist, A.
    LKAB.
    Sandström, D.
    Boliden Mineral AB.
    Rock support system in interaction with the rock2011Conference paper (Other academic)
  • 13.
    Saiang, David
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Malmgren, Lars
    The shotcrete/rock interface: direct shear, tension and compression2004In: Bergmekanikdag 2004, 2004, p. 99-109Conference paper (Other academic)
  • 14. Saiang, David
    et al.
    Malmgren, Lars
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Laboratory tests on shotcrete-rock joints in direct shear, tension and compression2005In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 38, no 4, p. 275-297Article in journal (Refereed)
    Abstract [en]

    A series of laboratory tests was performed on cemented shotcrete-rock joints to investigate the strength and stiffness of the interfaces, while simulating field conditions as close as possible. The direct shear test formed the core of the experimental work, while the tension and compression tests were complementary. To simulate loading conditions experienced in practical cases the direct shear tests were performed under fairly low normal stresses. In most practical cases when shotcrete is used with rock bolts, the normal load on shotcrete lining seldom exceeds 0.2 to 0.5 MPa. The direct shear test results show that, for such normal load range the shear strength is determined by the bond strength for genuinely bonded shotcrete-rock interfaces. For higher normal stresses (σn > 1.0 MPa), which rarely exist at the shotcrete-rock interface, the shear strength is largely influenced by friction resulting in the cohesive strength being less significant. Assessment of the shear surface revealed that the steel fibres in the shotcrete appeared to contribute significantly to the frictional component. The shear and normal stiffnesses of the interface were also determined, which were in principal the stiffnesses of the bond. An interesting observation was the complex interaction at the interface and the mechanisms that controlled the peak shear strength which depended on the surface roughness, the existence of natural flaws and the normal load.

  • 15.
    Saiang, David
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Malmgren, Lars
    Nordlund, Erling
    Strength and stiffness of shotcrete-rock interface: a laboratory study2004In: Ground Support in Mining and Underground Construction: Proceedings of the fifth international symposium on ground support / [ed] Ernesto Villaescusa; Yves Potvin, Leiden: Balkema Publishers, A.A. / Taylor & Francis The Netherlands , 2004, p. 555-564Conference paper (Refereed)
  • 16.
    Shirzadegan, Shahin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nyberg, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Zhang, Ping
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Malmgren, Lars
    Mining Technology R and D, LKAB Kiruna Mine.
    Rock support subjected to dynamic loading: Field testing of ground support using simulated rockburst2011In: Harmonising rock engineering and the environment: proceedings of the 12th ISRM International Congress on Rock Mechanics, Beijing, October 18 - 21, 2011 / [ed] Qihu Qian; Yingxin Zhou, Leiden: CRC Press/Balkema , 2011, p. 1269-1273Conference paper (Refereed)
    Abstract [en]

    Increasing the mining depth at LKABs Kiirunavaara mine located in the northern part of Sweden is leading to higher stress magnitudes, resulting in increased seismic activity and more rockburst 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. Therefore, a series of rockburst simulations will be conducted, using explosives to generate the dynamic load, on a number of support systems. This paper covers the results from the first trial test called Zero test-1. The test included ground motion measurements with a number of accelerometers, fracture investigation, ground and support motion imaging, as well as the deformation measurements. The methodology used to simulate rockbursts is discussed and the issues met in these tests are also addressed for further improvement.

  • 17.
    Shirzadegan, Shahin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nyberg, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Zhang, Ping
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Malmgren, Lars
    Mining Technology R and D, LKAB Kiruna Mine.
    Nordqvist, Anders
    LKAB.
    Andersson, Ulf Bertil
    LKAB.
    Large-scale dynamic testing of ground support system at the Kiirunavaara underground mine: Test 12013Report (Other academic)
  • 18.
    Shirzadegan, Shahin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nyberg, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Zhang, Ping
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Malmgren, Lars
    LKAB Research and Development.
    Nordqvist, Anders
    LKAB.
    Andersson, Ulf Bertil
    LKAB.
    Large-scale dynamic testing of ground support system at the Kiirunavaara underground mine: Tests 4 & 52013Report (Other academic)
  • 19.
    Shirzadegan, Shahin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nyberg, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Zhang, Ping
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Malmgren, Lars
    Mining Technology R and D, LKAB Kiruna Mine.
    Nordqvist, Anders
    LKAB.
    Andersson, Ulf Bertil
    LKAB.
    Large-scale dynamic testing of rock support system at the Kiirunavaara underground mine: Tests 2 & 32013Report (Other academic)
  • 20.
    Shirzadegan, Shahin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nyberg, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Zhang, Ping
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Malmgren, Lars
    Mining Technology R and D, LKAB Kiruna Mine.
    Töyrä, Jimmy
    LKAB.
    Nordqvist, Anders
    Andersson, Ulf Bertil
    LKAB.
    Large-scale dynamic testing of ground support system at the Kiirunavaara underground mine: Tests 6&72013Report (Other academic)
  • 21.
    Zhang, Ping
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Yi, Changping
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Shirzadegan, Shahin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nyberg, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Malmgren, Lars
    Mining Technology R and D, LKAB Kiruna Mine.
    Nordqvist, Anders
    LKAB.
    Numerical back-analysis of simulated rockburst field tests by using coupled numerical technique2013In: Ground Support 2013: Proceedings of the Seventh International Symposium on Ground Support in Mining and Underground Construction / [ed] Yves Potvin; B.G.H. Brady, Perth, Australia: Australian Center for Geomechanics , 2013, p. 565-581Conference paper (Refereed)
    Abstract [en]

    In order to assess the capacity of ground support systems when submitted to dynamic loading, simulated rockburst tests utilizing blasting have been performed for many years in different countries with limited success. In general, the blasts need to be carefully designed in order to reach the goal; however, different blast layouts (e.g. blasthole angle, burden) have been used based on researcher’s experience without conducting detailed analyses, the exception being a field test by CSIR. Recently, field trials have been conducted at the LKAB Kiirunavaara underground mine with some unexpected results which show that either the whole tested panel was destroyed or only a few fractures were formed without any ejections being observed. The aim of this paper is to investigate the failure mechanism in the simulated rockburst tests and improve the blast design by back-analyzing the test results using a coupled numerical modeling technique. The blast was simulated by using finite element method (LS-DYNA) and the dynamic interaction between the blasting generated waves and the opening was simulated by using discrete element modeling (UDEC) with the dynamic input from LS-DYNA. The numerical modeling showed that blasting can create both radial fractures radiating from the blasthole and fractures parallel or sub-parallel to the surface of the tested panel caused by reflected tensile stress waves. By comparing the results of the numerical modeling with the measured data, it is shown that the collapse failure was mainly controlled by the creation of a cone-shaped area formed by radial fractures and the burden seems to be a critical factor. In order to obtain fractures caused by reflected tensile stress waves and reduce blasting induced radial fractures, 2 parallel blastholes are suggested with larger burden (> 5 m) for future tests. Furthermore, the limitation of the current numerical modeling has also been discussed. The coupled 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 extrapolating results from simulated rockburst experiments if detailed geological structure and ground support system can be incorporated in the model and the model can be well calibrated.

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  • asciidoc
  • rtf