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  • 1.
    Sjöberg, Jonny
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Schill, Mikael
    DYNAmore Nordic AB, Linköping.
    Hilding, Daniel
    DYNAmore Nordic AB, Linköping.
    Yi, Changping
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nyberg, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Computer simulations of blasting with precise initiation2012Konferensbidrag (Refereegranskat)
    Abstract [en]

    Using blasting caps with electronic delay units, it has become possible to employ wave superposition in rock blasting. This paper presents computer simulations to investigate the hypothesis that fragmentation is improved in areas between blast holes where the tensile waves meet, overlap and interact. In this study, a numerical methodology using the code LS-DYNA was developed. LS-DYNA is a commercially available multi-purpose finite-element code, which is well suited to various types of dynamic modeling. Two different element formulations were used — Euler formulation in, and close to, the blast hole, and Lagrange formulation in the rock volume farther from the blast hole. The models used have a resolution (element size) of 50 mm and comprise approximately 20 million elements. Single and dual blast hole configurations have been studied, and a methodology to calculate possible fragmentation based on model interpretation was developed. The results showed that the amount of explosives and the blast hole spacing had the largest effect on fragmentation. The effect of varying delay times was small and local, implying that a significant increase in fragmentation should not be expected through wave superposition.

  • 2.
    Warema, Senzia
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser.
    Nordström, Emilia
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nordlund, Erling
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Dineva, Savka
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Zhang, Ping
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Yi, Changping
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Analysis of the rock mass support damages for seismic damaging events in Kiirunavaara mineManuskript (preprint) (Övrigt vetenskapligt)
  • 3.
    Yi, Changping
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Improved blasting results with precise initiation: Numerical simulation of small-scale tests and full-scale bench blasting2013Rapport (Övrigt vetenskapligt)
    Abstract [en]

    A series of numerical simulations of rock blasting has been conducted using the LSDYNA software in order to test the hypothesis proposed by Rossmanith, stating that interaction of stress waves could result in finer fragmentation by controlling the initiation times. The rock material was simulated with the RHT material model. After the calculation, the elements with damage level above 0.6 were removed to simulate complete fracturing of the rock.Firstly, a series of numerical simulations were conducted to model the small-scale tests performed by Johnasson et al. (2013). This work also involved simulating initial damage to the rock through previous blasting, and analyzing the resulting effects. The effect of different delay times showed that through a properly chosen delay time, improved fragmentation could be inferred. Moreover, the initial damage (from the previous row) clearly affected the fragmentation; however, the results indicated that longer delay times (in which the stress wave would have passed the boreholes) also resulted in improved fragmentation, implying that stress wave superposition may not be the primary factor governing the fragmentation. Secondly, full-scale tests conducted at the Aitik open pit mine were modeled. The simulation results indicated that the case of no interacting stress waves (6 ms delay) gavefiner fragmentation at most of the interpretation section cuts compared to the cases of interacting stress waves (0, 1 and 3 ms delay times). Both the simulation results of small scale tests and full scale tests indicate that the stress wave interaction effect due to delayed initiation can result in finer fragmentation compared to simultanious initiation. However, the results also indicate that relatively long delay times, leading to no stress wave superposition, induce even finer fragmentation compared to the use of very short delay times.

  • 4.
    Yi, Changping
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Improved blasting results with precise initiation: Numerical simulation of sublevel caving blasting2013Rapport (Övrigt vetenskapligt)
    Abstract [en]

    A series of numerical simulations of rock blasting using LS-DYNA software havebeen conducted to investigate the effect of short delay time on the fragmentation inunderground mines. The purpose was to test the hypothesis proposed by Rossmaniththat stress wave interaction could result in finer fragmentation by controlling theinitiation times. The blasted rock was simulated with RHT material model. After thecalculation, the elements with damage level above 0.6 were removed to simulate thefracture of the rock.The size of model and the borehole pattern were based on the blasting design of theLKAB Malmberget mine. Several simulations were run to investigate the effects ofinitiation time, primer position and boundary conditions. The results are presented asaccumulated area plots where the level of fragmentation can be observed at certainpositions in the model.The results show that the fragmentation for simultaneous initiation is coarsercompared to initiation with delay times in SLC blasting. It is difficult to identify anyeffect of stress wave interaction from the damage distribution in the blasted blockbecause the borehole pattern is in a fan shape. Thus, the distance between twoadjacent boreholes is not constant and the boreholes are of various lengths. Thenumerical modeling results showed that the fragmentation for the case of 2 ms delaytime is finer than that of simultaneous initiation and the 1 ms delay time case. Thecomparison among the cases with different primer positions shows that if the top ofthe block was set as free face, the bottom primer cases yielded the finer fragmentationthan the top primers cases and the middle primer cases; if the top of the block was setas non-reflecting boundary, the top primer cases yielded the finest fragmentation. Theeffect of overlying waste rock above the block cannot be neglected in simulations.The real boundary conditions of the top of the block and the effect of primer positionneed to be studied further. Some recommendations are proposed for the futureresearch about SLC blasting.

  • 5.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Discrete Element Modelling of Blast Fragmentation of a Mortar Cylinder2015Konferensbidrag (Refereegranskat)
    Abstract [en]

    Blasting techniques are widely used to fragment rock masses into smaller pieces. Numerical modelling is an efficient method employed by many researchers in the blasting field. It is difficult for a conventional continuum-based approach such as the finite element method (FEM) to model the rock fragmentation by blasting and the expansion work on the rock by explosive and its detonation products. In this paper, the particle blast method (PBM) was employed to model the behaviour of the detonation and a bonded particle model (BPM) was used to model the brittle material to be blasted. A mortar cylinder with a centrally placed hole for the explosive was modelled and the results were compared to the experimental data. The blast process from crack initiation to fragment formation was analysed. The influence of coupling ratio on fragmentation was also investigated.

  • 6.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi. Swedish Blasting Research Centre, Luleå University of Technology, Sweden.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi. Swedish Blasting Research Centre, Luleå University of Technology, Sweden.
    Greberg, Jenny
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Effects of in-situ stresses on the fracturing of rock by blasting2018Ingår i: Computers and geotechnics, ISSN 0266-352X, E-ISSN 1873-7633, Vol. 104, s. 321-330Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Blasting is widely applied in deep rock excavation. The effect of in-situ stresses on the fracturing of rock due to blasting was investigated. A theoretical model was used to explain the effect mechanism of in-situ stresses on crack propagation due to blasting. Four cases with different in-situ stress conditions were numerically investigated. The numerical results indicate that the crack propagation is governed by the blast load in the vicinity of the blasthole while the high in-situ stresses can influence the crack propagation in the far-field. The crack propagation trends towards the direction in which the high initial pressure is applied.

  • 7.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi. Swedish Blasting Research Centre, Luleå University of Technology, Sweden.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi. Swedish Blasting Research Centre, Luleå University of Technology, Sweden.
    Nyberg, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi. Swedish Blasting Research Centre, Luleå University of Technology, Sweden.
    Numerical investigation for timing effects on fragmentation based on a coupled FEM-BPM-PBM model2018Konferensbidrag (Refereegranskat)
  • 8.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nyberg, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Numerical modelling on short delay blast-induced fragmentation and vibration2018Ingår i: Blasting and Fragmentation, ISSN 1937-6359, Vol. 12, nr 2, s. 105-116Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Blasting operations can fragment rock mass into smaller pieces and meanwhile induce vibration anddamage in remaining rock mass. A series of small-scale laboratory tests were carried out to investigatethe effects of short delay times on fragmentation. These tests were modeled using a coupledFEM-BPM-PBM model in the LS-DYNA code. In the model, the remaining rock is representedby a finite element model (FEM) and the rock to be blasted is represented by a bonded particlemodel (BPM). The detonation of explosives is described with a particle blast method (PBM). Thefragment size distribution was obtained with a code developed in Perl programming language. Theblast-induced vibration and damage in the remaining rock mass were evaluated. The results showthat the coupled FEM-BPM-PBM model can be employed to evaluate both fragmentation in theblasted domain and the blast-induced damage and vibration in the remaining rock mass.

  • 9.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nyberg, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Scattering of SH-waves by a shallow circular lined tunnel with an imperfect interface2016Ingår i: Proceedings of the 8th International Symposium on Ground Support in Mining and Underground Construction / [ed] E. Nordlund, T.H. Jones and A. Eitzenberger (eds), 2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    The analytic solutions for the dynamic response of a shallow circular lined tunnel with an imperfectly bonded interface subjected to plane SH-waves are presented in the paper. Complex variable method was used and the imperfect interface was modelled with a linear spring model. The case that the rock is harder than the liner was investigated. The effects of the contact stiffness of the interface, the incident angle, the frequency of the incident wave and the depth of the tunnel were investigated. The results indicate when the frequency of incident waves is low, the variation of contact stiffness of the imperfect interface has a slight effect on the distribution of dynamic stress concentration factor (DSCF) in the rock mass but there is a significant effect on the distribution of DSCF in the liner. When the frequency of incident waves is high, the distribution of DSCF is complicated in the rock mass and in the liner. The variation of the depth of tunnel leads to the cyclical variation of DSCF. The incident angle significantly affects the distribution and value of DSCF. The phenomenon of resonance scattering can be observed when the bond of the interface is extremely weak

  • 10.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nyberg, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Beyglou, Ali
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Stress wave interaction between two adjacent blast holes2016Ingår i: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 49, nr 5, s. 1803-1812Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Rock fragmentation by blasting is determined by the level and state of stress in the rock mass subjected to blasting. With the application of electronic detonators, some researchers stated that it is possible to achieve improved fragmentation through stress wave superposition with very short delay times. This hypothesis was studied through theoretical analysis in the paper. First, the stress in rock mass induced by a single-hole shot was analyzed with the assumptions of infinite velocity of detonation and infinite charge length. Based on the stress analysis of a single-hole shot, the stress history and tensile stress distribution between two adjacent holes were presented for cases of simultaneous initiation and 1 ms delayed initiation via stress superposition. The results indicated that the stress wave interaction is local around the collision point. Then, the tensile stress distribution at the extended line of two adjacent blast holes was analyzed for a case of 2 ms delay. The analytical results showed that the tensile stress on the extended line increases due to the stress wave superposition under the assumption that the influence of neighboring blast hole on the stress wave propagation can be neglected. However, the numerical results indicated that this assumption is unreasonable and yields contrary results. The feasibility of improving fragmentation via stress wave interaction with precise initiation was also discussed. The analysis in this paper does not support that the interaction of stress waves improves the fragmentation.

  • 11.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nyberg, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Sjöberg, Jonny
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Numerical simulation for the influence of delay time on the rock fragmentation2013Ingår i: Rock Fragmentation by Blasting, FRAGBLAST 10: Proceedings of the 10th International Symposium on Rock Fragmentation by Blasting / [ed] Pradeep K. Singh; Amalendu Sinha, Boca Raton, Fla.: CRC Press/Balkema , 2013, s. 213-220Konferensbidrag (Refereegranskat)
    Abstract [en]

    With the application of electronic detonators and with short delay times, it may be possible to achieve improved fragmentation through stress wave superposition. This hypothesis was studied through a series of small scale laboratory tests. The results from these tests have subsequently been modeled using the numerical FEM code LS-DYNA and the RHT (Riedel-Hiermaier-Thoma) material model, applying a newly developed methodology for three-dimensional computer simulation of blasting. This work also involved simulating initial damage to the rock through previous blasting, and analyzing the resulting effects. The effect of different delay times showed that through a properly chosen delay time, improved fragmentation could be inferred. Moreover, the initial damage (from the previous row) clearly affected the fragmentation; however, the results indicated that longer delay times (in which the stress wave would have passed the boreholes) also resulted in improved fragmentation, implying that stress wave superposition may not be the primary factor governing fragmentation

  • 12.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Lu, Wenbo
    Rock Mechanics in Hydraulic Structural Engineering, Ministry of Education.
    Zhang, Ping
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nyberg, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Effect of imperfect interface on the dynamic response of a circular lined tunnel impacted by plane P-waves2016Ingår i: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 51, s. 68-74Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A theoretical method for studying the dynamic response of a circular lined tunnel with an imperfectly bonded interface subjected to plane P-waves is presented in the paper. The wave function expansion method was used and the imperfect interface was modeled with a spring model. Two cases were discussed in the paper. In the first case rock is harder than the lining and vice-versa in the second case. The results indicated that the variation in the stiffness of the interface has much influence on the distribution of dynamic stress concentration factors (DSCF) in the rock and the lining. The imperfection of the interface has a more noticeable influence on the DSCF in the rock mass and the lining at high frequency incident wave's scenario than low frequency incident wave's scenario. The resonance scattering phenomena can be observed when the bond is extremely weak. Limiting cases were considered and a good agreement with the solutions available in the literature was obtained.

  • 13.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi. Swedish Blasting Research Centre, Luleå University of Technology, Sweden.
    Nyberg, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi. Swedish Blasting Research Centre, Luleå University of Technology, Sweden.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi. Swedish Blasting Research Centre, Luleå University of Technology, Sweden.
    Calibration and Validation of Reactive Flow Model Parameters for an emulsion explosive2018Konferensbidrag (Refereegranskat)
  • 14.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nyberg, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Parameter Determination of an Ignition and Growth Model from Emulsion Explosive Tests2015Ingår i: 11th International Symposium on Rock Fragmentation by Blasting: FragBlast11, Carlton VIC: The Australasian Institute of Mining and Metallurgy, 2015, s. 585-589Konferensbidrag (Refereegranskat)
    Abstract [en]

    Emulsion explosives are a common industrial explosive and have a non-ideal detonation behaviour. The detonation performance for a given product changes with the charge diameter, ground conditions, confinement and density. The burning process of an emulsion explosive has been modelled with an ignition and growth model in the LS-DYNA code. The parameters in the burning rate function are calibrated by the detonation velocities and the detonation front curvature radii from emulsion explosive tests. A Perl program was developed for an efficient estimation of the parameters, and the results show that the calibrated parameters can predict both detonation velocities and the detonation front curvatures.

  • 15.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Sjöberg, Jonny
    Itasca Consultants AB.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Numerical modelling for blast-induced fragmentation in sublevel caving mines2017Ingår i: Tunnelling and Underground Space Technology, ISSN 0886-7798, E-ISSN 1878-4364, Vol. 68, s. 167-173Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The flow behavior of the ore and waste significantly affect the dilution in sublevel caving (SLC) mines. Drill and blast issues are identified as having a substantial impact upon SLC material flow. In the paper, blast-induced fragmentation in SLC was numerically investigated using the LS-DYNA code. A method was presented to evaluate fragmentation based on the damage description and a fragment identification routine implemented in the LS-PREPOST (a pre- and post-processing tool of LS-DYNA). The effects of the delay time and the primer position on fragmentation were investigated. The results indicated that a long delay time gives a finer fragmentation for the cases discussed in the paper. The results also showed that the middle primer and the top primer in SLC can give a fine fragmentation. The limitations of numerical modelling were also discussed.

  • 16.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Sjöberg, Jonny
    Itasca Consultants AB.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Petropoulos, Nikolaos
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    A numerical study of the impact of short delays on rock fragmentation2017Ingår i: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 100, s. 250-254Artikel i tidskrift (Refereegranskat)
  • 17.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Zhang, Ping
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nyberg, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Dynamic analysis for a circular lined tunnel with an imperfectly bonded interface impacted by plane SH-waves2014Konferensbidrag (Refereegranskat)
  • 18.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Zhang, Ping
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Johansson, Daniel
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nyberg, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Dynamic response of a circular lined tunnel with an imperfect interface subjected to cylindrical P-waves2014Ingår i: Computers and geotechnics, ISSN 0266-352X, E-ISSN 1873-7633, Vol. 44, s. 165-171Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The analytic solutions for the dynamic response of a circular lined tunnel with an imperfect interface subjected to a cylindrical P-wave were presented in the paper. The wave function expansion method was used and the imperfect interface was modeled with a spring model. The interface separating the liner from the surrounding rock was considered to be homogeneous imperfect. The dynamic stress concentration factors (DSCF) of the rock and liner were evaluated and discussed. The effects of incident wave’s frequency, bonding conditions and distance between the wave source and the tunnel were examined. The results showed that the low-frequency incident wave leads to a higher DSCF than the high-frequency incident wave. The bonding conditions have a great effect on the dynamic response of the lined tunnel. When the bond is extremely weak, the resonance scattering phenomenon can be observed. When the distance between the wave source and the tunnel, depending on frequency of the incident wave, is considered as large, the cylindrical wave can be treated as a plane wave. Limiting cases were considered and good agreement with the solutions available in the literature was obtained.

  • 19.
    Yi, Changping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Zhang, Ping
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nordlund, Erling
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Shirzadegan, Shahin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nyberg, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Numerical modelling of dynamic response of underground openings under blasting based on field tests2016Ingår i: Proceedings of the 8th International Symposium on Ground Support in Mining and Underground Construction / [ed] E. Nordlund, T.H. Jones and A. Eitzenberger (eds), 2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    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.

  • 20.
    Zhang, Ping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nordlund, Erling
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Swan, Graham
    Rock Mechanics and Mine Design, Sudbury, Canada.
    Yi, Changping
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Velocity Amplification of Seismic Waves Through Parallel Fractures Near a Free Surface in Fractured Rock: A Theoretical Study2019Ingår i: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 52, nr 1, s. 199-213Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    To determine the dynamic demand for support design under rockburst conditions, one of the most important issues is the prediction of ground motion parameters at the site of interest. Field monitoring has shown that the peak ground motion at the surface of an excavation in fractured rock is preferentially amplified compared to the motion in solid rock at a similar distance from the source. However, the traditional scaling laws used in rock support design do not account for the effect of free surface (excavation) and fracturing of rock. Recent studies have shown that high ground motion might be generated when a seismic wave crosses through fractures near a free surface in fractured rocks which is very complex and is not well understood. In this paper, particle velocity amplification was theoretically studied by investigating the dynamic interaction between seismic wave and multiple fractures near a free surface using the method of characteristics and the displacement discontinuity model. A harmonic load was applied on a model with a fractured zone near a free surface to investigate this phenomenon. After the harmonic wave propagated normally through multiple parallel fractures, the velocity amplification factor (VAF) was calculated as a function of the ratio of the magnitude of the peak particle velocity at the free surface of the model to the peak input velocity. The VAF can be as high as 3.77 and varies depending on the state of the fractured rock and the characteristics of the seismic wave. Parameter studies were conducted to investigate the effects of seismic load and multiple fractures on wave propagation, especially in terms of the wave frequency, the fracture spacing, the number of fractures and the stiffness of fractures. The results have proved that the interaction of the seismic wave and multiple fractures near the free surface strongly influences the ground motion. Quantitative relationships between the various influential factors and the corresponding VAF were developed. It is anticipated that such relationships can provide criteria to improve the current design procedures and help mining engineers to improve their rock support practice for rockburst-prone areas.

  • 21.
    Zhang, Ping
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Yi, Changping
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nordlund, Erling
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Shirzadegan, Shahin
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Nyberg, Ulf
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    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 technique2013Ingår i: 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, s. 565-581Konferensbidrag (Refereegranskat)
    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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