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  • 1.
    Ask, Daniel
    Luleå tekniska universitet.
    Evaluation of measurement-related uncertainties in the analysis of overcoring rock stress data from Äspö HRL, Sweden: a case study2003In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 40, no 7-8, p. 1173-1187Article in journal (Refereed)
    Abstract [en]

    A re-evaluation of overcoring results from the Borre Probe and the CSIRO HI cell was carried out at the Äspö HRL. The re-analysis revealed a number of measurement-related uncertainties for the two cells, e.g. bonding, temperature effects and identification of elastic parameters. These uncertainties were corrected and the re-analyzed strains were then used to determine the in situ stress field using standard least-squares technique. The results indicate lower stress magnitudes compared to the original interpretations and the results are in good agreement with existing hydraulic fracturing data as well as with theoretical vertical stress. Overall, the re-analysis indicates that the stress field at Äspö HRL is well constrained and relatively consistent with depth.

  • 2.
    Ask, Daniel
    Luleå tekniska universitet.
    Measurement-related uncertainties in overcoring data at the Äspö HRL, Sweden: Part 2: Biaxial tests of CSIRO HI overcore samples2006In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 43, no 1, p. 127-138Article in journal (Refereed)
    Abstract [en]

    This paper is the second dealing with measurement-related uncertainties of overcoring data undertaken at the Äspö Hard Rock Laboratory and focuses on the biaxial test data from CSIRO HI overcore samples. The first paper dealt with measurement-related uncertainties in connection with the overcoring phase [1]. The uncertainties identified in connection to biaxial tests of CSIRO HI overcore samples include too large applied pressures and poor sampling frequency. At the Aspo HRL, the results yield that most overcore samples fractured during biaxial testing, meaning that a significant part, 56%, of available strain gauge combinations were removed from calculations of the elastic parameters. Remaining strain gauge combinations indicate average values of 62′5 GPa for Young's modulus and 0.25′0.01 for Poisson's ratio, which are considerably lower than previously published values [2-5], and are in good agreement with results from biaxial tests on Borre Probe overcore samples .[6-10]. The stress calculations were obtained from re-analyzed elastic parameters and strains, and show primarily a reduction in stress magnitudes. Overall, the stress field obtained with different stress measurement methods and its variation with depth is now quite well resolved. The overcoring data suggest that the principal stresses are inclined with a vertical component dipping about 65° from the horizontal over the investigated rock volume (140-420 m depth). This is interpreted as a result of influence from the sub-vertical NE-2 Fracture Zone that divides the stress data into two stress domains [11], although it may also be an artefact because the σ[2]- and σ[3]-magnitudes are of the same order of magnitude.

  • 3.
    Ask, Daniel
    Luleå tekniska universitet.
    New developments in the integrated stress determination method and their application to rock stress data at the Äspö HRL, Sweden2006In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 43, no 1, p. 107-126Article in journal (Refereed)
    Abstract [en]

    The Integrated Stress Determination Method (ISDM) is a powerful tool for estimating the regional stress tensor from in-situ measurements of local stress tensors using a wide variety of stress measuring techniques. This study presents new developments of the ISDM: The stress field may be described with up to 12 model parameters; and is applicable to data from CSIR- and CSIRO HI-type of overcoring devices, hydraulic fracturing, hydraulic tests of pre-existing fractures (HTPF), as well as to combined data sets. Furthermore, in combined data sets, the hydraulic fracturing and/or HTPF data may be used to constrain the average elastic parameters, Young's modulus and Poisson's ratio. The new ISDM developments were applied to the extensive and recently re-analysed rock stress data at the Äspö Hard Rock Laboratory. The results reveal a good fit of the re-analysed data. Overall, the re-analysis indicates that the stress field at Äspö HRL is relatively well constrained and consistent with depth. The NE-2 Fracture Zone influences the stresses, and dividing the regional stress field into a NW and a SE stress domain. When the hydraulic fracturing data were used to constrain the average elastic parameters, Young's modulus, E, and Poisson's ratio, ν, quite similar results were obtained (E=50.8 GPa and v=0.33) compared with results from biaxial tests of overcore samples (E=61.6 MPa and v=0.26).

  • 4.
    Ask, Daniel
    et al.
    Vattenfall Power Consultant AB, Luleå.
    Cornet, F.H.
    Institute de Physique du Globe de Strasbourgh.
    Fontbonne, F.
    GEO-energies, Clermont-Ferrand.
    Nilsson, Tommy
    Jönsson, L.
    Hydraulikmontage i Luleå AB.
    Ask, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    A quadruple packer tool for conducting hydraulic stress measurements in mines and other high stress settings2009In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 46, no 6, p. 1097-1102Article in journal (Refereed)
  • 5.
    Ataei, Mohammad A.
    et al.
    Shahrood University of Technology, Faculty of Mining, Petroleum & Geophysics, Shahrood University of Technology.
    Mikaeil, Reza
    Department of Mining and Metallurgy Engineering, Urmia University of Technology, Faculty of Mining, Petroleum and Geophysics, Shahrood University of Technolog.
    Hoseinie, Hadi
    Faculty of Mining, Petroleum and Geophysics, Shahrood University of Technolog.
    Hosseini, Seyed Mehdi
    Department of Mining, Shahrood Branch, Islamic Azad University, Shahrood.
    Fuzzy analytical hierarchy process approach for ranking the sawability of carbonate rock2012In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 50, p. 83-93Article in journal (Refereed)
    Abstract [en]

    A new classification system is presented to evaluate and ranking the sawability of carbonate rock. The sawability of carbonate rock is classified into five categories: excellent, good, fair, poor and very poor. The sawability is assumed to depend on the uniaxial compressive strength, Young's modulus, Mohs hardness, and a new abrasivity index. The FAHP approach is used to determine the weights of the above-mentioned parameters by decision makers. Moreover, in this paper, a new classification system was developed to modify Schimazek's F-abrasiveness factor. In this new abrasivity classification, each parameter has a different importance coefficient. The new abrasivity index of carbonate rocks can be obtained from this new abrasivity classification system. The calculated sawability index of developed classification is applied for Iranian carbonate rocks to evaluation the energy consumption in rock sawing process. A variety of two groups of carbonate rocks (seven types) were saw using a fully instrumented laboratory sawing rig at different feed rates, peripheral speeds, and depth of cut. Then, a new statistical model was obtained using multiple regression method based on operating parameters and rock sawability index

  • 6.
    Castro, Raul
    et al.
    Julius Kruttschnitt Mineral Research Centre, University of Queensland.
    Trueman, Robert
    Julius Kruttschnitt Mineral Research Centre, University of Queensland.
    Halim, Adrianus
    Julius Kruttschnitt Mineral Research Centre, University of Queensland.
    A study of isolated draw zones in block caving mines by means of a large 3D physical model2007In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 44, no 6, p. 860-870Article in journal (Refereed)
    Abstract [en]

    Block caving methods rely on gravity to break and transport large amounts of ore and waste. Despite the importance of gravity flow, there is debate within the literature about the influence that the height of draw, particle size and particle size distribution has on the geometry of extraction and movement zones. This paper presents the results of an experimental programme conducted in the largest three-dimensional (3D) physical model to investigate the mechanisms of flow of cohesionless materials when drawing from a single drawpoint. Experimental results showed that isolated draw zones are mainly influenced by mass drawn and height of draw. Particle size was found to have a slight effect on extraction zones and no significant effect on movement zone width. Particle size composition (wide or narrow distributions) and drawpoint width were found not to have a major role on drawzone geometry. Those conclusions were based on statistical analysis of experimental data to define the controlling parameters in isolated draw. Model theory principles were used to investigate within the physical modelling framework the possibility of directly scaling the geometry of the extraction zones, which indicated that flow zones could be scaled in cohesionless materials under a set of assumptions. A mechanistic model of isolated draw is also postulated from experimental data from observations of stresses and the IMZ’s geometry.

  • 7.
    Gheibie, Sohrab
    et al.
    Faculty of Mining Engineering, Sahand University of Technology, Tabriz.
    Aghababaei, H.
    Faculty of Mining Engineering, Sahand University of Technology, Tabriz.
    Hoseinie, Hadi
    Faculty of Mining Engineering, Geophysics and Petroleum, Shahrood University of Technology.
    Pourrahimian, Yashar
    Department of Civil and Environmental Engineering, University of Alberta, Edmonton.
    Modified Kuz-Ram fragmentation model and its use at the Sungun Copper Mine2009In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 46, no 6, p. 967-973Article in journal (Refereed)
    Abstract [en]

    Rock fragmentation, which is the fragment size distribution of blasted rock, is one of the most important indices for estimating the effectiveness of blast work. In this paper a new form of the Kuz-Ram model is proposed in which a prefactor of 0.073 is included in the formula for prediction of X50. This new equation has a correlation coefficient that is greater than 0.98. In addition, a new approach is proposed to calculate the Uniformity Index, n. A Blastability Index (BI) is used to correct the calculation of the Uniformity Index of Cunningham, where BI reflects the uniformity of the distribution. Interestingly, this correction also can be observed in the Kuznetsov-Cunningham-Ouchterlony (KCO) model, which uses In situ block size as a parameter for calculating the curve-undulation in the Swebrec function. However, it is in contrast to prediction of X50 as the central parameter in Swebrec and Rosin-Rammler distribution functions. The new model is a two parameter fragmentation size distribution that can be easily determined in the field. However, it does not consider the timing effect, or upper limit for sizes, as does the original Kuz-Ram model. The model is used at the Sungun Mine, and it does a good job of predicting the fines produced during blasting

  • 8.
    Ghosh, Rajib
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Gustafson, Anna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Development of a geological model for chargeability assessment of borehole using drill monitoring technique2018In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 109, p. 9-18Article in journal (Refereed)
    Abstract [en]

    In the mining industry, the ability to charge and blast a production borehole is fundamental. However, if rock mass conditions are challenging, with cavities, fracture zones or even unstable boreholes, the charging crew may fail to insert the required amount of explosives, resulting in bad fragmentation and significant production disturbances in the downstream process. Prior detailed knowledge of the chargeability of each production fan or ring will improve both the planning and execution of the charging work in a mine. The paper describes a study using the drill monitoring technique to assess the chargeability of production boreholes. For the study, data were collected on four drill parameters, penetration rate, rotation pressure, feed pressure and percussive pressure, from 23 drill fans with a total of 186 boreholes. A parameter called fracturing was calculated based on penetration rate variability and rotation pressure variability. Sixty-three boreholes were filmed to establish different rock mass conditions: solid rock, cavities, fractured zones and cave-ins. Principal Component Analysis (PCA) was performed to model the relationship between drill monitoring data and the geological features. The developed model shows high potential by identifying charging problems directly from drill monitoring data, and has been verified and validated in a real charging operation in an operating mine.

  • 9.
    Ghosh, Rajib
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Gustafson, Anna
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Development of a geo-mechanical model for chargeability assessment of borehole using drill monitoring techniqueIn: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545Article in journal (Refereed)
  • 10.
    Ghosh, Rajib
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Kumar, Uday
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Evaluation of operating life length of rotary tricone bits using Measurement While Drilling data2016In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 83, p. 41-48Article in journal (Refereed)
  • 11.
    Hoseinie, Hadi
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics. Faculty of Mining Engineering and Geophysics, Shahrood University of Technology.
    Aghababaei, H.
    Faculty of Mining Engineering, Sahand University of Technology, Tabriz.
    Pourrahimian, Y.
    Faculty of Mining Engineering, Sahand University of Technology, Tabriz.
    Development of a new classification system for assessing of rock mass drillability index (RDi)2008In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 45, no 1, p. 1-10Article in journal (Refereed)
    Abstract [en]

    The drilling process and its results are affected by various parameters of the rock material and rock mass. The effects of rock material have been emphasized in various studies; however lack of perfect knowledge of rock mass structural parameters may lead to unpredictable results. This paper presents a new classification system for specifying the rock mass drillability index (RDi). For this purpose, six parameters of the rock mass, including texture and grain size, Mohs hardness, uniaxial compressive strength (UCS), joint spacing, joint filling (aperture) and joint dipping have been investigated by physical modeling and rated. Physical modeling in particular has been used for investigating the effects of joint characteristics on drilling rate. In the proposed RDi system, each rock mass is assigned a rating from 7 to 100, with a higher rating corresponding greater ease of drilling. Based on the RDi rating, the drilling rate may be classified into five modes: slow, slow-medium, medium, medium-fast, and fast.

  • 12.
    Hoseinie, Hadi
    et al.
    School of Mining Engineering, Petroleum and Geophysics, Shahrood University of Technology.
    Ataei, Mohammad A.
    Shahrood University of Technology, Faculty of Mining, Petroleum & Geophysics, Shahrood University of Technology, School of Mining Engineering, Petroleum and Geophysics, Shahrood University of Technology.
    Osanloo, Morteza
    Faculty of Mining Engineering and Metallurgy, Amirkabir University of Technology, Tehran.
    A new classification system for evaluating rock penetrability2009In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 46, no 8, p. 1329-1340Article in journal (Refereed)
    Abstract [en]

    This paper presents a new classification system called the Rock Penetrability index (RPi). An evaluation model based on the fuzzy Delphi analytic hierarchy process (FDAHP) has been used for estimation of penetrability and drillability of rocks. For this purpose, five parameters of the rock material, including uniaxial compressive strength, Schimazek's F-abrasivity, mean Moh's hardness, texture and grain size and Young's modulus have been investigated and rated. In the RPi system, a number from 10.25 to 100 can be assigned to each rock, with higher values corresponding to greater ease of drilling and penetration into rock. Based on the RPi classification, rocks are classified into five modes from the view point of penetrability: very poor, poor, medium, good and very good

  • 13.
    Huang, Yi
    Luleå tekniska universitet.
    Application of artificial neural networks to predictions of aggregate quality parameters1999In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 36, no 4, p. 551-561Article in journal (Refereed)
    Abstract [en]

    A back propagation neural network was applied for predictions of aggregate quality parameters, impact value (SPR), abrasion value I (SL) and abrasion value II (KK) in a data set including 56 rock samples from south-west Sweden. The Leaving-One-Out technique was used to determine error rates for the difference between values predicted by the neural network and observed values. The predictive power of the neural network was compared with statistical regression models established previously. The optimal configuration of the neural networks as well as the optimal number of training epochs were established from experiments

  • 14.
    Kou, Shaoquan
    et al.
    Luleå University of Technology.
    Kiu, Hongyuan
    Luleå University of Technology.
    Lindqvist, Per-Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Tang, C.A.
    Center for Rock Instability & Seismicity Research, Northeastern University, Shenyang.
    Rock fragmentation mechanisms induced by a drill bit2004In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 41, no Suppl. 1, p. 527-532Article in journal (Refereed)
    Abstract [en]

    In most of the mechanical excavation methods the fundamental process is indentation of the rock by a bit. The present paper focuses on discussing how the rock is fragmented under the action of a drill bit. The discussions are mainly based on numerical modelling using the rock and tool interaction code (R-T2D) and taking rock heterogeneity into consideration. The simulated results concerning rock penetrations with one, two and multiple indenters are, however, compared with experiments available from the literature. The emphasis is put on discussion of the formation of side-cracks and crushed zones that constitute the major rock removal fractures. The agreement between numerical simulation and experimental observations are reasonably good. This reveals the mechanisms of crack initiation, propagation and coalescence induced by the action of button bits to form the rock fragmentation in a drilling process. The investigation can contribute not only to improving percussive drilling but also to understanding other rock fragmentation and comminution methods and equipment since indentation is also the fundamental process for them.

  • 15.
    Kou, Shaoquan
    et al.
    Luleå University of Technology.
    Lindqvist, Per-Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Tang, C.A.
    Centre for Rockbursts and Induced Seismicity Research, Northeastern University, Shenyang, Liaoning.
    Xu, X. H.
    Centre for Rockbursts and Induced Seismicity Research, Northeastern University, Shenyang, Liaoning.
    Numerical simulation of the cutting of inhomogeneous rocks1999In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 36, no 5, p. 711-717Article in journal (Refereed)
    Abstract [en]

    In this study, the possible modes of crack initiation and propagation leading to chip formation in rock cutting are studied numerically by using a rock failure process analysis code referred to as RFPA. By using this approach, additional information is obtained on the tool-rock interaction and the failure mechanisms of rock under mechanical tools.

  • 16.
    Kou, Shaoquan
    et al.
    Luleå University of Technology.
    Liu, Hongyuan
    Luleå University of Technology.
    Lindqvist, Per-Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Tang, C. A.
    Center for Rock Instability & Seismicity Research, Northeastern University, Shenyang.
    Xu, X. H.
    National Key Laboratory of Nonlinear Mechanics, Chinese Academy of Sciences, Beijing.
    Numerical investigation of particle breakage as applied to mechanical crushing: Part 2: Interparticle breakage2001In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 38, no 8, p. 1163-1172Article in journal (Refereed)
    Abstract [en]

    A numerical approach to interparticle breakage is applied using the rock failure process analysis code, RFPA2D. A 2D particle assembly in a container is first numerically simulated to obtain the fringe patterns of stress fields that resemble the photoelastic test. Then, in addition, the interparticle breakage of the particle assembly in a chamber is conducted. The chamber consists of a steel container and a steel platen for transferring the load, and contains 15 particles of arbitrary sizes and irregular shapes. A plane strain condition is assumed. The particle bed is loaded under form conditions, in which the size reduction and the applied force are a function of the displacement. The numerical results indicate that, during the crushing process, three principal regimes appear: (i) the elastic deformation regime, where each particle deforms elastically; (ii) the fragmentation regime, where the particle assembly is crushed in a particle-by-particle fashion; and (iii) the assembly hardening regime, where the densified assembly recovers a significant stiffness. The dominant mode of failure is at first splitting, which is more or less parallel to the loading direction, and then progressive crushing, which mainly depends on the confinement from the chamber walls. The analysis of the load–displacement curves of the assembly obtained from the simulations reveals a high undulating load plateau, which suggests a macro-ductile behaviour.

  • 17.
    Li, Chunlin
    et al.
    Luleå tekniska universitet.
    Stillborg, Bengt
    Luleå tekniska universitet.
    Analytical models for rock bolts1999In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 36, no 8, p. 1013-1029Article in journal (Refereed)
    Abstract [en]

    Three analytical models have been developed for rock bolts: one for bolts subjected to a concentrated pull load in pullout tests, one for bolts installed in uniformly deformed rock masses, and one for bolts subjected to the opening of individual rock joints. The development of the models has been based on the description of the mechanical coupling at the interface between the bolt and the grout medium for grouted bolts, or between the bolt and the rock for frictionally coupled bolts. For rock bolts in pullout tests, the shear stress of the interface attenuates exponentially with increasing distance from the point of loading when the deformation is compatible across the interface. Decoupling may start first at the loading point when the applied load is large enough and then propagate towards the far end of the bolt with a further increase in the applied load. The magnitude of the shear stress on the decoupled bolt section depends on the coupling mechanism at the interface. For fully grouted bolts, the shear stress on the decoupled section is lower than the peak shear strength of the interface, while for fully frictionally coupled bolts it is approximately the same as the peak shear strength. For rock bolts installed in uniformly deformed rock, the loading process of the bolts due to rock deformation has been taken into account in developing the model. Model simulations confirm the previous findings that a bolt in situ has a pick-up length, an anchor length and a neutral point. It is also revealed that the face plate plays a significant role in enhancing the reinforcement effect. In jointed rock masses, several axial stress peaks may occur along the bolt because of the opening of rock joints intersecting the bolt.

  • 18.
    Liu, Hongyuan
    et al.
    Luleå University of Technology.
    Kou, Shaoquan
    Luleå University of Technology.
    Lindqvist, Per-Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Tang, C. A.
    Luleå University of Technology.
    Numerical simulation of the rock fragmentation process induced by indenters2002In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 39, no 4, p. 491-505Article in journal (Refereed)
    Abstract [en]

    Rock fragmentation processes induced by single and double indenters were examined by a numerical method. The simulated results reproduce the progressive process of rock fragmentation in indentation. Rock deforms elastically at the initial loading stage. Then tensile cracks are initiated around the two corners of the truncated indenter and propagate in the well-known conical Hertzian manner. The rocks immediately under the indenter are in a highly tri-axial stress state, and some of them fail in the ductile cataclastic mode with the stress satisfying the ductile failure surface of the double elliptic strength criterion. With the tensile cone cracks and ductile cataclastic failure releasing the confining pressure, the rocks under the indenter are compressed into failure and the crushed zone gradually comes into being. With increasing loading displacement, the re-compaction behaviour of the crushed zone occurs. Side cracks initiated from the crushed zone or bifurcated from cone cracks are driven by tensile stress associated with the crushed zone to propagate in a curvilinear path and finally intersect with the free surface to form chips. It is pointed out that the curvilinear path is caused by heterogeneity. The simulated force-penetration curve is in fact the indication of the propagation of cracks, the crushing of microstructural grains and the formation of chips. It is found that the confining pressure has an important influence on the indentation results. With decreasing confining pressure, there is a decrease in the indentation strength and a change in the rock failure process from the formation of rock chips to a vertically axially splitting failure. The simulated fragmentation process in the double indenter test reproduces the side cracks, which are induced by two indenters, propagate, interact and finally coalesce, chipping the rock between the indenters. The line spacing is an important factor that affects the fragmentation efficiency in multiple indenter tests. It is pointed out that simultaneous loading with multiple indenters with an appropriate line spacing seems to provide a possibility of forming larger rock chips, controlling the direction of subsurface cracks and consuming a minimum total specific energy. According to the simulated results, it is believed that the numerical simulation method will contribute to an improved knowledge of rock fragmentation in indentation, which will in turn help to enhance mining and drilling efficiency through the improved design of mining tools and equipment.

  • 19.
    Liu, Hongyuan
    et al.
    Luleå University of Technology.
    Kou, Shaoquan
    Luleå University of Technology.
    Lindqvist, Per-Arne
    Tang, C.A.
    Center for Rock Instability & Seismicity Research, Northeastern University, Shenyang.
    Numerical simulation of shear fracture (mode II) in heterogeneous brittle rock2004In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 41, no Suppl. 1, p. 14-19Article in journal (Refereed)
    Abstract [en]

    The fracture process of a heterogeneous brittle rock in the shear-box test is numerically investigated by means of the rock and tool interaction code (R-T2D). On the basis of the simulated results, the mode II fracture toughness is calculated, which is KIIC =7.72MPa root m, and the influence of heterogeneity and confinement on the formation and characteristics of shear fracture is discussed. It is found that with the confinement increasing, the fracture mechanisms in the shear-box test of heterogeneous brittle rock change from mixed tensile and shear failure but are dominated with tensile failure to dominant shear failure. It is concluded that the shear-box test under a confined condition is favourable for creating a condition for mode II fracture and a suitable method for measuring the mode II fracture toughness.

  • 20. 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.

  • 21. 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

  • 22.
    Navarro, Juan
    et al.
    Universidad Politécnica de Madrid – E.T.S.I. Minas y Energía, Madrid, Spain.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Ghosh, Rajib
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Segarra, Pablo
    Universidad Politécnica de Madrid – E.T.S.I. Minas y Energía, Madrid, Spain.
    Johansson, Daniel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Sanchidrián, José Ángel
    Universidad Politécnica de Madrid – E.T.S.I. Minas y Energía, Madrid, Spain.
    Application of drill-monitoring for chargeability assessment in sublevel caving2019In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 119, p. 180-192Article in journal (Refereed)
    Abstract [en]

    Currently, the charging procedure for sublevel caving mining is carried out with no prior information of the rock mass condition. Thus, engineers are blindsided to unexpected rock conditions and ill-prepared to address issues associated with collapsing boreholes. This results on charging problems and, as consequence, bad fragmentation of the rock after blasting which difficult ore loading and transportation as the gravity flow of the rock is reduced.

    This paper builds up the work done by Ghosh et al. (IJRMMS, 2018), to classify the geotechnical rock condition into five classes (solid rock, fractured rock, cave-in, minor and major cavity). From it, two applications based on the Measure While Drilling (MWD) technique have been developed: one for geotechnical rock condition of orebodies and the other for predicting the risk of collapse in boreholes. The work of Ghosh et al. has been improved into a geotechnical rock condition block model to simplify the quantitative assessment and automatic recognition of rock trends. A thorough correction of the MWD parameters has been also applied to minimize external influences other than the rock mass. From it, the risk of borehole collapses model has been developed by comparing different combinations of the geotechnical rock condition block-model with the charging length of 102 production fan-holes. The assessment of the number of collapsed and non-collapsed blastholes and the charging length/blasthole length ratio has been used to assign high, medium or low risk of collapse to each combination. The results predict collapses in the first half of the fan-holes for the high risk, collapses in the second half of the fan-hole for the medium risk and no collapses along the hole for the non-risk holes. The two models have been applied in large scale for two orebodies in the Malmberget mine, Sweden, which comprises 20 drifts and 5060 fan shape long-holes.

  • 23.
    Rao, Qiuhua
    et al.
    Central South University, College of Resource, Environment and Civil Engineering, Changsha.
    Sun, Zongqi
    Central South University, College of Resource, Environment and Civil Engineering, Changsha.
    Stephansson, O.
    Royal Institute of Technology.
    Li, Chunlin
    Luleå University of Technology.
    Stillborg, Bengt
    Luleå University of Technology.
    Shear fracture (Mode II) of brittle rock2003In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 40, no 3, p. 355-375Article in journal (Refereed)
    Abstract [en]

    Mode II fracture initiation and propagation plays an important role under certain loading conditions in rock fracture mechanics. Under pure tensile, pure shear, tension- and compression-shear loading, the maximum Mode I stress intensity factor, K (sub I max) , is always larger than the maximum Mode II stress intensity factor, K (sub II max) . For brittle materials, Mode I fracture toughness, K (sub IC) , is usually smaller than Mode II fracture toughness, K (sub IIC) . Therefore, K (sub I max) reaches K (sub IC) before K (sub II max) reaches K (sub IIC) , which inevitably leads to Mode I fracture. Due to inexistence of Mode II fracture under pure shear, tension- and compression-shear loading, classical mixed mode fracture criteria can only predict Mode I fracture but not Mode II fracture. A new mixed mode fracture criterion has been established for predicting Mode I or Mode II fracture of brittle materials. It is based on the examination of Mode I and Mode II stress intensity factors on the arbitrary plane theta ,K (sub I) (theta ) and K (sub II) (theta ), varying with theta (-180 degrees < or =theta < or =+180 degrees ), no matter what kind of loading condition is applied. Mode I fracture occurs when (K (sub II max) /K (sub I max) )(K (sub IIC) /K (sub IC) ) and K (sub II max) = K (sub IIC) at theta (sub IIC) . The validity of the new criterion is demonstrated by experimental results of shear-box testing. Shear-box test of cubic specimen is a potential method for determining Mode II fracture toughness K (sub IIC) of rock since it can create a favorable condition for Mode II fracture, i.e. K (sub II max) is always 2-3 times larger than K (sub I max) and reaches K (sub IIC) before K (sub I max) reaches K (sub IC) . The size effect on K (sub IIC) for single- and double-notched specimens has been studied for different specimen thickness B, dimensionless notch length a/W (or 2a/W) and notch inclination angle alpha . The test results show that K (sub IIC) decreases as B increases and becomes a constant when B is equal to or larger than W for both the single- and double-notched specimens. When a/W (or 2a/W) increases, K (sub IIC) decreases and approaches a limit. The alpha has a minor effect on K (sub IIC) when alpha is within 65-75 degrees . Specimen dimensions for obtaining a reliable and reproducible value of K (sub IIC) under shear-box testing are presented. Numerical results demonstrate that under the shear-box loading condition, tensile stress around the notch tip can be effectively restrained by the compressive loading. At peak load, the maximum normal stress is smaller than the tensile strength of rock, while the maximum shear stress is larger than the shear strength in the presence of compressive stress, which results in shear failure.

  • 24.
    Sanchidrián, José A
    et al.
    Universidad Politécnica de Madrid.
    Ouchterlony, Finn
    Montanuniversität Leoben.
    Moser, Peter
    University of Leoben, Montanuniversität Leoben.
    Segarra, Pablo
    Universidad Politécnica de Madrid.
    Lopéz, Lina M
    Universidad Politécnica de Madrid.
    Performance of some distributions to describe rock fragmentation data2012In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 53, p. 18-31Article in journal (Refereed)
    Abstract [en]

    Ten functions (Weibull, Swebrec, Gilvarry, Grady and Lognormal, and their bi-component versions) are fitted to 448 sets of screened fragment size data from blasted and crushed rock. The ordinary least squares criterion has been used for the fits and two minimization techniques have been tested, in both cases running the problem repeatedly with different initial values of the unknown parameters in order to ensure a global minimum. There is a distinct behavior of errors across the passing range, which has been divided in four zones, coarse (>80%), central (80%–20%), fine (20%–2%) and very fine (<2%). The representation of fragmentation data by some of the distributions can be made with good accuracy in the coarse and central zones, with moderate accuracy in the fine zone and with considerably poor accuracy in the very fine zone. As expected, bi-component distributions generally perform better than the single-components, though there are important differences among them. Extended Swebrec is consistently the best fitting distribution in all zones, with maximum relative errors of less than 25% in the coarse, 15% in the central, and 50% in the fine zones. Bimodal Weibull, bimodal Gilvarry and bimodal Grady's errors are statistically equivalent to extended Swebrec's in the central and fine zones. In the very fine zone, relative errors have a high probability of being in excess of 100%, with maximum expected values being several times that, even for the best fitting functions in this zone. Swebrec is by far the best single component function in all zones, with errors comparable to the best bi-components in the coarse and central.

  • 25.
    Schunnesson, Håkan
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering.
    Rock characterisation using percussive drilling1998In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 35, no 6, p. 711-725Article in journal (Refereed)
    Abstract [en]

    Despite considerable advantages such as reliable hardware, no disturbance in production, fast analysis and presentation of results and very low operational cost, the use of percussive drill monitoring to retrieve geological and geomechanical information concerns the drilled rock has not become a standard investigation tool in the underground industry. One major obstacle is the analysis of data. The monitored "raw" data can be affected by a significant influence from the operator, who often adjusts the drill settings in order to achieve the best drilling result. Furthermore, the advanced control system on a modern drill rig adjusts drill parameters independently to avoid drilling problems and damage to the drill string and machine. In order to use percussive drill monitoring in industrial applications, the performed analysis must be able to handle variations among monitored drill parameters, but still separate rock dependent variation from other influences on the monitored drilling data. Once the external influences on the drilling data have been normalised only leaving the rock dependant variation, rock properties can be predicted using theoretical or heuristic relations, or calibrated with observed rock conditions using statistical analysis. The method of analysis suggested in this paper is based on a step-wise normalisation of raw drilling data, where hole length dependent variation initially is removed, followed by a normalisation of the thrust dependent variation, and finally, by removing the influence of penetration rate on torque pressure. The analysis shows that major classification errors can be made if raw data are used instead of normalised data. The technique is applied on modern drill monitoring data from three different drilling sites, in crystalline rock masses in Sweden. The drill data selected were obtained during normal drilling conditions, where no special steps had been taken to promote the analysis or the interpretation. Examples from each site show good potential to predict ore boundaries and fracturing based on normalised drill parameters from percussive drilling.

  • 26. Tang, C. A.
    et al.
    Fu, Y. F.
    Kou, S. Q.
    Lindqvist, Per-Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Numerical simulation of loading inhomogeneous rocks1998In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 35, no 7, p. 1001-1007Article in journal (Refereed)
  • 27.
    Tang, C A
    et al.
    Center for Rock Instability & Seismicity Research, Northeastern University, Shenyang.
    Xu, X H
    Center for Rock Instability & Seismicity Research, Northeastern University, Shenyang.
    Kou, S Q
    Luleå tekniska universitet.
    Lindqvist, Per-Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Liu, H Y
    Luleå tekniska universitet.
    Numerical investigation of particle breakage as applied to mechanical crushing: Part I, Single-particle breakage2001In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 38, no 8, p. 1147-1162Article in journal (Refereed)
    Abstract [en]

    A numerical approach to particle breakage is applied using the Rock Failure Process Analysis code, RFPA (super 2D) . The numerical tool is validated by simulating the Brazilian test with a two-dimensional disk sample. Then two irregularly shaped particles with an exact geometry and exact mechanical properties are numerically modelled to investigate their breakage behaviour under unconfined and confined loading conditions. The numerical results indicate that the dominant mode of failure is catastrophic splitting and progressive crushing, which mainly depends on the loading conditions with respect to confinement. The analysis of the load-displacement curves obtained from the simulations suggests a brittle-ductile transition between the two cases. The lateral constraint increases the initial stiffness and the maximum breakage strength of the particle. Most of the energy released during the failure process comes from the crushing of highly stressed areas, particularly, in the vicinity of the contact points where a crushed zone forms. It is also found that the particle shape governs the breakage strength in addition to the material properties themselves, and that the heterogeneity of the particles governs the fracture propagation paths

  • 28.
    Trueman, Robert
    et al.
    University of Queensland, Brisbane.
    Castro, Raul
    University of Chile, Santiago.
    Halim, Adrianus
    Anglo Coal Australia.
    Study of multiple draw-zone interaction in block caving mines by means of a large 3D physical model2008In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 45, no 7, p. 1044-1051Article in journal (Refereed)
    Abstract [en]

    Current production level design guidelines in block caving mines are based on the concept of interaction of movement zones and the spacing of draw-points at which mass flow is achieved. The limit of the isolated movement zone (IMZ) interaction has been determined by observations of the flow of sand and finely fragmented caved rock. This paper presents a study of the mechanisms and limit of IMZ interaction in coarse fragmented caved rock using a large 3D physical model. Results showed that when drawing from multiple drawpoints, the unmoved zone between IMZs is characterised by an increase in vertical load and a decrease in horizontal load. However, it was observed that the unmoved zones between the movement zones of adjacent draw-points did not enter the flow zone, despite drawpoints being spaced at less than 1.2 times the width of the IMZ. This result is in marked contrast to previous findings obtained in sand models, where movement zones have been observed to interact at draw-point spacings up to 1.5 times the width of the IMZ. The major reasons for the differences between the two different model results was found to be that significant stress arching and less induced vertical stress during flow was observed in the gravel model, in contrast to limited stress arching and more induced vertical stress in the sand models. It is hypothesised that significant stress arching would occur in block caving mines, and therefore that the results obtained in the gravel model maybe more representative of full-scale conditions. Movement zones in block caving mines may therefore not interact at draw-point spacings greater than the width of the isolated movement zone.

  • 29.
    Tuomas, Göran
    et al.
    Luleå tekniska universitet.
    Gustafsson, Anna-Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Architecture and Water.
    Evaluation of ground thermal conductivity from drilling data2004In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 41, no Suppl 1, p. 241-247Article in journal (Refereed)
    Abstract [en]

    In this paper a new method for evaluating ground thermal conductivity is suggested. The principle is based on ordinary drilling where energy is injected into the borehole in the form of pressurised fluid, mechanical torque, and mechanical feed force, which all dissipate into heat. Part of the heat leaves the borehole with the fluid while the rest is mainly transferred into the formation. By determining the energy flows, ground thermal conductivity can be estimated. This new measurement method would have many advantages. Ground conductivity values would be continuously estimated along the borehole, meaning that values are obtained through the formation. This quality could, for example, be used during production drilling in a mine to instantly detect lithological boundaries, resulting in increased ore extraction efficiency. Energy storage systems could be dynamically designed since the system capacity could be recognized and verified during drilling. Presented simulation results, where realistic drilling parameters were used, show that the method has the potential to be practically applied.

  • 30.
    Wang, Q Z
    et al.
    Department of Civil Engineering and Applied Mechanics, Sichuan University.
    Jia, X M
    Department of Civil Engineering and Applied Mechanics, Sichuan University.
    Kou, S Q
    Luleå tekniska universitet.
    Zhang, Z X
    Luleå tekniska universitet.
    Lindqvist, Per-Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    More accurate stress intensity factor derived by finite element analysis for the ISRM suggested rock fracture toughness specimen-CCNBD2003In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 40, no 2, p. 233-241Article in journal (Other academic)
  • 31.
    Wang, Q Z
    et al.
    Department of Civil Engineering and Applied Mechanics, Sichuan University.
    Jia, X M
    Department of Civil Engineering and Applied Mechanics, Sichuan University.
    Kou, S Q
    Luleå tekniska universitet.
    Zhang, Z X
    Luleå tekniska universitet.
    Lindqvist, Per-Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    The flattened Brazilian disc specimen used for testing elastic modulus, tensile strength and fracture toughness of brittle rocks: analytical and numerical results2004In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 41, no 2, p. 245-253Article in journal (Refereed)
    Abstract [en]

    The flattened Brazilian disc specimen is proposed for determination of the elastic modulus E, tensile strength sigma (sub t) and opening mode fracture toughness K (sub IC) for brittle rocks in just one test. This paper is concerned with the theoretical analysis as well as analytical and numerical results for the formulas. According to the results of stress analysis and Griffith's strength criteria, in order to guarantee crack initiation at the centre of the specimen, which is considered to be crucial for the test validity, the loading angle corresponding to the flat end width must be greater than a critical value (2alpha > or =20 degrees ). The analysis shows that, based on the recorded complete load-displacement curve of the specimen (the curve should include the "fluctuation" section after the maximum load), E can be determined by the slope of the section before the maximum load, sigma (sub t) by the maximum load, and K (sub IC) by the local minimum load immediately subsequent to the maximum load. The relevant formulas for the calculation of E, sigma (sub t) , K (sub IC) are obtained, and the key coefficients in these formulas are calibrated by finite-element analysis. In addition, some approximate closed-form formulas based on elasticity are provided, and their accuracy is shown to be adequate by comparison with the finite-element results.

  • 32.
    Yi, Changping
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Sjöberg, Jonny
    Itasca Consultants AB.
    Johansson, Daniel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Petropoulos, Nikolaos
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    A numerical study of the impact of short delays on rock fragmentation2017In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 100, p. 250-254Article in journal (Refereed)
  • 33. Zhang, Ping
    et al.
    Li, Ning
    Xi'an University of Technology.
    Li, Xibing
    School of Resources and Safety Engineering, Central South University, Changsha.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Compressive failure model for brittle rocks by shear faulting and its evolution of strength components2009In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 46, no 5, p. 830-841Article in journal (Refereed)
    Abstract [en]

    A physical theory for brittle failure is presented that aims to explain both the phenomenological and micro-structural observations. The objective of this model is to capture the important attributes inferred from micro-structural experiments so as to arrive at constitutive relations that describe macroscopic failure behaviour. Based on experimental results, the micromechanical failure character- isation is summarised first. The localised failure process of rock will experience two stages: the brittle breakage stage (bond rupture of rock bridge) and the sliding stage (frictional resistance of failure plane mobilisation). A physical model is developed by dividing the sample into elastic and localised shear zones. Furthermore, the deformation process of the localised shear zone is divided into bond loss and frictional resistance mobilisation in two stages. To combine the micro-characteristics with the macromechanical properties, the chain models in localised shear zone, and the homogenisation method are adopted. The model is validated against the experimental data of Yumlu and Ozbay's. Subsequently, the localised progressive failure characteristics of rock are analysed by changing the model's parameters. The intrinsic effects and influential factors such as geometrical effects (size effect, shape effect), the strain softening phenomenon and Class II stress-strain curves are revealed. Finally, in order to be used easily by engineers, the simplified description of rock failure process and its evolution of strength components are given based on the model.

  • 34.
    Zhang, Z. X.
    et al.
    Luleå tekniska universitet.
    Kou, S. Q.
    Luleå tekniska universitet.
    Jiang, L. G.
    University of Science and Technology, Beijing.
    Lindqvist, Per-Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Effects of loading rate on rock fracture: fracture characteristics and energy partitioning2000In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 37, no 5, p. 745-762Article in journal (Refereed)
    Abstract [en]

    By means of the Scanning Electron Microscope (SEM), an examination was performed of the fracture surfaces (including their vertical sections) of both Fangshan gabbro and Fangshan marble specimens fractured at the loading rates k = 10-2 ≈ 106 MPa m1/2 s-1. The results showed that one or more branching cracks near the fracture surfaces of dynamic rock specimens were clear and the cracks increased with increasing loading rates. However, such branching cracks were rarely seen near the static fracture surfaces. In addition, with the aid of the Split Hopkinson Pressure Bar (SHPB) testing system and a high-speed framing camera, the energy partitioning in the dynamic fracture process of a short rod (SR) rock specimen was analysed quantitatively. The total energy WL absorbed by an SR specimen in the dynamic fracture process mainly consisted of the fracture and damage energy WFD and the kinetic energy WK of flying fragments. The energies WL and WK could be quantitatively calculated through stress wave measurement and high-speed photography in the SHPB testing system. Thus, the fracture and damage energy WFD could be obtained. The results showed that: (1) the energy WK increased with an increase in the impact speed of the striker bar or the loading rate; (2) the energy WFD for dynamic rock fracture was markedly greater than that for static rock fracture, and the WFD increased with an increase in the impact speed of the striker bar or the loading rate; and (3) the value WL/WB (WB is the energy input into the loading system) in the case of dynamic fracture is much lower than that in the case of static fracture. In addition, the ratio decreases with an increase in the loading rate or the impact speed of the striker bar. This means that the energy utilisation decreases when the loading rate or the impact speed of the striker bar rises. Finally, some application problems are discussed in the paper.

  • 35. Zhang, Z. X.
    et al.
    Kou, S. Q.
    Yu, J
    Yu, Y
    Jiang, L. G.
    Lindqvist, Per-Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Effects of loading rate on rock fracture1999In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 36, no 5, p. 597-611Article in journal (Refereed)
    Abstract [en]

    By means of a wedge loading applied to a short-rod rock fracture specimen tested with the MTS 810 or SHPB (split Hopkinson pressure bar), the fracture toughness of Fangshan gabbro and Fangshan marble was measured over a wide range of loading rates, =10−2–106 MPa m1/2 s−1. In order to determine the dynamic fracture toughness of the rock as exactly as possible, the dynamic Moiré method and strain–gauge method were used in determining the critical time of dynamic fracture. The testing results indicated that the critical time was generally shorter than the transmitted wave peak time, and the differences between the two times had a weak increasing tendency with loading rates. The experimental results for rock fracture showed that the static fracture toughness KIc of the rock was nearly a constant, but the dynamic fracture toughness KId of the rock (≥104 MPa m1/2 s−1) increased with the loading rate, i.e. log(KId)=a log +b. Macroobservations for fractured rock specimens indicated that, in the section (which was perpendicular to the fracture surface) of a specimen loaded by a dynamic load, there was clear crack branching or bifurcation, and the higher the loading rate was, the more branching cracks occurred. Furthermore, at very high loading rates (≥106 MPa m1/2 s−1) the rock specimen was broken into several fragments rather than only two halves. However, for a statically fractured specimen there was hardly any crack branching. Finally, some applications of this investigation in engineering practice are discussed.

  • 36.
    Zhang, Z X
    et al.
    Luleå tekniska universitet.
    Yu, J
    University of Science and Technology, Beijing.
    Kou, S.Q.
    Luleå tekniska universitet.
    Lindqvist, Per-Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Effects of high temperatures on dynamic rock fracture2001In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 38, no 2, p. 211-225Article in journal (Refereed)
    Abstract [en]

    The dynamic fracture toughness of Fangshan Gabbro and Fangshan Marble subjected to high temperature was measured by means of the split Hopkinson pressure bar (SHPB) system. The specimens for measuring the fracture toughness were manufactured according to the requirements for the Short Rod (SR) specimen suggested by ISRM. Two cases were investigated: (1) the SR specimens of the gabbro and marble were fractured at high temperature (100-330 degrees C), and (2) the specimens of the rocks were first pre-heat-treated at 200 degrees C for the marble and 600 degrees C for the gabbro, and then fractured at room temperature. The experimental results showed that under dynamic loading the fracture toughness of both the gabbro and the marble tested in the above-mentioned cases increased with increasing loading rates. The relationship between the fracture toughness and the loading rates in the two cases is similar to that obtained in the room temperature environment, i.e., without high temperature. (This is defined as the third case.) It can be concluded that temperature variation affects the dynamic fracture toughness of the two rocks to a limited extent within the temperature ranges tested. This is different from the results obtained under the static loading condition. Furthermore, by means of the scanning electronic microscope (SEM), the vertical sections of the fracture surfaces for some gabbro specimens were examined. In addition, the fractal dimensions of the fracture surfaces of some specimens were measured by means of fractal geometry. The results showed that under dynamic loading: (1) macro-crack branching near the fracture surfaces was universal; (2) the fractal dimensions increased with increasing loading rates; (3) in the sections of the specimens tested at high temperature there were many micro-cracks that were probably induced by thermal cracking. On the basis of the above macro- and micro-experimental investigation, an energy analysis of the process of dynamic rock fracture was performed. The results showed that the energy utilisation in dynamic fracture was much lower than that in static fracture.

  • 37.
    Zhang, Zongxian
    et al.
    Luleå University of Technology.
    Kou, Shaoquan
    Luleå University of Technology.
    Lindqvist, Per-Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    In-situ measurements of TBM cutter temperature in Äspö Hard Rock Laboratory, Sweden2001In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 38, no 4, p. 585-590Article in journal (Refereed)
  • 38.
    Zhang, Z.X.
    Luleå tekniska universitet.
    An empirical relation between mode I fracture toughness and the tensile strength of rock2002In: International Journal of Rock Mechanics And Mining Sciences, ISSN 1365-1609, E-ISSN 1873-4545, Vol. 39, no 3, p. 401-406Article in journal (Refereed)
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