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  • 1.
    Ask, D.
    et al.
    Vattenfall Power Consultant AB, Luleå.
    Stephansson, O.
    GeoForschungsZentrum Potsdam.
    Cornet, F.H.
    Institut de Physique du Globe de Strasbourg.
    Ask, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Rock stress, rock stress measurements, and the Integrated Stress Determination Method (ISDM)2009In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 42, no 4, p. 559-584Article in journal (Refereed)
    Abstract [en]

    The primary objectives of this work are to (1) improve the understanding of the prevailing stress distribution at the Äspö Hard Rock Laboratory (HRL) in SE Sweden by employing an integrated stress determination approach, and in order to accomplish this (2) extend the existing stress integration methodology denominated integrated stress determination method (ISDM; Cornet in Comprehensive Rock Engineering vol 3, Pergamon Press, Oxford, pp 413-432, 1993a). The new developments of the ISDM involve a 12-parameter representation of the regional stress field in the rock mass (i.e., the full stress tensor and its variation with depth) that is applicable to hydraulic stress data (sleeve fracturing, hydraulic fracturing, and hydraulic tests on pre-existing fractures), overcoring data (CSIR- and CSIRO-type of devices), and to combinations of hydraulic and overcoring stress data. For the latter case, the elastic parameters of the overcoring technique may be solved in situ by allowing the hydraulic stress data to constrain them. As a result, the problem then involves 14 model parameters. Results from the study show that the ISDM effectively improves the precision of the prevailing stress field determination and that it is especially powerful for identification of consistencies/inconsistencies in an existing data set. Indeed, this is the very basic premise and goal of stress integration; combine all available data to achieve as complete a characterization of the mechanical stress model as possible, and not to identify a solution that fits only loosely the maximum amount of stress data.

  • 2.
    Ask, Maria
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Ask, Daniel
    GEOSIGMA, Uppsala.
    Elvebakk, Harald
    Norges Geologiske Undersøkelse.
    Olesen, Odleiv
    Norges Geologiske Undersøkelse.
    Stress Analysis in Boreholes Drag Bh and Leknes Bh, Nordland, North Norway2015In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 48, no 4, p. 1475-1484Article in journal (Refereed)
    Abstract [en]

    Nordland in northern Norway is characterized by enhanced seismicity and uplift that makes it the most tectonically active area in Norway. This study is part of a project entitled Neotectonics in Norway—Implications for Petroleum Exploration, which aims at enhancing the understanding of regional-scale stress and strain dynamics in Nordland, and to impact risk and hazard assessment and petroleum exploration. This paper attempts to constrain the orientation of in situ horizontal stress using high-resolution acoustic televiewer logging data. The Geological Survey of Norway has drilled two 0.8 km deep near-vertical boreholes on opposite sides of the Vestfjord in Nordland, the open bight of sea that separates the Lofoten archipelago from the Norwegian mainland. Both boreholes are drilled just North of 68_ N, with borehole Leknes Bh located near the geographic center of the Lofoten archipelago, and borehole Drag Bh located on approximate equal distance from the shore, on the Norwegian mainland. The results of this study are in most practical aspects inconclusive, mainly due to poor data quality. The data analysis has revealed erroneously high-borehole diameter, and several artifacts such as eccentric logging tool, rugose borehole wall, spiral hole, tool sticking and missing data. Four intervals with passive in situ stress indicators (borehole breakout and drilling-induced fractures) were found in travel time and amplitude images of the Drag Bh, suggesting approximately N–S orientation of maximum horizontal stress. However, these intervals are not found in cross-plots. Either result yields the lowest World Stress Map ranking quality (E).

  • 3.
    Bondarchuk, Alexander
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Ask, Maria
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Geosciences and Environmental Engineering.
    Dahlström, Lars-Olof
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Rock mass behavior under hydropower embankment dams: a two-dimensional numerical study2012In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 45, no 5, p. 819-835Article in journal (Refereed)
    Abstract [en]

    Sweden has more than 190 large hydropower dams, of which about 50 are pure embankment dams and over 100 are concrete/embankment dams. This paper presents results from conceptual analyses of the response of typical Swedish rock mass to the construction of a hydropower embankment dam and its first stages of operation. The aim is to identify locations and magnitudes of displacements that are occurring in the rock foundation and grout curtain after construction of the dam, the first filling of its water reservoir, and after one seasonal variation of the water table. Coupled hydro-mechanical analysis was conducted using the two-dimensional distinct element program UDEC. Series of the simulations have been performed and the results show that the first filling of the reservoir and variation of water table induce largest magnitudes of displacement, with the greatest values obtained from the two models with high differential horizontal stresses and smallest spacing of sub-vertical fractures. These results may help identifying the condition of the dam foundation and contribute to the development of proper maintenance measures, which guarantee the safety and functionality of the dam. Additionally, newly developed dams may use these results for the estimation of the possible response of the rock foundation to the construction

  • 4.
    Edelbro, Catrin
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Different approaches for simulating brittle failure in two hard rock mass cases: a parametric study2010In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 43, no 2, p. 151-165Article in journal (Refereed)
    Abstract [en]

    One of the aims of rock mechanics analysis is to predict fallouts in underground excavations. The objective of this paper was to study the relative importance of different strength parameters and their significance on the simulation of brittle failure and fallouts. This work was conducted as a parametric study, using numerical modelling and a number of approaches. The results were compared with observed fallouts. More obvious and distinct shear bands could be observed with decreased element sizes close to, and at, the boundary. The maximum shear strain was the most reliable indicator for fallout prediction. The results of the (instantaneous) cohesion softening friction softening models were sensitive to changes of the peak strength parameters and less sensitive to variations in residual parameters. The result from the cohesion-softening friction-hardening (CSFH) model, when using a peak cohesion equal to the intact rock strength, best captured the observed rock behaviour.

  • 5.
    Fakhimi, Ali
    et al.
    New Mexico Institute of Mining and Tecnology.
    Villegas, Tomas
    Application of dimensional analysis in calibration of a discrete element model for rock2007In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 40, no 2, p. 193-211Article in journal (Refereed)
    Abstract [en]

    A discrete element approach was used in the simulation of rock fracture. The numerical synthetic material was made of rigid circular particles or cylinders that have interaction through normal and shear springs. The cylinders were bonded to each other at the contact points to withstand the applied loads. To characterize the microscopic properties of this synthetic material, a dimensional analysis approach was presented. It was shown that the dimensionless parameters and graphs obtained were useful tools for fast and efficient calibration of a synthetic material. This calibration method was employed for finding a numerical model for Pennsylvania Blue Sandstone. The numerical model could mimic many deformational and failure characteristics of the sandstone in both conventional and some non-conventional stress paths.

  • 6.
    Ghosh, Rajib
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Operation, Maintenance and Acoustics.
    Zhang, Zongxian
    University Centre in Svalbard.
    Nyberg, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Borehole instability in Malmberget Underground Mine2015In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 48, no 4, p. 1731-1736Article in journal (Refereed)
  • 7.
    Jing, Lanru
    et al.
    Luleå tekniska universitet.
    Stephansson, Ove
    Luleå tekniska universitet.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Study of rock joints under cyclic loading conditions1993In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 26, no 3, p. 215-232Article in journal (Refereed)
    Abstract [en]

    A conceptual model for the behaviour of rock joints during cyclic shear and under constant normal stresses was proposed according to results from shear tests with 50 concrete replicas of rock joints. The shear strength and deformability of joint samples were found to be both anisotropic and stress dependent. Based on these experimental results, a two-dimensional constitutive model was developed for rock joints undergoing monotonic or cyclic loading sequences. The joint model was formulated in the framework of non-associated plasticity, coupled with empirical relations representing the surface roughness degradation, appearance of peak and residual shear stresses, different rates of dilatancy and contraction, variable normal stiffness with normal deformation, and dependence of shear strength and deformability on the normal stress. The second law of thermodynamics was represented by an inequality and used to restrict the values of some of the material parameters in the joint model. The new joint model was implemented into a two-dimensional Distinct Element Method Code, UDEC, and its predictions agreed well with some well-known test results.

  • 8.
    Johansson, Daniel
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Ouchterlony, Finn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Shock wave interactions in rock blasting: the use of short delays to improve fragmentation in model-scale2013In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 46, no 1, p. 1-18Article in journal (Refereed)
    Abstract [en]

    A series of detailed small-scale tests have been made to investigate the use of short delays to promote better fragmentation caused by shock wave interactions. The block design had a size of 650/660 × 205 × 300 mm (L × W × H) and two rows with five Ø 10-mm blastholes in each row. The spacing (S) and burden (B) were 110 and 70 mm, respectively, giving an S/B ratio of 1.6. The results showed no distinct differences or high improvements of the fragmentation when the delays were in the time range of interactions compared with no shock wave interactions. The decrease of x 50 (mean size) was around 20 % at a delay time ~1.1 ms/m burden compared with longer delays like 2 ms/m. A statistical analysis of the results has been made to evaluate the minimum at short delays and it is not significant

  • 9.
    Jones, Tristan
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering. Luossavaara-Kiirunavaara AB, Malmberget, Sweden.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Wettainen, Thomas
    Luossavaara-Kiirunavaara AB, Malmberget, Sweden.
    Mining-Induced Deformation in the Malmberget Mine2019In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 52, no 6, p. 1903-1916Article in journal (Refereed)
    Abstract [en]

    The Norra Alliansen orebody of the Malmberget sublevel caving mine consists of iron ore interspersed with biotite schist and granitic inclusions. The schist is squeezed between the ore and the host rock and in direct contact with the ore along the majority of the length of the footwall. The schist exhibits high deformation when exposed to stress. SMART cable bolt roof deformation measurements are re-analyzed to draw conclusions regarding the patterns of deformation in the mine. Each bolt’s head is placed at the origin of a spherical coordinate system and the radius and inclination angle between the bolt and every production blast occurring during the bolt’s recorded lifetime are calculated. The deformation experienced by each instrument is investigated by comparing the long-term recorded movements with the developed geometric variables. Patterns of deformation magnitude and rate are found with respect to production-blast distance and inclination angle, instrument location, rock quality designation, and likely mining-induced stresses. Results show that deformation magnitude tends to be higher when driven by production blasting occurring on the production level above the instrumentation when accounting for the effects of distance, but average deformation magnitude for very-near production blasts tends to be higher than that for production blasts occurring directly above the instrument. Correlations also exist between the measured RQD, estimated rockmass parameters, and the measured deformation. Empirical evidence allows the identification of six scenarios which account for 91% of the recorded high-deformation-rate events. These scenarios help determine which production activities are most likely to cause high deformation rates.

  • 10.
    Kulatilake, P.H.S.W.
    et al.
    Department of Mining and Geological Engineering, University of Arizona, Tucson.
    Ucpirti, H.
    Department of Mining and Geological Engineering, University of Arizona, Tucson.
    Wang, S.
    Department of Mining and Geological Engineering, University of Arizona, Tucson.
    Rådberg, Gunnar
    Luleå tekniska universitet.
    Stephansson, Ove
    Luleå tekniska universitet.
    Use of the distinct element method to perform stress analysis in rock with non-persistent joints and to study the effect of joint geometry parameters on the strength and deformability of rock masses1992In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 25, no 4, p. 253-274Article in journal (Refereed)
    Abstract [en]

    To use the distinct element method, it is necessary to discretize the problem domain into polygons in two dimensions (2 D) or into polyhedra in three dimensions (3 D). To perform distinct element stress analysis in a rock mass which contains non-persistent finite size joints, it is necessary to generate some type of fictitious joints so that when they are combined with the non-persistent joints, they discretize the problem domain into polygons in 2 D or into polyhedra in 3 D. The question arises as to which deformation and strength parameter values should be assigned to these fictitious joints so that they behave as intact rock. In this paper, linear elastic, perfectly-plastic constitutive models with the Mohr-Coulomb failure criterion, including a tension cut-off, were used to represent the mechanical behaviour of both intact rock and fictitious joints. It was found that, by choosing the parameter values for the constitutive models as given below, it is possible to make the fictitious joints behave as intact rock, in a global sense

  • 11.
    Leijon, Bengt A.
    et al.
    Luleå tekniska universitet.
    Stillborg, B.L.
    James Askew Associates.
    A comparative study between two rock stress measurement techniques at Luossavaara Mine1986In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 19, no 3, p. 143-163Article in journal (Refereed)
    Abstract [en]

    As part of a comprehensive geomechanical pre-investigation scheme, rock stress measurements were conducted at four locations, representing three different rock types, in the Luossavaara Mine, located within the Kiruna iron ore fields in northern Sweden. Two similar triaxial overcoring techniques, the CSIRO Hollow Inclusion Technique and the LUH Triaxial Technique, were used in a parallel fashion in order to obtain redundant results, but also with the intention of comparing the field applicability of the two methods. The results show that the state of stress is characterized by a sub-horizontally directed maximum stress with a magnitude of about 10 MPa. The agreement in terms of stress results between the two methods was generally good. The study demonstrated that the technical differences between the two devices used were of little significance as compared to the observed, often non-ideal mechanical characteristics of the rock. The latter added considerable uncertainty to the data, regardless of the measuring technique used, and it is therefore concluded that the rock quality is a major factor in the application of any overcoring method. Finally, it was shown that the biaxial test method, which is frequently used for the determination of rock properties in connection with stress measurements, is not always relevant for this purpose.

  • 12.
    Li, Chunlin
    Luleå tekniska universitet.
    A method for graphically presenting the deformation modulus of jointed rock masses2001In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 34, no 1, p. 67-75Article in journal (Refereed)
    Abstract [en]

    A method to graphically present the deformation modulus of jointed rock masses is presented. A global co-ordinate system is used in the approach to define the geometry of rock joints. The deformation modulus of jointed rock masses is determined by the number of joints, the geometry of joints and the stiffness of the joint planes as well as the Young's modulus of the intact rocks

  • 13.
    Li, Chunlin
    et al.
    Luleå tekniska universitet.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Effects of couplants on acoustic transmission1993In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 26, no 1, p. 63-69Article in journal (Refereed)
  • 14. Li, Chunlin
    et al.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Experimental verification of the Kaiser effect in rocks1993In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 26, no 4, p. 333-351Article in journal (Refereed)
    Abstract [en]

    The Kaiser effect is a measure of damage developed in rock. It was investigated using 61 core specimens of eight types of rocks under uniaxial cyclic loading. The effects of the delay time between subsequent loading cycles and the holding time on the Kaiser effect were examined in granite specimens. The characteristics of AE occurring during unloading and holding were also studied. The experimental results showed that most of the rocks, with the exception of some iron ores, showed an obvious Kaiser effect before the load was very near the level of the strength. The delay and holding times did not strongly influence the Kaiser effect. Breakdown of the Kaiser effect was expressed by the felicity ratio that may be taken as a measure of the quality of rock. The onset of the continuously increasing AE in the first loading cycle can be taken as a measure of the damage in rock. The mechanism of the Kaiser effect was studied with the aid of a micromechanical model. An expression for the damage surface in the stress space was derived from the model. The theoretical expression was compared with the results of the Kaiser effect tests, which showed a satisfactory consistence.

  • 15.
    Li, Chunlin
    et al.
    Luleå tekniska universitet.
    Stillborg, Bengt
    Luleå tekniska universitet.
    Design of underground drainage boreholes in foliated formations1996In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 29, no 2, p. 99-105Article in journal (Refereed)
    Abstract [en]

    The principle for the design of a directional drainage borehole in a foliated formation is such that the borehole is drilled so that it crosses all the interested foliation planes. If the inclination angle of the borehole is not appropriately selected, the borehole might never reach the concerned foliation planes. In other words, there exists a critical inclination angle for the borehole. The borehole is able to cross the concerned foliation planes only at an inclination angle larger than the critical angle. The critical inclination angle depends on the geological structure of the foliation planes as well as the trend of the drift. The method to determine the critical inclination angle is described both graphically and analytically in this paper. A case for design of drainage boreholes in a copper mine, using the developed method, is also presented

  • 16.
    Lindqvist, Per-Arne
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Stress fields and subsurface crack propagation of single and multiple rock indentation and disc cutting1984In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 17, no 2, p. 97-112Article in journal (Refereed)
    Abstract [en]

    Indentation stress fields of one- and two-point loads applied on an ideal elastic half-space are presented. Laboratory observations, although few, are in surprisingly good agreement with long median and cone-type tensile cracks predicted by normal principal stresses. Results indicate that simultaneous loading by multiple indenters offers a possibility partly to control the direction and length of such cracks. This suggests the development of new cutter configurations with a possible increase in efficiency, as compared with present rock boring and rock cutting practice. A simple fracture mechanics calculation of the length of subsurface cracks is performed by applying indentation fracture studies of ceramics. Results demonstrate the influence of material parameters such as fracture surface energy, hardness and elastic constants.

  • 17.
    Lindqvist, Per-Arne
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Lai, Hai-Hui
    Institute of Mining and Metallurgy, Changsha.
    Behaviour of the crushed zone in rock indentation1983In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 16, no 3, p. 199-207Article in journal (Refereed)
    Abstract [en]

    Micro hardness tests of compressed crushed rock indicate that the plastic behavior of powder of ductile rocks, in this case a marble, resembles that of intact rock, irrespective of the deformation history of the crushed material. The inelastic deformation of such rocks under a bit can then be treated by plasticity theory. The deformation properties of crushed material of granite and sandstone are of a brittle nature.

  • 18.
    Liu, H. Y.
    et al.
    Luleå University of Technology.
    Kou, S. Q.
    Luleå University of Technology.
    Lindqvist, Per-Arne
    Tang, C. A.
    Dalian University of Technology.
    Numerical modelling of the heterogeneous rock fracture process using various test techniques2007In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 40, no 2, p. 107-144Article in journal (Refereed)
    Abstract [en]

    A series of numerical tests including both rock mechanics and fracture mechanics tests are conducted by the rock and tool (R-T2D) interaction code coupled with a heterogeneous masterial model to obtain the physical-mechanical properties and fracture toughness, as well as to simulate the crack initiation and propagation, and the fracture progressive process. The simulated results not only predict relatively accurate physical-mechanical parameters and fracture toughness, but also visually reproduce the fracture progressive process compared with the experimental and theoretical results. The detailed stress distribution and redistribution, crack nucleation and initiation, stable and unstable crack propagation, interaction and coalescence, and corresponding load-displacement curves can be proposed as benchmarks for experimental study and theoretical research on crack propagation. It is concluded that the heterogeneous material model is reasonable and the R-T2D code is stable, repeatable and a valuable numerical tool for research on the rock fracture process.

  • 19.
    Ma, Xu
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering. Department of Mining and Minerals Engineering, Virginia Tech, Blacksburg, USA.
    Westman, Erik
    Department of Mining and Minerals Engineering, Virginia Tech, Blacksburg, USA.
    Malek, Farid
    Creighton Mine, Vale Canada Limited, Sudbury, ON, Canada.
    Yao, Mike
    Mining and Mineral Processing TEC, Vale Canada Limited, Sudbury, ON, Canada.
    Stress Redistribution Monitoring Using Passive Seismic Tomography at a Deep Nickel Mine2019In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453XArticle in journal (Refereed)
    Abstract [en]

    High magnitude seismic events (HMSE), also called major events, triggered at underground mines can severely threaten safety and structures in mines. The aims of this work are to assess stress evolution with the occurrence of them and identify patterns in stress change. Several methods were used to help understand the stress redistribution and rock mass behavior related to two HMSE with moment magnitude greater than 1.0 in a deep nickel mine. Approximately 46,500 seismic events were compiled with 2 HMSE at this mine and used seismic tomography to obtain high-resolution images and temporal-spatial velocity changes before and after these events. This work exhibited surrounding stress evolution and geological structures. Seismic imaging results show that velocity increased in the nearby regions of HMSE before they were triggered. Stress subsequently reduced in the relaxation process after the occurrence of HMSE. Conversely, regions predominantly occupied by low-velocity anomalies increased to higher stress levels after HMSE. Overall, the stress redistributed toward an equilibrium state following HMSE. This study highlights the value of utilizing seismic tomography for estimating stress evolution associated with HMSE. The findings illuminate the applications of seismic imaging around HMSE of hard-rock mines, providing insights into seismic hazard mitigation for deep mining.

  • 20.
    Petropoulos, N.
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Wimmer, Matthias
    LKAB, Kiruna.
    Johansson, D.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nordlund, E.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Compaction of confining materials in pillar blast tests2018In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 51, no 6, p. 1907-1919Article in journal (Refereed)
    Abstract [en]

    Two confined pillar tests were conducted at the Kiirunavaara mine to investigate the degree of compaction of three materials, i.e., 0–32-mm backfilled material, a blend of ore and waste material and caved material. Two blastholes were drilled parallel to each pillar wall, and several measurement holes were drilled in between the blastholes through each pillar. Both the measurement holes and backfilled materials, except the caved material, were instrumented. Two types of measurements were taken: dynamic measurements with accelerometers, and static measurements which considered the location of the instrumentation pre- and post-blast. Dynamic measurements involved the burden movement and the confining material behavior, and static measurements contained the final location of sensors inside and the angle of repose of the confining material. The results showed that the size distribution of the confining material affects its behavior under dynamic loading. The backfilled materials showed an apparent cohesion forming an agglomeration on the surface of the blasted burden. The burden moved as one slab due to simultaneous detonation. A gap was formed between the blasted burden and the new face. This gap was partially filled with burden erosion material which was finer fragmented than the blasted burden material.

  • 21.
    Pérez, Kelvis
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Comparison between stress and strain quantities of the failure-deformation process of Fennoscandian hard rocks using geological information2013In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 46, no 1, p. 41-51Article in journal (Refereed)
    Abstract [en]

    The aim of this paper was to compare the stress and strain quantities that are related to the failure-deformation process of hard rock. The data used here was obtained from laboratory uniaxial compression tests performed on different types of Fennoscandian hard rocks. The failure-deformation process quantities were compared at each deformation stage and for each single specimen. Moreover, geological information such as the rock origin process and the rock characteristics of the specimens were studied and linked to the stress and strain quantities. The purpose was to investigate the influence of the rock origin process and rock characteristics on these quantities. The main results of this study showed that the normalized crack damage lateral strain (ε 3cd/ε 3 p) and the volumetric strain (ε crv-ci and ε v-cd) quantities were strongly affected by the grain size. The normalized and volumetric quantities are weakly dependent on the mineral composition

  • 22.
    Přikryl, R.
    et al.
    Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Prague.
    Lokajíček, T.
    Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic.
    Li, Chunlin
    Luleå tekniska universitet.
    Rudajev, V.
    Institute of Rock Structure and Mechanics, Academy of Sciences of the Czech Republic.
    Acoustic emission characteristics and failure of uniaxially stressed granitic rocks: the effect of rock fabric2003In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 36, no 4, p. 255-270Article in journal (Refereed)
    Abstract [en]

    Laboratory experiments on rock samples were carried out to understand the relationship between the acoustic emission (AE) parameters and rock fabric. AE activity was recorded during the uniaxial compression with constant stress rate of several granitic rocks showing variable microfabric (e.g. grain size, shape and crystallographic preferred orientation) and macrofabric (e.g. magmatic isorientation, metamorphic banding). A broad band multichannel recording system with a high dynamic recording range enabled individual acoustic emission events to be analysed in a wide frequency and energy range. The microfabric of the rocks was studied by quantitative petrographic analysis of thin sections allowing precise description of mode, grain size and shape. It has been proved that the energy-frequency distribution of AE events strongly reflects the fabric of the samples. The characteristic energy value of AE events reflects the most frequently occurring grain dimensions. The AE parameters like acoustic rate or cumulative energy are highly sensitive to fabric arrangement in rocks with pronounced fabric (e.g. foliation, lineation etc.).

  • 23.
    Rånman, Karl-Erik
    Luleå tekniska universitet.
    A model describing rock cutting with conical picks1985In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 18, no 2, p. 131-140Article in journal (Refereed)
    Abstract [en]

    In continuous cutting the rock surface is to a large extent affected by previous cuts. It is difficult to quantify the influence this will have on the cutting result. Even in a homogeneous rock there will be chips of many different shapes and sizes, since the models are not exact descriptions of actual cutting. This paper deals, initially, with the validity of the geometrical assumption, i. e. chips of similar size and shape. In the second part, a model based upon measurements of actual cutting force is presented. These two parts are based upon two separate series of tests.

  • 24. Saiang, David
    et al.
    Malmgren, Lars
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Laboratory tests on shotcrete-rock joints in direct shear, tension and compression2005In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 38, no 4, p. 275-297Article in journal (Refereed)
    Abstract [en]

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

  • 25. Saiang, David
    et al.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Numerical analyses of the influence of blast-induced damaged rock around shallow tunnels in brittle rock2009In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 42, no 3, p. 421-448Article in journal (Refereed)
    Abstract [en]

    Most of the railway tunnels in Sweden are shallow-seated (<20 m of rock cover) and are located in hard brittle rock masses. The majority of these tunnels are excavated by drilling and blasting, which, consequently, result in the development of a blast-induced damaged zone around the tunnel boundary. Theoretically, the presence of this zone, with its reduced strength and stiffness, will affect the overall performance of the tunnel, as well as its construction and maintenance. The Swedish Railroad Administration, therefore, uses a set of guidelines based on peak particle velocity models and perimeter blasting to regulate the extent of damage due to blasting. However, the real effects of the damage caused by blasting around a shallow tunnel and their criticality to the overall performance of the tunnel are yet to be quantified and, therefore, remain the subject of research and investigation. This paper presents a numerical parametric study of blast-induced damage in rock. By varying the strength and stiffness of the blast-induced damaged zone and other relevant parameters, the near-field rock mass response was evaluated in terms of the effects on induced boundary stresses and ground deformation. The continuum method of numerical analysis was used. The input parameters, particularly those relating to strength and stiffness, were estimated using a systematic approach related to the fact that, at shallow depths, the stress and geologic conditions may be highly anisotropic. Due to the lack of data on the post-failure characteristics of the rock mass, the traditional Mohr-Coulomb yield criterion was assumed and used. The results clearly indicate that, as expected, the presence of the blast-induced damage zone does affect the behaviour of the boundary stresses and ground deformation. Potential failure types occurring around the tunnel boundary and their mechanisms have also been identified

  • 26.
    Sanchidrián, J.A.
    et al.
    Universidad Politécnica de Madrid.
    Segarra, P.
    Universidad Politécnica de Madrid.
    Ouchterlony, Finn
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    López, L.M.
    Universidad Politécnica de Madrid.
    On the accuracy of fragment size measurement by image analysis in combination with some distribution functions2009In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 42, no 1, p. 95-116Article in journal (Refereed)
    Abstract [en]

    Size distributions of fragments of crushed rock in conveyor belts and of blasted rock in a muckpile obtained by sieving are compared with the size distributions obtained by digital image analysis of photographs of the same materials taken on-site. Several calculation methods are tested, based on the raw distribution of fragment areas and on the volume-transformed ones. The influence of the calibration of the system on the results and the performance of the system in a non-calibrated mode are evaluated. The capacity of some distributions (Rosin-Rammler, Swebrec and lognormal) to fit the data in the coarse region (where particles can be delineated, i.e. discriminated individually) and to extrapolate to the non-delineated fines (where particles cannot be outlined and their contour delineated) is assessed. The error between the sizes measured and the sizes of the reference distributions (determined by sieving) increases from the coarse to the fines region. The maximum error at a given size depends primarily on its value relative to the fines cut-off (FCO) of the image analysis. In general, at sizes greater than the FCO, where the system is able to delineate fragments reliably, both volume and surface-based, calibrated, calculations can determine the sizes with maximum error expectancy of about 30%. Below the FCO, only the calibrated, volume calculation maintains a maximum error of 30%, down to sizes of about one fourth the FCO, rapidly increasing for smaller sizes. Where the calibration is done based on data above the FCO, errors can be large below this point, in excess of 80% at sizes half the FCO. In the fines range (sizes smaller than 0.2 times the FCO) the maximum errors can be close to or greater than 100% for most of the calculations and function fittings. Of the distributions tested, all of them are acceptable at sizes above the FCO; below that, the Swebrec function seems to adapt better towards the fines than the Rosin-Rammler and lognormal.

  • 27.
    Shirzadegan, Shahin
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Zhang, Ping
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Large Scale Dynamic Testing of Rock Support System at Kiirunavaara Underground Mine2016In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 49, no 7, p. 2773-2794Article in journal (Refereed)
    Abstract [en]

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

  • 28.
    Svartsjaern, Mikael
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering. Itasca Consultants AB Luleå .
    A Prognosis Methodology for Underground Infrastructure Damage in Sublevel Cave Mining2019In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 52, no 1, p. 247-263Article in journal (Refereed)
    Abstract [en]

    In sublevel caving (SLC), the caving of the hangingwall due to ore extraction emphasises placement of the mining infrastructure in the footwall. While the footwall in general is less affected by ground settlement compared to the hangingwall, the changes in stress field from mining are significant. The footwall infrastructure must thus be positioned sufficiently far into the footwall to avoid damage from the mining-induced stress; however, placing the infrastructure farther into the footwall increases costs associated with additional drifting and operational distances. This paper presents a case study in which a robust prognosis tool for predicting infrastructure damage associated with SLC mining is developed. The concept of the proposed methodology was developed for the Luossavaara-Kiirunavaara Aktiebolag Kiirunavaara SLC mine. Initial steps are data collection through systematic damage mapping followed by conceptual modelling of the general rock mass response to mining. The results of the conceptual models are used as the basis for refined calibrated models detailing the damage development and failure mechanisms. The main system behaviour, failure mechanism and associated damage evolution are incorporated into a bilinear equation using the studied depth and local ore width as input to estimate the final horizontal damage extent from the footwall contact after mining of any specific level. The proposed relationship accurately replicates the current damage pattern within 40 m for more than 70% of the recorded observations up until current mining. The anticipated future damage extent is also shown to be well correlated with current micro-seismic event locations. The connection between seismic rock mass damage and subsequent infrastructure damage during de-confinement suggests that current seismic records from operations, which currently experience no stability issues, might become important at later mining stages.

  • 29.
    Svartsjaern, Mikael
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Saiang, David
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Eitzenberger, Andreas
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Conceptual Numerical Modeling of Large-Scale Footwall Behavior at the Kiirunavaara Mine, and Implications for Deformation Monitoring2016In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 49, no 3, p. 943-960Article in journal (Refereed)
    Abstract [en]

    Over the last 30 years the Kiirunavaara mine has experienced a slow but progressive fracturing and movement in the footwall rock mass which is directly related to the sublevel caving (SLC) method utilized by Luossavaara-Kiirunavaara Aktiebolag (LKAB). As part of an on-going work, this paper focuses on describing and explaining a likely evolution path of large-scale fracturing in the Kiirunavaara footwall. The trace of this fracturing was based on a series of damage mapping campaigns carried out over the last two years, accompanied by numerical modelling. Data collected from the damage mapping between mine levels 320 and 907 m was used to create a 3D surface representing a conceptual boundary for the extent of the damaged volume. The extent boundary surface was used as the basis for calibrating conceptual numerical models created in UDEC. The mapping data, in combination with the numerical models, indicated a plausible evolution path of the footwall fracturing that was subsequently described. Between levels 320 and 740 m the extent of fracturing into the footwall appears to be controlled by natural pre-existing discontinuities, while below 740 m there are indications of a curved shear or step-path failure. The step-path is hypothesised to be activated by rock mass heave into the SLC zone above the current extraction level. Above the 320 m level the fracturing seems to intersect a sub-vertical structure that daylights in the old open pit slope. Identification of these probable damage mechanisms was an important step in order to determine the requirements for a monitoring system for tracking footwall damage. This paper describes the background work for design of the system currently being installed.

  • 30.
    Vatcher, Jessika
    et al.
    Itasca Consultants AB, Luleå.
    McKinnon, S.D.
    Robert M. Buchan Department of Mining, Queen’s University, Kingston, Canada.
    Sjöberg, Jonny
    Itasca Consultants AB, Luleå.
    Rock mass characteristics and tomographic data2018In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 51, no 5, p. 1615-1619Article in journal (Refereed)
  • 31.
    Yi, Changping
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Johansson, Daniel
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nyberg, Ulf
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Beyglou, Ali
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Stress wave interaction between two adjacent blast holes2016In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 49, no 5, p. 1803-1812Article in journal (Refereed)
    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.

  • 32.
    Zhang, Ping
    et al.
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Nordlund, Erling
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Swan, Graham
    Rock Mechanics and Mine Design, Sudbury, Canada.
    Yi, Changping
    Luleå University of Technology, Department of Civil, Environmental and Natural Resources Engineering, Mining and Geotechnical Engineering.
    Velocity Amplification of Seismic Waves Through Parallel Fractures Near a Free Surface in Fractured Rock: A Theoretical Study2019In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 52, no 1, p. 199-213Article in journal (Refereed)
    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.

  • 33.
    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 cutter forces on boring machine at Äspö Hard Rock Laboratory. Part 2: Characteristics of cutter forces and examination of cracks generated2003In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 36, no 1, p. 63-83Article in journal (Refereed)
    Abstract [en]

    By means of spectral analysis, the measured normal forces, tangential forces, and side forces acting on two button cutters on the boring machine in Äspö Hard Rock Laboratory were analysed and the basic characteristics of the cutter forces were determined. After the measurements of the cutter forces, some rock core samples were taken from the bottom and the wall of the test borehole. These samples were cut, polished, and examined by means of a Scanning Electron Microscope (SEM). The lengths of the major cracks in the rock samples were measured, and a relation between the length of the median cracks and the relevant cutter forces was investigated.

  • 34.
    Zhang, Zongxian
    et al.
    Luleå University of Technology.
    Kou, Shaoquan
    Luleå University of Technology.
    Tan, Xiangchun
    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 cutter forces on boring machine at Äspö Hard Rock Laboratory. Part 1: Laboratory calibration and in-situ measurements2003In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 36, no 1, p. 39-61Article in journal (Refereed)
    Abstract [en]

    This paper presents the testing methods used and the results obtained in an investigation of the cutter forces on a Boretec DS 1.6 boring machine during field boring in Äspö Hard Rock Laboratory. Two button cutters, one front cutter and one gauge cutter, were used in the field measurements. A total of 6 strain gauges were bonded on the shaft of each cutter. And each group of two gauges was used to measure a one-orthogonal cutter force component, i.e. the normal force, tangential force, and side force, respectively. In order to measure the cutter forces successfully, a telemetry system composed of a transmitter and a receiver was employed to transfer the signals from the strain gauges to a computer.A three-direction-loading system was employed in the laboratory calibration so as to solve the force-coupling problem appearing in the cutter force measurements. Correspondingly, a mathematical treatment of the force-coupling problem was performed. Then, by means of the established testing system, which was proved successful in the laboratory, the normal force, tangential force, and side force of the two button cutters on the boring machine were measured in the field. In addition, the penetration rate, thrust, and rotation speed of the boring machine were also recorded in the field. The results show the following. (1) A force-coupling phenomenon really exists and it should be considered. (2) All three directional force components always show quite a high peak value every few seconds. (3) The cutter forces of the front cutter are always much larger than the respective cutter forces of the gauge cutter. Moreover, as expected, the normal force of each cutter is much larger than the tangential force and side force of the cutter in question.

  • 35.
    Zhang, Zongxian
    et al.
    Luleå University of Technology.
    Yu, J.
    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.
    On study of influences of loading rate on fractal dimensions of fracture surfaces in Gabbro2001In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 34, no 3, p. 235-242Article in journal (Refereed)
    Abstract [en]

    Studies of the effects of loading rates on rock fracture were performed for decades. However, the previous work on static or dynamic rock fracture was mainly limited to a macro-experimental study. The present investigation measures the fractal dimensions of the fracture surfaces of the gabbro specimens fractured at various loading rates covering static and dynamic loading, and explores the relationship between the fractal dimensions and the fracture toughness of the rock.

  • 36.
    Zhang, Z.X.
    Luleå tekniska universitet.
    Estimate of loading rate for a TBM machine based on measured cutter forces2004In: Rock Mechanics and Rock Engineering, ISSN 0723-2632, E-ISSN 1434-453X, Vol. 37, no 3, p. 239-248Article in journal (Refereed)
    Abstract [en]

    Various aspects of a tunnel boring machines (TBM) were presented. The loading rate of a TBM machine can be estimated on the basis of its cutter force measurements. The method can also be used to estimate the loading rate of other similar rock breakage machines. On the basis of the cutter forces measured in the field, the loading rate of the Boretech D1.6 boring machine was estimated. Results show that the loading rate of the machine is within a typical quasi-static loading

1 - 36 of 36
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