Rock Mechanics.pdf - Mining and Blasting

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Figure 3.29 Computer generated contoured stereographic projection (after Rocscience, 1999). ROCK MASS CLASSIFICATION 3.7 Rock mass classification 3.7.1 The nature and use of rock mass classification schemes Whenever possible, it is desirable that mining rock mechanics problems be solved using the analytical tools and engineering mechanics-based approaches discussed in later chapters of this book. However, the processes and interrelations involved in determining the behaviour of the rock surrounding a mining excavation or group of excavations are sometimes so complex that they are not amenable to enginerring analysis using existing techniques. In these cases, design decisions may have to take account of previous experience gained in the mine concerned or elsewhere. In an attempt to quantify this experience so that it may be extrapolated from one site to another, a number of classification schemes for rock masses have been developed. These classification schemes seek to assign numerical values to those properties or features of the rock mass considered likely to influence its behaviour, and to combine these individual values into one overall classification rating for the rock mass. Rating values for the rock masses associated with a number of mining or civil engineering projects are then determined and correlated with observed rock mass behaviour. Aspects of rock mass behaviour that have been studied in this way include the stable spans of unsupported excavations, stand-up times of given unsupported spans, support requirements for various spans, cavability, stable pit slope angles, hangingwall caving angles and fragmentation. A number of these assessments made from geotechnical data collected in the exploration or feasibility study stages of a mining project may provide useful guides to the selection of an appropriate mining method. Although the use of this approach is superficially attractive, it has a number of serious shortcomings and must be used only with extreme care. The classification scheme approach does not always fully evaluate important aspects of a problem, so that if blindly applied without any supporting analysis of the mechanics of the 77
ROCK MASS STRUCTURE AND CHARACTERISATION problem, it can lead to disastrous results. It is particularly important to recognise that the classification schemes give reliable results only for the rock masses and circumtances for which the guide-lines for their application were originally developed. It is for this reason that considerable success has been achieved in using the approach to interpolate experience within one mine or a group of closely related mines, as described by Laubscher (1977), for example. Hoek and Brown (1980), Goodman (1993) and Brown (2003), among others, have reviewed the considerable number of rock mass classification schemes that have been developed for a variety of purposes. Two of these schemes, the NGI tunnelling quality index (Q) developed by Barton et al. (1974) and the CSIR goemechanics or Rock Mass Rating (RMR) scheme developed by Bieniawski (1973, 1976), are currently widely used in civil engineering and in mining practice. Bieniawski’s RMR scheme has been modified by Laubscher (1977, 1990), particularly for use in cave mining applications. Because of their widespread use in mining practice, the basic RMR and Q systems will be outlined here. The more recent GSI system introduced by Hoek (1994) and developed further by Marinos and Hoek (2000) will also be discussed. 3.7.2 Bieniawski’s geomechanics classification Bieniawski (1973, 1976) developed his scheme using data obtained mainly from civil engineering excavations in sedimentary rocks in South Africa. Bieniawski’s scheme uses five classification parameters. 1 Strength of the intact rock material. The uniaxial compressive strength of the intact rock may be measured on cores as described in section 4.3.2. Alternatively, for all but very low-strength rocks, the point load index (section 4.3.9) may be used. 2 Rock Quality Designation (RQD) as described in section 3.3. 3 Spacing of joints. In this context, the term joints is used to describe all discontinuities. 4 Condition of joints. This parameter accounts for the separation or aperture of discontinuities, their continuity or persistence, their surface roughness, the wall condition (hard or soft) and the nature of any in-filling materials present. 5 Groundwater conditions. An attempt is made to account for the influence of groundwater pressure or flow on the stability of underground excavations in terms of the observed rate of flow into the excavation, the ratio of joint water pressure to major principal stress, or by a general qualitative observation of groundwater conditions. The way in which these parameters are incorporated into Bieniawski’s geomechanics classification for jointed rock masses is shown in Part (a) of Table 3.5. For various ranges of each parameter, a rating value is assigned. The allocation of these rating values allows for the fact that all parameters do not necessarily contribute equally to the behaviour of the rock mass. The overall Rock Mass Rating (RMR) is obtained by adding the values of the ratings determined for the individual parameters. This RMR value may be adjusted for the influence of discontinuity orientation by applying the corrections given in Part (b) of Table 3.5. The terms used for this purpose are explained in Table 3.6. (When falling or sliding of blocks of rock from the roof or walls of an excavation is a possibility, this approach should not be relied upon. A wedge analysis of the type described in Chapter 9 should be used.) Part (c) of 78
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Rock Mechanics
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Rock Mechanics for underground mini
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Contents Preface to the third editi
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CONTENTS 9 Excavation design in blo
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CONTENTS ix Appendix A Basic constr
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PREFACE TO THE THIRD EDITION Mining
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PREFACE TO THE SECOND EDITION In th
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PREFACE TO THE FIRST EDITION design
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ACKNOWLEDGEMENTS Safety in Mines Re
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Figure 1.1 (a) Pre-mining condition
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ROCK MECHANICS AND MINING ENGINEERI
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Figure 1.4 Principal features of a
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10 Figure 1.5 Definition of activit
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Figure 1.7 Components and logic of
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Figure 2.1 (a) A finite body subjec
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Figure 2.2 Free-body diagram for es
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STRESS AND INFINITESIMAL STRAIN As
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STRESS AND INFINITESIMAL STRAIN In
Page 43 and 44: Figure 2.3 Free-body diagram for de
Page 45 and 46: Figure 2.5 Problem geometry for det
Page 47 and 48: Figure 2.7 Rigid-body rotation of a
Page 49 and 50: STRESS AND INFINITESIMAL STRAIN the
Page 51 and 52: STRESS AND INFINITESIMAL STRAIN str
Page 53 and 54: ⎡ ⎢ ⎣ xx yy zz xy yz zx STRES
Page 55 and 56: Figure 2.11 Cylindrical polar coord
Page 57 and 58: STRESS AND INFINITESIMAL STRAIN fre
Page 59 and 60: Figure 2.13 Construction of a Mohr
Page 61 and 62: STRESS AND INFINITESIMAL STRAIN fun
Page 63 and 64: 3 Rock Figure 3.1 Sidewall failure
Page 65 and 66: Figure 3.2 Jointing in a folded str
Page 67 and 68: Figure 3.5 Diagrammatic longitudina
Page 69 and 70: Figure 3.7 Discontinuity spacing hi
Page 71 and 72: Figure 3.9 Illustration of persiste
Page 73 and 74: Figure 3.11 Typical roughness profi
Page 75 and 76: ROCK MASS STRUCTURE AND CHARACTERIS
Page 81 and 82: Figure 3.17 Sample number vs. preci
Page 83 and 84: Figure 3.19 Diagrammatic illustrati
Page 87 and 88: Figure 3.20 Computerised depiction
Page 89 and 90: Figure 3.23 Stereographic projectio
Page 91 and 92: Figure 3.26 Polar stereographic net
Page 93: Figure 3.28 Contours of pole concen
Page 99 and 100: Figure 3.30 Geological Strength Ind
Page 103 and 104: Figure 4.1 Idealised illustration o
Page 105 and 106: ROCK STRENGTH AND DEFORMABILITY wit
Page 107 and 108: Figure 4.4 Influence of end restrai
Page 109 and 110: ROCK STRENGTH AND DEFORMABILITY whe
Page 111 and 112: Figure 4.8 Principle of closed-loop
Page 113 and 114: Figure 4.12 Two classes of stress-
Page 115 and 116: Figure 4.14 Point load test apparat
Page 117 and 118: Figure 4.15 Biaxial compression tes
Page 119 and 120: Figure 4.18 Results of triaxial com
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Page 123 and 124: Figure 4.23 Coulomb strength envelo
Page 125 and 126: Figure 4.25 Extension of a preexist
Page 127 and 128: Figure 4.29 The three basic modes o
Page 129 and 130: Figure 4.30 Normalised peak strengt
Page 131 and 132: ROCK STRENGTH AND DEFORMABILITY Tab
Page 133 and 134: Figure 4.32 The normality condition
Page 135 and 136: Figure 4.33 Variation of peak princ
Page 137 and 138: Figure 4.35 Direct shear test confi
Page 139 and 140: Figure 4.37 Shear stress-shear disp
Page 141 and 142: Figure 4.40 Peak and residual effec
Page 143 and 144: Figure 4.43 Effect of shearing dire
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Figure 4.45 Relations between norma
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Figure 4.47 Coulomb friction, linea
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ROCK STRENGTH AND DEFORMABILITY whe
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Figure 4.49 Composite peak strength
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Figure 4.50 Hoek-Brown peak strengt
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Figure 4.52 Determination of the Yo
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ROCK STRENGTH AND DEFORMABILITY 4 A
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5 Pre-mining Figure 5.1 Method of s
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Figure 5.2 The effect of irregular
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PRE-MINING STATE OF STRESS surround
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PRE-MINING STATE OF STRESS induced
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Figure 5.5 (a) Definition of hole l
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Figure 5.6 (a) Core drilling a slot
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Figure 5.7 Principles of stress mea
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PRE-MINING STATE OF STRESS strength
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PRE-MINING STATE OF STRESS A second
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PRE-MINING STATE OF STRESS by the e
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PRE-MINING STATE OF STRESS extend i
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PRE-MINING STATE OF STRESS (d) Dete
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METHODS OF STRESS ANALYSIS quantita
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METHODS OF STRESS ANALYSIS It is in
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Figure 6.2 A thick-walled cylinder
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METHODS OF STRESS ANALYSIS For the
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Figure 6.3 Problem geometry, coordi
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Figure 6.4 Problem geometry, coordi
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METHODS OF STRESS ANALYSIS When the
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Figure 6.5 Superposition scheme dem
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METHODS OF STRESS ANALYSIS The disc
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Figure 6.7 Development of a finite
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METHODS OF STRESS ANALYSIS Solution
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Figure 6.8 A simple finite element
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Figure 6.9 A schematic representati
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METHODS OF STRESS ANALYSIS block ce
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METHODS OF STRESS ANALYSIS where ˚
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METHODS OF STRESS ANALYSIS The prin
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EXCAVATION DESIGN IN MASSIVE ELASTI
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Figure 7.2 A logical framework for
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Figure 7.3 (a) Axisymmetric stress
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Figure 7.6 A plane of weakness, ori
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Figure 7.8 A flat-lying plane of we
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Figure 7.10 Shear stress/normal str
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Figure 7.12 Ovaloidal opening in a
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Figure 7.15 States of stress at sel
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Figure 7.16 Prediction of the exten
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Figure 7.18 Contour plots of princi
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Figure 7.19 Problem geometry for de
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8 Excavation Figure 8.1 An excavati
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EXCAVATION DESIGN IN STRATIFIED ROC
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Figure 8.4 Experimental apparatus f
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Figure 8.7 Free body diagrams and n
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Figure 8.8 Assumed distributions of
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Figure 8.9 Flow chart for the deter
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Figure 8.10 Normalised arch thickne
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EXCAVATION DESIGN IN STRATIFIED ROC
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Figure 8.11 Normalised deflection a
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9 Excavation Figure 9.1 Generation
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Figure 9.3 (a) A finite, non-tapere
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(a) (b) Figure 9.4 (a) Vertical cro
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(a) (b) (c) EP EP Reference circle
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Figure 9.10 JP 100 is the only JP w
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Figure 9.12 Traces of the views of
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EXCAVATION DESIGN IN BLOCKY ROCK In
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Figure 9.14 Free-body diagrams of a
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EXCAVATION DESIGN IN BLOCKY ROCK di
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Figure 9.16 Symmetrical wedge in th
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Figure 9.17 (a) Geometry for determ
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Figure 9.18 Problem geometry demons
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Figure 9.20 Cut-and-fill stope mine
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Figure 9.22 Chart to determine fact
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EXCAVATION DESIGN IN BLOCKY ROCK Th
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Figure 10.1 (a) Pre-mining state of
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Figure 10.3 (a) Dynamic loading of
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Figure 10.5 (a) Pre-mining and (b)
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Figure 10.6 Problem definition and
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ENERGY, MINE STABILITY, MINE SEISMI
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Figure 10.9 Force and stress compon
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Figure 10.12 Distribution of radial
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Figure 10.15 Problem geometry for d
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Figure 10.17 (a) Schematic represen
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Figure 10.20 Elastic/post-peak stif
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Figure 10.24 Relation between frequ
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Figure 10.28 Six possible ways that
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Figure 10.29 First motions for P an
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11Rock support and reinforcement 11
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Figure 11.1 (a) Hypothetical exampl
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Figure 11.4 Non-linear support reac
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Figure 11.5 Idealised elastic-britt
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Figure 11.6 Calculated required sup
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ROCK SUPPORT AND REINFORCEMENT The
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Figure 11.9 Ground reaction curves
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Figure 11.12 Use of grouted reinfor
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ROCK SUPPORT AND REINFORCEMENT If,
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Figure 11.16 Local reinforcement ac
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Figure 11.18 Typical working sketch
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Figure 11.19 Permanent support and
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Figure 11.22 Basis of natural coord
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Figure 11.24 Distributions of (a) s
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Figure 11.26 Resin grouted rockbolt
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Figure 11.28 Alternative methods of
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ROCK SUPPORT AND REINFORCEMENT Tabl
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Figure 11.31 Toussaint-Heintzmann y
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MINING METHODS AND METHOD SELECTION
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Figure 12.2 Elements of a supported
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Figure 12.6 Schematic layout for bi
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Figure 12.8 Layout for shrink stopi
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Figure 12.9 Schematic layout for VC
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Figure 12.11 Key elements of longwa
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Figure 12.13 Mining layout for tran
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13 Figure 13.1 Schematic illustrati
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Figure 13.3 Layout of barrier pilla
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Figure 13.5 Principal modes of defo
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Figure 13.8 Geometry for tributary
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PILLAR SUPPORTED MINING METHODS str
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Figure 13.10 Distribution of vertic
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Figure 13.12 Pillar behaviour domai
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PILLAR SUPPORTED MINING METHODS Lun
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Figure 13.15 Options in the design
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Figure 13.17 Relation between yield
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Figure 13.19 Model of yield of coun
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Figure 13.20 North-south vertical c
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Figure 13.23 Stope-and-pillar layou
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Figure 13.25 Calibrated stability c
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PILLAR SUPPORTED MINING METHODS wor
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Figure 13.28 Pillar performance, de
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Figure 13.29 (a) Stope and pillar l
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Figure 13.31 (a) Plane strain analy
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PILLAR SUPPORTED MINING METHODS Pan
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14 Artificially supported mining me
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ARTIFICIALLY SUPPORTED MINING METHO
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Figure 14.2 Simplified view of stru
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Figure 14.5 Confined block model fo
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Figure 14.7 Crown and sidewall stre
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Figure 14.10 Sublevel open stoping
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Figure 14.12 Some applications of c
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15 Longwall and caving mining metho
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Figure 15.2 Shear stress drop in th
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LONGWALL AND CAVING MINING METHODS
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Figure 15.6 Hydraulic prop reaction
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Figure 15.7 Development and extract
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Figure 15.8 Vertical stress redistr
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Figure 15.11 Distribution of observ
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Figure 15.13 Plan view of microseis
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Figure 15.16 Ground-support interac
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Figure 15.18 Roadway support and re
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Figure 15.25 Comparison of isolated
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Figure 15.26 Geometry of a sublevel
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Figure 15.28 Theoretical determinat
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Figure 15.31 Deterioration of a cro
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Figure 15.32 Distinct element simul
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Figure 15.34 Extended Mathews stabi
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Figure 15.36 Comparison of postand
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Figure 15.39 Idealised plan illustr
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Figure 15.41 Idealised vertical sec
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Figure 15.42 Vertical slice through
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16 Figure 16.1 Trough subsidence ov
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MINING-INDUCED SURFACE SUBSIDENCE c
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Figure 16.4 North-south section, At
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Figure 16.6 (a) Rectangular block g
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MINING-INDUCED SURFACE SUBSIDENCE f
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Figure 16.8 Relation between stope
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MINING-INDUCED SURFACE SUBSIDENCE M
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MINING-INDUCED SURFACE SUBSIDENCE
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Figure 16.14 Chart developed to est
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Figure 16.16 Progressive hangingwal
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Figure 16.19 Idealised model used i
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Figure 16.21 Longitudinal section,
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MINING-INDUCED SURFACE SUBSIDENCE t
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MINING-INDUCED SURFACE SUBSIDENCE w
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MINING-INDUCED SURFACE SUBSIDENCE F
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Figure 16.25 Subsidence troughs pre
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Figure 16.28 Predicted and measured
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17 Blasting mechanics 17.1 Blasting
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Figure 17.1 An empirical matching o
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Figure 17.2 A finite difference mod
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Figure 17.4 Reflection of a cylindr
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BLASTING MECHANICS means that no ci
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Figure 17.8 Layout of blast holes i
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Figure 17.9 Influence of field stat
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Figure 17.11 Generation of surface
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BLASTING MECHANICS The components o
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BLASTING MECHANICS amplitudes of th
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BLASTING MECHANICS 17.9 Evaluation
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Figure 17.15 (a) Schematic cross se
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BLASTING MECHANICS in Figure 17.17,
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MONITORING ROCK MASS PERFORMANCE (a
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MONITORING ROCK MASS PERFORMANCE su
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MONITORING ROCK MASS PERFORMANCE Ta
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Figure 18.2 The Distometer ISETH, a
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Figure 18.5 Self-inductance multipl
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MONITORING ROCK MASS PERFORMANCE is
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Figure 18.9 Biaxial vibrating wire
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MONITORING ROCK MASS PERFORMANCE me
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Figure 18.12 Cross section at 6650N
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Figure 18.13 Examples of convergenc
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Figure 18.15 Longitudinal section l
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Figure 18.16 (Cont.) MONITORING ROC
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Appendix A Basic constructions usin
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Figure A.3 Determining the angle be
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APPENDIX A USE OF HEMISPHERICAL PRO
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APPENDIX B STRESSES AND DISPLACEMEN
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Figure A.6 Axisymmetric tunnel prob
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Figure A.9 Bolt load-extension curv
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APPENDIX D LIMITING EQUILIBRIUM ANA
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ANSWERS TO PROBLEMS 2 (a) 0.087 - 0
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ANSWERS TO PROBLEMS 3 wp = 38.6 m,
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REFERENCES Symp. & 17th Tunn. Assn
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REFERENCES Brady, B. H. G. and Bray
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REFERENCES Collier, P. A. (1993) De
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REFERENCES Drescher, A. and Vardoul
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REFERENCES Gustafsson, P. (1998) Wa
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REFERENCES Hood, M. and Brown, E. T
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REFERENCES Kaiser, P. K. and Tannan
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REFERENCES Lorig, L. J. and Brady,
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REFERENCES Ortlepp, W. D. (1994) Gr
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REFERENCES Rojas, E., Molina, R. an
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REFERENCES Spottiswoode, S. M. and
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REFERENCES Villaescusa, E., Windsor
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Index Page numbers appearing in bol
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INDEX Coulomb (cont.) parameters 96
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INDEX Excavation (cont.) support ra
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INDEX Jaeger’s plane of weakness
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INDEX Panel caving 470-2, 473, 474,
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INDEX Seismic (cont.) moment 306, 3
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INDEX Strength (cont.) residual 86,
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INDEX United States (USA) 395, 396,
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