Rock Mechanics.pdf - Mining and Blasting

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SUPPORT AND REINFORCEMENT DESIGN of rock mass classification-based design rules and more comprehensive numerical analyses. Quite often in practice, these approaches are used in combination. Rock-support interaction calculations. These may be carried out using the methods discussed in section 11.3 and the calculation procedures set out in Appendix C. Although idealisations of the problem have to be made, and some factors and techniques cannot be specifically allowed for in the calculations, use of this approach permits the designer to develop a clear understanding of the relative merits of candidate reinforcement systems in a particular application. In most cases, it will be necessary to carry out a series of calculations for a number of trial designs before an appropriate design can be selected for a field trial. Empirical design rules. A wide range of empirical support and reinforcement design rules have been developed over the last 50 years. These rules, which are based on precedent practice, generally apply to permanent underground excavations rather than to temporary mining excavations such as stopes. They are geometrically based and do not account explicitly for the stress field induced around the excavation or for the quality of the rock mass. For these reasons, they must be used with extreme caution and only for making preliminary estimates which must be checked by making more complete assessments. The range of empirical design rules available has been reviewed by Stillborg (1994) and by Rachmad et al. (2002) in the context of their application to the support and reinforcement of production drifts in a block caving mine. One of the most useful and long-lived set of empirical design rules is that developed by Lang (1961) for pattern rockbolting of permanent excavations during the construction of the Snowy Mountains Hydro-electric Scheme in Australia. Although Lang’s rules are described here as empirical, they were established on the basis of a range of laboratory, field and theoretical studies which have been reviewed by Brown (1999a). Lang (1961) gives the minimum bolt length, L, as the greatest of (a) twice the bolt spacing, s; (b) three times the width of critical and potentially unstable rock blocks defined by the average discontinuity spacing, b; or (c) 0.5B for spans of B < 6m, 0.25 B for spans of B = 18–30 m. For excavations higher than 18 m, the lengths of sidewall bolts should be at least one fifth of the wall height. The maximum bolt spacing, s, is given by the least of 0.5L and 1.5b. When weld or chain mesh is used, a bolt spacing of more than 2 m makes attachment of the mesh difficult if not impossible. Figure 11.18 shows a preliminary layout of a rockbolting pattern for a horse-shoeshaped excavation in jointed rock, prepared using Lang’s rules. This figure also illustrates the basis on which Lang’s rules were developed, namely the establishment of a self-supporting compressed ring or arch around the excavation. If a highly compressible feature such as a fault or a clay seam crosses the compression ring, it is possible that the required compression will not be developed and that the reinforcement will be inadequate. Rock mass classification schemes. Schemes such as those due to Barton et al. (1974) and Bieniawski (1973, 1976) were developed as methods of estimating support 333
Figure 11.19 Permanent support and reinforcement recommendations based on the Q system of rock mass classification (after Barton, 2002). ROCK SUPPORT AND REINFORCEMENT requirements for underground excavations, using precedent practice. Barton et al. proposed 38 categories of support based on their tunnelling quality index, Q, and the excavation support ratio, ESR, which varies with the use of the excavation and the extent to which some degree of instability is acceptable. These proposals have been discussed in detail by Hoek and Brown (1980) who point out the dangers involved in blindly adopting their provisions, particularly where the nature of the excavation and the properties of the rock mass differ from those in the case histories that were used in developing the recommendations. Figure 11.19 shows the recommendations for the support and reinforcement of permanent excavations offered by Grimstad and Barton (1993) and Barton (2002) which update the original recommendations of Barton et al. (1974) and allow for, in particular, subsequent advances in shotcrete technology. Comprehensive analysis of general or systematic reinforcement. In a rock mass subject to fracture and yield, the spatially-extensive model of reinforcement is more 334
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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
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Figure 2.3 Free-body diagram for de
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Figure 2.5 Problem geometry for det
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Figure 2.7 Rigid-body rotation of a
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STRESS AND INFINITESIMAL STRAIN the
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STRESS AND INFINITESIMAL STRAIN str
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⎡ ⎢ ⎣ xx yy zz xy yz zx STRES
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Figure 2.11 Cylindrical polar coord
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STRESS AND INFINITESIMAL STRAIN fre
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Figure 2.13 Construction of a Mohr
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STRESS AND INFINITESIMAL STRAIN fun
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3 Rock Figure 3.1 Sidewall failure
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Figure 3.2 Jointing in a folded str
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Figure 3.5 Diagrammatic longitudina
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Figure 3.7 Discontinuity spacing hi
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Figure 3.9 Illustration of persiste
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Figure 3.11 Typical roughness profi
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ROCK MASS STRUCTURE AND CHARACTERIS
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Figure 3.17 Sample number vs. preci
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Figure 3.19 Diagrammatic illustrati
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Figure 3.20 Computerised depiction
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Figure 3.23 Stereographic projectio
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Figure 3.26 Polar stereographic net
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Figure 3.28 Contours of pole concen
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Figure 3.30 Geological Strength Ind
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Figure 4.1 Idealised illustration o
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ROCK STRENGTH AND DEFORMABILITY wit
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Figure 4.4 Influence of end restrai
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ROCK STRENGTH AND DEFORMABILITY whe
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Figure 4.8 Principle of closed-loop
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Figure 4.12 Two classes of stress-
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Figure 4.14 Point load test apparat
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Figure 4.15 Biaxial compression tes
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Figure 4.18 Results of triaxial com
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ROCK STRENGTH AND DEFORMABILITY was
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Figure 4.23 Coulomb strength envelo
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Figure 4.25 Extension of a preexist
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Figure 4.29 The three basic modes o
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Figure 4.30 Normalised peak strengt
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ROCK STRENGTH AND DEFORMABILITY Tab
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Figure 4.32 The normality condition
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Figure 4.33 Variation of peak princ
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Figure 4.35 Direct shear test confi
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Figure 4.37 Shear stress-shear disp
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Figure 4.40 Peak and residual effec
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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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Page 301 and 302: ENERGY, MINE STABILITY, MINE SEISMI
Page 307 and 308: Figure 10.12 Distribution of radial
Page 309 and 310: Figure 10.15 Problem geometry for d
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Page 315 and 316: Figure 10.20 Elastic/post-peak stif
Page 319 and 320: Figure 10.24 Relation between frequ
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Page 327 and 328: Figure 10.29 First motions for P an
Page 329 and 330: 11Rock support and reinforcement 11
Page 331 and 332: Figure 11.1 (a) Hypothetical exampl
Page 333 and 334: Figure 11.4 Non-linear support reac
Page 335 and 336: Figure 11.5 Idealised elastic-britt
Page 337 and 338: Figure 11.6 Calculated required sup
Page 339 and 340: ROCK SUPPORT AND REINFORCEMENT The
Page 341 and 342: Figure 11.9 Ground reaction curves
Page 343 and 344: Figure 11.12 Use of grouted reinfor
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Page 347 and 348: Figure 11.16 Local reinforcement ac
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Page 353 and 354: Figure 11.22 Basis of natural coord
Page 355 and 356: Figure 11.24 Distributions of (a) s
Page 357 and 358: Figure 11.26 Resin grouted rockbolt
Page 359 and 360: Figure 11.28 Alternative methods of
Page 361 and 362: ROCK SUPPORT AND REINFORCEMENT Tabl
Page 363 and 364: Figure 11.31 Toussaint-Heintzmann y
Page 365 and 366: MINING METHODS AND METHOD SELECTION
Page 367 and 368: Figure 12.2 Elements of a supported
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Page 377 and 378: Figure 12.8 Layout for shrink stopi
Page 379 and 380: Figure 12.9 Schematic layout for VC
Page 381 and 382: Figure 12.11 Key elements of longwa
Page 383 and 384: Figure 12.13 Mining layout for tran
Page 387 and 388: 13 Figure 13.1 Schematic illustrati
Page 389 and 390: Figure 13.3 Layout of barrier pilla
Page 391 and 392: Figure 13.5 Principal modes of defo
Page 393 and 394: Figure 13.8 Geometry for tributary
Page 395 and 396: PILLAR SUPPORTED MINING METHODS str
Page 397 and 398: Figure 13.10 Distribution of vertic
Page 399 and 400: 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
Page 617 and 618:
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,
Page 645:
INDEX United States (USA) 395, 396,
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