Rock Mechanics.pdf - Mining and Blasting

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Figure 11.25 Types of rockbolt and dowel (after Hadjigeorgiou and Charette, 2001). MATERIALS AND TECHNIQUES in corrosive environments, rockbolts are usually fully grouted with cement or resin grout for improving both pull-out strength and corrosion resistance. Rockbolts are often classified according to the nature of their anchorages. Early rockbolt anchors were of the mechanical slot-and-wedge and expansion shell types. It is often difficult to form and maintain mechanical anchors in very hard or in soft rocks. Mechanical anchors are also susceptible to blast-induced damage. Anchors formed from Portland cement or resin are generally more reliable and permanent. A third category of rockbolt anchorage is that utilised by friction (Split Set and Swellex) bolts which rely on the generation of friction at the rock-bolt contact along their lengths for their anchorage and strength. As with mechanical anchors, friction bolts depend for their efficacy on the sizes and accuracy of the drilling of the holes in which they are installed. They are also susceptible to corrosion. Although they may be given a pre-tension to ensure that an anchorage is formed, friction bolts are usually not installed with the levels of pre-tension (5–20 tonnes) used for other rockbolts. In this case, they act a dowels rather than rockbolts. Other types of dowel are usually grouted along their lengths on installation and develop their tension with deformation of the rock mass in which they are installed. Grouting of Split Set bolts and dowels may increase their load carrying capacity for longer term applications (Thompson and Finn, 1999). Figure 11.25 shows a number of types of rockbolt and dowel classified according to the anchorage method used but with several types of shank illustrated. Figure 11.26 shows further details of the installation and grouting of a resin anchored and grouted bolt made from threaded bar. Resin encapsulated rockbolts are widely used for the reinforcement of longer term openings in metalliferous mines.(e.g. Slade et al., 2002). 11.6.3 Cable bolts Cable bolts are long, grouted, high tensile strength steel elements used to reinforce rock masses. They may be used as pre-or post-reinforcement and may be left untensioned or be pre- or post-tensioned. Windsor (2001) defines the following terms associated with cable bolting: Wire – a single, solid section element. Strand – a set of helically spun wires. 339
Figure 11.26 Resin grouted rockbolt made from threaded bar (after Hoek and Brown 1980). ROCK SUPPORT AND REINFORCEMENT Cable – an arrangement of wires or strands. Tendon – pre-tensioned wires or strand. Dowel – un-tensioned wires or strand. Cable bolting as defined here was first used in underground metalliferous mines in South Africa and Canada but it was probably in Australia that cable bolt and dowel reinforcement was first developed as a major form of systematic reinforcement in cut-and-fill mining (Clifford, 1974, Brown, 1999b). Figure 11.27 summarises the development of cable bolt configurations. Windsor (2001) notes that the development of hardware for cable bolting has been matched by improvements in design philosophy and methods. In this context, design includes choosing a suitable type of cable bolt, the bolt orientations, lengths and densities, an appropriate installation procedure, and determining whether to use preor post-reinforcement in conjunction will pre- or post-tensioning. In mining practice, these decisions are influenced by logistics, equipment availability, precedent practice in similar circumstances and, in the case of installation procedures, the levels of training of the work force. Installation practice has the potential to dictate the mechanical performance of cable bolting. The length and transverse flexibility of cable bolts create a number of difficulties in ensuring a high quality installation. Installation can be influenced by a number of factors relating to the drilling of the hole, the configuration and state of the cable, and the grouting and tensioning of the cable. A full discussion of these factors is outside the scope of this text. For further details, the reader is referred to the books by Hoek et al. (1995) and Hutchinson and Diederichs (1996), and the papers by Windsor (1997, 2001), for example. Figure 11.28 illustrates two alternative methods of grouting cable bolts into upholes. These methods may be described as gravity retarded and gravity assisted, respectively. In the grout tube method, the tube may be withdrawn progressively from the hole as it fills with grout. This method has 340
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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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Figure 10.9 Force and stress compon
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Page 305 and 306: 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
Page 311 and 312: Figure 10.17 (a) Schematic represen
Page 315 and 316: Figure 10.20 Elastic/post-peak stif
Page 319 and 320: Figure 10.24 Relation between frequ
Page 325 and 326: Figure 10.28 Six possible ways that
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
Page 345 and 346: ROCK SUPPORT AND REINFORCEMENT If,
Page 347 and 348: Figure 11.16 Local reinforcement ac
Page 349 and 350: Figure 11.18 Typical working sketch
Page 351 and 352: Figure 11.19 Permanent support and
Page 353 and 354: Figure 11.22 Basis of natural coord
Page 355: Figure 11.24 Distributions of (a) s
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
Page 375 and 376: Figure 12.6 Schematic layout for bi
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
Page 401 and 402: PILLAR SUPPORTED MINING METHODS Lun
Page 403 and 404: Figure 13.15 Options in the design
Page 405 and 406: 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
Page 619 and 620:
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
Page 625 and 626:
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,
Page 641 and 642:
INDEX Seismic (cont.) moment 306, 3
Page 643 and 644:
INDEX Strength (cont.) residual 86,
Page 645:
INDEX United States (USA) 395, 396,
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