Rock Mechanics.pdf - Mining and Blasting

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Figure 11.29 Some support mechanisms developed by shotcrete: (a) a single block; (b) a beam anchored by bolts; (c) a roof arch; (d) a closed ring (after Brown, 1999b). MATERIALS AND TECHNIQUES Some of the support mechanisms developed by shotcrete on the peripheries of excavations are illustrated in Figure 11.29. The support functions, modes of failure and methods of design of shotcrete as a component of hard rock support and reinforcement systems are discussed by Holmgren (2001) and by Kaiser and Tannant (2001). Hoek et al. (1995) provide a set of detailed recommendations for the use of shotcrete in a range of rock mass conditions likely to be encountered in hard rock mining. Shotcrete is prepared using either the dry-mix or the wet-mix process. In the drymix process, dry or slightly dampened cement, sand and aggregate are mixed at the batching plant, and then entrained in compressed air and transported to the discharge nozzle. Water is added through a ring of holes at the nozzle. Accurate water control is essential to avoid excessive dust when too little water is used or an over-wet mix when too much water is added. In the wet-mix process, the required amount of water is added at the batching plant, and the wet mix is pumped to the nozzle where the compressed air is introduced. A comparison of the dry- and wet-mix processes is given in Table 11.2. Until the last decade dry-mix method was more widely used, mainly because the equipment required is lighter and less expensive, and because the dry material can be conveyed over longer distances, an important advantage in mining applications. However, wet-mix methods have important advantages for underground mining applications in terms of reduced dust levels, lower skill requirements and the need for less equipment at the application site. They have now become the industry standard (Brown, 1999b, Spearing, 2001). Shotcrete mix design is a difficult and complex process involving a certain amount of trial and error. The mix design must satisfy the following criteria (Hoek and Brown, 1980): (a) Shootability – the mix must be able to be placed overhead with minimum rebound. 343
ROCK SUPPORT AND REINFORCEMENT Table 11.2 Comparison of wet- and dry-mix shotcreting processes (after Spearing, 2001). Wet Process Dry process Little dust Considerable dust Low maintenance cost High maintenance cost High capital cost Low capital cost Low rebound, typically about 5% to 10% High rebound, usually more than 25% Moderate to high placement rate, between 4 and 25 m 3 /hr Low to moderate placement rate, up to 6 m 3 /hr Low transport distance, up to 200 m High transport distance Moderate to high placed quality Moderate placed quality (b) Early strength – the mix must be strong enough to provide support to the ground at ages of a few hours. (c) Long-term strength – the mix must achieve a specified 28 day strength with the dosage of accelerator needed to achieve the required shootability and early strength. (d) Durability – adequate long-term resistance to the environment must be achieved. (e) Economy – low-cost materials must be used, and there must be minimum losses due to rebound. A typical basic mix contains the following percentages of dry components by weight: cement 15–20% coarse aggregate 30–40% fine aggregate or sand 40–50% accelerator 2–5% The water : cement ratio for dry-mix shotcrete lies in the range 0.3–0.5 and is adjusted by the operator to suit local conditions. For wet-mix shotcrete, the water : cement ratio is generally between 0.4 and 0.5. The efficacy of the shotcreting process depends to a large extent on the skill of the operator. The nozzle should be kept as nearly perpendicular to the rock surface as possible and at a constant distance of about 1 m from it. A permanent shotcrete lining is usually between 50 mm and 500 mm thick, the larger thicknesses being placed in a number of layers. The addition of 20–50 mm long and 0.25–0.8 mm diameter deformed steel fibres, or plastic fibres, has been found to improve the toughness, shock resistance, durability, and shear and flexural strengths of shotcrete, and to reduce the formation of shrinkage cracks. Fibre-reinforced shotcrete will accept larger deformations before cracking occurs than will unreinforced shotcrete; after cracking has occurred, the reinforced shotcrete maintains its integrity and some load-carrying capability. However, fibre-reinforced shotcrete is more expensive and more difficult to apply than unreinforced shotcrete. 11.6.5 Wire mesh Chain-link or welded steel mesh is used to restrain small pieces of rock between bolts or dowels, and to reinforce shotcrete. For the latter application, welded mesh is preferred to chain-link mesh because of the difficulty of applying shotcrete satisfactorily through the smaller openings in chain-link mesh. For underground use, weld mesh typically has 4.2 mm diameter wires spaced at 100 mm centres. In some mining 344
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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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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
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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
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 and 356: Figure 11.24 Distributions of (a) s
Page 357 and 358: Figure 11.26 Resin grouted rockbolt
Page 359: Figure 11.28 Alternative methods of
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
Page 407 and 408: Figure 13.19 Model of yield of coun
Page 409 and 410: 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
Page 615 and 616:
REFERENCES Gustafsson, P. (1998) Wa
Page 617 and 618:
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
Page 627 and 628:
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
Page 639 and 640:
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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