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Rock Excavation. Rock Characteristics. Igneous Rock – granite, basalt Sedimentary Rock – sandstone, shale, limestone Metamorphic Rock – originated as igneous or sedimentary and then changed by heat, pressure, chemical reaction – slate, marble, schist

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rock characteristics
Rock Characteristics
  • Igneous Rock – granite, basalt
  • Sedimentary Rock – sandstone, shale, limestone
  • Metamorphic Rock – originated as igneous or sedimentary and then changed by heat, pressure, chemical reaction – slate, marble, schist
  • Hardness – Moh’s scale 1- talc -> 10 diamond
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Rock
  • Difficulty in excavation due to
    • Rock type, extent of fractures, other planes of weakness, amount of weathering, predominant grain size, brittleness or hardness
investigation
Investigation
  • Drilling – core samples, tv dropped down shaft
  • Test pits – only good for soft rock
  • Seismic measurements
rock handling
Rock Handling
  • 4 phases
  • Loosen – blast or rip
  • Load – shovel or loader
  • Haul – truck or wagon
  • Compact - roller
tunneling
Tunneling
  • Old days drill and blast
  • Now tunnel boring machines (TBM)
    • F 8-4
    • Usually 1 use machine
    • Rotating head with debris handling system and
  • Jumbo – large mobile frame so that you can drill a complete rock face at one time
tunneling7
Tunneling
  • Hydraulic jumbo – self propelled machine with hydraulic arms with drills – drills blast holes in entire face F 8-5
  • Mucking machine – form of shovel used to load fractured rock into haul units
drilling equip
Drilling Equip
  • Percussion – jackhammer, drifters, wagon drill, track drill operates by hitting a bit which rotates between blows F 8-6
  • Rotary drill – diamond tipped cutter head – well drilling machine F8-7
  • Rotary-percussion T 8-2
  • Down hole drills F 8-8
    • Percussion device is mounted directly above drill bit at bottom of hole
    • Less noise, less air required to clear hole, longer drill life higher efficiency
drilling equip9
Drilling Equip
  • Drill rate depends on rock hardness, drill type, drill energy, bit type Increased air pressure = increased drill production also increases costs
  • Raise boring
    • Drill pilot hole down and then raise rotating reaming head
    • 1,000,000 # upward thrust,400,000# torque
drill bits
Drill Bits
  • F8-10
  • Tungsten Carbide steel
  • Drill steel – connects drill bit to percussion machine
  • Drill pipe connects rotary bit to machine
drill patterns
Drill Patterns
  • Size of hole, depth, spacing & amount of explosive depends on degree of rock break desired, rock type, soundness, explosive used
  • Usually test blast to determine exact pattern
  • F 8-11 shows patterns
drill patterns12
Drill Patterns
  • Volume/hole = (S^2*H)/27
  • S = hole spacing
  • H = effective hole depth (* usually 90% of hole depth)
  • Rock volume/ft of hole = Volume per ft of hole/ drill hole depth
explosives
Explosives
  • Dynamite
    • Has been replaced by next three due to lower cost and easier to handle than dynamite
  • Ammonium nitrate
  • Ammonium nitrate in fuel oil
  • slurries
detonators
Detonators
  • Electric blasting caps
    • Instantaneous or time delayed
    • Ignite primers – usually placed at bottom of hole
      • Either primer or primacord
  • Amount of explosive required to produce desired rock fracture = powder factor.
    • Pounds/bcy
    • Blast holes loaded with explosive except for last several feet
    • Stemming is placed on top of explosive – inert material