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Rock Excavation

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 Excavation

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  1. Rock Excavation

  2. 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

  3. Rock • Difficulty in excavation due to • Rock type, extent of fractures, other planes of weakness, amount of weathering, predominant grain size, brittleness or hardness

  4. Investigation • Drilling – core samples, tv dropped down shaft • Test pits – only good for soft rock • Seismic measurements

  5. Rock Handling • 4 phases • Loosen – blast or rip • Load – shovel or loader • Haul – truck or wagon • Compact - roller

  6. 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

  7. 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

  8. 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

  9. 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

  10. Drill Bits • F8-10 • Tungsten Carbide steel • Drill steel – connects drill bit to percussion machine • Drill pipe connects rotary bit to machine

  11. 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

  12. 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

  13. 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

  14. 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

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