Rock Excavation Rock Characteristics Igneous Rock granite basalt

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Rock Excavation

Rock Excavation

Rock Characteristics • Igneous Rock – granite, basalt • Sedimentary Rock – sandstone, shale,

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

Rock • Difficulty in excavation due to – Rock type, extent of fractures, other

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 • Drilling – core samples, tv dropped down shaft • Test pits –

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

Rock Handling • • • 4 phases Loosen – blast or rip Load –

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

Tunneling • Old days drill and blast • Now tunnel boring machines (TBM) –

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

Tunneling • Hydraulic jumbo – self propelled machine with hydraulic arms with drills –

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 • Percussion – jackhammer, drifters, wagon drill, track drill operates by hitting

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 F 8 -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 Equip • Drill rate depends on rock hardness, drill type, drill energy, bit

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 # upward thrust, 400, 000# torque

Drill Bits • F 8 -10 • Tungsten Carbide steel • Drill steel –

Drill Bits • F 8 -10 • Tungsten Carbide steel • Drill steel – connects drill bit to percussion machine • Drill pipe connects rotary bit to machine

Drill Patterns • Size of hole, depth, spacing & amount of explosive depends on

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 Patterns • Volume/hole = (S^2*H)/27 • S = hole spacing • H =

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 • Dynamite – Has been replaced by next three due to lower cost

Explosives • Dynamite – Has been replaced by next three due to lower cost and easier to handle than dynamite • Ammonium nitrate in fuel oil • slurries

Detonators • Electric blasting caps – Instantaneous or time delayed – Ignite primers –

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