Underground Mining Methode

Two Main Methods

  1. Room And Pillar – Mostly with continuous miners
  2. Longwall – Develop longwall panels with room and pillar using continuous miners
  3. About 10% of underground production still comes from drilling and blasting
  4. Total underground output = 421mt (1997 data)

ROOM AND PILLAR

  • Mine “streets & avenues” (entries and crosscuts)
  • Leave pillars to support roof (may mine later) – Designed by formula
  • Plan view-looks like city with “greenbelts” – “Greenbelts” are large barrier pillars left to separate work areas
  • Use continuous miner

MINE PLAN

  • Main entries (7-9 openings)
  • Submains (5-7 openings)
  • Panels (panel entries, butt entries)
  • Rooms (at times)
  • Openings limited to 20-ft width – Openings serve as air ducts and travelways – Return air is isolated from fresh air, two escapeways must be provided from face
  • Longwall panels are solid coal blocks, usually 1000 ft by 10,000 ft, accessed by “gate” roads

ROOF SUPPORT

  • Insert bolts into the roof on regular pattern (3’-8’ length, usually) – 4’ x 4’ or 5’ x 5’ most common
  • Either “glue” (resin) a re-bar bolt in, or
  • Use expansion bolt anchors or
  • Glue in the anchor only – Anchors allow pre-tensioning of bolts

VENTILATION

  • Provides oxygen, dilutes methane & dust – Methane explosive when at 5-15% concentration
  • Most coninuous miners have dust scrubber – Draw air into ducts at front of miner – Efficiency up to 96-97%
  • Air directed to working face with brattice cloth (plastic curtains)
  • Alternatively, hang tubing & use fan to draw air to face

PRODUCTION RATES

  • 150 – 400 ft/shift usual, tonnage depends on seam thickness – 500 – 2000 tons/shift (usual)
  • New miners load at 10 – 25 tpm
  • Most continuous miners load only 60-120 min/shift – Load only 12 – 10-25% of shift time

LONGWALL

  • More nearly continuous method
  • Analogous to “deli meat slicer” (shearer)
  • Shearer mounted on chain conveyor – Coal cut falls onto conveyor
  • Width of face usually 850 – 1100 ft – Depth of slice is 30 – 42 inches
  • Behind face supported for 20’ or so by steel supports – each 1.50 or 1.75 m wide – Each support holds up to 600-1200 tons
  • Supports connected to conveyor – By pushing, lowering & pulling – can walk conveyor and selves forward

CONTINUOUS MINER
SUMMARY

  • Capital for section is $3-5 million
  • Flexible, can move readily to other reserves
  • One longwall usually requires three continuous miners for development
  • Annual output for miner section is 0.3 – 0.8 million tpy

ENVIRONMENTAL
Longwall strata caves behind supports

  • Surface subsides to maximum of 50-70% of seam thickness
  • “Tilt” area may damage structures, so must provide special support methods at the structures to minimize damage
  • Subsidence trails face position by a few days to a week or two, about 95% occurs in a few weeks

LONGWALL SUBSIDENCE

  • Ground water flow is altered
  • Some wells lose flow, temporarily or permanently; a few gain
  • May need to drill wells deeper
  • Connection from near surface to mine is possible if depth to aquifer is less than 40 x seam thickness (240 ft for 6-ft seam)

SUMMARY

  • Longwall (45% of UG output from only 60 faces - average of 3 million tpy each) – High output, high capital – Low operating cost, 70-80% (?) reserve recovery – Low flexibility
  • Continuous Miners – Medium output, low-medium capital – Moderate operating cost, 40-60% reserve recovery – High flexibility
Underground Mining Methode | admin | 4.5
Optimization WordPress Plugins & Solutions by W3 EDGE