Underground Mining Methods:

By:

Tayyab anwar (12MN01)Asif Morio(12-11MN60)

Ihsan Ali(12MN89)Sadam(12MN91)

Mining: The activity,occupation and industry concerned with the extraction of minerals.Underground mining: Mineral exploitation in which all the extraction is carried out beneath the surface of earth. Underground mining methods: These are the methods/techniques employed when the depth of the deposit,the stripping ratio of the overburden to ore,or both becomes excessive to surface exploitation.Choice of an underground mining method is often closely related to the Geology of the deposit and degree of ground support necessary to make the method productive and safe.There are three classes of methods are recognized: Based on extent of supports utilized,

• Supported• Unsupported • Caving.

Supported Methods:Those methods that require some type of backfill to provide substantial amounts of artifitial supports to maintain stability in the exploitation openings of mine.when the production opening will not remain standing during their life and when major caving and subsidence cannot be tolerated.

• There are three methods in this class:1) Cut and fill stoping.2) Stull stoping.3) Square set stoping.

1)Cut and fill stoping: The only method of supported class in common use today, cut-and-fill stoping, normally used in an overhand fashion.the ore is extracted in horizontal slices and replaced with backfill material.

The fill material varies,depending on the support required,and the material available.

Conditions:1.Ore strength: Moderately weak to strong.2.Rock strength: weak to fairly weak.3.Deposit shape: tabular; can be irregular,discontinuous.4.Deposit dip: >450

5.Deposit size: 2 to 30m.6.Depth: <4000 to 8000 ft or 1.2 to 2.4 km.7.Ore grade:Fairly high.8.Ore uniformity: moderate,variable

• Cycle of operations: Drilling+Blasting+Loading+Haulage.

(2)Stull stoping: Stull stoping is infrequently used and relatively unimportant today; as it accounts for less than 1% of underground mine production.Timbers are placed between the foot wall and hanging walls, which constitute the only artificial support provided during the excavation of a stope.

Conditions:1.Ore strength: Fairly strong to strong.2.Rock strength: moderate to fairly weak.3.Deposit shape: Approximately tabular; can be irregular.4.Deposit dip: works best at <450

5.Deposit size: relatively thin(12ft or 3.6m)6.Depth: <3500 ft or 1.1km.7.Ore grade:Fairly high to high8.Ore uniformity: moderate.

• Cycle of operations:• Drilling+Blasting+Loading+Haulage

Each timber set consists of a post, cap and girt.

Conditions:1.Ore strength: Weak to very weak.2.Rock strength: Weak to very weak.3.Deposit shape: Angular to irregular.4.Deposit dip: Any, preferably >450 so that gravity flow can be used.5.Depth: Deep(upto8500ft or 2.6km).7.Ore grade: High8.Ore uniformity: Variable.

Cycle of operations:Drilling+Blasting+Loading+HaulageIn square set stoping the most essential auxiliary operations are, handling, standing timber and filling with waste.Ventilation is also vital.

Unsupported Methods: The unsupported class consists of the methods in which the rock is

essentially self supporting and for which no major artificial support(artificially placed pillars or fill)is necessary to carry the load of overlying rockThe use of roof bolts or supports of timber or steel, provided that such supports doesn't alter the load-carrying capacity of the natural rock. The load is too high but the geological material can sustain the load.

• Following are considered as unsupported methods;(1)Room-and-pillar mining.(2) Stope-and-pillar mining.(3)Shrinkage stoping.(4)Sublevel stoping.

(1)Room-and-pillar mining method:• Room-and-pillar mining is very old method applied to horizontal or

nearly horizontal deposits that has been adopted and refined over the years. The method is used in both coal and non coal mining.

• In room-and-pillar mining openings are driven orthogonally and at regular intervals in a mineral deposit ,forming rectangular and square pillars for natural supports. The development openings(entries)and production openings(rooms)closely resemble each other; both are driven parallel and in multiple.

• Pillar may be left un-extracted either permanently or they are extracted while retreating.

• Up to 6 meter thickness the ore body can be extracted in a single pass. • Inclination of the seam should not exceed 300 with horizontal. • Driving several openings at one time increases production and efficiency

by providing multiple working places.• In addition it provides for better ventilation and transportation routes at

the working faces.

Cycle of operations:Conventional Mining: In Room-and-pillar mining of coal with conventional equipments includes cutting operation to improve coal breakage during light blasting.The production cycle then becomesProduction cycle= cut+drill+blast+load+haul.Roof control, ventilation and clean up are the auxiliary operations.Continuous Mining: Continuous mining is a method that has been practiced primarily in coal since about1950.The method depends heavily upon ruggedness and reliability of continuous miner. The continuous miner breaks and load the coal mechanically and simultaneously eliminates the step of cutting, blasting and loading.

Production cycle= Mine+Haul.

• (2)Stop-And-Pillar Mining: It is the method in which openings are driven horizontally in regular and random patterns to form pillars for ground support. It is one of the large mining method accounting for about 50% of U.S noncoal production.

• The stope-and-pillar is same as Room-and pillar mining if it meets following qualifications:

1.Pillars are irregularly shaped and sized and either randomly located 2.Deposit thickness is <20ft(6m) openings are higher than they wide.3.The commodity being exploited is a mineral other than coal, although

some noncoal deposits are also mined by room-and-pillar method but no coal deposit s are mined by the stop-and-pillar method.

Production cycle = Drill+blast+load+haul.

(3)Shrinkage Stoping: It is called vertical stoping method in which the ore is mined in horizontal slices from bottom to top and remains in the stope as temporary support to the walls and to provide a vertical platform for the miners.Stope width 3 to 100ft (1-30m),length 150 t 300ft (45-90m) and height from 200 to 300ft(60-90m).

Conditions:1.Ore strength: strong.2.Rock strength: Fairly strong .3.Deposit shape: tabular, lanticular.4.Deposit dip: 60 to 900 (ore flow)5.Depth: <2500ft or 750m7.Ore grade: fairly high.8.Ore uniformity: uniform.

(4)Sublevel Stoping: It is a vertical mining method in which large open stope is created within the vein, this open stope is not meant to be occupied by miners, therefore all work of drilling and blasting must be performed from sublevel within the ore block.

Conditions:1.Ore strength: Moderate to strong.2.Rock strength: Fairly strong to strong.3.Deposit shape: tabular or lanticular4.Deposit dip: fairly steep.5.Depth:shallow to deep(8000 ft or 2.4km)7.Ore grade: moderate.8.Ore uniformity: fairly uniform.

Caving Methods: Caving methods are those associated with induced, controlled, massive caving of the ore body, the overlying rock, or both, essential to the conduct of mining.(1) Longwall mining:Longwall mining is an exploitation method used in flat-lying, relatively thin, tabular deposits, in which the long faces are established to extract the mineral.Established b/w head gate entry and tailgate entry.The longwall face is kept open by a system of heavy duty, powered yielding supports that form a cantilever or umbrella of protection over the face.As a cut or slice is taken along the length of the wall, the supports are collapsed, advanced closer to the face and reengaged, allowing the roof to cave behind,The caved area is called gob.Large scale exploitation(80%face can be exploited) and is considered as on of the cheapest method.

Cycle of operations: same as room-and-pillar mining method using continuous miner.Mining(breakage and loading):shearer(normally a double drum version),plow.Haulage: armored chain-and-flight face conveyor, normal belt conveyor utilized in the head gate entry set.

Sublevel caving: In sublelvel caving over all mining progress downward while the ore

b/w sublevel is broken overhand; the overlying waste rock (hangingwall or capping)caves into the void created as the ore is drawn off. Sub level caving is applicable to near-vertical deposits of metal and nonmetal. In sublevel caving both the ore and the rock are normally involved in caving, the caving proceeds in a columnar fashion to the surface, the result is massive subsidence. Mining is conducted on sublevels from development drifts and crosscuts, connected to the main haulage.

Conditions:1.Ore strength: strong(requires sufficient competence to withstand without excessive supports against blasting.2.Rock strength: weak to fairly strong, should be fractured, jointed & cavable.3.Deposit shape: tabular or massive.4.Deposit dip: >600 or vertical,falte if deposit is thick.5.Depth:<4000ft or 1.2 km7.Ore grade: Moderate.8.Ore uniformity: Moderate.

Cycle of operations:Sublevel caving employs a conventional cycle of operations in nearly every

application.Drill+last+load+haul. The important auxiliary operations are ground control and ventilation. Ventilation is

easily carried out if the multiple sublevel crosscuts are interconnected,otherwise,vent tubing is necessary.

Other auxiliary operations include health and safety measures,maintenance,power supply, drainage, and material supply.

Block Caving:It is the method in which masses, panels or blocks of ore are undercut to induce caving, permitting the broken ore to be drawn off below. if the deposit is overlain by capping or bounded by hangingwall, it caves too, breaking into the void created by drawing the ore.•A grid of tunnel is driven under the ore body, the rock mass then undercut by blasting.•Ideally the rock will break under its own weight, then ore is taken from draw points.Block caving is utilized to produce about 10% of U.S underground metal and nonmetal and 3% of all underground minerals.

Conditions: 1.Ore strength: weak to moderate or fairly strong.2.Rock strength: weak to moderate.3.Deposit shape: massive to thick tabular deposit.4.Deposit dip:>600 or vertical.

5.Depth:>600m to <1200m.7.Ore grade: low.8.Ore uniformity: uniform and homogeneous.

Cycle of operations: For exploitation, a truncated cycle of operation is followed, because only the loading and haulage operations are utilized(rock breakage is performed by caving action).

Drill+blast+load+haul.Like the other caving methods, block caving requires elaborate ground control measures. Reinforcement and concrete linings as well as conventional supports, are often required in development openings(raises, ore pass, slushier drifts, haulage drifts)that perform a production function.The most important auxiliary operation is ventilation.Drainage,material supply,maintainance and power supply are other key functions.

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