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Methods of excavation

Published: 3rd Feb, 2022

The two main types of mining operations are surface mining and underground mining. Sur­face mining as the name indi­cates is about locating coal at the surface! Obvious you would say! Well, actually even this has two categories, one being the stripping or open cast mining and the second being hill slope boring

Open cast Mining

Stripping or open cast mining

  • Open cast mining or stripping is well suited for areas where coal seam lies at or near the surface not more than 60m deep.
  • The seam should be more or less hori­zontal with the prerequisite of a thin and soft overlying strata, very much like a crumbly black current pie.
  • This is the easiest way to mine, as it hardly disturbs the under­lying stratas, although large tracts of agricultural land may be devastated.
  • Modern conser­vation techniques have now re­stored areas of open cast min­ing, especially in the Appala­chian areas and Australia.

Hill Slope Boring

  • Giant sized augers (boring in­struments) are used to dig out coal on hill slopes. These augers can reach as far as 105m below the ground.

Underground Mining

Drift or Adit Mining

  • A tunnel called drift or adit is cut into the coal bearing stratum.
  • This type of mining operation is undertaken in hilly areas with a slightly inclined or hori­zontal coal seam with a thick over burden.

Slope Mining

  • This is practised in areas with steeply tilted coal seams or where coal is below a thick overburden.
  • An inclined tunnel known as slope is constructed and a con­veyor belt or a cable car is used for bringing out coal through the tunnel.

Shaft Mining

  • This method of mining is used for reaching deep -seated seams (305m to 1525m below the surface).
  • Vertical shafts are sunk to reach the coal bed, and a net­work of galleries is dug under­ground. Lifts or box like cages are used to access the mine.
  • Often explosives are set in the coal face for loosening coal into lumps.
  • Shaft mining is the most ex­pensive of the mining meth­ods because of the overhead costs of ventillation, lighting, water supply and underground haulage.
  • The safety in the mines has to be ensured by providing proper ventilation so that the fire accidents don't occur, which would also help reducing the health hazards miners face.
  • They should be aided by better geological in­formation pertaining to the seasonal movement of the wa­ter tables in order to equip them against the danger posed by the crushing in-flow of wa­ter.
  • There should be efficient pumping stations to pump the water out of the mines.
  • The mining company must take precautions against such possibilities as gas poisoning, explosions, floods and the collapse of tunnel roofs.




  • Coal occupied a very significant role in the development of heavy industrial centres in the USA like Pittsburgh, Detroit, Chicago etc.
  • Largely, the coal-producing regions are concentrated in the eastern part of the country and comprise the states of Pennsylvania, Virginia, Kentucky and Ohio.
  • Important coalfields of this region include the Appalachian coalfield especially the regions like Pittsburgh, Alabama, Tennessee, the Allegheny plateau, and Grand Kanawha. Pennsylvania produces half the world's anthracite (from the Lehigh, Schuylkill and Susquehanna valleys) while the Appalachian field is the centre of bituminous coal.
  • In the central, western and south part of the US the coalfields are scattered as opposed to the eastern part.
  • Important collieries of the central regions are situated in Illinois. Missouri, Ouachita Mountains of Arkansas and Oklahoma.
  • In the western US the Rocky Mountain region has the largest coal reserve of the US but it is not fully exploited.
  • Important coal reserves are located in Utah, Montana, Colorado, Dakota etc. In the southern US, coal deposits alongwith the oilfields are situated mainly in Texas.
  • Interestingly all the coal mines in the US are privately owned.


  • Before the break up of the USSR in 1991, the Donetz basin or the Donbas situated near the Black Sea in Ukraine was the most important coalfield of USSR.
  • However, in the present day Russia important coalfields include the Tula coalfields near Moscow, which mainly produces lignite and the Kuzbas or Kuznetsk coalfield near the Ural Mountains.
  • In the Siberian region of Russia lie large but untapped reserves of coal, especially in the Tungus and Lena basins.
  • Other coalfields include the Pechora, Vorkuta in the northern region, Cheremkhovo in Siberia and Sakhalin islands in the eastern most part.


  • UK was the birthplace of the coal based industrial revolution occupying the leading position as the producer as well as the exporter of coal in the world in the 8th and 9'h centuries.
  • Though, unlike the U.S the coal mining in the U.K is nationalised, nevertheless coal has been the major source of energy for the ship building industry in Glasgow, cotton textile industry of Lancashire, iron and steel industry of Midland and South Wales and automobile industry at Coventry.
  • However, coal mining in U.K is being discouraged because of the high costs involved in it.
  • This is so because unlike the wider and expanded coalfields of the U.S, those of the U.K are limited in extent and have a faulted topographical formation, which escalates the mining and maintenance cost of coal


  • Europe's richest coalfield is the Ruhr-Westphalia region in the Rhine basin.
  • The second important coalfield is the Saar coalfield.
  • In addition there are Saxony coalfields, and lignite deposits at Cologne and Bavaria.
  • The Ruhr—Westphalia coal complex is the industrial base of Germany.
  • The coal and iron ore reserves located in close proximity to each other has aided the establishment of basic industries of iron and steel as well as other heavy industries.
  • The industrial towns that grew up around Ruhr coal-field are Essen, Solingen , Remscheid, Wuppertal, Cologne and Dusseldorf.
  • There are smaller coal fields at Aachen and Lignite fields at Bavaria and Cologne.
  • Apart from Germany other important producers of coal in Europe are France, Belgium and Poland.
  • During this age, about 320 million years ago trees and plants of the hot humid areas where vegetation was prolific, accumu­lated in marsh swamps and bogs.
  • Over time, layer upon layer got laid some­what like you lay layers of cheese, but­ter and sausages upon your sandwich.
  • This sedimentary process gave rise to intense heat, and compressional forces under the surface of the earth which resulted in the formation of coal.
  • You may be already aware that the mass of vegetative materials was changed into coal not only by the heat and pressure generated by sediments but also by earth movements and contortions.
  • Thus coal was born as a sedimentary rock deposit.
  • There are many types of coal which differ in their composition and content.
  • Also the heat value of any given coal deposit is governed by such factors as carbon and moisture content and the presence of volatile matter.
  • In India, coal is categorised in Gondwana and Tertiary coal.
  • Gondwana coal is that which is formed during the carboniferous age, and is found primarily in the river valleys of Damodar, Son, Godavari and Wardha Tertiary deposits indicate coal formed more recently in the geologic age.
  • These deposits have mainly resulted due to the earth movements that accompanied Himalayan orogeny.
  • Tertiary coal is found in the states of Assam, Nagaland, Meghalaya and Jammu and Kashmir.


It is the first stage in the formation of coal and contains high amount of moisture but very low carbon content. It looks like charcoal and is also known as bog coal. Because of the low carbon content (i.e. 25-30%), peat has a low heat value, and therefore it is not gener­ally used as industrial fuel. You will be surprised to note that its calorific value is only 75 therms per tonne as compared to bituminous which is approximately 275 therms.


It is also called brown coal as it is usually brownish in colour. It has a high moisture content emit­ting a lot of vapour and smoke when burned. It is soft in disposition, has little heat value (because its carbon con­tent is only 35 to 40% and the calorific value is even less than 24MJ/kg) and easily cracks and crumbles when exposed to air. It is generally used only as a supplement to bituminous or anthracite coal


It is the most widely used coal type in the world. Its carbon content is very high, about 80 %, giving it a black appearance and a hard texture. Its high carbon content also renders a high heat value of 26.7 megajoules/kilogram. In addition, low emission of smoke and minimal deposits makes bituminous coal soar the popularity charts. Bituminous coal may also serve as fu­els in steamships, industry, transport and households. It is this coal when heated in a special oven produces coke, which is an essential raw material for the iron and steel industry.


It is the hardest and the best type of coal with a shiny black appearance. And why not, with a car­bon content above 90-95 % and little impurities it is bound to look good. With such a lot of carbon in the coal it is obvious that its heating capacity will be high, it will burn for a longer time and leave little residue and smoke. But then why is it that anthracite, though the best, is not particularly popular„ Firstly, the deposits of such a mag­nificent type are scarce. Secondly, its texture is the hard­est and mining anthracite is not only difficult but expen­sive too. Thirdly anthracite has a high ignition tempera­ture, and takes a long time to kindle. Thus, anthracite constitutes only about 5 % of the total coal production of the world and, is not commonly used in industry and transport. However, it may be used for domestic heating, bakeries and for boilers.

  • Although coal mining in India started in 1774 at Raniganj in West Bengal, nevertheless progress in coal- mining began only after the independence with the establishment of key sectors and basic industries.
  • Coal mining in India is a government undertaking under the organisation Coal India Limited (CIL).
  • Bituminous coal deposits in India are largely concentrated in the river valleys of Damodar, Son, Mahanadi and Godavari (collectively called the lower Gondwana region).
  • Leading coal producing states include Jharkhand (earlier south Bihar), West Bengal, Madhya Pradesh, Orissa, Andhra Pradesh and to some extent Maharashtra as well.
  • Other states such as Assam, Meghalaya, Arunachal Pradesh, Nagaland and Jammu and Kashmir (called the Tertiary region) also produce a little amount of lignite.
  • India is the second largest producer of coal in the world. Since indepen­dence, India has made astounding progress in coal production.
  • This steady increase is also reflected in the increased industrialisation of the country.

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