Mining Methods

Opencast mining for coal as we know it today started in 1942 as a wartime expedient. To boost vitally needed coal output, surface mining became the responsibility of the Mines Department of the Board of Trade and was carried on by the Ministry of Works until 1945, then by the Ministry of Fuel and Power.

In 1952 the National Coal Board, now British Coal Corporation, was given responsibility for opencast coal production and the Opencast Executive was established.

In the early years opencast operations were limited by the size of the excavating plant then available. Maximum depths were only about 10 metres and ratios of strata above the seams — overburden — to coal were restricted to about 5 to 1. Over the years, however, there were substantial increases in the size of plant and by 1948 the maximum depth of excavation had increased to 30 metres.

http://www.dmm.org.uk/history/ocast00.htm

Room & pillar, pillar & stall, and board & pillar are the name variations of partial extraction mining. A method of mining in which roadways are driven into the coal seam, usually at right angles to each so that the seam is divided into a large number of pillars.

This system is preferred for thick seams where surface subsidence is to be avoided and for the exploitation of shallow deposits due to the high percentage extraction obtained; the pillars may be extracted as a separate operation known as stopping.

http://www.energy.eu/dictionary/data/1583.html