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Room and pillar or pillar and stall is a variant of breast stoping. It is a mining system in which the mined material is extracted across a horizontal plane, creating horizontal arrays of rooms and pillars.
Once room and pillar mines have been developed to a stopping point limited by geology, ventilation, or economics, a supplementary version of room and pillar mining, termed second mining or retreat mining, is commonly started. Miners remove the coal in the pillars, thereby recovering as much coal from the coal seam as possible.
General layout of a room-and-pillar mine. Retreat mining is the removal of pillars in the underground mining technique known as room and pillar mining.. In the first phase of room and pillar mining, tunnels are advanced into the coal or ore body in a rectangular pattern resembling city streets.
Longwall mining is a form of underground coal mining where a long wall of coal is mined in a single slice (typically 0.6–6.0 m (2 ft 0 in – 19 ft 8 in) thick). The section of rock that is being mined, known as the longwall panel, is typically 3–4 km (1.9–2.5 mi) long, but can be up to 7.5 km (4.7 mi) long and 250–400 m (820–1,310 ft) wide.
Advanced Placement (AP) United States Government and Politics (often shortened to AP Gov or AP GoPo and sometimes referred to as AP American Government or simply AP Government) is a college-level course and examination offered to high school students through the College Board's Advanced Placement Program.
WASHINGTON − The federal government released new guidelines regarding "sex-based definitions," Health and Human Services Secretary Robert F. Kennedy Jr. announced Wednesday. “This ...
In politics of the United States, "fourth branch of government" is an unofficial term referring to groups or institutions perceived variously as influencing or acting in the stead of the three branches of the US federal government defined in the Constitution of the United States (legislative, executive and judicial). [1]
(The Center Square) – Renaming and redirecting chain of command is proposed in the North Carolina General Assembly for the agency the state’s 11 million residents access for driver’s ...