Shield Mining

a method of mineral extraction in which a mineral is broken up by mechanized means or by drilling and blasting under a special roof shield. The method was proposed in the USSR in 1935 by N. A. Chinakal and others.

When mechanized breaking is employed, shield units are used. A shield unit consists of hydraulic barrier-load-bearing supports (seePOWERED SUPPORT) and a Loebbe plow, which excavates the mineral and conveys it under the shield to a side chute. Shield units are used in beds with a thickness of 0.7–2.2 m and an angle of dip of more than 45°. They provide for the complete mechanization of operations at the working face.

When coal is broken up by drilling and blasting, flat sectional shields, which are called Chinakal shields in the USSR, are used. Such shields consist of from three to five sections; less often, they are arched and not sectional. A section is a metal frame in which timber flooring is installed in several rows. The flooring is rigidly fastened to the frame, but the sections are flexibly connected. Sectional shields are used in the working of beds with a thickness of 3.6–11 m and an angle of dip of more than 55°. The bed in an excavation area is worked in strips along the dip.

When drilling and blasting is used, a mineral is excavated in two stages. In the first stage, blastholes are drilled and explosives are detonated first in the gallery and then in the pillars that support the shield. In the second stage, the loosened mineral is thrown into the mining excavations driven under the sections and is conveyed to the haulage level, and the shield is advanced 0.8–1.2 m. The cycle of operations is then repeated.

Shield mining is most widely used in the steeply dipping coal seams of the Kuznetsk Coal Basin.