1、翻译部分英文原文Introduction of Longwall MiningExecutive SummaryLongwall mining is one of the principal underground mining methods in the United States. Its importance as a coal production technique has grown steadily since the introduction of modern longwall technology into this country in the 1950s and 19
2、60s. In the past decade longwall production and productivity grew rapidly, as a result of significant improvements in longwall equipment and operating practices. By 1993, longwall mining accounted for 40 percent of the Nations underground coal productionup from 27 percent in 1983. Labor productivity
3、 at longwall mines more than doubled between 1983 and 1993. Productivity is now higher for longwall mining than for other underground production methods, and productivity is expected to keep g rowing as new technological advances are introduced.Longwall mining is one of two basic methods of under gr
4、ound coal mining. The other method is room-and-pillar mining, historically the traditional method used in the United States. In room-and-pillar mining, “rooms” are excavated, and pillars of coal are left in place between the rooms to support the mine roof. In contrast, longwall mining involves the e
5、ssentially complete extraction of the coal contained in a large rectangular block or “panel” of coal, and the roof in the mined-out area is allowed to collapse.The sequence of operations in longwall mining is basi- cally simple. The rectangular longwall panel, averaging nearly 800 feet wide, 7,000 f
6、eet long, and 7 feet high, is “blocked out” by excavating passageways around its perimeter. Room-and-pillar mining is used to block out the panel. Excavation of the coal in the panel is an almost continuous operation. Working under the steel canopies of hydraulic, movable roof supports, a coal cutti
7、ng machine runs back and forth along the 800-foot face, taking a cut ranging anywhere from a few inches to 3-1/2 feet deep during each pass. The cut coal spills into an armored chain conveyor running along the entire length of the face. This face conveyor dumps the coal onto belt conveyors for trans
8、port out of the mine. As the cutting machine passes each roof support, the support is moved closer to the newly cut face to prop up the exposed roof. The roof is allowed to collapse behind the supports as they are advanced towards the face. Mining continues in this manner until the entire panel of c
9、oal is removed.Because longwall mining is essentially a continuous, highly mechanized operation, longwall productivity is potentially higher than room-and-pillar productivity. Longwall mining also offers improved safety through better roof control, more predictable surface subsidence, and better opp
10、ortunity for full automation. On the other hand, capital costs for longwall equipment are much higher than for room-and-pillar equipment, productivity during development (“blocking out”) of the longwall panels is typically low, and large amounts of dust and methane are generated during the mining pr
11、ocess.IntroductionLongwall mining is one of the principal underground mining methods in the United States. In 1993,longwall mines accounted for 40 percent of the Nations under-ground coal outputcompared with 27 percent in 1983. Although basic longwall mining techniques were de- veloped in England in
12、 the 17th century, there was little interest in longwall mining in the United States until the 1950s, when new German technology was introduced. As the technology was developed further in the United States, longwall production grew steadily. By 1993, 85 longwall units were operating in 12 States. La
13、bor productivity at longwall mines more than doubled between 1983 and 1993. Productivity is now higher for longwall mining than for other underground production methods, and productivity is expected to keep growing as new technological improvements are introduced. The purposes of this report are to
14、describe the longwall mining process, analyze the most important changes in longwall mining over the past decade, and discuss factors that will shape the future of longwall mining.The History of Longwall MiningLongwall mining is not a new approach to coal mining.In fact, the basic principles of long
15、wall mining have beentraced back to the latter part of the 17th century to Shropshire and other counties in England, where it was described as a “totally different method of mining” called the “Shropshire method.” Many modifications in the original methods have occurred, but all longwall mining has
16、involved extracting coal from a long wall or face. The area from which the coal was extracted, the “gob” (from a Celtic word for cave or hollow), was partly or wholly filled with stone and refuse, upon which the overlying strata settled.Until the early 1900s, coal mining in England was mostly by the “bord and pillar” method (equivalent to “room-and-pillar”). The “bords,” or passages, were areas 12 to 20 feet wide from which the coal was extracted; th
