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1、Un dergr ound MiningMost present-day mining in Europe occurs under 2000 to 4000 ft of overburden, as more easily mined coal deposits have been depleted. At this depth most mines are developed as shaft mines. All pers onn el, material, and coal have to be hoisted trough these shaft. Con sideri ng the
2、 two factors of hoist ing capacity and required len gth of shaft, a con siderable inv estme nt is n ecessary to reach the coal-beari ng strata. The requires huge inv estme nts. Openings at this depth have to be equipped with costly supports, and periodicrework ingand repair isn ecessary.Mines not on
3、ly exte nd horiz on tally but also vertically through the development of new levels. The life of the mines is thus exte nd con siderably, and surface in stallati ons can be amortize over a Ion ger period.The more limited reserves have forced companies into mining less favorable deposits, andEuropean
4、 government require thatall possible deposits be mined to con serve the n ati on s en ergy resources. These factor and the large perce ntage of in cli ned seams and faults make mining very difficult and costly. The populationdensity and the heavy surface buildup causeadditi onalexpe nse in the form
5、of payme nts for subside needamage to surface structures.Therefore,backfilli ng isfreque ntly practiced to reduce subside nee. The close spac ing of faults often severely limits the size of a mining section, forcing freque nt moves and excessive developme nt work.The thickness of the overburden resu
6、lts in very high ground pressure. This would require extremely large pillars if the room and pillar method was applied. Additi on ally, support is required for any opening,adding prohibitive costs to amultiple-entry room and pillar operation.As a result, single-entry Iongwall operations requiring th
7、e minimumnumber of entries and allowing maximunrecovery of resources is the mi ning method almost exclusively practiced.Shaft mines dominate the European coal mining industry. Shafts 20 to 30 ft in diameter, with circular cross section, lined with masonry, concrete, or steel are the dominant meansof
8、 gaining access to the coal-beari ng strata. They are ofte n extended beyond the last mining level to provide for future expansion. As in the Unite States, shafts are developed by drilling,blasting,and excavatingor by large-diametershaft-boring equipment. Shaft boring is more frequently used, partic
9、ularly on the smaller and shorter subshaft, which connect the differe nt levels but do not exte nd to the surface.Haulage in the shaft is usually accomplished by hoist ing of the filled mine cars on multistage cages or by skips. Pumping of coal slurry is also done in special cases.The complex system
10、 of forces and the resultingrockmecha ni cal problems developed by miningactivities atdiffere nt levels result insig nifica nt differe nces betwee nEuropea n and US un dergro und developme nt. The rock mecha ni cal interactionof the extraction operations at the various levelsrequire that all deposit
11、s be mined as completely as possible. Pillars left after mining create zones of extreme and ofte n unman ageable ground con trol problem, as well as a high probability of roof boun ce.Since the number of entries is kept to a minimum because of cost, no bleeder systems are provided. If retreat mining
12、 is practiced, on ly two en tries are adva need in to a new mi ning area.Pan els are laid out as large as possible. The large-pa nel layout is used asano ther mea ns of reduc ingthe nu mber ofen tries. Min ded- out pan els are sealed off topreve ntspontan eous combusti on through the removal of oxyg
13、e n.The main levels, with extensive entry systems, are used for coal, supply, and pers onnel haulage and for ven tilati on. They are often spaced with little regard to the positionof the coalseams, because the deposits are reached selectively through other means. In the past, 165-or330-ftintervalswe
14、re selectedwhilein creas inggro und pressures and developme ntandmaintenance in crease substa ntially,requiri ng large volumes ofair for cooli ng. As a result, entry cross secti ons at these levels have to be in crease.Fig.9.1Germa n multilevel, multiseam shaft-type coalmine.Un dergro und facilities
15、:(1) main shaft with skip hoisting;(2) exhaust ven tilati on shaft with multistage cage;(3) third-level statio n;(4) blind shaft with cylindrical storage bin;(5) bli nd shaft with car-hoist ing facilities;(6) main entry;(7) main entry;(8) secti on or panel en try;(9) road headi ng machi ne(10) Ion g
16、wall secti on with plow;(11) Iongwall section with shearer;(12) Ion gwall secti on in a steeply pitchi ng seam mined manu ally with air picks;(13) Ion gwall secti on in steeply pitchi ng seam with plow;(14) min ded-out gob area;(15) ven tilati on lock;(16) belt conv eyor as main haulage;(17) main car haulage;(18) storage bin and skip-loading facilities;(19) supply
