headings can be used to service the retreat face on both sides of intervening pillars, due to account should be taken of the depth of cover to plan adequate pillars. It is important to prevent the first retreat face from influencing the stability of the crosscut [37] junctions [38]. Such junctions should be kept in minimum to avoid support problems at face-ends when the second face retreats. This can be major problems at depths greater than 300m.
E. A retreat system with multiple entries [39]: this system is the typical layout for longwall mining in the U.S.A. This system separates entry development from coalface operation and represents an integration of both pillar and longwall mining concepts. The development entries usually consist of triple roadways and continuous mines with room-and-pillar mining technology are used to develop the entries. The longwall is mined in retreat with a shearer type of machine and the roadway towards the gob area is allowed to collapse with the gob.
The ventilation system can become complex due to the existence of many entries and the need to provide positive ventilation [40] to individual working.
The least width of the chain pillars [41] has to be determined to protect the roadways of the retreating face against excessive closure effects from the abutment pressure zone. This method also requires good roof condition to avoid roof control problems at crosscut intersections during longwall retreating.
NOTES TO THE TEXT
[1] longwall mining system：长壁式开采采煤系统
[2] inclined coal seams：倾斜煤层
[3] longwall advance mining： 长壁前进式开采
[4] longwall retreat mining：长壁后退式开采
[5] strata pressure：岩层压力
[6]roadway：平巷
[7] panel：区段
[8] capital outlay：基本建设费用
[9] geological conditions：地质条件
[10] single entry：单巷
[11] abutment pressure：支承压力
[12] shearer：（滚筒式）采煤机
[13] gob：采空区
[14] arches set：拱形支架
[15] pack：（巷旁）充填带
[16] Pump Pack：泵站
[17] roadway maintenance：平巷维护
[18] double entries：双巷
[19] rib pillars：长方形煤柱
[20] deformation：变形
[21] gob closure ：采空区顶底板移近
[22] offset：补偿，抵消
[23] block-out：划分出
[24] high stress：高应力
[25] stability：稳定性
[26] reinforcement：加强，加固
[27] down-dip：沿倾斜向下
[28] strike：走向
[29] integrated advance and retreat system：前进与后退式相结合的采煤系统
[30] face-end：工作面端头
[31] ‘Z’ system：“Z”形采煤系统
[32] maingate：区段运输平巷，下顺槽
[33] tailgate：区段回风平巷，上顺槽
[34] bleeder roadway：通风平巷（用于水平煤层房柱式开采）
[35] methane emissions：沼气泄出
[36] headings：平巷掘进头
[37] crosscut：石门，短联络横巷
[38] junctions： 巷道交叉点
[39] multiple entries：多巷
[40] positive ventilation：正压（压入式）
