许厂煤矿1.8 Mta新井设计含5张CAD图.zip
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“三下”压煤开采技术研究摘要:建筑物下、铁路下、水体下开采,简称“三下”开采。据目前不完全统计,我国国有骨干大中型矿井“三下”压煤量达到140亿吨以上,其中建筑物下压煤占整个“三下”压煤量的60%以上,水体下(包括承压废岩水上)压煤占28%左右,铁路下压煤占12%左右,然而,到目前为止,我国仅从“三下”采出的煤炭约有10亿吨,只占整个“三个”压煤量的7%左右。关键词:“三下”开采;理论;措施 0引言据目前不完全统计,我国国有骨干大中型矿井“三下”压煤量达到140亿吨以上,其中建筑物下压煤占整个“三下”压煤量的60%以上,水体下(包括承压废岩水上)压煤占28%左右,铁路下压煤占12%左右,然而,到目前为止,我国仅从“三下”采出的煤炭约有10亿吨,只占整个“三个”压煤量的7%左右。1国内外现状1.1建筑物下采煤波兰,从1950年起开始进行建筑物下采煤试验,到1980年,已从各种煤柱中采出近7000万t左右,占产量的40一42。英国在建筑物下开采只对井筒和绞车房留保安煤柱,其它一律不留保安煤柱进行开采。德国对城市和建筑物下采煤研究最早,从1902年就开始用水沙充填法回采重要建筑物下的保安煤柱。例如埃森采了九个煤层总厚达10.2m。1.2铁路下采煤铁路下开采系指铁路干线与支线下所压煤层的开采,矿区专用线下开采已不存在问题,故不包括在内。过去对铁路的保护也是采用留设矿柱的方法,目前对铁路矿柱的开采已取得了足够的经验。如波兰在卡托维茨通往沃波雷省的干线和具托姆车站下进行了开采、采厚达20m,车站普遍下沉了3m,最多达3.7m。我国矿区专用线下开采,在技术上已完全过关,所以铁路下开采不包括专用线下开采;支线下开采效果良好,如焦李、三万、薛枣、娄邓等;干线下开采的不多。在鸡西麻山、滴道两矿的林口密山干线下开采获得成功、本溪局在沈阳丹东的干线下试采。还有枣庄局在邹坞车站下,阜新局在露天剥离站下。开滦及平顶山、涟邵在铁路桥下,南桐局在二万线的板塘隧道下开采都取得成功。1.3水体下采煤水体下开采的实质是如何确定防水和防砂矿柱的高度,此上限到地面的垂高,就是安全开采深度。水体下开采主要是防止覆水和泥砂溃人井下,有时还要保护地面水体,如水库、堤坝等。水体下开采通常用疏干、排放、隔离等措施,使资源尽量采出,还要减少排水费用。前苏联已在一些较大河流下来出了干百万吨的煤炭;日本、英国、加拿大和智利等国家海下开采经验丰富。我国在淮河下、微山湖下、资江河漫滩下来煤也取得了不少的经验。2.地表移动变形的基本规律2.1岩体采动引起的围岩及地表变化根据岩层移动的特征和破坏形态,如下面一组图所示。图2-1岩体移动分带图2-2开采水平矿层充分采动时的地表移动盆地示意图图2-3开采倾斜矿层时的地表移动盆地示意图图2-4岩层与地表移动中常用的几种角2.2地表移动与变形参数的分类及计算图2-5主断面内地表点移动示意图2.2.1变形参数(1)倾斜:地表相邻两点的下沉由于不均匀,便在地表产生连点间的相对位移,出现倾斜变形。通常用T表示,单位为mm/m,(2)曲率:如果地表相邻两点的倾斜也不均匀,则地表将出现弯曲。因此,单位长度内的倾斜变化就为曲率,用K表示,单位用/m或mm/,。(3)水平变形:它是由于相邻两点的水平移动不均匀而产生的。在外缘区产生拉伸变形,在内边缘区产生压缩变形。通常用表示,单位为mm/m。图2-6倾斜矿层非充分采动时主断面内地表移动和变形分布规律移动变形曲线间的函数关系下沉曲线 =倾斜曲线 =曲率曲线 =图2-7急倾斜矿层非充分采动时主断面内地表移动和变形规律水平移动曲线 =B水平变形曲线 =B2.3主断面地表移动变形的计算2.3.1概述单元开采图图1-3-1指开采的范围无限小的单位开采,其体积为111的无限小单元。在地下采出一个单元立方体(111)(图2-8)后,在Z水平形成一个单元下沉盆地,其面积为 =,这一下沉事件的发生,等于以下两个事件同时发生:在剖面B-B上x处的一段岩石条内有下沉发生,同时在D-D剖面上y处的一段岩石条。内有下沉发生。因此,发生下沉这件事的概率即为发生次二事件的概率之积:=式中平方是由对称性所致。令单元下沉为,则在走向剖面上: =在倾斜剖面上: =在空间条件下,开采面积与采高皆为一个微小单元时: =图2-8单元开采引起的岩层下沉的概率2.4水平矿层半无限开采地表移动与变形计算2.4.1 移动变形曲线函数式(1)下沉曲线函数如图2-9,采深为H,采厚为m,坐标原点通过开采边界,设在s距离处采出宽度的一段矿层,在其上方水平形成单元下沉盆地其表达式为: dW=qm(x-s) dW=qm当矿层自s=0采到s=时,地表(z=H)稳定后的下沉盆地表达式为: =qm则 =这就是随机介质理论法下沉曲线的积分表达式,是克诺泰1937年首先提出的。图2-9下沉盆地剖面方程(2)倾斜曲线 = (3-2)倾斜曲线最大值:=其中 h=,r叫主要影响半径为了弄清h与r间的关系,如图1-4-2所示:在图中,做下沉曲线拐点处的切线,与及=的水平线分别交于1点和2点,则得到这两点的水平距离,以r表示。此切线的斜率就是相应曲线的最大斜率(当斜率角时就不相切了)。 tg=, 即=因此: h=通过对矿区实测资料的分析,在地表移动盆地的边缘区,在拐点两侧各一个r的范围内,地表变形值较大,在外边缘区一个r的位置下沉值为0.0063,在内边缘区的一个r的位置,下沉值为0.9937,所以在此区域内是对地面建筑破坏最严重的,因此把r叫做主要影响半径,或主要影响范围。主要影响范围也可以由角圈定。如图2-10所示,可知: th=角叫做主要影响范围角,简称主要影响角。r及均由岩层性质决定。图2-10参数h与主要影响半径r的含义将h=带入(3-2)式: = (3-3)当x=0时,=,带入(3-3)式: = (3-4)(3)曲率曲线倾斜的变化便产生曲率,使地面弯曲,故斜率是倾斜的导数: = (3-5)求极值:令=0,得x=0.4r,带入(3-5)式: =1.52=1.52(4)水平移动曲线水平移动曲线的分布与倾斜曲线相似,二者为线性关系。 =B=B令b=,b也叫做水平移动系数,代入上式: =b (3-6)求极值:令=0,x=0,则=b,带入(3-6)式: =(5)水平变形曲线 =-求极大值:令=0,得x=0.4r =1.52b表2-1列出了移动变形的基本表达式,以及各自的最大值和最大值的位置。表2-12.4.2实用计算表将移动变形曲线表达式进行变换,化为无因次的量: = 上式的左边表示各分布值相当于最大值的量,叫做分布函数。每个式中都有,都是的函数,这样,取不同的值,即可得到相应分布系数值。因次,把作为横坐标,按百分之一取值,计算出相应的分布函数、值,作为纵坐标,可以做出地表移动和变形的无因次曲线(如图2-11) 图2-11移动及变形分布函数3.“三下”采煤技术的发展3.1建筑物下采煤及地表保护措施 (1)充填法(2)部分开采法部分开采法包括两个方面的内容:一是条带开采法,即在开采范围内开采一条,保留一条,用保留条带煤柱支撑顶板,以达到减少地表下沉的目的。3.1.1留宽与采宽的计算一、采宽b的确定1、在保证地表不出现波浪形的条件下,以水平变形=2mm的临界值,对建筑物不产生破坏的前提下,主要影响半径与采高之比r/m应大于20,用诺模图(如图3-1,图3-2)来确定采宽b。图中的阴影部分为可选取范围。2、根据经验。采宽按来选取,如采宽较大,应在顶板初次周期来压之前结束工作面。采宽选定后,再计算留宽a。图3-1确定采宽b的诺模图3、要考虑顶板初次来压和周期来压。当采宽不太大时,b应不超过顶板的初次来压步距,工作面不受初次来压影响。b如较大,则应不大于初次来压步距与周期来压步距之和以保证在周期来压之前结束工作面,应避免刚发生过周期来压就结束工作面。二、留宽a的确定。确定留宽a的原则应能使矿柱承受的载荷比矿柱实际承受的载荷要大,这时矿柱的安全系数K1,表明矿柱是稳定的。在一般情况下,为了提高回采率,安全系数K取1,即矿柱能承受的载荷等于实际承受的载荷。另外,矿柱的承载能力与矿柱的形状有关,矿柱的形状一般有方形、矩形和长条形。下面分别列出矿柱留宽a0.1mH时以上三种形状矿柱能承受的极限载荷值的公式:图3-2确定采宽b的诺模图 (r/b=1.5;r/b=2.0)方矿柱: (t)矩形矿柱: (t)长矿柱: (t)计算矿柱实际承受的载荷值公式:方矿柱: (t)矩形矿柱: (t)长矿柱: (t/m)式中 、分别为方形、矩形、长条形矿柱能承受的极限载荷; 、 、分别是方形、矩形、长条形矿柱实际承受的载荷; d保留条带矿柱的长度; 、分别为沿矿层走向方向和倾斜方向矿柱之间的采出值。 现以K=1为条件,推导出计算保留条带矿柱留宽的公式,在设计时,大部分按宽矿柱中的长矿柱进行计算:长矿柱的留宽: 为了长壁工作面搬家运设备材料的方便,在保留矿柱的中部开一联络巷,此时应按矩形矿柱进行计算。矩形矿柱的留宽: 采出率验算: 回收率s可依开采条件确定。设矿层倾角水平,埋深为H(cm),开采之前,作用于矿层的垂直应力等于: =rH式中 r矿层覆岩平均容重(kg/)。当条带开采后,矿柱上所承受的垂直平均应力将增加为: =rH (61)而必须小于矿柱的许可抗压强度,矿柱才能不被压坏,即: 我们取等号,并带入(61)式中,得: S=1-这样,只要知道,就可以算出s了。我们令矿柱极限抗压强度为,强度备用系数为n,则: =式中 矿样单向抗压强度; n强度备用系数,对于充填条带法n=1.5,对于冒落条带法n=2.0。由此,回采率s可表示为: S=1- (62)由上式可以看出,矿层深度小,强度大,覆岩平均容重小,用充填条带法开采时,回采率就高。单向受力状态下留宽a的计算用下式: a=式中的S由(62)式求得即可。进而可以计算出条带开采时的极限开采深度: 3.1.2消除或减少开采影响的叠加当几个煤层(或厚煤层几个分层)或同一煤层的几个部分同时开采时,如果采区边界布置不合理,或者采面推进的时间、方向不适当,就会造成开采影响的叠加,从而使地表移动变形值增加,如图3-1-3所示。图3-3在同时开采两个煤层(或分层)时,如图2-3-1(a),开采影响的叠加可能是推进着的工作面上方地表移动与变形的叠加(即采面同时由左向右推进时的情形),也可能是开采边界(或停止推进的工作面)上方地表移动与变形的叠加。图2-3-2(b)表示同一煤层两个部分同时开采时地表移动变形的叠加。在这种情况下,不管1,2两部分采面如何推进(采煤面相对、相背或相平行),在煤柱上方地表的移动和变形都要经受开采过程中的叠加,以及采动以后煤柱做为两个开采边界的地表移动变形叠加。这些都说明地表移动变形的叠加与采面推进的时间和开采边界的位置有关,即与时间和空间因素有关。为了减少或消除开采影响的叠加,可以采用以下措施:(1)顺序开采就是要一层一层或一个分层一个分层地进行开采,并要求两层或两个分层的开采间隔时间要足够长。(2)合理布置各煤层或分层开采边界的位置地下开采对地表的有害影响,主要在开采边界的两侧。为了减小或消除开采边界及附近地表移动变形值的叠加,可将各个煤层的开采边界彼此错开一定的距离,让它们不重叠,一个垂直剖面内(如图6-2)。(3)干净回采(4)正确安排工作面推进方向开采建筑物和构筑物保护煤柱时,一般采用由煤柱一侧向另一侧推进的方法,即采用单翼开采方法。3.1.4协调开采协调开采就是数个煤层和分层同时进行开采,使所产生的地表拉伸变形和压缩变形互相抵消,以达到减少开采对地表的影响。协调开采的主要方法有以下几种:(1)数个煤层协调开采两个或多个煤层同时开采时,如果将这些煤层的工作面互相错开一定距离,使开采一个煤层所产生的地表压缩变形区准确地位于开采另一个煤层开采所产生的地表拉伸变形区内。这样,地表的变形值就可以抵消一部分,从而减少对建筑物和构筑物的有害影响。(2)数个煤层分层协调开采若将厚煤层的数个分层同时开采,各分层工作面之间错开一定距离,同样可以使地表变形抵消一部分。图3-4两个分层工作面错开的距离由下式计算:式中:r主要影响半径; H开采深度。3.1.5消除开采边界的影响开采对地表影响最严重的地区是开采边界两侧附近上方地表移动盆地的边缘区。消除开采边界影响的主要措施是使受采动的建筑物下采煤范围不出现开采边界和不使工作面长期停顿。主要措施有:(1)长工作面开采当用一个工作面开采时,要确定合理的工作面长度,应尽可能使被保护的建筑物位于开采后的地表均匀下沉区。(2)连续开采即一个工作面接着一个工作面,一个采区接着一个采区,一个小阶段(或水平)接着一个小阶段(或水平)开采下去,中间不能间隔时间过长。(3)联合开采如果保护煤柱范围内是分属于几个矿进行开采,则必须由几个矿联合进行协调开采,以避免产生开采边界。3.1.6提高回采速度在已经稳定的地表移动盆地区,最大变形值出现在盆地边缘区,盆地中间区的地表变形值较小,但是在开采过程中地表点都要经过拉伸、压缩到稳定的过程,其动态变形值的大小与回采速度(工作面的推进速度)有密切的关系。工作面的推进速度愈大,动态变形值愈小。但提高工作面推进速度会造成地表下沉速度和变形速度增加,而建筑物较易适应地表的缓慢变形,如变形速度很快往往也会导致建筑物的损坏。因此,拟提高开采速度时,应综合考虑各方面的因素。3.2水体下采煤3.2.1覆岩破坏规律一、影响覆岩破坏规律的因素在近水体采矿时覆岩破坏规律是指导水裂缝带的分布形态和最大高度。影响覆岩破坏 规律的因素如下:1、覆岩力学性质及结构的影响 2、采矿方法和顶板管理方法的影响 采矿方法和顶板管理方法对覆岩破坏的影响主要表现在开采空间大小、岩体冒落、断裂的充分程度以及垮落岩体的运动形式。3、煤层倾角的影响 煤层倾角对覆岩破坏高度的影响主要表现在破坏形态上的不同。开采水平及缓倾斜矿层(=035)时,垮落岩体不产生再次移动,就地堆积、压实,但由于工作面边界存在悬顶现象,使冒落带、导水裂缝带呈中间低两端高的马鞍形 (见图3-5) 。开采倾斜矿层 ( =3654)时,由于垮落岩体在自重的作用下向采空区下边界滑动,使下边界岩体垮落不充分,上边界岩体垮落超限,从而在倾斜方向上,使冒落带、导水裂缝带的形态呈抛物线型分布。开采急倾斜矿层(=5590)时,上边界覆岩的破坏高度更高,下边界覆岩的破坏高度更低,破坏范围由抛物线型逐渐变为椭圆形(见图3-6)。 图3-5倾斜矿层开采覆岩破坏形态 图3-6急倾斜矿层开采覆岩破坏形态 4、开采厚度和采空区面积的影响 5、时间的影响 6、重复采动的影响 由于初次开采使岩体产生破裂,岩体的性质发生变化,重复采动时,覆岩破裂的高度与累积开采厚度不成正比例关系,而是逐次重复采动时破坏高度增长率分别为1/6、1/12、1/20、 1/30、。二、覆岩破坏高度计算1、冒落带高度的计算: 冒落带高度主要与采动破裂岩体的碎胀性、覆岩的移动量以及采动次数有关。(1)开采单一矿层时,冒落带高度(Height of Caved Zone)计算 式中,冒落带的高度,m;M矿层开采厚度,m;W冒落工程中顶板的下沉值,m;K冒落岩石的碎胀系数,一般为1.101.40;矿层倾角。(2)厚矿层分层开采冒落带最大高度为:坚硬岩层(=4080Mpa) : 中硬岩层(=2040Mpa) : 软弱岩层(=1020Mpa) : 极软弱岩层(10Mpa) : 式中,M矿层累积厚度。2、导水裂缝带高度计算(=054)导水裂缝带高度(Height of( Leaking WaterFractured Zone)计算具有两组公式,具体为:(1)经验公式一:坚硬岩层:中硬岩层:软弱岩层:极软弱岩层:(2)经验公式二坚硬岩层: 中硬岩层:软弱岩层:以上经验公式适用范围为:单层采厚13m,累计采厚小于 15m。3、开采急倾斜矿层(=5590 )时,冒落带和导水裂缝带高度计算(1)导水裂缝带高度计算坚硬岩层:中硬、软弱岩层:式中,h回采阶段垂高,m;M矿层的法向厚度,m。(2)冒落带高度计算坚硬岩层:=(0.40.5)中硬、软弱岩层:=(0.40.5)式中,H 导为对应岩性的导水裂缝带高度。 4、煤层群开采时 Hm 和 Hli 的计算在近距矿层开采时,其冒落带、导水裂缝带高度的计算较为复杂,需要考虑上、下矿层开采的相互影响,即 图3-7近距矿层开采导水裂缝带和冒落带高度计算(1)上、下两矿层的垂距h 大于回采下层矿层引起的冒落带最大高度时,下层冒落带对上层开采的影响很小,可按上下矿层开采分别各自的导水裂缝带高度,取其中标高最高者作为两矿层的导水裂缝带高度。冒落带高度取上层矿层的冒落带高度(图3-5a)。(2)下层矿层的冒落带接触到或完全进入上层矿层时,上层矿层的导水裂缝带高度按本层的厚度计算,下层矿层的导水裂缝带最大高度则采用上、下矿层的综合开采厚度计算,取其中标高最大者作为两层矿层的导水裂缝带最大高度(图3-6b) 。上下两矿层的综合厚度按下式计算: 式中:、矿层的厚度,m;矿层间的间距,m;下层矿层的冒高采厚比。(3)层间距很小时,综合开采厚度取两层煤厚度之和。3.2.2水体下采煤的技术措施水体下采矿的安全技术措施有:留设安全煤岩柱、处理水体和采取安全措施。有时单纯采用一种方法不能解决问题,而必须多种方法联合使用。一、留设安全煤岩柱根据保护目的不同,安全煤岩柱可分为:防水安全煤岩柱、防砂安全煤岩柱和防塌安全煤岩柱。1、防水安全煤岩柱 防水安全煤岩柱的高度等于预计的导水裂缝带最大高度加上适当的保护层厚度。如果上覆岩层无松散层覆盖或采深较小,在留设防水安全煤岩柱时还应考虑地表裂缝的深度,即: 式中,地表裂缝的深度,根据经验确定。如果松散层为强或中等含水层,且直接与基岩接触,而基岩风化带也含水,在留设防水安全煤岩柱时应考虑基岩风化带的深度,则有 式中,基岩风化带厚度,m,根据勘探资料确定。2防砂安全煤岩柱其作用是防止冒落带进入或接近松散层,确保泥砂不溃入井下,但可允许一部分导水裂缝带进入松散层中的弱含水层。矿井的涌水量可能会增加,但不会发生溃水、溃砂事故。防砂安全煤岩柱等于冒落带高度加上保护层厚度 ,即 式中,冒落带高度,按本节前述公式计算。 在开采急倾斜矿层时,一般只留设防水安全煤岩柱。只有在十分有利的条件下,才留设防砂安全煤岩柱,并且在留设时一定要考虑矿层本身的抽冒及重复采动的影响。 3、防塌安全煤岩柱在松散粘土层和已经疏干的松散含水层底界面与矿层开采上限之间为防止泥砂溃入采 空区而保留的矿层和岩层块段称为防塌安全煤岩柱。防塌安全煤岩柱也称煤皮煤柱, 留设防塌安全煤岩柱时是允许导水裂缝带和冒落带波及松散弱含水层底部,矿井的涌水量会增大。 防塌安全煤岩柱的垂高接近或等于冒落带高度(图3-6) ,即二、处理水体 处理水体是水体下采矿的一项有效而又不得已的措施。主要包括两方面:疏降水体和处理水体补给来源。1、疏降水体措施 疏降水体的方法有钻孔疏降、巷道疏降、联合疏降、回采疏降和多矿井分区排水联合疏降。联合疏降是根据地质采矿条件、含水层特点,采用巷道、钻孔联合疏降水体。具体为先 掘进疏水巷道和石门,然后再在其中打钻孔穿过含水层放水进行疏降。回采疏降就是通过开采离含水层远的工作面,使含水层水通过这些工作面的采动影响缓 慢流出,以降低含水层水位,达到疏降的目的。回采疏降适合于弱含水层和补给来源有的限 含水层。多矿井分区排水联合疏降是根据地下水连通的特点,采用多个矿井排水联合疏降,以达到快速疏水的目的。2、处理水体补给来源 处理水体补给来源就是在回采前用水文地质、工程地质的方法对补给水体的主要来源进行处理。四、开采技术措施采用开采措施的目的是减小顶底板岩体的破坏范围,以达到安全采矿的目的。开采措施 主要有:试探开采、充填开采、柱式开采、分区开采、间歇式开采、协调开采等,下面分别叙述。1、试探开采生产实践表明,试探开采是水体下开采的一个重要技术原则。试探开采就是先采远离水体、后采近邻水体下面的煤层;先采隔水层厚、后采隔水层薄的煤层;先采地质条件简单、后采地质条件复杂的煤层;先采较深部,后采较浅部的煤层。通过先易后难地试探性开采, 逐步接近水体。2、充填开采 3、部分开采 部分开采包括条带开采、房柱式开采、刀柱式开采等短壁开采方法。4、分区开采 分区开采是水体下开采减少灾害损失的一个重要措施。分区开采有两种方法,一是在同一矿井(或井田)内隔离采区进行开采;二是建立若干单独矿井同时开采或分别开采。方该 法的目的就是使各采区相互独立, 防止矿井突水时淹没整个矿井。 在浅部开采和水源补给充足的条件下常采用此方法。5、分层(分阶段)间歇开采分层间歇开采是将厚矿层分成几个分层进行开采的方法。从前面的冒落带、导水裂缝带高度计算式中可见,冒落带、导水裂缝带高度随矿层采动次数的增加,其增加幅度逐渐减小。6、协调开采 协调开采是水体上采矿减小底板采动破坏的有效方法。其目的就是通过适当地布置两矿层的工作面,以减小采动的支承压力和底板岩体破坏的深度。3.3铁路下采煤3.3.1地下开采对路基及上部建筑的影响铁路线路主要由路基、道床、轨枕和钢轨组成,如图3-3-1所示。图3-8铁路横断面图1路基;2道床;3轨枕;4钢轨一、路基的移动和变形1、路基的下沉过程及其分布特征地下煤层开采后,采空区上覆岩层的移动从下至上逐渐发展到地表,使位于采动影响范围内的路基开始下沉。当下沉值很小时,地表就已达到较大的下沉范围。随着工作面的推进,路基的下沉量和下沉范围逐渐增大。一般情况下,路基的移动范围比其下方采空区的范围要大得多,从移动边界到最大下沉点之间的下沉分布是连续渐变的。如果路基在下沉过程中在竖直方向上产生拉伸变形,将引起路基本身的松动,还可能在不同土质的介面上产生脱层现象,从而影响路基的承载能力。但科研人员通过工程实践表明,路基在下沉过程中,在竖直方向上不产生拉伸变形,也不会发生松动、脱层等病害。2、路基的水平移动和变形路基下沉的同时伴随有水平方向的移动。垂直于路基轴线的横向水平移动,将使路基原来的方向发生变化其具体变化情况主要取决于线路与采空区之间的相对位置关系。长期的实地观测结果表明,路基的横向水平移动也具有大范围、连续渐变的特征,且产生横向水平移动的范围与地表下沉的范围基本相同。沿路基纵向的水平变形,使其受到拉伸和压缩,在拉伸变形区,路基的密实度降低,孔隙度增大,以至产生裂经。在压缩变形区,路基的密实度增大。由于土质路基有一定的孔隙度,能够吸收地下开采引起的压缩变形。在拉伸变形区内,路基孔隙率的增量很小,而且是在较长时间内由小到大缓慢发展的。在此期间,路基还会被列车的动荷载压实。因此,路基在采动过程中始终具有足够的强度。如果路基上产生裂缝,一般也只是出现在局部地段,且要经历一个较缓慢的发育过程,在列车动荷载的作用下,裂缝发展到道床内会被压实。但是,如果出现了未被压实的较大裂缝,则必须进行填充并夯实。二、线路上部建筑的移动和变形线路上部建筑由钢轨、轨枕、道床、联接零件、道岔以及防爬设备等组成。钢轨是线路上部建筑最主要的组成部分它直接承受列车的荷载,并通过轨道和道床将荷载传给路基,此外,它还起着列车运行的导向作用。地表移动和变形通过路基传递给上部建筑,由此导致线路上部建筑产生移动和变形。线路的移动可分解为三个分量:竖直方向上的下沉、水平方向上的横向移动和纵向移动。由于这三种移动量的不均匀,就使线路产生坡度的变化、竖曲线形状的变化、两条钢轨水平的变化、线路方向的变化、轨距的变化以及轨缝的变化。1、线路垂直移动和变形的影响铁路下采煤的实测资料表明,在正常条件下,铁路的线路移动量与地表移动量基本相同。在不出现突然下沉的条件下,铁路路基是随着地表下沉而下沉的,线路上部建筑是紧贴着路基下沉的。因此,线路轨面的下沉量与地表下沉量是基本一致的。在铁路下采煤时,轨面随地表下沉而下沉,这将引起线路的坡度、竖曲线的形状以及两轨道水平的变化。A线路坡度的变化移动盆地内沿线路方向的地表倾斜使线路原有的坡度发生变化。当地表倾斜的方向与线路坡度方向一致时,线路坡度将增大;反之将减小,甚至出现反坡。线路坡度的增减使下沉盆地内有的区段列车运行阻力增加,而有的区段运行阻力减小。在采动影响期间,必须保持增加后的阻力不超过该线路的允许阻力。线路的允许阻力是按铁路的级别采用限制坡度的办法来控制的。所以,在铁路下来煤时,只要采动后线路的坡度不超过其限制坡度,就不会引起列车超载运行。B竖曲线形状的变化线路纵断面上的坡度变更点处均设有竖曲线,以保证列车运行的安全。地下开采引起的地表的正曲率变形可使线路原凸曲线的半径变小,线路原凹竖曲线的半径变大,长坡道变成凸形竖曲线。地表的负曲率变形可使线路原凸竖曲线的半径变大,线路原凹竖曲线的半径变小,长坡道变成凹形竖曲线。竖曲线半径变小和长坡道变成竖曲线,都不利于列车的运行,但只要适时地进行维修,使其不超过有关规定,均不会造成行车事故。实际上,尽管地表的曲率变形能改变线路纵断面的形状,但由于地表曲率变化缓慢,只要采取相应的维修措施,附加的曲率变形可以消除,上述有关规定能够得到满足。C.两轨水平的变化垂直于线路方向的地表倾斜,可使直线路段的两股钢轨原有水平状态发生变化,可使曲线段改变外轨与内轨的超高度。如果两轨高度的变化超过允许值,尤其是当曲线段部分出现反超高现象时,将对列车运行产生较大影响。 但是,在正常条件下,地表的倾斜变形也是连续的渐变的,可以通过维修将其对两轨水平的影响控制在允许范围之内。a.线路水平移动和变形的影响在地表水平移动的影响下,线路会因横向位移而改变方向,会因纵向位移而出现爬行或发生轨缝的变化。线路直线段发生横向移动时,会逐渐变成为半径很大的曲线,使原有方向发生变化,其具体的变化情况决定于线路与采空区之间的相对位置关系。如图3-9所示。图3-9线路方向变化与工作面相对位置的关系1线路原始方向;2煤层开采后线路移动方向;3停采后线路最终方向;4开切眼;5停采线不在下沉盆地主断上的线路,其横向移动总是指向采空区。当线路与采空区边界斜交时,线路将由直线变为“S”形的曲线(图3-10)。 图3-10采空区边界斜交时其方向的变化1下沉盆地平底区;2采空区;3地表移动边界2.3.2铁路下采煤的技术措施1、满足一定的采深与采厚比。长壁垮落法开采时,铁路下方开采煤层的深度和厚度之比要满足建筑物、水体、铁路及主要井巷煤柱留设与压煤开采规程规定的数值,且最小深度中的基岩厚度必须大于垮落带高度。2、防止地表突然下沉或塌陷。在下列条件下,地表可能发生突变性的下沉或塌陷:浅部的近水平、缓斜或中倾斜煤层;顶板坚硬、煤层露头附近的急倾斜煤层;浅部有采空区积水、岩溶和充水裂隙带空间,矿井深部疏水后。开采浅部的近水平、缓倾斜和中倾斜厚煤层时,应采用分层采煤法,并适当减少第一和第二分层开采厚度。开采急倾斜煤层时,在露头附近,当煤层顶板坚硬,不易冒落时要采用人工强制放顶,并要留有足够尺寸的煤柱,且应防止采空区上部煤柱抽冒。对于浅部有采空区积水,或煤层上方覆岩为石灰岩含水层或充水裂隙带空间时,要防止采动时疏干浅部积水造成地表突然塌陷。3、减少地表下沉。减少地震下沉最有效的方法是采用全部充填法,采用条带采煤法。4、消除和减轻地表变形的叠加影响。采用无煤柱开采、顺序开采及协调开采等方法,可减少和减轻地表变形的叠加,减少地表变形对铁路的影响。采用协调开采时,常因几个工作面同时开采,使地表下沉速度增大,要全面考虑协调开采的利弊。5、合理布置工作面。应尽量将开采区域布置在铁路的正下方,使线路处于移动盆地的主断面上,且工作面推进方向与铁路线路平行,以减少线路的横向水平移动和变形。6、留设好铁路煤柱。7、采取地面维修技术措施。在开采过程中,随着线路的下沉和横向移动,对路基要进行阶段性的抬高与加宽,使其尽量恢复到开采前的状态。采用起道和顺坡的方法消除线路下沉,使线路纵断面恢复到原有状态。采用拨道和改道的方法消除横向水平移动对线路的影响。线路纵向移动主要反映在轨缝的变化上,因此,必须调整轨缝,消除其有害影响。参考文献1郭宝华,涂敏.浅谈我国大采高综采技术.中国矿业,2003, 12(10), 40-422刘涛.厚煤层大采高综采技术现状.煤炭工程,2002 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In view of still increasing production the cooling of the air is critical for the attainable production on the one hand. On the other hand, the increasing gas emissions have to be controlled as well.This is achieved by fans of high capacity as well as by cross-sections in the underground workings, which are as big as possible, especially in the gateways. Furthermore, increasing cooling power is installed.The air volumes cannot be enlarged unlimited, yet, and rapidly reach their limit due to national statutory regulations concerning the maximal allowed air velocities.Besides that, a methane concentration of 1Vol.-% in the maximum must be maintained in general, which is allowed to be exceeded only with the agreement of the mining authority in defined parts of workings up to a limit of 1,5Vol.%.Due to a dense sequence of coal seams in the German hard coal deposits, the firedamp is released during the exploitation not only from the worked seam, but essentially from the seams in the roof and in the floor behind the passage of the longwall. A gas drainage on the base of an efficient technique is necessary, firstly in order to fulfil the safety regulations and secondly to achieve a maximal production in the working.An investigation, recently finished and executed concerning the improvement of the gas drainage indicated that, by means of rock mechanical calculations and interpretations, an increase in the efficiency of gas drainage boreholes is still possible.IntroductionThe methane emissions in mining operation depend principally on geologic conditions. In rock sequences with a small portion of coal in the roof and the floor, only the released gas quantity from the exploited seam also defined as basic gas emission has to be diluted with the air flow. This methane flow can reduce the exploitation relevantly by an increasing desorbable gas content in the coal. In particular, the coal mass flow quickly exploited with high-capacity production can release very high methane quantities from the accompanying seams. This high methane flow generates an exceeding of the threshold values and leads to switch off of the electrical equipment and to the interruption of production.In a rock sequence with a high portion of coal in the roof and the floor additional gas from the accompanying seams in the area of gas emissions is released into the air flow behind the passage of the longwall. In the Ruhr Basin this gas flow, also defined as additional gas emission, is normally many times higher than the basic gas emission.Figure1 illustrates the loosening of layers caused by longwall mining operation in flat layers. These loosenings can be according to their degree - flow ways for the released gas from the accompanying seams. The coloured areas mark the degree of loosening with red for intensive, dark blue for light and grey for no loosening.Figure 1: Example for the loosening of the rocks in the roof and the floor of a longwall operation (view of the left side only; the right side is symmetric)There can be a high rate of additional gas emissions according to the seam thickness in the area of gas emissions and according to their gas content. Figure 2 shows that the production can decrease dramatically already at low gas contents if there is no gas drainage for the suction of the additional gas emission.This extreme reduction of saleable output and advance of production requires extreme increasing of the air flow and furthermore gas drainage is necessary. Thereby the legal regulations for the German hard coal mining have to be observed, which are the following:maximum air velocity6m/smaximum methane concentration1Vol.-%exceptional methane concentration1,5Vol.-%minimum negative pressure in the gas drainage100hPaFigure 2: Example for the decline of production in case of (increasing) additional gas emissionImprovement of the gas drainage for maximising the output After increasing the air flow following the legal regulations, and with the permission by the authorities for maximum methane concentrations of 1,5 Vol.-%, and after commissioning a gas drainage system, the output can be increased to a quantity, which is again profitable (see figure 3).Normally, the efficiency of the gas drainage system is up to 50% of the total methane flow occurring during exploitation. An additional optimising of the gas drainage above that also increases the face output.A longwall in seam H of the mine Prosper Haniel serves as an example for optimising gas drainage results (figure4).The length of the panel of approx. 960 m was mined with a daily advance of production of approx. 7 m/d in 140 work days although the desorbable gas contents were at approx. 8 m/t and the gas make from the additional gas emission was 30 m on the average per exploited ton. The drained methane quantities were up to approx. 650.000 m per week (approx. 65 m/ min). The gas drainage efficiency reached up to 72%.The gas drainage boreholes were drilled from both gate ways into the roof and the floor. The distance from one another was 10 m. Figure3: Example of increased output by doubling of air flow and installation of a gas drainage system with 50% efficiency.A gas pipe of 500 mm diameter was available in the loader gate. In the tail gate, a gas pipe of 300 mm width was installed behind the face and extended according to the advance of the exploitation.The total air flow for the panel was up to 85 m/s. In the working area methane concentrations of up to 1,5 Vol.-% were locally allowed. Outside the working area towards the air return shaft the limit of 1%-methane concentration had to be observed.Principles for gas drainageA basic draft (figure5) shows the function of a gas drainage: Gas boreholes are drilled along the goaf shortly behind the longwall. In general, the roof emits the most gas. However, from the floor a considerably additional gas flow can be expected in the case of high gas contents. According to the rock properties, the gas boreholes are tubed at their beginning at a length of 7.5m to 20 m and the annular space between tube and fractured rocks near to the roadway is sealed with plastic material (adhesive or foam plastic). This technology reduces unwanted leakages. The diameters of these boreholes are 75mm to 115 mm. Their length depends on the distance of gassy layers (accompanying seams), which have to be drained from the exploited seam. The length varies normally between 30m and 60 m. In particular cases the length can be 100m and more if there are special rock mechanical conditions.The incline of the borehole to the roadway axis is between 75 gon and 90 gon. According to the occurring gas volume, the distance between the boreholes can be 10 m to 50 m. The boreholes are connected to the gas pipes by plastic tubes with adequate adapters.For planning and dimensioning of gas drainage systems, it is necessary to calculate the occurring quantities of gas mixtures in the planned mining operations at an early stage (prediction of gas emissions)Most important factors concerning the technology of gas drainageDimensioning of pipesPipes are the most important part of a functional and high-capacity gas drainage system. If they are not dimensioned according to the flow characteristic of the gas quantities to be expected, the success of the gas drainage is put into question. Even high-capacity pumping stations cannot compensate the pressure loss due to pipe cross sections, which are too small. In the range of negative pressure there is only a very small margin of 300 hPa to 400 hPa available for the compensation of pressure consumption (pipe friction, water accumulation, installations, bends of the pipeline).The normal operating range of the pumps is in general at a negative pressure of 400 hPa to 450 hPa. At the end of the gas collection pipe in the mining area there should be a negative pressure of at least 100 hPa according to the German rules. That means that only approx. 300 hPa to 350 hPa are available for all pressure losses in the gas piping net.Figure4: Arrangement of gas boreholes and air supply of a longwall in seamH, mine Prosper-Haniel.The context between quantities of gas mixtures, which have to be drained, and pressure losses due to small-dimensioned pipes is illustrated in the following diagram (figure6):Figure5:Basic draft for gas drainage boreholes (schematic diagrams)A pipe diameter of less than 400 mm is unfavourable. A tolerable pressure loss in the system normally occurs, when there are flow velocities of between 10 m/s and 15 m/s. However, the length of the pipeline has to be taken into consideration (in fig.6 for 1000m).Even at diameters of 300 mm the pressure loss is four times higher compared to a pipe width of 400 mm. The pressure consumption graph rises steeply, when there is a diameter below 300 mm.The false gas pipe cross section has quickly negative effects on the accessible output of a mining operation due to reduced efficiency of the gas drainage.High capacity pumpsThe pumps to be used should produce negative pressure of up to 500 hPa. Water ring pumps or rotary pumps are suitable here, which are available on the market for any capacity. When planning a pumping station a certain tolerance for capacity modification has to be kept in mind in case the gas quantities increase during the life of the mine. Figure6: Pressure consumption depending on pipe diameterThe single capacities of the pumps should be dimensioned according to the minimum and maximum of the gas quantities to be expected (pumps with graduated capacities). A reserve pump is prescribed by law. Water ring pumps have certain advantages compared to rotary pumps if higher negative pressures have to be reached. In case of a pipe system sufficiently dimensioned, the construction types are equivalent.The drive capacities installed in the gas drainage stations of the German hard coal mines for high gas quantities are 1.5 MW and more, if required. This can cope with volume flows of up to 175 m/min pure methane, which corresponds to gas mixture quantities of 21000 m/h at a methane concentration of 50%.Rock mechanical aspects for the optimisation of the gas drainageConsidering rock mechanical aspects helps to optimise the gas drainage. A preferably precise reproduction of the rock sequence in a rock mechanical computer model offers conclusions for the ideal arrangement and length of gas boreholes. A visual implementation of rock mechanical calculations of the processes of loosening allows insights into the rocks and therefore an idea about the area of gas emissions in the area of loosening of mining operations.The following figure7 of a working at the mine Walsum, shows as an example of a single case plastifications and consequently the occurring flow ways - reaching far into the roof (visible by the light red areas). The dip angle of the rock sequence amounts 20gon.Figure7: Plastifications in the roof and the floor of a working at Walsum mineBy use of this model of rock mechanical reactions, the existing drilling schema was modified (figure8):Figure8: Increase of gas emissions in the case of incline and length modification of the gas boreholes (Walsum mine)After modifying the bore angle from approx. 80 gon to 90 gon and the bore length from 55 m to 110 m, there was a significantly higher efficiency of the single boreholes (see top graph). As a result, at this working and also in the following working the efficiency of gas drainage could be increased up to more than 70%.Due to a study of the years 2004 and 2005 led by support of the DMTGmbH, rock mechanical calculations were made for a high number of workings with various rock sequences of the Carboniferous in the Ruhr Basin. Thereby, processes of rock loosening, which can influence the gas emission, were analysed.At the same time, occurring rock tensions behind passage of the longwall in the rocks were analysed, which might influence the height and the time of the gas release. This study offers an extensive collection of experiences in this regard, which allow to evaluate future methane flows better and to plan gas drainage systems more reliable.The following illustration (figure9) serves as a last example of the complexity of the relations between rock mechanics and gas release.Here, the processes of loosening (on the left) are compared to the occurring rock tensions (on the right). A sandstone layer of 25 m to 30 m thickness near above the worked seam is remarkable in this example. Compared to the softer kinds of rocks this layer shows only minor plastifications. This fact corresponds to the present mining experiences.Concerning the rock mechanical comparison to rocks with less solidness, an essentially higher and longer lasting pressure relief of the layers lying above this sandstone occurs.This means with respect to the gas emissions that the seams lying above the sandstone also underly to a higher and longer lasting pressure relief than it is normally the case for less solid accompanying rocks. For this reason, they emit in total much more methane than one has to expect according to a conventional gas emission.Figure 9: Plastification and relief of mechanical pressure in the area of looseningof a longwall operation with a thick, hard sandstone layer in the roofIn a single case up to three times higher methane inflows occurred in a seam in a working at the mine Ost than calculated before.In the meantime the gas drainage system was extended to a capacity of 15.000m gas mixture per hour. Furthermore, a special piping method was developed for the safe suction of the additional gas emission above the sandstone layer. This method guarantees a lifetime of the gas boreholes of more than 12 months.Additionally, the underground piping net, which has to bridge a length of approx. 12 km from the drainage station at the surface to the exploitation, was extended in a way that two thirds of the pipelines consist of parallel strings with 500 to 600mm diameter.Completing CommentsOn the whole, increasing gas contents and consequently higher additional gas emissions limit the increase of production.According to the national laws there must be a high expense for ventilation as well as gas sucking technology to achieve a maximum output. Safety, which is an important factor of production, as well as economical aspects will be maintained.Additionally, the utilisation of the methane emissions can compensate financial expenses at least partially. However, the gas drainage systems have to be dimensioned optimal. Here, it is important to coordinate the underground gas pipe nets and the above ground gas drainage stations for the gas flows to be expected in the mining operations.Essen, 04.05.2007References1Gao Y F,Shi L Q,Lou H J,et al.Water-Inrush Regularity and Water-Inrush Preferred Plane of Coal Floor.Xuzhou:China University of Mining&Technology Publishing House,1999.(In Chinese)2Qian M G,Miao X X,XU J L.The Key Strata Theory of Controlling the Rock Seam.Xuzhou:China University of Mining &Technology Publishing House,2000.(In Chinese)3Zhang J C,Zhang Y Z,Liu T Q.The Seepage Flow in Rock and the Water Inrush in Coal Floor.Beijing:Geological Publishing House,1997.(In Chinese)4Wang L G,Song Y.The Non-Linear Characteristic and the Forecast of Water Inrush from Coal Floor.Beijing:Coal Industry Press,2001.(In Chinese)5Gong S G.The Basic Application and Example Analysis of ANSYS.Beijing:Machine Press,2003.(In Chinese)6Li H Y,Zhou T P,Liu X X.The Tutorial of Engineering Application of ANSYS.Beijing:China Railway Press,2003.(In Chinese)7Wang L G,Song Y.A model to risk assessment for mine water-inrush.Journal of Engineering Geology,2001,09(02):158163.8Miao X X,Lu A H,Mao X B,et al.Numerical simulation for roadways in swelling rock under coupling function of water and ground pressure.Journal of China University of Mining&Technolog,2002,12(2):121125.9Wang L G,Bi S J,Song Y.Numerical simulation research on law of deformation and breakage of coal floor.Group Pressure and Strate Control,2004,(4):3537.(In Chinese)10Wang L G,Song Y,Miao X X.Study on prediction of water-inrush from coal floor based on cusp catastrophic model.Chinese Journal of Rock Mechanics and Engineering,2003,22(4):573577.11Jiang J Q.The Stress and the Movement of the Rock Around the Stope.Beijing:Coal Industry Press,1997.(In Chinese)中文译文2007年中国(淮南)煤层气控制技术国际座谈会瓦斯抽放在德国煤矿的高效运作Joachim Brandt博士DMT GmbH公司,艾森,德国Essen,2007年4月5日摘要:在提高德国硬煤开采生产过程中,通风技术部分作为生产要素的也变得越来越重要。一方面,针对还在增加的生产空气冷却十分重要。另一方面,也必须对不断增加的瓦斯释放加以控制。可以通过使用大功率通风机或在井下,尤其是在巷道内设置尽可能大的联络巷,可以实现这一点。此外,越来越多的制冷设备也得以安装。除此之外,甲烷的浓度必须控制在1Vol.-%常规以内,常规规定甲烷最高浓度可以在采矿专家定义的井下浓度上限1,5Vol.%。由于德国的硬煤沉积中煤层沉积致密,瓦斯不仅从废弃煤层释放,而且尤其从顶板岩层和长壁工作面后方的两巷释放。高效的瓦斯抽采很有必要,首先是为了达到安全规定,其次是达到生产最大化。最经一项已经完成并投入使用的实验表明,通过岩体力学计算和解释,提高瓦斯抽放钻孔的效率仍有可能。说明在采矿工程中甲烷排放量主要取决于地质条件。在那些顶、底板含有少量煤炭的岩层中,只有那些从已开采煤层且被定义为基本瓦斯排放的瓦斯释放量才需要用气流加以稀释。煤炭中瓦斯含量越高,这种瓦斯气流就越容易导致开采工作的减缓。特别是,煤炭开采速度越快、量越大,就越容易导致工作面瓦斯的大量释放。这种高甲烷产生的流量超过阈值并导致关掉电气设备和中断生产。在那些顶底板含有大量煤的岩层中,从位于瓦斯卸压释放区的临近层中释放的额外瓦斯被四方到工作面后方的废弃两巷。在鲁尔盆地,这种被称为额外瓦斯释放的瓦斯气流通常比基本瓦斯释放大好几倍。图1说明了在水平层中因长壁采煤作业而引起的煤层卸压。依据它们的卸压程度,这种卸压可以为临近煤层中的瓦斯释放提供缝隙。彩色区域标志着卸压程度:红表示强烈,深蓝表示轻微,灰表示未卸压。根据瓦斯释放区的煤层厚度和瓦斯含量,会有大量的额外瓦斯释放。图2表示如果没有瓦斯抽放来吸收额外瓦斯释放,采煤作业能够迅速的把瓦斯含量降到一个较低值。这种极端的输出下降和生产进尺需要急剧的增大风流,并且,瓦斯抽采也是必要的。因此,针对德国硬煤开采的合法规定必须被遵守,规定如下:最大风速:6m/s最大甲烷浓度:1Vol.-%特殊甲烷浓度:1,5Vol.-%瓦斯抽采最低负压:100hPa图1:长壁采煤作业的顶底板卸压的示例(只看左边,右边为对称)基于提高产量的瓦斯抽采技术改进通过遵循法定的条例来增加风量,经过官方允许的最大瓦斯含量(1,5 Vol.-%),并且经过调试瓦斯抽放系统,产量又可以重新达到一个可观值。(见图3)图2:额外瓦斯释放量递增时引起的生产下降。通常,瓦斯抽放系统的效率是可以抽出煤炭开采过程中50%的瓦斯释放量。一个经优化后数值大于前面数值的系统也能带来工作面产量的提高。Prosper Haniel煤矿的一个位于H煤层的长壁工作面作为优化瓦斯抽采系统的结果的示例(图4)该区段推进长度约960m,在140个工作日内日进7m,尽管瓦斯解析量约为8 m/t且加上额外瓦斯释放得到的总瓦斯含量为平均每吨30 m。每周的瓦斯抽放量达到650.000 m左右(排放速度65 m/ min左右)。瓦斯抽放时间利用率达到72%。从工作面两顺槽向顶底板打抽放钻孔,钻孔间距10m。一个直径500mm的瓦斯抽放管可以布置在运输巷,在轨道巷,在工作面后面布置一个直径300mm的管子,并依据开采适时延长。区段总风流可达85米/ s。在工作区域的局部可以允许甲烷浓度达到1、5 Vol. - %。工作面以外的浓度不得高于1%。图3:风量加倍且安装一套效率50%的瓦斯抽采系统后的产量增长示例图4:Prosper-Haniel矿一个长壁工作面的瓦斯抽放钻孔的布置及风量供给瓦斯抽放的原则一个基本的草案(图5)表明瓦斯抽放的机理:紧随工作面,沿着采空区打抽放钻孔。一般来说,顶板释放大部分瓦斯。然而,若地板含有大量瓦斯,就有可能出现大量的额外瓦斯气流。根据岩石特性、气体钻井是布置在他们开头长度为7.5米到20米长。另外,抽放管和钻空间的环状空间由塑料材料(胶或泡沫塑料)充填。该技术减少不必要的泄漏。这些钻孔直径为75毫米到115毫米。它们的长度取决于含瓦斯层(临近层)的距离,这些瓦斯必须从已经形成的缝隙加以抽放。不同的长度通常在30米,60米之间。在特定的情况下, 如果有特殊的岩石力学状况,长度可以达到100米或更多。钻孔与顺槽轴间倾角介于75到90几何角。根据已测得的瓦斯体积,钻孔间距可以从10m到50m。用带有足够的适配器的塑料管来将钻孔和瓦斯管道连接起来。图5:瓦斯抽放钻孔基本草稿(原理图)对于规划与瓦斯抽放系统定型,有一步是必要的,那就是在早期(瓦斯释放预测)的计算出区段回采作业工作中既得混合气体的量。有关瓦斯抽放技术的最重要因素管道尺寸管道是可用和大容量的瓦斯抽放系统中最重要的部分。如果它们的尺寸不是根据预期的瓦斯流量特性来定制,瓦斯抽放就很难成功。即便大容量泵站也不能补偿因管道交叉环节太小引起的压力损失。在负压阶段,只有一个非常小范围的300到400hpa的压力可用于补偿的压力消耗(管摩擦、积水、设施、弯曲的管道)。在泵的正常工作范围,负压一般在400到450hpa。根据德国规定,在回采区的瓦斯回收管的末尾应该至少有100hpa的负压。这意味着只有大约300到350hpa的压力可作用于所有的管道网络压力损失。下表(图6)解释了必须被抽放的混合气的量和由小尺寸管路引起的压力损失间的关系。图6:压力消耗取决于管的直径管道直径小于400毫米是不利的。当流速介于10 m/s和15m/s,一些在允许范围内的压力损失会经常发生。然而,管道的长度必须被考虑(图6为1000m)。即使在直径300毫米,压力损失高出管道宽度400毫米时的四倍。当有一个直径300毫米以下,压力损耗图大幅上涨。瓦斯管路交叉环节的无效会很快对因瓦斯抽放效率的降低而引起的回采作业的产出产生负面影响。高容量泵泵的使用将产生达到500hpa的负压。水环泵或扶轮泵适合这种能力,可在市场上买到任何容量的。当设计一个泵站时必须牢记要留有一定的容量变动余地,以防在煤矿服务年限内瓦斯数量增加。泵的单个性能需要根据预期的瓦斯的最大、最小量加以定型(容量分等级的泵)。依据规定留有备用泵。如果有更大的负压要求,相比扶轮泵,水环泵有一定的优势。一旦管路系统经充分定型,工程类型是等价的。在德国的硬煤煤矿的瓦斯抽采站,如果需要的话,用以抽采大量瓦斯的驱动功率可以达到1.5MW或更多。这足以匹配达到175 m/min的纯瓦斯流量。这种流量
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