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煤巷锚杆支护技术的研究及应用摘 要 ： 锚杆支护因其技术经济的优越性，成为煤巷支护改革的发展方向，是煤矿实现高产高效生产必不可少的关键技术之一。关键词 ：锚杆支护;支护理论;煤巷1 引言随着矿井产量和效率的不断提高，要求的巷道断面越来越大，成巷速度越来越快，传统的棚式支护越来越不能满足生产需要。近年来，煤巷锚杆支护技术发展极为迅速。与棚式支架支护相比，锚杆支护显著提高了巷道支护效果，降低了巷道支护成本，减轻了工人劳动强度。更重要的是，锚杆支护大大简化了采煤工作面端头支护和超前支护工艺，改善了作业环境，保证了安全生产，为采煤工作面的快速推进创造了良好条件。目前，锚杆支护技术已在国内外得到普遍应用，是煤矿实现高产高效生产必不可少的关键技术之一。从1996年开始，我国在引进、吸收、消化国外先进技术经验的基础上，结合我国煤矿具体情况，经过大规模研究和试验，初步形成了适合我国煤矿条件的煤巷锚杆支护成套装备和技术。放顶煤工作面沿底板掘进的顶煤巷道锚杆支护技术、冲击地压及破碎顶板锚杆支护技术等重点项目的顺利完成，成功地解决了困难回采巷道支护问题，显著扩大了锚杆支护的使用范围。例如，邢台矿区采用高强度锚杆支护系统和小孔径锚索支护技术，有效地控制了煤顶巷道和复合顶板巷道围岩的强烈变形，保持了巷道的稳定性，取得了显著的技术经济效益；兖州矿区采用高强度锚杆支护系统成功地解决了煤顶巷道支护难题，不仅支护效果好，技术经济效益显著，而且解决了以前采用棚式支架出现的煤层自燃等问题；新汶矿区冲击地压和破碎顶板条件下的巷道维护十分困难，采用高强度锚杆支护后，巷道围岩的强烈变形得到有效控制，稳定性得到可靠保证，而且显著降低了巷道支护和维修费用。1998年以来，煤巷锚杆支护技术又有了新的发展。例如，潞安常村煤矿采用新型的小孔径树脂注浆联合锚固预应力锚索和高强度锚杆组合支护系统，成功地支护加固了多条大断面、围岩松软破碎、受地质构造和小煤柱影响的困难巷道，在没有影响矿井正常生产的条件下，保证了巷道安全状况，同时节约了大量支护费用；西山矿区在原有锚杆支护技术的基础上，又与科研院所合作进行了全面、系统的开发研究，形成了西山矿区煤巷锚杆支护成套技术，解决了复合顶板巷道、近距离煤层巷道等多个支护难题，每年节约上千万元的支护费用；阳泉矿区集中精力进行了综采放顶煤回采巷道锚杆支护技术攻关，不仅圆满解决了顶煤巷道支护难题，而且取消或简化了工作面超前支护和端头支护，显著提高了采煤工作面的推进速度；兖州矿区采用高强度锚杆与锚索成功地支护了综采放顶煤沿空掘巷支护难题，进一步扩大了锚杆支护技术的使用范围。2 煤巷锚杆支护技术2.1 锚杆支护理论完善的锚杆支护理论是正确设计锚杆支护参数的基础，随着煤巷锚杆支护技术在我国的应用，近年来，锚杆支护理论研究有了进一步的发展，基于高预应力锚杆的应用，本文提出了基于高水平地应力的“刚性梁”理论及基于高垂直地应力的“刚性”墙理论。2.1.1 现有锚杆支护理论(1) 悬吊理论悬吊理论对锚杆支护机理作出了最朴素的解释：锚杆的作用在于将下位松软和/或破碎岩层悬吊于上位坚硬岩层。对于在巷道顶板一定范围内存在坚硬岩层时，采用悬吊理论进行锚杆支护设计是完全可行的，也是最简单、最经济的方法。(2) 组合梁理论组合梁理论是从经典的材料力学中借用而来的。在美国七十年代无拉力全长胶结锚杆盛行时，组合梁理论被广泛用来解释锚杆的支护机理，其主要要点是：锚杆将各个薄的岩石分层贯穿在一起形成一个厚的组合梁，薄的岩石分层能独立抗拒的拉应力较小，而厚的组合梁抗拉强度大大提高。在锚杆与岩石层面横交处，锚杆与胶结物一起共同阻止岩层沿层理面的水平错动。材料力学中的组合梁理论本身不考虑水平侧压的影响，而只考虑垂直载荷。(3) 组合拱理论组合拱理论认为：在拱形巷道围岩的破裂区中安装预应力锚杆时，在杆体两端将形成圆锥形分布的压应力，如果沿巷道周边布置锚杆群，只要锚杆间距足够小，各个锚杆形成的压应力圆锥体将相互交错，就能在岩体中形成一个均匀的压缩带，即承压拱(亦称组合拱或压缩拱)，这个承压拱可以承受其上部破碎岩石施加的径向载荷。在承压拱内的岩石径向及切向均受压，处于三向应力状态，其围岩强度得到提高，支撑能力也相应加大。因此，锚杆支护的关键在于获取较大的承压拱厚度和较高的强度，其厚度越大，越有利于围岩的稳定和支撑能力的提高。组合拱理论在一定程度上揭示了锚杆支护的作用原理，在岩石或煤层拱形巷道中可以作为锚杆支护参数的设计依据。(4) 围岩松动圈支护理论围岩松动圈理论认为： 地应力与围岩相互作用会产生围岩松动圈； 松动圈形成过程中产生的碎胀力及其所造成的有害变形是巷道支护的主要对象，松动圈尺寸越大，巷道收敛变形也越大，支护越困难。 依据松动圈的大小采用不同的原理设计锚杆支护。小松动圈(040cm)采用喷射混凝土支护即可；中松动圈(40150cm)采用悬吊理论设计锚杆支护；大松动圈(150cm)采用组合拱原理设计锚杆支护参数。由于围岩松动圈是随着时间、巷道支护形式及支护强度的变化而变化，并且在同一断面上由于岩性的差异，围岩松动圈的大小也是不一样的。所以，在复杂条件下围岩松动圈理论(如煤巷、软岩巷道)并没有得到应用。松动圈支护理论对于锚杆支护的指导作用主要在于确定普通锚杆(如普通圆钢锚杆、水泥药卷锚杆等等)的适用条件和范围。(5) 最大水平地应力理论自从八十年代以来，水平应力对巷道稳定性的影响已经引起了人们的普遍关注。澳大利亚W.Gale博士，通过数值模拟分析及现场观测，得到了水平应力对巷道稳定性的最基本的认识：巷道轴向与最大主应力方向平行时，巷道受水平应力的影响最小；二者垂直时，巷道受水平应力的影响最大；二者呈一定夹角时，巷道其中一侧会出现水平应力集中而另一侧应力较低，因而顶底板的变形会偏向巷道的某一侧。并提出在最大水平地应力的作用下，顶底板岩层易于发生剪切破坏，出现错动与松动而造成围岩变形，锚杆的作用即是约束其沿轴向岩层膨胀和垂直于轴向的岩层剪切错动，因此要求锚杆必须具有强度大、刚度大、抗剪切阻力大的特点才能起到约束围岩变形的作用。所以，澳大利亚锚杆支护特别强调锚杆高强及全长胶结。2.1.2 锚杆支护新理论根据垂直地应力v与水平地应力h的关系，可以将地层的应力状态分为四种情况：即 高水平应力状态：当hv/(1-) 低水平应力状态：当h4时，取N=4，N值无量纲。7174运巷本次取值为N=3。表3.1-1 煤岩物理力学性质测试结果岩石名称岩性平均厚度/m单向抗压强度/MPa备注老顶细砂岩7.6767.5469.14裂隙发育，其中夹泥质条纹直接顶砂质泥岩8.449.054.1含砂不均，裂隙发育煤层7#煤3.022.825.4黑色，碎块状直接底7#煤2.7322.825.4巷道底板为7#煤老底砂质泥岩7.3850.8水平层理，裂隙较发育 巷道煤柱宽度。护巷煤柱宽度是指顺槽一侧的实际煤柱宽度，单位为米。当巷道两侧为实煤体时，取X=100；当无煤柱护巷时，取X=0.7174运巷本次取值为X=100。具体计算的结果为：7174运巷的围岩稳定性类别为 类即中等稳定围岩。(3) 巷道断面设计7174工作面上、下顺槽均沿7#煤上分层顶板布置，为了不破坏顶板岩层的完整性，充分利用顶板岩层的悬吊梁作用，提高巷道自身的承载能力，巷道均设计成不规则四边形，如图3.1-1。图3.1-1 巷道断面(4) 支护参数的确定根据煤炭工业出版社1999年出版的煤矿巷道锚杆支护技术中介绍的锚杆支护参数的计算方法(计算方法略)，确定巷道两帮破坏深度c值为0.937m，顶板破坏高度b=0.965m，顶板载荷集度Qr=131.24kN/m，巷帮载荷Qs=27.47kN/m。 顶锚杆参数a 锚杆长度Lbr=b+=1.465(m) (3.1-1)式中：锚杆外露长与锚固长之和，取0.5m。b 锚杆杆体直径(d)：选用高强度锚杆，设计锚固力为100kN，取锚杆直径为d=20mm。c 锚杆间排距Dr=1.2m。d 支护形式为：锚杆+钢筋梁+金属网。 帮锚杆参数a 锚杆长度：Lbs=c+=1.437(m)，b 取Lbs=1.6m。c 每排锚杆个数：取整数Ns=3。d 支护形式为：锚杆+金属网+木托板。通过计算，顶锚杆采用202000mmMnSi，支护形式为锚杆+钢筋梁+金属网支护；帮锚杆采用161600A3钢树脂锚杆，支护形式为锚杆+金属网+木托板，锚杆间排距均小于1.2m。(5) 施工工艺施工工艺主要分为两个部分：一是巷道掘进，二是支护。7174工作面顺槽采用钻爆法施工，胶带、刮板输送机，采用“三八”工作制、边掘边锚、小班双循环的作业方式，每一循环进度为1.6m，沿7#煤顶板施工。为保证巷道成型，可在巷道上帮预留0.5m的松散煤壁，用风镐刷至设计断面。施工工艺：交接班打眼装药放炮临时支护出煤打装顶板锚杆、铺网刷帮出煤打装帮锚杆、铺网清理。两帮锚杆支护在一般情况下与顶板锚杆支护可平行作业，但进度上可滞后顶板二排锚杆。质量要求： 巷道必须沿煤层顶板施工，按设计断面要求搞好成型； 锚杆角度严格按设计及作业规程要求，两肩窝角锚杆向煤体倾斜2040； 打顶锚杆时必须首先安装好临时超前支护，可选用吊环式前探梁或单体液压支柱打临时点柱。安装锚杆前，应将顶板或煤壁的浮矸、浮煤找净。安装时，要使托板紧贴岩面，螺帽扭矩符合设计要求，锚杆外露长度不大于30mm，锚杆间排距误差不大于设计值的100mm； 树脂药卷必须送到孔底，搅拌时间不得少于规定，以确保顶、帮锚杆锚固力不小于设计要求。3.1.2锚杆支护围岩监测系统图3.1-2 表面收敛示意图为了检测锚杆的施工质量，验证锚杆的支护效果，科学评价支护参数的合理性，反映锚杆在围岩中的受力状况或围岩的变化信息，我们建立了锚杆支护巷道监测系统。其内容、目的及手段见表3.1-2。采用巷道表面位移监测时，我们通常在试验巷道中布置两个测站，间距为50m，每个测站内布置两个观测断面，间距为8m，观测断面靠迎头布置。巷道围岩的收敛观测采用十字布点法(如图3.1-2)，a、a、b、b、c、c分别为布置在观测断面上的基点，通过连续量测cc、aa、bb的值，可得到其各自的变化量，该值即为巷道两帮及顶、底板的移近量；通过量测ob的变化量可得到巷道底鼓量。表3.1-2 监测内容、目的及手段一览表图3.1-3、3.1-4为掘进期间试验巷道围岩移近量变化曲线图。巷道刚掘出时，围岩移近较快，随着迎头距观测断面的距离加大，其移近量渐小，当其间距离为90m时，围岩基本趋于稳定。图3.1-3 第观测站第1断面巷道围岩移近量曲线图3.1-4 第观测站第2断面巷道围岩移近量曲线从统计来看，掘进过程中，两帮的最大累计移近量为87mm，顶、底板最大累计移近量为73mm，其中顶板最大累计下沉量为10mm，巷道最大累计底鼓量为63mm，底鼓量较大的占顶底板移近量的86%。主要是由于7174工作面未受周边采动影响，且巷道顶板为较坚硬的砂质泥岩，底板为煤层，较松软，易于底鼓。今后施工中可将两帮底角的锚杆向底板倾斜，以降低底鼓量。采用LBY型顶板离层指示仪对顶板的离层进行监测。7174溜子道总共布点12个，间距50m，断层带处增设2个测点。每个测点安设两个基点，深基点监测锚固范围外的顶板离层，固定在锚杆上方稳定岩层内300mm处；浅基点固定在锚杆端部位置，监测锚固范围内的顶板离层。在掘进期间每天监测一次。从监测结果来看，巷道顶板总离层量在10mm以下，而观测点距迎头超过60m基本趋于稳定。在7174运巷中段过落差2.5m断层处顶板离层量达40mm左右，后采取补打加长锚杆给予加固。3.1.3经济效益与社会效益 锚杆支护与架棚巷道相比，降低生产成本，架棚巷道每米支护成本约455.65元(工字钢按复用2次计算)，锚网支护巷道每米支护成本为410.02元，每米比架棚支护降低45.63元(以上计算费用均不包括爆破材料、钉道材料、配件材料等)，同时也降低了运输、回棚及巷道修复费用。 简化了综采工作面上、下顺槽的超前支护，加快回采速度，综采工作面上、下顺槽采用架棚支护时，必须提前进行替棚，用工多，速度慢，严重制约工作面的推进度。而锚网支护可以有效减少回采超前压力对巷道的破坏，省掉替棚工序，从而加快工作面推进度，提高单产。 减轻了工人劳动强度，减少了支护材料的运输，采用锚网支护后，不需要运输大量的工字钢及其它材料，从根本上降低了工人劳动强度，从而可以提高工效。3.2 煤巷锚杆支护技术在石台矿的应用石台矿是一个年产120万t的大型矿井，主采煤层为3#煤层，23113轻放面位于 1采区下部，煤厚3.04.5m，平均为3.5m，煤层倾角512，平均8，f =1.5左右。直接顶为深灰色块状泥岩，局部含粉砂岩条带，厚0.76.0m，平均厚3.25m，老顶为灰白色细、中粒砂岩，厚1.04.1m，平均2.65m；直接底为灰至深灰色泥岩，厚89.5m，平均为6.5m；老底为灰黑色细、中粒砂岩，厚9.0m。该区域内煤层赋存稳定，煤层上部受岩浆侵蚀，岩浆岩和天然焦厚0.11.2m，平均0.8m。自2000年以来，已施工锚杆支护巷道近万米，通过摸索、实践、总结，目前初步形成一整套适应各类条件的巷道施工经验，但23113轻放切眼是我矿第一个轻放工作面切眼，巷道断层大，局部丢煤顶施工，对技术管理人员来说，是一个新的挑战，通过大家共同努力，制定出新型“锚梁(带)网”配合锚索联合支护的施工方法，取得了比较理想的效果。3.2.1 断面及支护方式的选择根据工作面支架安装和生产要求，切眼整体跟顶施工。考虑机巷、风巷跟底施工，所以切眼上、下口段必须跟天然焦或丢顶煤施工，一方面保证平车场长度，另一方面确保巷道的安全使用。切眼断面为斜矩形：净宽5.0m，净高2.2m。支护方式：顶板采用“锚梁网”联合支护；上、下口各10m由于跟天然焦或丢顶煤施工，顶部焦厚1m左右，所以采用“锚带网”联合支护；两帮均采用“锚梁塑网”支护。3.2.2 支护参数的确定(1) 顶板锚杆长度的确定根据中国煤矿巷道围岩控制、围岩松动圈分类法与设计建议中所提供的经验类比法，23113切眼顶板属于中等稳定的类围岩，松动圈范围为6001300mm，锚杆支护参数按悬吊理论进行计算：L=L1+L2+L3 (3.2-1)式中：L锚杆长度；L1锚杆外露长度，取100mm；L2不稳定岩层的厚度，取1300mm( 类围岩的松动圈)；L3锚杆伸入稳定岩层的长度，取500mm。计算得L=1900mm，取锚杆长度为2000mm。上下口考虑顶部留有1m左右的煤或天然焦，所以锚杆长度取2200mm。(2) 锚杆间排距的确定根据每根锚杆悬吊的岩石重量确定，即锚杆悬吊的岩石重量等于锚杆的锚固力。通常锚杆按等距排列，即a=b，则有：a= (3.2-2)式中：a，b锚杆间、排距；Q锚固力，由拉拔试验确定，取100kN；k锚杆安全系数，一般为23，此取3；y岩石体积力，取25kN/m2；L21300mm。计算得a=1000mm，根据3#煤层及切眼顶板的情况，取锚杆间排距为900900mm，上下口间排距900800mm。(3) 锚杆直径的确定选用20Mnsi高强螺纹钢锚杆，根据杆体承载力与锚固力等强度原则。锚杆直径D按下列公式计算： D= (3.2-3)式中：y被悬吊岩石容重，取25kN/m3；a，b锚杆的间排距，取900mm；h被悬吊岩层的厚度1300mm；锚杆屈服强度，取340MPa；k安全系数，取3。计算得：D=17.2mm，取锚杆直径18mm。为确保安全，顶板采用高强度锚杆配树脂锚固剂加强锚固，锚固长度不小于1000mm，用K2335和Z2350各一卷，初锚力不小于15kN，锚固力大于100kN。(4) 加强支护23113切眼及上、下口断面大，顶部天然焦厚1m左右，受巷道高度限制，锚杆长度不能太大，因此锚杆的锚固范围较小，对锚固区外的围岩变形起不到良好的控制作用，很容易引起顶板锚固区外的煤体膨胀和离层，达到一定程度就会导致顶板大面积冒落，因此需要加强支护，目前常用小孔径预应力锚索加强支护，根据顶板围岩赋存条件，确定采用锚索加强支护，锚索段深6m，钢绞线长6.4m，每4排锚杆安装两套锚索，锚索布置在距切眼两帮1.2m处，每套锚索配K2335一卷和Z2350两套，并且导峒与刷帮侧梯子梁、锚索交错布置，如图3.2-1所示。图3.2-1 加强支护示意图(5) 帮锚杆支护方式的选择由于帮锚杆锚固力3050kN基本可以满足支护需要，所以采用161600mm的高强锚杆，根据现场实际情况间距1000mm，排距800900mm，使用树脂锚固剂加长锚固，K2335和Z2350药卷各一支。另外附加钢筋梯子梁、塑料网联合支护，初锚力不小于15kN，锚固力不小于30kN。3.2.3 施工方法及技术保障措施由于切眼跨度达5m，采用“导峒、刷帮”和“钻爆”施工方法，先施工宽2.6m的巷道，贯通后再刷老塘帮至设计断面。施工顺序：打眼放炮临时支护打顶部锚杆铺金属网安梯子梁(W钢带)上托盘拧紧螺母至规定扭矩；帮锚杆施工顺序类似顶锚杆。具体技术保障措施如下：掏槽眼应布置在中下部，顶眼距离顶板不小于500mm，小装药，用小断面爆破，风镐找至设计尺寸，受岩浆侵蚀地段采用多打眼、少装药、松动爆破，尽可能减少对顶板的震动破坏。每次放炮的深度为1000mm，放炮后及时支护，锚杆够一排打一排，减少顶板的暴露时间，充分发挥围岩的自稳能力。严格按程序打眼、安装锚杆、网及梯子梁、钢带，打眼至设计深度，并且眼要直，不出现台阶，安装药卷顺序不能颠倒，搅拌(1520s)和等待(2030s)时间要充分。18mm的锚杆配23mm的树脂药卷和27mm的钻头，实现锚固区钻孔、树脂药卷、锚杆二者的两径匹配，达到最佳锚固效果。上、下口跟天然焦或丢顶煤段风镐掘进，禁止放炮，采用“锚带网”联合支护，并且加密锚索间排距，核算贯通点标高，保证上部平车场长度，找准变坡点位置，确保巷道安全贯通。导峒为煤壁侧，刷帮为老塘侧，合理安排安装时间，尽可能减少顶板的下沉，有利于采面的安装。图3.2-2 支护示意图导峒煤壁侧要架设一梁三柱走向支护，如图2-3-2。梁为2.6m的型钢梁，柱为DZ-22单体液压支柱。设专人管理走向棚，保证支柱正规有劲，观察顶板来压，及时给支柱补液，确保初撑力不小于50kN。刷帮施工只能放松动炮，减少对导峒侧锚杆及顶板的破坏；刷帮侧钢筋梯子梁、锚索要与导峒侧钢筋梯子梁、锚索，交错布置；锚索预应力要同锚杆初锚力一致，一般为2030kN。帮锚杆均使用金属锚杆(金属锚杆、钢筋梯子梁、塑网等均可回收)，保证初锚力不小于15kN。由于锚杆支护隐蔽性大，必须加强现场监督和质量检测，保证初锚力符合设计要求，对不合格的锚杆必须及时重新补打；要定期观测巷道帮顶的位移量，及时反馈信息进行科学分析，优化支护设计，确保工程质量和安全生产。3.2.4 经济效益分析(1) 提高巷道支护质量，有利于安全生产锚杆支护为主动及时支护，能有效地控制围岩的变形，变荷载为承载体，通过组合、悬吊、强化等作用来组合强化围岩；抑制顶板下沉离层，巷道稳定性高，修复量小，有利于安全生产。(2) 节约材料，降低成本锚杆支护与传统的金属支架相比，不仅能节约大量的工字钢，而且还可以减少坑木和小材料的消耗，大幅度降低支护成本，工字网按三次复用计算，轻放切眼每米支护成本740元；帮锚杆按三次复用计算，锚杆锚索支护成本每米607元，每米可节约经费近百元。考虑运输、加工、回收、损失率等因素，综合成本每米节约还要更多。(3) 降低劳动强度，改善作业环境锚杆支护重量轻，易操作，运输量少，提高了机械化程度；尤其在回采工作面的安装和两巷管理，操作简单，降低了工人的劳动强度，提高安装效率，降低安装成本。另外，锚杆支护巷道断面的利用率比架棚支护断面的利用率高，有利于工作面快速推进，实现高产高效。通过23113轻放切眼的施工和安装，收到良好的经济效果，从支护效果和经济效益来看，使用锚杆支护比架棚支护有许多优点，但是锚杆支护在应用中没有固定的模式，要在今后的实践中不断探索，不断总结，选择最佳支护形式和支护参数，为生产建设服务。4 锚杆技术的前进方向经过近年来的研究与实践，我国煤巷锚杆支护成套装备与技术基本形成，而且在实际应用中解决了多个巷道支护难题，取得了巨大的技术经济效益，为高效、安全开采创造了良好条件。锚杆支护已成为高产高效矿井必备的配套技术。为了将这项技术推广应用得更好，为煤炭工业带来更大的技术经济效益和社会效益，在以下几方面还需做进一步的工作。(1) 积极开展巷道围岩地质力学测试巷道围岩地质力学参数，包括地应力、围岩强度和结构是锚杆支护设计的重要基础参数，是保证锚杆支护合理、有效、可靠、安全的前提条件。目前我国仅有少数矿区进行了比较全面、系统的测试工作。今后，应该把巷道围岩地质力学测试放在十分重要的位置，并把它列为锚杆支护技术必不可少的工作。(2) 煤巷锚杆支护设计方法的研究与推广煤巷锚杆支护设计方法已经从过去简单的经验法、计算法，发展到现在以数值计算、现场监测为基础的动态信息设计法。但是，目前我国许多矿区还是以经验法为主，锚杆支护的合理性、安全性无法保证。在我国煤矿应积极推广先进的设计方法，使现场工程技术人员能够掌握和实际应用。(3) 锚杆支护材料系列化与标准化目前，煤巷锚杆支护材料品种很多，一些材料力学性质达不到工程要求。我国锚杆支护材料生产厂家太多，不同层次厂家的产品质量相差悬殊。有必要根据我国煤巷围岩条件，制定锚杆支护材料系列及相应的标准。建立比较完善的产品质量保证体系，根除伪劣产品。(4) 完善与提高锚杆支扩施工机具，开发新的产品近年来，我国在煤巷锚杆钻机方面做了大量工作，开发了多种产品。但是由于我国煤巷地质与生产条件复杂多变，现有的锚杆钻机还不能完全满足使用要求，无论是性能与质量都还需进行完善与提高。随着锚索支护技术的推广应用，有必要开发研制专用锚索钻机，提高锚索施工速度。掘锚联合机组在国外已经应用，为巷道掘进和锚杆施工创造了极为有利的条件。我国也应根据国情开展掘锚联合机组方面的研究与开发工作。(5) 完善锚杆施工质量检测与监测技术锚杆支护是隐蔽性工程，必须进行质量检测。目前普遍应用的是锚杆拉拔计、扭矩扳手等。有必要开发研制非接触、无损质量检测仪器，以达到快速、准确、大面积测量的目的。锚杆支护监测对保证巷道安全十分重要，我国许多矿区对此十分重视。但是这项工作还有待于标准化、日常化，纳入到正常生产中。参 考 文 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第126页 Why Longwall in India has not Succeeded as in other Developing Country Like ChinaProf A K GhoseAbstract Of the global hard coal production of some 3300 million tonnes during 2000-2001, China headed the league table with a production of 970 million tonnes, and with a production level of 320 million tonnes India ranked third. Both of these developing nations have large resource endowment in bituminous coal, the proved recoverable reserves at end 1999 stood at 114500 million tonnes in China and at 84396 million tonnes in India according to Survey of Energy Resources 2001 of the World Energy Council1. Coal occupies the centre-stage in the energy economy of both the nations, coal has a share of 75% of the consumption of primary energy in China while in India the share of coal is around 64% in the current mix of commercial energy2. However, any comparison between the technology levels of the two giant nations in coal production would perhaps be invidious, dictated as these are by a whole host of imponderables including the site-specific conditions of the resource endowment, differing thrusts of national policy and the socio-cultural and political milieu. Underground coal mining has a predominant share of some 94% of Chinese coal production, while in India the share is only 21%. To examine and analyze the palpable reasons for not so successful application of Longwall technology in India vis-a-vis China, one needs to examine the chronological evolution of the technology in the two nations, appraise the technogenesis of Longwall technology in both the countries and then home in on the contributory factors. This paper attempts a foray in unravelling the reasons fully cognizant of the fact that any post hoc analysis, as of date, can only outline a hypothesis of the multitude of reasons behind the apparent failure of Longwall technology in India due to subjective interpretation and perception of the issues involved. It is also not always possible to reflect by hindsight on the compulsions of the planner/decision-maker in choosing a specific strategy at any given point of time. Be that as it may, we examine here on a broad canvass the remarkable saga of growth in Longwall technology in China and the apparent under-performance of Longwall in India.Keywords Longwall, Geotechnology, Moonidih colliery, Coal seamsLONGWALL TECHNOLOGY GENESIS AND EVOLUTIONFigure 1 Longwall tons (st) per 8-h machine shift (annual average for a single mine) since 1984The seventeenth century innovation of Longwall system in Shropshire in England has made giant strides over the past three centuries to emerge as the predominant bulk production system in global coal industry today with a share of nearly 70% of the aggregate production and is recognized as the safest, the most productive and cost effective method as well for extraction of coal seams by underground mining3. Longwall mining made its debut in Indian coal mining scene reportedly around 1870s; despite such head start however the progression of the technique in Indian coal industry milieu has been extremely slow and halting. From the early application to stowing faces, caved Longwalling was attempted only around early 1960s and the first mechanized powered support face, the new-age Longwall, was launched in August 1978 at Moonidih Colliery. While this marked the beginning of a major initiative in transfer of innovative Longwall technology in the relatively low technology milieu of Indian coal industry, the overall performance has fallen short of expectations and despite experiences in deploying some 33 mechanized powered support packages to date in Coal India and Singareni Collieries Company, Longwall technology in India remains a laggard, straggling miles behind the global best practices. One could cite the case of Console Energy which operated 14 Longwall mining systems of the 59 operating Longwalls in the United States in 2000, where the best Longwalls annual production average is close to 8100 clean tonnes per 8-h machine shift. Figure 1 shows the evolution of Longwall tons (short tons) per 8-h machine shift (annual average for single console mine) since 19845. There are examples galore of such high performance faces in the United States, Australia and even in China. In benchmarking the performance of Indian Longwall faces with those of China, it is necessary to examine the evolution of coal mining technology in India and China to provide a backdrop. India gained Independence in 1947 and commenced on the national economic planning journey in 1951. China as a nation-state came into existence in 1949 when its coal output was 32.43 million tonnes, very close to Indias coal output.While both the nations started almost at the same base level, Chinas coal odyssey has been marked by a quantum jump in production level which touched an all-time high of 1.3 billion tonnes in 1997 encompassing the three elements of the coal industry, the state-controlled mines, local mines and collective ownership and small mines. Since then, a massive restructuring of Chinese coal industry with closure of over 40 000 small coal mines has curtailed the production level to just around 970 million tonnes in 2000-2001. It is also important to highlight a major difference between Indian and Chinese Longwall experiences. Longwall mining, using the first generation mechanization systems comprising friction/hydraulic props, AFC, and shearer, kicked off almost contemporaneously around 1962-63 both in China and India. Since then, Chinas leap forward in Longwall has been phenomenal and while India has been toying with a handful of powered support Longwall faces with a production of 4.52 million tonnes from 14 faces during 2000-2001, in state-controlled mines in China in 1997 there were 238 fully mechanized faces with an average annual output of 784,000 tonnes. During 1997, more than 76 fully mechanized Longwall systems produced over 1 million tonnes, of which 12 faces produced over 2 million tonnes annually. During 1999, one team in Dongtan mine of Yangzhou Coal Mining Group, Shandong Province produced 5.12 million tonnes with an OMS of 246.96 tonnes6. Benchmarking Indian Longwall faces with those of China in effect is a comparison between unequals! Between 1978 and 1985, about 200 sets of Longwall face equipment were imported in China; such acquisition of technology not only had a direct impact on increased production, but also led to direct replication of imported equipment and the domestic manufacturing capacity was significantly upgraded7. In 1980, some 75% of fully mechanized Longwall equipment were imported in China; by 1995, with absorption of new techno-logy and sheer copying of imported equipment, the share of imported equipment fell to 13.8%6. Through sustained R&D efforts over the past three decades, China has made a major breakthrough in Longwall technology for thick seams using sub-level caving (soutirage) and has emerged as the world leader in this area with record production levels and manufacture of equipment packages for sub-level caving. In 1996, there were 86 fully mechanized sub-level working faces with an aggregate output of 67 million tonnes.Even if China lags behind the performance of the super heavyduty Longwalls in the United States or Australia, the policy thrust of the coal sector in China, the massive investment in imported and indigenous faces, the focus on walking on two legs, fast decision-making and above all the work culture in a mandarindominated society made it possible for China to launch the Longwall odyssey purposefully and achieve a quantum jump in production levels in Longwall, backed by a highly developed manufacturing base for mining equipment8. The critical success factors that were obtainable in China were simply missing in the Indian coal industry context. It is in this backdrop that one needs to appraise the less than adequate performance, an euphemism for poor performance, of Longwall technology in India.APPRAISING THE SCORECARD FOR LONGWALL TECHNOLOGY IN INDIAThe under-performance of Longwall technology, especially of the high-investment powered support Longwall face, which made its debut in August 1978 at Moonidih Colliery, has led to much soul- searching, introspection and articulation of concern over the past 25 years in India. The collapse of heavy-duty Longwall installations at Churcha West (1989) and Kottadih (1997) has merited the attention of the Government and a number of Committees have been appointed over the years to examine the entire gamut of problems of Longwall technology and to suggest remedial measures for bringing about performance improvement. These include the H B Ghosh Committee (1983-84), the Strategic Action Group under the Chairmanship of Shri K A Sinha (1988-89), the S K Chowdhury Committee (1990) to enquire into the circumstances leading to the collapse of Churcha West Face and finally the Mahendru Committee (1998) which, besides enquiring into the collapse of Kottadih face was also charged with the responsibility of studying the performance of all past and operating Longwall faces in the country to assess and recommend the applicability of Longwall technology under Indian geo-mining conditions.By and large, the contributory factors that have been identified for the not so successful operation of Longwall systems converge on the following: n Inadequacy of geological and geotechnical assessment of Longwall locales n Flawed equipment selection with inadequate rating of supports, shearers and coal clearance systems n Management failure in planning, operation, provision of service back-up and spares availability n Failure in inculcating a culture for mechanized Longwall and creating a cadre of Longwall personnel who could serve as change agents in implementing the technology n Issues of power supply, materials supply, ventilation, dust control and availability of clean water for hydraulic emulsions n Absence of a viable manufacturing capacity for Longwall equipment.All these factors culminated in either poor performance or led to collapse of faces which eroded the confidence of the industry on Longwall technology. In a number of papers, the author has undertaken critical studies on Longwall under-performance in Indian coal industry, analysed the problem dimension and pinpointed the major factors which have beleaguered Longwall technology in India8 - 11. The factors which conjointly have blighted Longwall technology can now be examined in depth under three main headings:a) Geological and geotechnical site factorsb) Flawed planningc) Management lacuna.Geological and Geotechnical Site factorsAnalysis of Longwall performance in 28 Longwall faces underscores the fact that investment in pre-mining geological and geotechnical investigations could have averted some of the face collapses or even reduced the risk of operations besides contributing to more careful selection of appropriate face equipment. Accurate and reliable delineation of the geology of a panel is sine qua non for establishing face and panel length avoiding any geological surprises. There are examples galore of disruptions to Longwall operations in practically every Longwall face. A few aberrant experiences include:n Faces at Moonidih encountered a series of step faults at the face and stringers of small dykes, the existence of which were not known at the time of face development.n The face at Seetalpur encountered an igneous intrusion at mid-height of the coal seam and also a massive inrush of water from an overlying seam.n Kottadih panel collapsed because of inadequate support capacity where the support design had been based on data from a single borehole which failed to detect the massiveness of the overlying strata.n At GDK-11A Incline in SCCL serious failure of Longwall units took place because of inadequate support capacity.Flawed PlanningLongwall technology has not been able to take its roots in Indian coal industry soil or establish itself as a preferred system primarily because of flawed planning in the first generation powered support Longwall faces.Instead of providing a conducive seed bed to germinate, to be absorbed and transferred, and then diffused, a large majority of Longwall faces was commissioned at sites where conditions were singularly adverse right from inception. In Seetalpur Longwall face, quite apart from the adverse mining conditions at the face, such as gassiness, and intrusion in the coal seam, the face performance was baulked by the outbye coal clearance capacity with multiple conveyors which constituted weak links in the evacuation system. The Gleithobel plough installed at Moonidih colliery in 1988 could work only two panels due to non-availability of suitable working areas. The coal seam hardness, structure and other workability indices were difficult for ploughing. Many of the sites selected for Longwall application were replete with adverse geological conditions, constrained by panel size and coal clearance system.In general, the parameters of Longwall technology were driven by equipment manufacturers under tied aids and no serious efforts were made by Indian planners to vet the plans, including the equipment specifications, keeping in view the then state-of-theart of Longwall technology. In the process, the coal industry was saddled with technology packages which were backdated (archaic?) in some cases, and often a complete mismatch with the site factors. There was no conscious effort either in choosing the best equipment or proven advanced mining technology. The mix of Longwall equipment, f