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分凉水井矿浅埋煤层开采岩层控制摘要：根据浅埋煤层顶板岩层的赋存特点和长壁开采时基岩老顶的断裂下沉特征，应用关键层理论探讨了初次来压期间基岩老顶的灾害机制和灾害控制，其浅埋煤层工作面顶板主要形成“短砌体梁”和“台阶岩梁”两种结构，给出了控制台阶下沉和维持顶板稳定的支护力计算公式。研究发现，顶板破断后岩块处于不平衡状态，台阶下沉的机制是结构的滑落失稳；岩块触矸前后的台阶下沉分别与断裂下沉和开采高度之间存在着确定的关系；顶板强烈来压主要是由结构滑落失稳造成的，控制台阶下沉的实质是控制岩块沿煤壁的滑落失稳。关键词：浅埋煤层；关键层；岩层控制1研究背景及研究意义1.1研究的背景煤炭是我国的主要能源，在国民经济建设中具有重要的战略地位。长期以来，墙炭在我国一次能源生产和消费构成中均占2/3以上。根据研究预测，2015年煤炭占全国能源消费总量不会低十55%，2050年也将不低十50%。近年来，我国原煤产量总体保持快速增长势头。2009年，在山西煤炭资源整合的情况下，全国累计完成原煤产量296477.24万吨，同比增恤2.69%。近年来我国的煤炭生产和消费量一直居世界第准据预测，到2020年我国煤炭产量占世界煤炭产量的比例将由目前的35%上升到50%左右。我国赋存有大量埋深在150m以内的浅部煤田，如神府、东胜、灵武、黄陵等。最典型的是神府、东胜煤田。神府、东胜煤田探明储量2236亿t，占全国探明储量的1/3，相当于70个大同矿区、160个开滦矿区，是我国目前探明储量最大的煤田，也是世界七大煤田之一。我国西部地区煤炭资源丰富，尤其是陕北侏罗纪煤田已经成为我国煤炭资源富集度最高、煤质最好、开发前景最好的区域之一，具有良好的开发前景。陕北榆神府矿区煤炭大规模开发始于1987年，截至2008年底，榆林市境内侏罗纪煤田生产矿井有260余处，占全省矿井总数的59%，原煤产量占全省的67%以上，成为陕西省乃至全国最重要的煤炭生产基地之一，2007年榆林市原煤产量达到1.32亿吨，2008年1.55亿吨，近年来以每年2000万吨左右的速度递增。榆神府矿区主要由榆神和神府两个矿区组成，而凉水井矿正是属于榆神矿区。浅埋煤层的典型赋存特点是埋深浅、基岩顶板比较薄、表土覆盖层比较厚。生产实践表明，煤层埋藏浅并不一定矿压小，浅埋煤层长壁工作面普遍出现“台阶下沉”现象，支架压毁，矿压显现剧烈，顶板控制具有特殊性。神府矿区的主要特征为煤层埋藏浅，一般在100m左右，基岩薄、单一关键层结构、上覆厚松散层，赋存有大量的典型浅埋煤层。榆神矿区是陕北侏罗纪煤田地质条件、煤质特征最好的地区。该区突出特征匙旱层埋深一般大十150m,煤层厚度大，基岩一般较厚，存在双(多)关键层。近年来，陕北侏罗纪煤田开发速度很快，神北矿区大多数井田已建井投产。榆神矿区部分规划井田建井，多数井田未开工，但也在积极开展前期工作2009年全国接近2/3的原煤产量增量都集中在内蒙古和陕北等西北地区。山西由于煤炭资源整合，原煤产量下降，西北地区原煤产量的快速增长使我国煤炭生产中心加速西移，从客观上促进了陕北榆神矿区近浅埋煤田的大力开发。榆神府矿区早期的开采实践表明，煤层埋藏浅并不代表工作面顶板压力小，相反工作面现场实测顶板压力很大，工作面顶板往往出现台阶下沉和整体切落现象。国内学者对典型浅埋工作面进行了大量研究，并形成了理论。随着近几年来榆神府矿区近浅埋煤田的大力开发，近浅埋煤层长壁工作面开采的特殊的矿压显现日益突出。目前国内学者对近浅埋煤层长壁工作面的矿压规律和顶板来压机理的研究还不多，此类问题还待深入研究。榆神府矿区浅埋煤层大致可分为2种类型。基岩比较薄、松散载荷层较厚的浅埋煤层。其顶板破断为整体切落形式，易于出现顶板台阶下沉，此类浅埋煤层称为典型浅埋煤层。可以概括为:埋藏浅，基载比小，基本顶为单一关键层结构的煤层。基岩较厚、表现为两组关键层，其矿压显现规律介十普通工作面与典型浅埋工作面之间，存在轻微的台阶下沉现象，可称为近浅埋煤层。根据现有浅埋工作面矿压观测结果，得出典型浅埋煤层工作面主要有如下特征。（1）顶板基岩沿全厚切落，基岩破断角较大，破断直接波至地表。来压期间有明显的顶板台阶下沉和动载现象。工作面覆岩不存在“三带”，基本上为冒落带和裂隙带“两带”。（2）浅埋煤层工作面顶板一般为单一主关键层类型，老顶岩块不易形成稳定的砌体梁结构。基岩厚度比较大时，会出现两个关键层组，形成大小周期来压现象，其矿压显现特征介于浅埋煤层采场和普通采场之间。（3）基岩与载荷层厚度之比Jz(简称基载比)，对来压显现有重要影响。典型浅埋煤层可以采用以下指标判定:埋深不超过150m，基载比Jz小于1，顶板体现单一主关键层结构特征，来压具有明显动载现象。随着我国西部大开发建设和国家建立陕北能源基地的契机，榆神府矿区浅埋煤层的建井和投产速度口益加快。随着开采强度的加大，开采深度的增加，该区对厚基岩斜井下的近浅埋煤层的开采口益增多。近浅埋煤层上覆基岩厚度一般比较大，上覆双关键层结构，其矿压规律、工作面顶板破断运动规律与典型浅埋煤层(薄基岩，厚松散砂土层)有一定区别。国内学者对榆神府矿区典型浅埋煤层工作面顶板来压机理的研究已开展不少，而对近浅埋煤层工作面矿压规律和顶板来压机理研究很少，此类条件的工作面矿压规律和顶板来压机理研究还有待于深入。1.2浅埋煤层国内外研究现状(1)国外研究现状国外学者在浅埋煤层顶板岩层控制方面做了大量的研究工作，前苏联M.秦巴列维奇对莫斯科近郊的浅埋煤田做了系统研究，提出了台阶下沉假说。该假说认为当煤层埋藏较浅时，上覆岩层可视为均质。随工作面的推动，顶板将呈斜六面体沿煤壁上方垮落直至地表，支架上所受的载荷应考虑整个上覆岩层的作用。同时前苏联B.B.布德雷克对莫斯科近郊浅埋煤田矿压研究后指出:在埋深100m以内，在存在厚粘土层条件下，放顶时支架出现动载现象，说明浅埋煤层顶板来压迅猛且与普通采场顶板逐次垮落失稳形成的缓和来压有明显的区别。80年代初，澳大利业B.霍勃尔瓦依特对当地浅埋煤层长壁开采的矿压特征进行了研究，发现地表最大下沉量为采高的60%，最大下沉量的85%发生在距工作面40m的范围内。这说明采空区被迅速压实，煤壁附近上覆岩层迅速发生整体移动。印度对江斯拉矿浅埋煤层综采工作面进行了开采实践，得出江斯拉矿浅埋煤层综采工作面上覆岩层破断运动规律和一般埋深的工作面有所不同，并认为浅埋煤层工作面上覆岩层垮落带与裂隙带交叉，形成周期性断裂，步距较短，具有裂隙较密集的特点。英美等国为了控制浅部煤田开采所造成的地表沉陷破坏，多采用房柱式开采，并且进行了地表岩层移动和采前地表地震波探测与工程地质评价等工作。有些南美国家也因缺乏有关技术未能采用长壁开采，主要开展了房柱式开采地表沉陷预计和煤柱载荷确定的研究工作。综上所述，国外对十浅埋煤层的研究总体上认为浅埋煤层开采上覆岩层的破断直接波及到地表，支架有动载现象，上覆岩层往往发生整体切落下沉。国外文献中仅对浅埋工作面长壁开采的一些矿压现象进行了描述，更多的研究在于对矿压及地表塌陷现象实测分析，没有对近浅埋煤层长壁工作面的矿压显现规律和顶板破断运动规律进行研究，更没有对近浅埋煤层工作面顶板的来压机理进行研究。（2)国内研究现状随着神东矿区浅埋煤层的开采，我国学者对浅埋煤层长壁工作面矿压的研究逐渐开展起来。1991年，神东公司与西安科技大学石平五、黄庆享等对大柳塔煤矿C202试采工作面进行了现场观测。结果表明，工作面顶板周期来压较为明显，出现台阶下沉现象，浅埋煤层长壁工作面仍表现有明显的矿压显现。随后黄庆享等对大柳塔1203综采面进行了相似模拟及数值分析。工作面顶板初次来压和周期来压都表现为上覆基岩一次性全厚破断，台阶下沉严重，来压剧烈。研究认为，基岩层内的剪切力是引发工作面顶板基岩破断及其全厚切落的主因，上覆基岩整体台阶下沉使工作面上覆岩层活动和一般埋深工作面有所不同，薄基岩、单一关键层结构的浅埋煤层顶板不能形成稳定的砌体梁结构。1992年西安科技大学石平五教授在煤炭科学基金“浅埋煤层矿压显现和岩层控制”较为系统地研究了神府矿区浅部初期开采的一些规律性问题，主要形成浅埋煤层白似下认识:煤层埋藏浅，地表覆盖层作为重要影响层有可能直接参与工作面矿压显现;一般情况下难以形成稳定的“砌体梁”结构，来压显现较为剧烈；采动损害传递较快，地表大多形成不连续沉陷。1995年以后，我国学者开始对薄基岩、上覆厚松散层的浅埋煤层长壁开采工作面板来压机理及其控制进行研究。黄庆享在“浅埋煤层的矿压特征与浅埋煤层定义”中根据3个不同条件的浅埋深煤层工作面矿压实测，得出了浅埋深煤层顶板破断规律与普通采场不同，并提出了以关键层基载比和埋深为指标的浅埋深煤层定义，为建立顶板结构模型和进行顶板控制奠定了基础。黄庆享还在“浅埋煤层长壁开采顶板结构理论与支护阻力确定”中建立了浅埋煤层初次来压的“非对称三铰拱”结构模型。1.3研究的意义有关学者利用关键层理论对典型浅埋工作面的矿压显现特征作出了的解释，并揭示了其来压机理，但还很少应用关键层理论对近浅埋煤层工作面的矿压规律和顶板来压机理进行过系统研究。本文将在前人研究基础上对近浅埋煤层长壁开采的矿压显现规律、顶板破断运动规律、顶板来压机理等进行深入研究，形成榆神府矿区近浅埋煤的顶板结构理论。从而对近浅埋长壁开采的矿压规律和顶板控制研究提供理论指导，进一步促进榆神府矿区近浅埋工作面的安全高效开采。2浅埋煤层上覆岩层运动特征及浅埋煤层定义2.1浅埋煤层上覆岩层运动的主要特征根据矿压观测结果（表1），浅埋煤层工作面上覆岩层运动有如下主要特征：（1） 顶板基岩沿全厚切落，破断直接波及地表。（2） 来压期间有明显的顶板台阶下沉和动载现象。（3） 工作面上覆岩层基本上为冒落带和裂隙带“两带”，如图1。（4） 典型的浅埋煤层顶板为单一关键层类型，老顶不易形成稳定的砌体梁结构。（5） 顶板基岩厚度大时，会出现两个关键层，形成大小周期来压现象。（6） 基岩与载荷层厚度之比Jz（简称基载比），对来压显现有重要影响。当Jz 0.8时一般不出现顶板台阶下沉。表1 工作面地层组成与矿压显现一览表工作面顶板组成（m）来压步距（m）支架阴力（kN/架）台阶下沉（mm）基岩层载荷层Jz初次周期Dz初撑力工作阻力初次周期C20217.348.30.3624.07.563.2306234.66458120318.032.00.5627.012.01.26201228001000架后120932012280010002060145.042.51.0635.411.11.1647285283很小很小2060442.661.40.69836665063200100注：基载比Jz=基岩厚度/载荷层厚度；Dz为动载系数；1203工作面周期来压Jz11.52.2浅埋煤层的定义浅埋煤层类型：典型的浅埋煤层，近浅埋煤层典型的浅埋煤层：对于基岩比较薄、松散载荷层厚度比较大的浅埋煤层，其顶板破断运动表现为整体切落和台阶下沉，称为典型的浅埋煤层。即，埋藏浅、基载比小、老顶为单一关键层结构的煤层。近浅埋煤层：对于基岩厚度比较大、松散载荷层厚度比较小的浅埋煤层，其矿压显现规律介于普通工作面与浅埋煤层工作面之间，顶板一般呈现两组关键层结构，存在轻微的台阶下沉现象，可称为近浅埋煤层。浅埋煤层采场的主要矿压特征：老顶破断运动直接波及地表，顶板不易形成稳定的结构，来压明显，支架处于给定失稳载荷状态。浅埋煤层的判定指标：埋深不超过150m，基载比Jz小于1，顶板体现单一主关键层结构特征，来压具有明显动载现象。冒落带裂隙带图1 工作面上覆岩层整体切落与台阶下沉3浅埋煤层长壁开采顶板砌体梁结构及其稳定性浅埋煤层长壁工作面在开采过程中，顶板关键层将产生周期性破断，破断后形成的岩块也将相互铰接形成砌体梁结构。由于浅埋煤层顶板单一关键层的特点，其顶板砌体梁结构也将呈现新的形态。根据顶板岩块的几何特征和铰接状态，浅埋煤层顶板形成“短砌体梁”和“台阶岩梁”两种结构形态。3.1老顶“短砌体梁”结构分析3.1.1老顶“短砌体梁”结构模型根据现场实测分析和模拟研究，浅埋煤层工作面顶板关键层周期性破断，形成的岩块比较短，岩块的块度i（岩块厚度与长度之比）接近于1，形成的铰接岩梁可以形象地称为“短砌体梁”结构。按照砌体梁结构关键块分析法，建立“短砌体梁”结构模型如图2所示。 图2 “短砌体梁”结构关键块的受力P1、P2块体承受的载荷；R2块体的支承反力；1、2、块体的转角；a接触面高度；QA，QBA，B接触铰上的剪力；l1，l2，岩块长度结构的几个参数：图2中很小，作用点的位置忽略了cos项。岩块在采空区的下沉量与直接顶厚、采高m及岩石碎胀系数有如下关系： （1） 根据岩块回转的几何接触关系，岩块端角挤压接触面高度近似为： （2）鉴于岩块间的是塑性铰接关系，水平力T的作用点可取0.5a处。3.1.2“短砌体梁”结构关键块的受力(1)力系平衡由于老顶周期性破断的受力条件基本一致，可以认为l1 = l2= l。在图中取=0，并近似认为= 可得： （3）同理对岩块取=0、=0可得： （4） （5）(2)确定两个关键力由几何关系，。根据文献8，令老顶岩块的块度，由（10-3）、（10-4）、（10-5）式求出： （6） （7）(3)初步的分析为老顶岩块与前方岩层间的剪力，顶板稳定性取决于与水平力T的大小。浅埋煤层工作面顶板周期破断的块度比较大，水平力T随块度i的增大而减小，随回转角的增大而减小。当i=1.01.4时，剪力=（0.931），工作面上方岩块的剪切力几乎全部由煤壁之上的前支点承担，这是“短砌体梁”结构容易失稳的根本原因。3.1.3“短砌体梁”结构的稳定性分析周期来压期间，顶板结构失稳一般有两种形式滑落失稳(Sliding)和回转变形失稳(Rotation)。下面分析“短砌体梁”结构关键块的稳定性，探讨浅埋煤层工作面顶板台阶下沉的机理。（1）回转失稳分析顶板结构不发生回转变形失稳的条件为： （8）式中，表示老顶岩块端角挤压强度；T /a表示接触面上的平均挤压应力。根据实验测定9=0.4，令为载荷层作用于老顶岩块的等效岩柱厚度，并将、及有关参数代入（8）式可得： （9）按照神府浅埋煤层厚梁特点，分别取块度i=1.0、1.4，基岩强度取40Mpa（实线）、60Mpa（虚线），将与的关系绘入图2中。由图可知，只要载荷层厚度小于180m都不会出现回转失稳。显然，老顶“短砌体梁”结构难以发生回转失稳。i =1.0i =1.4 图3 及与回转失稳的关系 图4 滑落失稳与及i的关系（2）滑落失稳分析防止结构在A点发生滑落失稳，必须满足条件： （10）式中，为岩块间的摩擦系数，由实验确定为0.5。将(10-6)、(10-7)式代入(10-10)式可得： （11）将上式关系绘于图10-8中，可见i值在0.9以上将出现滑落失稳。浅埋煤层工作面周期来压期间i一般在1.0以上，顶板易于出现滑落失稳。3.2老顶“台阶岩梁”结构分析3.2.1老顶的“台阶岩梁”结构模型及其稳定性分析根据浅埋煤层工作面现场实测和模拟实验，开采过程中顶板存在架后切落（滑落失稳）现象。其原因是在切落前关键块的前铰点位于架后（图5），老顶悬伸岩梁端角受水平力和向下的剪切力的复合作用，端角挤压系数仅为0.13。根据“SR”稳定条件，此时更容易出现滑落失稳。老顶架后切落形成的结构形态如图6所示，可以形象地称为“台阶岩梁”结构。结构中N岩块完全落在垮落岩石上，M岩块随工作面推进回转受到N岩块在B点的支撑。此时N岩块基本上处于压实状态，可取=。N岩块的下沉量为：其中，为直接顶厚度；m为采高；KP为岩石碎胀系数，可取1.3。取、，并代入可得： （12）图5 关键块架后切落前的状态图6 老顶“台阶岩梁”结构模型P1、P2块体承受的载荷；R2N块体的支承反力；1M块体的转角；a接触面高度；QA，QBA，B接触铰上的剪力； l岩块长度从图10-10可知，M岩块达到最大回转角时 （13）则有： （14）分别取为8（实线）和12（虚线），绘出水平力与块度及回转角的关系如图10-11所示。水平力随回转角的增大而减小，随块度i的增大明显下降，随最大回转角的增大而增大。将（10-12）、（10-14）式及=0.5代入（10-10）式，可得“台阶岩梁”结构不发生滑落失稳条件为： （15）按照浅埋煤层工作面一般条件，取=812，如图7所示，只有在块度小于0.9时才不出现滑落失稳。浅埋煤层老顶周期破断块度i一般在1.0以上，所以“台阶岩梁”也容易出现滑落失稳。 图7 水平推力T与及i的关系 图8 滑落失稳与及i的关系3.3 控制老顶结构滑落失稳的支护力确定根据浅埋煤层“短砌体梁”和“台阶岩梁”结构分析，两种结构形态都难以保持自身稳定而出现滑落失稳，这是浅埋煤层工作面顶板来压强烈和存在顶板台阶下沉现象的根本原因。浅埋煤层老顶周期来压控制的基本任务是控制顶板滑落失稳，必须对顶板结构提供一定的支护力R才能控制滑落失稳。确定维持顶板结构稳定的合理支护力条件为： （16）(1)控制“短砌体梁”结构滑落失稳的支护力将（10-6）、（10-7）式代入（10-16）式，取=0.5可得： （17）由图10-6可知，回转角由下式确定：支护力与块度和回转角的关系如图9所示，可见控制“短砌体梁” 结构滑落失稳的支护力随老顶块度i的增大而增大，随回转角的增大而减小。图9 控制“短砌体梁”结构的支护力R与i和的关系(2)控制“台阶岩梁”结构滑落失稳的支护力确定将（12）、（14）式代入（16）式，取=0.5可得： （18）支护力与i、和（8为实线，12为虚线）的关系如图9所示，支护力随老顶块度i的增大而增大，随回转角的增大而减小。4 浅埋煤层采场支护4.1浅埋煤层采场的支架围岩动态作用关系采场支护是顶板控制基本手段，确定合理支护阻力是顶板支护的关键参数。确定合理的支护阻力，首先必须根据顶板结构的稳定性研究支架与围岩的相互作用关系，以便确定最危险状态下的顶板压力。根据浅埋煤层采场周期来压的结构分析，顶板主要有“短砌体梁”和“台阶岩梁”两种结构形状。两种结构都属于滑落失稳类型，支架主要承受结构失稳形成的压力，最危险状态的载荷可以说是“给定”的，支架工作处于“给定失稳载荷”状态。必须提供必要的支护力才能维持顶板结构稳定，即由支架和顶板结构共同作用来平衡顶板的滑落失稳力、维持顶板结构的稳定性。由上一节关于合理的顶板结构支护力的分析可知（图8、图9），虽然浅埋煤层工作面支架处于“给定失稳载荷”状态，但控制顶板结构稳定所需的支护阻力不是恒定值，而是随岩块的回转运动而变化的。此外，在顶板切落运动过程中，关键块上的载荷层作用于关键块上的载荷不是上方岩柱的静态重量，存在载荷传递效应。必须提供足够的支护阻力控制顶板的初始切落运动，才能防止顶板结构的进一步恶化所引起的失稳载荷增大，达到以最小的支护阻力控制顶板的目的，这就是浅埋煤层周期来压期间的“支架围岩”动态作用关系。4.2合理支护阻力的确定下面首先以“短砌体梁”结构为例，说明支护阻力的确定方法。浅埋煤层工作面周期来压时顶板最危险的状态如图10所示，工作面支架的支护阻力Pm由直接顶岩柱重量W和老顶滑落失稳所传递的压力RD组成： （19）图10 “短砌体梁”结构的“支架围岩”关系老顶结构滑落失稳作用于支架的压力为：代入（17）可得： （20）周期来压期间老顶关键块上载荷层的计算仍然借鉴太沙基岩土压力计算原理，顶板载荷P1的构成如图11所示。图11 周期来压顶板载荷老顶关键块上的载荷层处于采场上覆岩层的离层区，该区的载荷层处于非压实状态。实测神府1203工作面地表最大下沉速度点滞后采场约30m，表明浅埋煤层工作面关键块上的载荷也不是载荷层的全部重量，存在载荷传递效应。载荷传递系数KG（0）可以表示为： 式中，Kr为载荷传递岩性因子；Kt为载荷传递的时间因子。由图10-15可知，老顶关键块的载荷P1由老顶关键层重量PG和载荷层传递的重量PZ组成： P1 = PG + PZ （21） （22） （23）式中，h为老顶关键层厚度；l为关键块长度（周期来压步距）；为基岩容重；h1为载荷层厚度；为载荷平均容重；KG（0）为载荷传递系数。由于载荷层厚度大，仍然按太沙基土压力计算原理近似估算载传递系数。作用于老顶岩块的载荷为： ， （24） 在长时间状态下取Kt =1，联立（23）和（24）可得周期来压时载荷传递岩性因子： （25） 由此可得周期来压时的载荷传递系数为： （26）式中，为载荷层的内摩擦角；为载荷层侧应力系数。由（21）、（22）、（23）可得作用于关键块的载荷为： =+， （27） 由（18）、（19）可得，控制顶板所需的支护阻力为： （28）按与“短砌体梁”结构支护阻力计算相同的方法，可以求得“台阶岩梁”结构条件下的控制顶板所需的支护阻力为： （29） 考虑支架的支护效率，工作面支架的工作阻力为： （30）其中，为支架的支护效率。参考文献1 钱鸣高、石平五.矿山压力及岩层控制. 徐州：中国矿业大学出版社，20032 岑传鸿、窦林名.采场顶板控制与监测技术. 徐州：中国矿业大学出版社，20043 钱鸣高、廖协兴、许家林. 岩层控制的关键层理论. 徐州：中国矿业大学出版社，20004黄庆享.浅埋煤层长壁开采顶板结构及岩层控制研究.徐州:中国矿业大学出版社，20005黄庆享.浅埋煤层的矿压特征与浅埋煤层定义.岩石力学与工程学报，20026黄庆享.浅埋煤层长壁开采顶板结构理论与支护阴力确定.矿山压力与顶板管理.2002任务书学院 专业年级 学生姓名 任务下达日期：20xx年1月8日毕业设计日期：20xx年3月12日 至 20xx年6月8日毕业设计题目：凉水井煤矿2.4 Mt/a新井设计毕业设计专题题目：凉水井矿浅埋煤层开采岩层控制毕业设计主要内容和要求：以实习矿井凉水井煤矿条件为基础，完成凉水井煤矿2.4Mt/a新井设计。主要内容包括：矿井概况、矿井工作制度及设计生产能力、井田开拓、首采区设计、采煤方法、矿井通风系统、矿井运输提升等。结合煤矿生产前沿及矿井设计情况，撰写一篇关于凉水井矿浅埋煤层开采岩层控制的专题论文。完成2010年国际岩石力学与采矿科学杂志上与采矿有关的科技论文翻译一篇，题目为“Longwall mining-induced fault reactivation and delayed subsidence ground movement in British coalfields”，论文5466字符。院长签字： 指导教师签字：第19页翻 译 部 分英文原文LONGWALL MINING-INDUCED FAULT REACTIVATION AND DELAYED SUBSIDENCE GROUND MOVEMENT IN BRITISH COALFIELDSAbstract: Faults located in areas undergoing mining subsidence during the longwall extraction of coal seams may undergo reactivation. This has been observed and documented throughout the UK (and in other major coalfields around the world) over the past 150 years. The impact of subsidence induced fault reactivation may cause moderate to severe damage to foundations, houses, buildings, structures and underground services, as well as damage to agricultural land through disruption of drainage and alteration of the gradient. Monitoring of faults, as they are affected by undermining, has resulted in a better understanding of fault reactivation mechanisms and of the various styles of fault reactivation, in different geological and mining settings.The duration of fault reaction is difficult to determine due to the lack of observational data. However, trough subsidence following longwall extraction of coal is rapid, often being completed within weeks to months. This is commonly followed, shortly afterwards, by a period of delayed subsidence known as residual subsidence, which in the British Coal Measures, rarely accounts for more than 10%of the total subsidence. In many circumstances, where faults are not present, residual subsidence is complete within four months, although several cases have been recorded where subsidence effects were still being observed more than two years after mining had finished. Generally, it is accepted that fault reactivation sometimes may extend over the period of residual subsidence.In parts of the abandoned or partially active coalfields in the UK, relatively smaller ground movements have been observed in the vicinity of fault outcrops many years after mining has ceased. The reasons for this are not fully understood. Nonetheless, prolonged periods of fault reactivation may have an important effect on land use and construction.The objectives of this paper are to consider fault reactivation and, in particular, to document examples of post-mining ground movements around fault outcrops and to discuss possible causal mechanisms. Features associated with these movements include increases in elevation of the ground surface and deformation (e.g. subsidence, scarps, compression and tension)of the ground surface in the vicinity faults. These features, in turn, may be associated with groundwater or mine water rebound.IntroductionFaults located in areas where longwall mining subsidence is taking place may be susceptible to reactivation. This may result in the generation of scarps at the ground surface. Fault scarps in the coalfields of the UK vary from subtle topographic deflections and flexures only recognizable across agricultural land or roadside verges, to distinct, high-angled fault scarp walls 3-4 m high and at least 4 km long. They occur in rural and urban parts of Britain in both the exposed and concealed coalfields. The consequences of fault reactivation may be damage to surface structures, services, utilities and transport networks. Frequently, reactivated faults also have disrupted agricultural land through alteration of drainage and gradient. In addition, fault reactivation may cause the failure of natural slopes, high-walls in opencast mines, engineered cuttings and embankments, and can influence stream and groundwater flows.Fault reactivation that is contemporaneous with mining subsidence occurs because of the release of strain accumulations along the fault zone. This can cause shear displacements, resulting in uneven subsidence on one side of the fault relative to the other. Unfortunately, the duration of fault reactivation associated ground movements is difficult to assess because of the lack of reliable observational data. Public safety often is of direct concern when incremental ground-surface displacements occur rapidly, as when blocks of ground move into open-spaces of underground workings.Overview of mining subsidenceThe majority of the coal mined in Britain in the twentieth century and at present, although now greatly reduced in amount, was and is by longwall mining. Longwall mining involves the total extraction of a series of panels of coal that are separated by pillars whose width is small compared to overburden thickness. The coal is exposed at a face 30 to 300 m in width between two parallel roadways. The roof is artificially supported temporarily at the working face and in, and near, the roadways. After the coal has been won and loaded the artificial face supports are advanced, leaving unsupported rock, in the areas where coal has been removed, to collapse. Subsidence at the surface more or less follows the advance of the working face and may be regarded as immediate and contemporaneous with mining, producing more or less direct effects at the surface. The subsidence that occurs over a completely mined out area in a seam is trough-shaped and extends outwards and upwards, beyond the limits of mining in all directions. Hence, the surface area affected by ground movement is greater than the actual area worked in the seam. The boundary of the surface area affected is defined by the angle-of-draw，depending on the geologic, structural and the actual datas.The lag-time taken for arrival of subsidence at a ground-surface point(P)to be completed is approximately inversely proportional to the rate of forward advance of the workings. The upward transmission of movement to the surface is almost in- stantaneous, commencing when the strata at seam horizon begin to relax, following the advancement of the temporary roof supports. In practice, measurable subsidence appears to occur when the face comes to be within a horizontal distance of 0.75d of a given point, P, on the surface and reaches approximately 15%of maximum when the face is directly below P. For all practical purposes, the magnitude of vertical subsidence is complete when the face has advanced for a lateral distance of about 0.8d beyond P. Residual subsidence then occurs, those points that are subsiding fastest experiencing the most residual subsidence.Residual subsidence may continue after instantaneous subsidence takes place for periods, normally, of up to two years or more. The magnitude of residual subsidence is proportional to the rate of subsidence of the surface and is related to the mechanical properties of the rocks above the coal seam concerned. For instance, strong rocks produce more residual subsidence than weaker ones. Residual subsidence rarely exceeds 10%of total vertical subsidence, if the face is stopped within the “critical area” but falls to 2 to 3%if the face has passed the critical width. Very occasionally, values greater than 10%have been recorded. For instance, after a study of five coal mines in Britain, Ferrari (1997)found that residual subsidence ranged from 8 to 45%of total subsidence and continued for up to 11 years after mining operations ceased. Singh noted that residual subsidence in the Kamptee Coalfield, India, varied between 7.4 and 22.4%of total subsidence and took place in less than two years. According to Yao and Reddish, the maximum residual subsidence in a level seam occurs at the lateral half-subsidence point along a longitudinal line to the workings while along a transverse line it occurs at the centre of the workings. The maximum residual subsidence in an inclined seam occurs at the ribside point.Faults and their reactivationIn areas where faults do not exist the contributory factors which influence the continuance of subsidence are as follows:Depth of workings, in general subsidence ceases sooner in the case of shallow workings.Soft coal and soft floor rocks may encourage yielding in the presence of abutment pressure along the extraction edgesIncomplete roof and floor convergence, which is influenced by the depth of workings and physical properties of the strata.Bed separation within an area undergoing subsidence provides the potential for the gradual closure of such voids.Changes in the physical support conditions of the goaf area can cause yield and further settlement of the overlying strataAs mentioned, pre-existing faults tend to become the loci of subsidence movement, by concentration of abnormal deformation of the ground surface. Fault reactivation not only occurs simultaneously with mining subsidence but the movement can take place over periods ranging from weeks to years, and may continue after normal subsidence has ceased. It can occur in phases separated by periods of where reactivation of faults ceases until the fault is approached by further longwall panels. Unfortunately, the precise duration of movement is impossible to determine. On the other hand, many faults have not reacted adversely when subjected to subsidence.The mechanisms involved in mining-induced fault reactivation have been reviewed by Donnelly. Such reactivation during longwall mining basically is controlled by several inter-related geological and mining factors. The geological factors that influence fault reactivation include the prevailing and pre-existing stress field, the geological history of the fault, the geotechnical properties along the fault, proximity of the fault to the ground surface, the local hydrogeological regime, and the incidence and orientation of discontinuities in adjacent rock masses. In general, it is the main faults, which define region structural cells that have the greatest tendency to undergo reactivation when they are subjected to mining subsidence. In general, main faults tend to have suffered more episodes of incremental displacement and therefore tend to have a lesser degree of inter-surface roughness, thus making them less resistance to forces of shearing. The mining factors that influence fault reactivation are the depth of extraction, the mine and fault geometry, the horizontal distance of the workings to the fault, the rate of mining, the thickness of the extraction, and the history and intensity of mining.In fact, faults also tend to act as boundaries controlling the lateral extent of the subsidence trough. If a fault is encountered during seam extraction and its throw is large, then if the workings terminate against the fault permanent strains are induced at the surface, which probably are accompanied by severe differential subsidence in the zone of influence of the fault. Indeed, a subsidence step may occur at the outcrop of such faults. When workings terminate against a fault plane that has an angle of hade larger than the angle-of-draw at the edge of the mine workings and the line joining this edge to the limit of significant ground movement at the surface,then the normal subsidence profile extends to the surface. Conversely, when the hade of the fault is less than the angle-of-draw, the fault determines the extent of the subsidence trough, which in this case is less than that normally expected. Faults are most likely to react adversely when their hade is less than 30, when they have simple form and the material occupying the fault zone does not offer high frictional resistance. Fault scarps tend to occur when faults represent single sharp stratal breaks. By contrast, if a fault consists of a relatively wide shatter zone, then the surface subsidence effects usually are less pronounced, due to a tendency to spread the deformation across many smaller surfaces making up the weak-rock zone. The abnormal subsidence associated with displacement concentrated along faults is influenced by the type of surface rocks. This explains why stepping is not consistent along a fault affected by subsidence. Furthermore, stronger surface rocks, such as some sandstones and limestones, tend to fracture and form blocks that cause more laterally-widespread damage because of the cantilevering effect of the fractured blocks. This may explain the reverse stepping that occurs at times. Where a fault passes through a block jointed formation that outcrops at the surface,then severe fissuring or fracturing can occur at the surface. The fissures generally run parallel to the line of the fault but can occur as broadly as up to 300 m outwardly away from it. The thickness and nature of the unconsolidated deposits above bedrock also can influence the magnitude of individual fault steps(see below). The type and extent of subsidence associated with faults also depends on the methods and extent of mining in relation to a particular fault plane. The most notable steps occur when the coal is worked beneath the hade of a fault, because the strain relieving process encourages directly-localised, increased movement along the fault plane, faces in other positions being much less likely to be brought into differential movement. Workings on the upthrown side of a fault are more likely to cause stepping than similar workings on the downthrown side, but this is not always the case. Steps are usually oriented downwards towards the goaf. The vertical displacement can vary along a fault step and may be accompanied by some degree of horizontal displacement. However, the size of step often appears to be consistent where the underground conditions are uniform. The extent of a step is very much limited directly to the magnitude of the area worked. Moreover, a single panel of small width-depth ratio approaching a fault at right angles is less likely to cause a step than a large width-depth ratio working parallel to a fault. A fault step is much more likely to develop when the fault has been affected by previous workings in the same mine, but stratigraphically above this horizon in shallow seams than it is for a single working in an unworked area. Once differential movement has been activated, then further movement in the immediate area can cause renewed movement along a fault, which at times may be out of proportion to the thickness and lateral extent of the coal extracted. The likelihood of fault reactivation increases with increasing number of seams worked and is associated more frequently with shallow workings. The cumulated effect of reactivation following multi-seam extraction may result in the generation of a large fault scarp in excess of 2 m in height. The morphology, height and persistence of mining-induced fault scarps may be naturally influenced by the geotechnical properties of the surface materials and the geomorphology. For instance, fault scarps in the South Wales Coalfield have been observed to grow to more than 4 m in height and up to 4-5 km in length where thick sandstones crop out. In addition, where a thin superficial cover is overlain by brittle engineered materials such as concrete surfaces or roads, then scarps tend to be distinctive, limited to single breaks, and may extend over hundreds of metres in length and be up to 2 m in height. However, the ground deformation on either side of the fault tends to be limited to a band of only a few metres. On the other hand, where weaker geologic ground exists, such as thick ablation tills, sands and gravels or clay, then these may not support the formation and preservation of a fault scarp, or may simply allow temporary scarps to develop before erosion destroys them. In such instances a flexure develops, with a reduced amplitude, but affecting a much broader area on either side of the fault. What is more, in weak or unconsolidated soils the main fault slippage plane may become detached or splay into multiple semi-parallel fractures. Some faults have been observed in exploratory trenches to generate listric slip surfaces and intricate deformation structures. Layered parallel detachment may occur when the superficial deposits are stratified in an approximately horizontal fashion. This may lead to the generation of secondary faults that may branch out into a multitude of fractures or die out before reaching the original ground surface. The formation of graben structures are also a common surface expression of fault reactivation, especially where their traces occur on roads or concrete surfaces and the faults lie more or less parallel to the road alignment, or where lateral spreading has occurred in the aforementioned step-wise fashion.Usually, horizontal displacements lateral shear only forms a component of ground movement at the outcrop of a fault. However, in some instances lateral shear displacements can dominate, with little or no vertical slip. Lateral shear tends to occur along faults when there is a significant change in strength of rock mass across the fault as, for instance, where a fault displaces sandstone against mudstone. It also is controlled by the geometrical relationships between mining and a fault.Compressional humps and heave may occur at fault outcrop positions during reactivation. According to Donnelly and Reddish, some compressional humps are due to translational shear along bedding planes and joints. Humps remain as permanent features on the ground surface but may become degraded in time due to, for example, weathering and erosion, the ploughing of farmland or road repairs. In the USA however, compressional humps have been reported to be temporary in nature that generally arrives and passes as a wave form.Faults, ground movements and mine water reboundField observations indicate that fault movements may occur during mining or after mining has ceased. The mining-contemporaneous movements along faults are associated with mining subsidence. Those movements that occur after mining has ceased may be associated with, for example, residual subsidence (see above), especially if it is significant, and mine water rebound. Unfortunately, it can be difficult or impossible to predict when the post-mining movements may occur. This can be of significance in Britain since insurance claims for mining subsidence compensation must be made within seven years of mining having taking place, according to the Subsidence Act 1994.The reason for this is that it is assumed, with traditional mining technical wisdom, that within seven years after the completion of mining most of the ground movement has taken place. Although this may seem to be reasonable, the authors have observed that such is not always the case, especially when faults occur within a subsidence trough.Both a change in elevation and deformation of the ground surface has been observed in the vicinity of fault outcrops during, and several years after mining has occurred. In addition, groundwater emissions and release of gas emissions may be associated with faults that have undergone reactivation.Underground mining generally has or had to overcome the problem of groundwater-induced effects by dewatering the workings. Early mines in favourable locations utilized gravity drainage via tunnels(soughs)discharging into rivers or the sea, but it was the late 18 th century development of the steam engine that enabled large volumes of water to be pumped from mines. Frequently, deeper coal workings were made complexly interlinked, often from one colliery to another, to facilitate dewatering, access, ventilation, coal removal etc. Hence, it became necessary to maintain a network of pumping stations utilizing old shafts or boreholes in abandoned areas of a coalfield, in order to protect working collieries from flooding. It follows that the complete closure of a coalfield and cessation of pumping results in the ultimate flooding of most, if not all, the old workings with subsequent rebound of groundwater levels, at least until an overall hydrostatic equilibrium is reached. There is sufficient borehole monitoring and observation evidence to conclude that generally there is, at present, a general condition of regional recovery of the groundwater levels in the British coalfields. In this context, mine water may be regarded as water that has had contact with mine workings. Mine water frequently can be distinguished as water that is highly ferruginous and often has a low pH value due to solution of pyrite oxidation products.Groundwater and mine water rebound may increase the pore water pressures associated with faults, causing a reduction in shear strength of the material involved. This is capable of counteracting part of the normal stress acting across a fault and therefore may result in reactivation. It is the pore water pressure rather than the moisture content that influences fault stability. Pore water is practically incompressible and so counteracts the normal stress acting across a fault plane. If pore water confined within a fault zone cannot escape it will support a part of the normal stress and reduce the stability of the material concerned. Indeed, Sibson and Donnelly regarded fluctuating groundwater levels and elevated water pressures within fault zones as one of the most significant factors controlling both tectonic and mining induced fault reactivation. As Britain is located on the relatively stable north-western European Platform it is generally regarded as a region of low seismicity and low tectonic deformation. There is no evidence to suggest that fault reactivation contemporaneous with mining subsidence and fault scarp generation in mining areas may have been caused by earthquakes and/or neotectonic processes. About 400 natural earthquakes occur each year in Britain, but these tend to be rarely perceived by persons, as they are recorded instrumentally, and occur deep within the basement, well beyond the upper 1000 m or so, where mining takes place. Although mining-induced seismicity occasionally occurs in Britain, this is likely to have been generated by the rock movements or failures resulting from changes in the state-of-stress in the rock mass in the vicinity of the mining excavation. These include; the collapse of the strong sandstone roof strata into goaf during longwall subsidence, bed separation or bed collapse. Mining-induced seismicity generates small to moderate magnitude earthquakes and in the past decade UK coalfield events account for approximately 10 to 25% of the earthquakes recorded annually by the British Geological Survey on the UK regional seismometer network.Wilde & Crook demonstrated the influence of elevated pore water pressures on fault stability. They were concerned about the effects of mining subsidence in the vicinity of the Winwick and Twenty Acre Faults, in the Warrington area of the Lancashire Coalfield, where major urbanisation redevelopment was planned. The Twenty Acre Fault was located to the east of the Winwick Fault and formed the eastern boundary of Bold Colliery. This provided an opportunity to investigate fault reactivation as it had been affected by mining subsidence. The superficial deposits consisted of weak alluvial soils and glacial lodgement till. A series of inclinometers and pneumatic piezometers were installed within these soils, and adjacent to the fault zone, to assess the pore water pressure variations prior to, during, and immediately following mining. In fact, the surface trace of the Twenty Acre Fault, gave rise to severe surface disruption, otably where it intersected the M62 motorway.The majority of the faults that have historically or recently reactivated in the currently active and abandoned coal mining regions of Britain now appear to be stable. There, however, have been observations of continued or renewed ground movements in the vicinity of fault outcrops several years after mining has ceased. For example, investigations by Smith & Colls at Swannington, provide examples of fault reactivation that occurred after mining ceased and yet were attributed to being caused by mine water rebound. In this instance, two scarps were observed to traverse a field. These were sub-parallel, 0.7 m high, trending NW to SE, and extended for a distance of 30-40 m, in weathered Coal Measures mudstone. The scarps appeared developed over an 18 month period. One of the scarps was more distinct than the other and there was offset damage to a tiled field drain.The Gelligaer Fault is a principal NW to SE trending fault in the South Wales Coalfield. Ground deformation monitoring was carried out in the late 1980s and early 1990s where the fault crosses the 1.2 m diameter, very high pressure Dowlais-to-Nelson natural gas main. It was considered necessary to monitor the movement of the fault for ground rupture and strain accumulations as it was affected by subsidence during the longwall working of the Seven Feet Seam. Reactivation of the fault caused the generation of a scarp with associated high lateral hump-type compression. Indeed, Donnelly reported ground movements in the vicinity of the fault outcrop that were observed to continue for 10 years after mining finished. The mechanism responsible for these ground movements are not fully understood but may be related to mine water rebound or associated fluctuations in groundwater levels, or both.At Easington, the fault scarps, over 300 m long, caused severe and widespread damage to rows of terraced houses and roads. These were occasionally accompanied by small-magnitude, non-seismic earth tremors according to local residents. The fault scarps appeared along the ground surface many years after mining finished at the former Easington Colliery. The graben was attributed to the dilation of fissures and reactivation of faults in the underlying bedrock of strong. This consists of an upper,20-70 m thick, strong, bedded dolomite that overlies the Marl Slate, a strong, laminated dolomitic siltstone of varying thickness. The mining ground movements along the faults and fissures were attributed to mine-water rebound. In the Durham Coalfield 300 years of groundwater pumping had dewatered the strata by depths of up to 150 m and rebound is now taking place. If the new groundwater level intersects faults that contain subsidence strain accumulations, then mining fault reactivation is possible.Fracturing in the carriageway of the A690 Sunderland to Durham road at a road cutting, in limes tones of the Raisby Formation, which were associated with post-mining fault reactivation, were reported in local newspapers in 2001.This and subsequent investigations drew public attention to the possible implications for potential contaminant transport from waste disposed in the Houghton Quarry landfill site, which lies close to the damaged road. Many other fissures were observed in the region, reported by Donnelly. Some of the fissures extended for a strike distance of at least 1 km and were associated with crown holes. Investigations again showed that the reactivation of the faults may be attributed to mine water rebound.Some effects of fault reactivation on land use planning and ground engineering .Post-mining fault reactivation can cause significant planning and engineering problems particularly where such features intersect linear infrastructure and light buildings and structures. The following are particularly vulnerable:linear structures such as roads, railways and pipelines;buildings with shallow foundations, particularly houses;agricultural land through disruption to drainage, injury to livestock falling into crown holes and fissures and disruption to mechanical farming;leakage from reservoirs and waste disposal sites;steeper natural slopes, opencast pit walls, embankments and cuttings.To reduce the risks, site investigation should be designed to address three specific questions:Is fault reactivation likely to occur in the area under investigation within the design lifetime of the proposed building or structure?Which fault or faults may be affected by fault reactivation?What are the spatial locations of these faults?As has been indicated, the areas that are likely to be affected by fault reactivation have been identified for the UK. Such reactivation is associated with areas in which mining has been abandoned and where mine water levels are rising. Such areas are often still experiencing ground level change, either subsidence or ground level rise, both of which can be identified by either ground surveying or satellite radar interferometry.Once it has been determined that an area might be susceptible to residual fault reactivation, individual susceptible faults must be identified. These will then need careful investigation to identify their exact location. T his will require a specific desk study involving large scale geological maps, mine plans and, possibly, local information in the media on previous ground movements. From these, likely fault traces at the ground surface should be estimated. These can then be investigated by large scale mapping to identify displaced kerbs, cracks in roads and buildings, crown holes , topographic steps in the ground surface and any other evidence of recent ground movement. Local landowners may be a useful source of information on deformation, even if they do not recognise the cause of any features. The results of the desk study and the mapping should be used to delineate the fault traces more accurately. Ground investigation then will be needed. Dependant on the particular ground conditions, this might involve geophysical methods and/or exploratory trenching across the surface trace of the fault. Where linear structures and services must traverse susceptible faults, they should be placed at right angles and with operational design features to accommodate anticipated movements.From a land-use planning point of view, it is desirable to identify a lateral zone of exclusion around traces faults that may reactivate, or at least make special planning conditions attached to any permission. Obviously, building over faults in areas likely to be subjected to subsidence should be avoided wherever possible because of the relatively uncertain nature of any associated surface ground movements and the fact that structures normally cannot be designed to withstand highly localized and attenuated differential subsidence. It has long been an empirical rule of Civil Engineers that differential vertical ground displacements of more than 12 mm in 13 m borders on a condition leading to structural damage. However, whilst subsidence damage to structures located close to, or on, the surface outcrop of a fault can be very severe, the areal extent of such damage is limited, often being confined to within a few linear metres of the outcrop .Anon and Donnelly recommended that structures be set back at least 10 m and 16 m respectively from the line of surface outcrop of a fault. This suggests that a buffer zone of around 15-20 m on each side of a fault trace may be necessary in vulnerable areas. Such planning controls would not need to be in place indefinitely, as post mining fault reactivation seems to be time limited.ConclusionsThe total extraction of coal, in unfaulted ground, by longwall mining, results in subsidence of the ground surface. This occurs virtually contemporaneously with mining, due to the almost instantaneous transmission of strains to the ground surface, to generate a subsidence trough. The time taken for subsidence to be completed is approximately inversely proportional to the rate of forward advance of the workings. For all practical purposes, subsidence is complete when the face has advanced 0.75d beyond a given point on the ground surface, residual subsidence then occurs. Residual subsidence rarely exceeds 10%of total subsidence and is usually complete within two years, with some instances taking six to seven years, and a few recorded cases taking 11 years. When coal is extracted in the vicinity of faults, they may undergo reactivation. This generates scarps, fissures or compression humps at the ground surface. Some faults scarps are subtle but many are distinct striking features. The consequences of fault reactivation may be widespread damage to land and existing structures. Fault reactivation and residual ground movements also may present a significant risk to new construction, planning and redevelopment.Ground movements in the vicinity of reactivated faults tend to occur and continue in increasing magnitude for longer periods of time than the normal residual subsidence window of approximately two to seven years. The magnitudes of the residual ground movements along faults are relatively small and are observed as increases in the height of the ground; increases in the height of fault scarps; exacerbation of wave-like compression humps and dilation of fissures. Increases in ground elevation may be caused by groundwater rebound and elevated pore water pressures within and adjacent to faults.The duration of post-mining ground movements is not currently possible to predict due to the lack of observational data. Fault scarps tend to be quickly repaired in the UK, because they present a risk to traffic, land may be required for development and construction, or scarps may be damaged by ploughing of agricultural land. This has prevented almost all proper monitoring of post-mining ground movement at fault outcrops. However, examples from South Wales, the Midlands and Durham coalfields tend to suggest that post-mining ground movements along and around reactivated tectonic faults may continue for about 15 years after mining has finished. This equates to an increase of over 100%, when compared to residual ground movements recorded during subsidence in unfaulted ground. It is not known if the few cases of residual subsidence at fault outcrops are representative of the duration of complete post-mining induced fault reactivation.The cause of post-mining induced fault reactivation is not fully understood, but is thought to be related primarily to groundwater flows and mine water rebound, caused by the cessation of mine water pumping schemes. These were required historically to suppress regional groundwater levels in the British coalfields, as a necessary feature of all forms of coal mining, from the 18 th through 20 th centuries.It is recommended that faults that have historically, or recently been reactivated during mining subsidence, should be avoided as far as houses, buildings, landfill, roads and utilities are concerned. If fault outcrop positions cannot be avoided, then a properly designed site investigation should be undertaken to obtain information on the geology, geomorphology, structural geology, hydrogeology, past mining, and the geotechnical properties and engineering behaviour of the ground. Such an investigation should aim to provide information that will allow a degree of engineered flexibility in design, to accommodate the ground conditions and/or to undertake appropriate ground treatment mitigative measures. This investigation should also consider the possibility of gas emissions, groundwater and mine water discharges, reduced bearing capacity and collapse-prone voids within the fault zone.Most faults that have reactivated during mining subsidence in Britain are now grown stable due to the long-term dissipation of ground strains and decline in deep longwall mining. Post- mining ground movements may continue to take place on some of the principal faults that define greater structural geologic blocks in the Coal Measures. It is not currently possible, however, to predict the timing and magnitude of such ground movements, or associated gas and/or groundwater emissions.中文译文长壁开采引起的断层活化和地面延迟沉降在英国煤田中的研究摘要：采用长壁法采煤的地区，正在承受由于采矿沉陷所引起的断层活化的影响。在英国（和其它世界各地的主要煤田），在过去的150年中，一直观察和记录着这些内容。因沉陷的影响所诱发的断层可能会一般的严重地损坏地基、房屋、建筑物、构筑物和地下设施，并通过破坏灌溉系统和改变地面坡度而损坏农业用地。 由于断层都是受地下采矿影响，在不同的地质和采矿条件下设置观测站，对断层进行监测，已经能够更好地理解断层的诱发机制和各种各样的诱发方式。由于缺乏观测数据断层诱发的持续时间很难确定。然而，在煤层采出后，槽壁也随之快速沉降， 并且被认为在数周至数月之内完成。不久之后，通过一段时间的延迟沉降称为残余沉陷，通常认为，这种沉陷在英国的煤田中几乎占了总沉陷量的10%。尽管一些实例表明在煤炭采完两年后仍能观察到沉陷的影响， 但是，在许多情况下，没有断层存在，残余沉陷在四个月内就能完成。一般来说，有时断层激活会延长残余沉陷是被人所接受的。在英国的一部分废弃或半工作的煤田中，已经观察到开采结束多年后，在断层露头附近仍有相对较小的地面移动。出现这种现象的原因尚未完全理解。不过，长期的断层活化，可能土地利用与建设有严重影响。 本文研究的目的是考虑断层活化，主要是根据已经公布的在断层露头处的地表移动资料来讨论有关的发生机制。在断层露头附近，这些移动的特征包括增加地表高程和地表变形（例如：下沉、斜坡、压缩和拉伸）。反过来，这些特点可能会导致地下水和矿井水涌出。引言位于长壁开采沉陷发生地区的断层可能会激活。这可能影响到地表附近的临近岩层。在英国的煤田内可以通过对农田和路边的挠度和弯曲度的准确测量来识别那些高达34米、长达4千米以上的断层露头。它们出现在英国部分乡村和城市地区的露天的和埋藏的煤田内。断层活化的后果可能会破坏地表的建筑物、服务设施、公共设施和运输网络。通常，活化的断层也会通过破坏灌溉系统和改变地面坡度而损坏农业用地。此外，断层活化可能破坏天然山坡、露天矿边坡、工程堤岸和边坡，并能影响溪流和地下水流量。与开采沉陷有关的断层活化是由于断层周围的岩石碎裂而产生的。这可以引起剪切位移不均匀沉降，造成一侧岩层相对于另一侧的不平坦沉陷。不幸的是，由于缺乏可靠的观测数据，与地表移动有关的断层活化的持续时间是很难确定的。通常是公共安全的关注地表岩层增量式位移直接发生得很快的时候，因为此时地表块体移动进入因地下开采所产生的额外空间。开采沉陷概述在二十世纪，英国大量开采的煤炭，目前，虽然大大降低，但都是用长壁开采。长壁开采是指全部开采出用煤柱分开的一系列煤炭，这写煤柱的宽度与上覆岩层相比是非常薄的。露在外面的、在两条平行铁轨之间的煤炭宽为30到300米之间。在工作面处以及在铁轨里面或附近的顶板是人工临时支撑的。采出煤炭之后，卸下人工预先设置的支撑体，留下没有支撑的岩石，在那些煤炭已经被才出的地方，岩石就会塌落。地表的沉陷随着工作面的推进而加剧，而且都可以看作与同时的采矿活动有或多或少的直接影响。发生在煤炭全部采出地区的沉陷是槽形的，并向外部扩展，而且在各个方向超越采矿边界。因此，受地表移动的范围要大于煤炭实际采出区域的边界。表面区域的边界的影响主要是由边界角确定，依靠的是地质结构特征和实测数据。在地表某点所测的下沉速度的延迟时间是与工作面的推进速度完全成反比例的。向上移动的传播几乎是瞬间的，它是随着顶板支撑的前移、采空区上部的岩层开始松软而开始移动的。在实际中，所测得的岩层移动出现于工作面的推进距离为采深的0.75倍处，当工作面推进到测点正下方时，测点的下沉量约为最大值的15%。在所有的实际测量中，垂直下沉的最大值发生在工作面推进到超过测点的距离为采深的0.8处。然后，这些点会以很快的速度经历残余沉陷。瞬时沉陷发生后，残余沉降会持续一段时间，通常为两年或更长时间。残沉降幅度正比于表面的沉降速率，并与煤层上部的岩石的力学性能有关。例如，坚硬的岩石比软弱的岩石产生更多的残余沉降。如果工作面停在临界区上，残余沉降很少超过总垂直沉降的10%，如果工作面已通过临界宽度，则只占2%到3%。很偶然，残余沉降大于10%的情况已被记录下来。例如，通过对英国五个煤矿的研究，Ferrari发现残余沉降占总沉降量的8%到45%之间，在煤矿废弃后，持续超过11年。Singh指出在印度的Kamptee煤田，不到两年时间内，残余沉降占到总沉降量的7.4%到22.4%。根据Yao and Reddish的研究，水平煤层的最大残余沉降发生在横向半下沉纵向线的工作点上，同时它沿着一条横向线在工作区中心发生。倾斜煤层的最大残余沉降发生在工作区边缘点上。断层及其活化 在没有断层存在的地方影响沉降持续的因素如下：（1）工作深度。一般情况下，在前工作深度情况下，沉降会很快停止；（2）较软的煤层和顶板可能会增强沿煤壁方向的支撑压力；（3）受采深和岩层物理性能的影响，采空区顶板和底板会受挤压而收敛；（4）一个正在进行的沉降，会逐渐闭合形成一个潜在的空洞；（5）在物质条件变化的区域可以导致采空区上覆地层的进一步移动。如前所述，预先存在的断层往往成为下沉运动轨迹变得不正常的主要原因。断层活化引起的地表沉陷不仅发生在采矿过程中，而且能够持续数周至数年，也可能在正常沉降完成后继续存在。它可以发生在不同的时期，直到更进一步的长壁开采接近断层，它才会停止。不幸的是，精确地移动持续时间还无法确定。另一方面，许多断层并没有对地表产生不利影响。Donnelly已经研究了采矿引起断层的有关机制。这种活化主要受岩层内部的地质采矿因素所控制。这种地质因素的影响包括原有的应力场、地质历史时期的古老断层、断层的工程性能、水文地质条件和临近大量岩层的影响。总的来说，这是决定地表建筑物受采矿影响而发生移动的主要因素。一般来说，主要的断层往往由于小的影响就会发生较大的移动，从而降低内部岩层接触面上的剪切力。影响断层活化的采矿因素是采深、地层条件、工作面距断层的距离、工作面推进速度、采厚、重复采动及采矿的剧烈程度。事实上，断层也能够控制采空区侧向边界的沉降槽。如果在采煤期间出现断层，并且它的区域很大，然后伴有严重区域沉降差异的断层对工作面和地表产生剧烈的影响。事实上，可以画一个角来确定断层的位置和影响区域，这个角度的两边能够确定一个明显的沉降运动极限表面，这个极限表面一直延伸到地表。相反地，当断层的倾角小于边界角时，在这种情况下，断层所引起的地表沉降范围比预计的要小。当断层的倾角小于30度，并且岩层之间不能提供足够的摩擦力时，在大多数情况下，断层会反映出不利的情况。当断层的岩层破裂时，会产生大量的碎片。相反，如果断层由破碎的岩石组成，由于这种表面积小的岩石组成的岩层很软弱，因此它的表面沉降效果往往并不显著。沿断层的地表岩石类型能够影响到异常沉降与沉降集中。这解释了为什么沿断层的沉降是不连续的。另外，地表坚硬的岩石，如砂岩和石灰岩，会由于悬臂岩石的损坏及破裂块度的影响，倾向于发生断裂，形成更多的石块，造成更严重的破坏。这也许可以解释地层翻转的的现象。在表面的岩层，通过断层裂隙形成一个块传递，然后严重的裂隙或破裂可能发生在地面。裂缝通常发生在离平行断层线300米外远离它的地方。也可广泛地发生在远离它的厚度较大的松散矿床上方的基岩也会影响断层交错（见下文）。沉陷的类型和程度不仅与断层有关，也取决于和开采程度有关的特定的平面开采范围。最引人注目的步骤当采煤工作面经过断层下方的过程中，沿断层平面的移动增加，而不太可能在表面的其他位置产生有差异的运动。对出现断层的上方巷道更有可能造成比下方一侧的更严重的沉降，但事实并非总是如此。通常的沉陷顺序是从采空区上部岩层一直发展到地表。沿断层的会发生垂直移动，并且伴有某种程度的水平位移。然而，当地下的采矿条件是一直时，沉陷的梯度呈现出连续性。直接对与一个较小的工作区域来说，沉陷涉及的范围是有限的。而且，一个宽深比接近断层倾角的采区相对于一个很大宽深比的采区来说，是不可能产生较大沉陷的。在同一矿区，当受到以前采矿影响时，断层将很可能会变得严重，但在未受采动影响的地表则不会很严重。一旦微笑的移动被激活，就会沿断层产生更多的新的运动，有时甚至在厚度和宽度上产生较大的比例。断层活化的程度随重复采动次数的增加而增加，并且与频繁的浅层开采联系较大。重复采动可能会是断层露头的累积升高达2米左右。断层的形态、高度和硬度可能会自然地受到地表的岩土的工程性质和地质条件的影响。例如，已经观测到在威尔士煤田断层露头是高度超过4米、长度为45千米长的粗粉砂岩。另外，被松碎的工程材料所覆盖的固结物和道路表面，其岩层露头是很独特的，它被限制于单块碎石，并且高达2米，延伸达几百米长。然而，在断层另一侧的地表变形往往限制于几米的范围之内。另一方面，在较弱的地质地存在的地方，如很厚的消融的冰碛、沙粒和砾石或者粘土，它们不支持断层露头的形成和发展，而且可能在断层发展之前摧毁它们。在这种情况下，一个以降低幅度，但影响更为广阔的地层收缩在断层的另一侧正在形成。更重要的是，在软弱或疏松土壤主要的断层面可能会滑脱断开或分裂成多个碎块。经过勘探发现，有些断层随着滑移面产生了构造复杂的变形。当地表的沉淀满足分层的要求时，相互平行的分离就有可能会发生。这可能会导致产生的二次断层在到达地表之前分裂成许多碎块或者消失。地堑的形成是断层作用于地表的一种常见形式，特别是当他们的路径经过道路或混凝土表面，就会或多或少的平行于道路的延伸方向，或在横向上产生阶梯式的变形。通常，横向剪切应变只在断层露