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城郊矿村庄下压煤开采技术研究摘 要：村庄压煤直接影响矿井当前生产，因村庄压煤不能开采，往往丢失资源，浪费已有的开拓工程，造成生产接替紧张，产量下降，服务年限短。地面村庄民房建筑质量往往参差不齐，同一村内从土坯房、砖石房或砖混平房同时存在，这些差别增加了采动保护保护技术的难度。关键词： 地表移动与变形 村庄下压煤 条带开采1 概 述 永夏矿区位于黄淮冲积平原东部，地势平坦开阔，土地肥沃。城郊矿井设计生产能力为4Mt/a永城市旧城区位于城郊井田中部，共有9911户，36970人，旧城区连同其周围规划 的 l9个搬迁安置区 (以下简称城区)共占地619km有1166户，44000人。建筑物多为砖结构和少量砖混结构及钢筋混凝土结构。永夏矿区是我国煤炭工业新兴的优质无烟煤基地，本文从设计角度论证分析了该矿区城郊矿井城下压煤开采的可行性 ，提 出了适合城郊井田地质条件和煤层赋存特点的条带采煤方案，并采用岩移计算软件包对条带开采后地表各种移动和变形值进行了预测验证。结论证明，对城郊矿井城下压煤进行条带开采是可行的，有助于提高社会效益和煤炭企业自身的经济效益。城郊煤矿是一个设计年产400多万t的现代化矿井。开拓方式为立井两水平上下山开拓 。开采水平为-500，-800 m。目前该矿实际生产能力已接近400万t/a，可采煤层为二叠系二、三。、三：、三、三煤层，共5层。主采二2煤层,平均厚2.98m，煤层倾角平均为7。，上方地表东部为董桥、赵庄居民区，西部为沱河运管处，南部为城关镇种鸡场 、烈士陵园和老城 区，北面为沱河。城郊矿地质储量7.50亿t，可采储量4.0亿t，但仅西城区(老城 区)下就压煤约022亿t，占整个城郊矿可采储量的5。所以，如何开采西城区下压煤是一个非常值得研究的问题。2.采煤方法的选择2.1地表移动与变形对建筑物的影响地下开采是引起矿区内地表移动与变形，并导致地面建筑物破坏的主要原因，但不是唯一的原因。地震、地下水位下降等自然原因也可能引起地表移动，建筑物本身结构设计有缺陷，或施工和材料质量差等人为因素也可能引起建筑物破坏。对具体的建筑物的破坏，应认真分析，区分开采影响与非开采影响引起的变形破坏，地下开采对地表建筑物的损害主要是由采动引起的地表在垂直方向的移动与变形（下沉、倾斜、曲率、扭曲），水平方向的移动与变形（水平移动、水平拉伸与压缩变形）以及地表平面内的剪切变形造成的。不同性质的地表移动与变形对建筑物的影响是不同的。采动引起地表产生的移动与变形，破坏了建筑物与基础之间的初始平衡状态。伴随着力系的重新建立，使建筑物结构中产生附加应力，从而导致建筑物变形，当这些变形超过了建筑物的抗变形能力时，建筑物就被破坏。一般来讲，建筑物在地表沉陷过程中要经受地表动态移动与变形的影响，如图1：图1 地表建筑物承受的移动与变形过程初始状态 最大拉伸变形位置 最大倾斜位置 最大压缩位置 地表稳态下沉盆地平底 r主要影响半径2.2村庄下开采的可行性分析2.2.1建筑物下采煤理论依据和可行性理论研究和生产实践表明，建筑物下采煤的理论依据有以下几个方面。1）建筑物允许变形值大于地表静态变形值，即固定开采边界上方的地表变形值对建筑物不产生有害影响。2）采取开采措施以减小地表变形值，使其达到上述要求。3）采取建筑加固措施以提高其抗变形能力，使其允许变形值大于地表动态和静态变形值。4）建筑物允许变形值接近于地表静态变形值，采后有可能对建筑物进行维修。符合上述条件之一者，建筑物下才可能进行安全开采，上述条件也是确定开采措施及建筑物加固措施的根本出发点。值得注意的是，建筑物所在地的地下潜水位是影响建筑物下能否开采的关键，当地下潜水位高时，如果无法降低地下水位，则必须减少地表的下沉值。2.2.2城郊矿采煤条件1）地表建筑物。城郊矿地表建筑物特点：密度大，多数为砖混结构；建筑物及其设施在抗变形能力上具有明显的方向性和差异性；街道两侧楼房多相互连接，整体尺寸较大，在地表变形影响下易遭到破坏。2）地质采矿条件。根据城郊煤矿综合柱状图，该地区表土层平均厚352.12m。上覆岩层由泥岩、砂质泥岩、砂岩、铝质泥岩等组成。基岩总厚度187.10m。在城郊矿T2202工作面轨道和胶带巷进行岩石 和煤采样 ，并按 照煤和岩石物理力学性质测定方法进行煤岩力学性 质测定。经测定二，煤层煤样平均抗压强度9.2MPa；直接顶砂质泥岩平均抗压强度为46.6MPa；直接底泥质砂岩平均抗压强度为34.8 MPa。3）村庄下采煤的特殊性村庄下采煤是建筑物下采煤的实例，村庄建筑物除供居住外，还有一些其它用途，、如储藏、畜用等，这些建筑物建造时间较长，建筑质量较差，以砖石结构土筑平房为主，抗变形能力差。村庄建筑物分布密集，排列没有规律。村庄建筑物的历史重要性程度较低，必要时可以搬迁村庄，当采用搬迁重建措施时，需大量征地，按土地管理法有关规定，需要安置农村剩余劳动力，办理农转非。在具体条件下研究采煤方法时要综合考虑这些特点。2.3村庄下的采煤方法2.3.1村庄下采煤方法设计准则在选择建筑物下开采方法时，首先应考虑下列技术原则。1）采动影响的特征与程度。根据采动影响理论的研究成果，采动影响的主要特征是地表移动与变形，设计建筑物下采煤方法时，应考虑地表移动与变形的特征与程度，在采深较小及急倾斜煤层时，还应考虑“上三带”的特征与程度。2）保护标准与要求。在设计和选择建筑物下采煤方法时，需要考虑另一个原则是保护标准与要求。例如:在建筑物下采煤时，是否允许采前拆旧房建抗变形房，或采后对建筑物进行维修加固等。3）资源回收率。为了减少采动有害影响，实现建筑物下采煤，有时需要采取降低回采率的开采措施。因此，如何处理资源回收率问题，是选择采煤方法的主要原则。根据近年来的采煤经验，在某些情况下，为了从总体上提高煤炭资源回收率，应积极采用各类充填采煤方法，必要时一可采用条带开采，适当降低回收率。2.3.2村庄下设计采煤方法的基本要求我国划分建筑物破坏（保护）等级的标准在我国矿区中，大多为砖混结构和砖木结构的房屋，还有大量的农村村庄的房屋，少量的木（竹）排架结构房屋和土筑平房。这些建筑以平房占多数。由于结构不同，建筑物抵抗变形能力不同，因此在划分建筑物破坏（保护）等级的标准时，应区别对待。原煤炭工业部制定的建筑物、水体、铁路及主要井巷煤柱留设与亚美开采规程总结了我国建筑物下开采的经验，对于长度或变形缝区段内长度小雨20m的装混结构建筑物，按地表不同变形值，划分了损坏等级和标准，如表1所列：表1 砖石结构建筑物的破坏（保护）等级破坏（保护）等级建筑物可能达到的破坏程度地表变形值处理方式倾斜imm/m曲率K10-3/m水平变形mm/m墙壁上不出现或仅出现少量宽度小于4mm的细微裂缝3.00.22.0不修墙壁上出现415mm宽的裂缝，门窗略有歪斜，墙皮局部脱落，梁支承处稍有异样6.00.44.0小修墙壁上出现1630mm宽的裂缝，门窗严重变形，墙身倾斜，梁头有抽动现象，室内地坪开裂或鼓起10.00.66.0中修墙身严重倾斜、错动、外鼓或内凹，梁头抽动较大，屋顶、墙身挤坏，严重者有倒塌危险10.00.66.0大修或拆除2.3.3城区下开采地质影响因素分析 1)采深。城区下煤层埋深大，二煤层采深采厚比约170，四层煤综合采深采厚70以上。大采深在采煤方法设计合理时，地表下沉平稳，下沉盆地宽缓，地面建筑物受不均匀沉降破坏程度减轻。另外，煤层埋深大，建筑物留设保护煤柱量随之增大，为减少资源损失，实行城区下采煤更有必要。 2)地理环境。井田内地势低平，潜水位较浅，在降雨量大的年份，容易引起 内涝积水。地表下沉量应控制在一定范围。但是，城区由于采用条带开采，而城区周围的采区开采后，其地面将比周围地面高，有利于排涝。3)厚表士冲积层 。井田内新生界表土层很厚，均达300 m以上。厚表土层可以缓和基岩受开采破坏的剧烈程度。如果基岩的断层在开采影响后被拉开或错动时，由于厚表土层 的缓冲。一般不会使地表产生不连续的裂缝和台阶。中国矿业大学对华东巨厚冲积层地表移动规律的研究表明，在表土层厚的地区下沉系数增大，主要影响角正切变小。使地表沉陷范围增大，地表坡度小，不均匀沉降小，有利于建筑的保护。但是 目前本矿区巨厚表土层建筑物下开采的实例较少，有待积累经验和实践的检验。 4)煤层厚度和倾角。二：煤层基本稳定，厚度变化不大，有利于地表均匀下沉和建筑物保护。煤层倾角平缓，大部分为近水平煤层，为条带法开采的条带布置提供了灵活性。有利于条带法采煤的稳定性。5)水文地质。4个含水组在正常情况下相互问有良好的隔水层，没有水力联系。第三、四系孔隙含水组对井下开采基本无影响，石炭系浅部和奥陶系灰岩承压水一般不会造成水患 ，但在有断层等特殊构造时，应注意因受开采影 响而突水的可能性。因此，设计在必要处留设了断层防水煤柱。二叠系裂隙含水层静储量不大，补给途径不畅，一般只对矿井涌水量有影响 ，不会引起水患。地表水一般对井下开采无影响。但对井下开采引起各处地表下沉不均使沱河河道等地面水系发生变化 、水流不畅等问题应予以注意。2.4采煤方法的选择由于本地区村庄较多，且地下水属于高潜水位型，若采用常规的采煤方法，不仅地表变形较大，沉陷区内亦出现大面积积水，将无法保证居民的生命财产安全。但由于本惊天煤层埋深较大，表土层较厚，主要可采煤层及倾角变化不大，当采用合理的采煤方法对村庄压煤进行开采是，将会使地表下沉平稳，下沉盆地宽缓，地表将不会出现台阶和裂缝现象，对保护地面建筑物较为有利。2.4.1村庄下采煤方案比较为了确定城区下采煤技术上可行、经济上合理的最优方案 。设计提了 5个方案进行选择 。 1)方案：搬迁。该方案采出率较大但存在以下缺点：（1）搬迁选址困难；（2）大规模搬迁扰乱居民的正常生产和生活，引起工厂迁建期停工；（3）搬迁资金难以落实 ；（4）新址需占大量土地，影响农业生产。因此，方案 I是不可行的。 2)方案：就地加固维修或村庄就地建抗变形房。本方案特点是井下用冒落长壁采煤法实行全采，地面采取采前加固、采后维修或村庄就地建抗变形房的措施 。该方案即使仅采二，煤层时 。地表下沉后即接近或在潜水位以下，将使建筑物区积水。各类建筑物均将达到 IV级以上破坏，需要大修或重建。对地面生产和生活干扰很大，严重时甚至可能造成事故，安全难以保障。故该方法也被淘汰。3)方案：条带法开采。条带法开采方法是采一条、留一条，在开采条带内用冒落法控制顶板。从前面分析可知城郊井田具有冒落条带法开采的许多有利因素。（1） 与常规采煤法基本相同，不必增加机械装备，不增大材料消耗，适应性较强；（2）地面建筑物保护效果好，不会造成地面积水，绝大部分建筑物不需维修，仅极少量劣质建筑物需小修，能确保居民安全；（3）经济效益好，可采出煤炭40左右；（4）不影响地 面居民的生产和生活。由此可见方案技术上合理可行，经济效益最好 。 4)方案IV：城区下留设煤柱不采。该方案显然是不合理的：城区下煤层为井底车场附近的高级储量块段，开采条件较好，如不开采，将影响矿井开拓部署的合理性和生产能力，增大工程量和投资城区处于井 田中部，有现成的开拓巷道可利用，开拓工程量小；留设大量煤柱将造成资源损失，缩短矿井的服务年限，降低投资效益。 5)方案V：水力充填采煤方案。水力充填就是应用水力将充填材料(一般为砂和碎石等)输入采空区，以减少地表下沉，保护建筑物。水力充填开采的缺点：（1）充填费用高，本地区无砂和碎石，购买价格较高，经济效益较差；（2）井上下需增加一套充填系统，占用大量设备设施，工艺复杂，生产组织管理困难 ；（3）井下潮湿，劳动条件不好；（4）煤层倾角小，褶皱发育，充填较困难。因此该方案不宜采用。根据以上分析，最后确定按方案进行开采。2.5采煤方法选择的评价条带开采法是一种局部开采方法，不需要额外的设备投资，管理较为简单，是一种较为理想的建筑物下采煤方法。从理论上讲离层注浆法也是减少地表移动和变形的好方法，曾经在很多矿区试用，对地表建筑物的保护效果也是很理想的，特别适用平原地区的农田保护，应用灵活，不需要改变现有的开拓系统。但是还有一些难点问题，比如离层带的确定，注浆时间和地点的控制，注浆体的配比，以及浆体与岩层的胶结效果等，这些问题还需要继续探讨。3.条带开采设计条带开采是把要开采的煤层划分成比较正规的条带进行开采,采一条,留一条,利用保留的煤柱支撑上覆岩层,从而减少覆岩沉陷,控制地表的移动和变形,达到地面保护目的的部分开采方法。条带开采法是保护地面建筑物的一种有效开采措施。条带开采法与一般长壁式采煤法相比，虽有回采率低、掘进率高、采煤工作面搬家次数多等缺陷，但条采却有引起围岩移动量小、地面沉陷小等突出特点。条带法适合于下述情况下的采煤：1.村镇密集建筑物群，结构复杂建筑物和纪念性建筑物下采煤；2.道路桥梁、隧道或铁路干线下采煤；3.水体下采煤以及受岩溶承压水威胁的煤层上方的煤层的开采；4.地面排水困难；5.煤层埋藏深度在400500m以内，深度太大，采出率过低；6.煤层层数少，厚度比较稳定，断层少；7.邻近采区的开采不至于破坏煤柱的稳定性。条带开采方法如图2：图2 条带采煤法条带布置（a）保留条带宽度 ；（b）采出条带宽度3.1条带开采的地表移动与变形特点条带开采法是一种保护地面建筑物的有效开采措施，能减少围岩移动，降低地面沉陷。条带开采如果开采尺寸适当，地表不会出现波浪形下沉盆地，而是出现单一平缓的下沉盆地，其它的变形分布规律与正规工作面回采类似。实测表明，在一定深度的界限以上下沉盆地是平缓的，在此界面以下则呈波浪形。通过力学分析证明，当采宽小于1/3倍采深时，地表不会出现波浪下沉盆地（如图3）。正规条带开采引起的地面移动与变形值是很小的，其地表移动和变形预测参数也相应减小。具体特点如下：1)条带工作面矿压显现特点条带开采时由于上覆岩层由保留条带支撑，破坏和移动减弱，断裂带高度降低，工作面基本顶来压现象减弱或消失，对底板的破坏也随之减弱，巷道矿压显现不明显。2)地表移动和变形特点(1)地表下沉系数小(2)主要影响角正切小(3)水平移动系数随采深增加变小图3 地表波浪形下沉盆地3.2条带开采设计步骤3.2.1条带开采设计原则开采后条带煤柱应有足够的强度和稳定性，能长期、有效地支撑上覆岩层，从而达到减少地表移动和变形的目的。条带的开采宽度，其尺寸应限制在不使地表出现明显的波浪状下沉盆地，而是仅出现单一平缓的下沉盆地范围内。结合城郊矿的生产能力和技术水平，城郊矿西城区下煤层的开采只能采用变条带协调开采方法应用变条带协调开采方案的设计原则为：在确保采动引起的地表移动与变形不影响地面建筑物安全使用的前提下，最大限度地回收煤炭资源；合理确定留设煤柱的宽度，保证留设煤柱有足够的强度支承上覆岩层的荷载，且保持长期稳定；确定合理的开采顺序和工作面推进速度，以减小采动引起的地表动态移动变形对建筑物的损害。3.2.2条带类型选择走向条带与倾斜条带。走向条带是条带长轴沿煤层走向布置，适用于煤层倾角小的缓倾斜煤层。当煤层倾角较大时，走向条带稳定性差。走向条带的优点是工作面搬家次数少。倾斜条带是条带长轴沿煤层倾向布置，其适应性较强，应用广，其缺点是工作面搬家次数较多。冒落条带与充填条带。煤层的采出部分用全部陷落法管理顶板时称为冒落条带，此法目前应用较多。采出部分用充填法管理顶板时称为充填条带。从最大限度地减小地表移动和变形角度看，充填条带效果较好。定采留比条带和变采留比条带。在一个采区内采留比固定不变是定采留比条带开采。该方法适用于采区地质条件比较简单的地段。在多煤层、厚煤层、分层开采时以及煤层倾角、采深差别不大时必须采用定采留比，否则，保证不了稳定性。在一个采区内采留比不固定，根据需要而变化的是变采留比条带开采。在采区地质条件变化较大的地段，变采留比有一定的优越性。该方法的条带布置比较灵活，适用于单一煤层。3.2.3采留比的确定方法具体步骤见3.3.23.2.4条带开采地表移动和变形预测根据实测资料可得，条带开采的地表移动和变形规律与正规工作面回采相似，条带开采的地表移动和变形可用概率积分法求解，但它的下沉系数、主要影响角正切、水平移动系数比正规工作面回采的小。3.3采区条带开采设计本设计以本矿井四采区为例确定条带开采采留煤柱的宽度。3.3.1计算原则本采区矿井条带开采设计遵循以下原则：1)开采后条带煤柱应有足够的强度和稳定性，能长期、有效地支撑上覆岩层，从而达到减小地表移动和变形的目的；2)条采的每一采出宽度，其尺寸应限制在不使地表出现明显的波浪状下沉盆地，而仅出现单一平缓的下沉盆地。在合理地确定留宽和采宽的前提下尽量提高回采率。根据地面地形条件，可以采用变采留比条带开采，在建筑物密集地区和浅部，采宽适当小一些，远离村庄建筑物地区和深部，采宽大一些，尽可能提高回采效率；3)应弄清煤和上覆岩层的物理力学性质及其组成。如有无坚硬岩层存在，能否起积极的作用等；4)为减少工作面搬家次数，推进长度尽可能远一些；5)选定的保留条带煤柱的宽度不得过小，以免煤柱因丧失稳定性而失去承载能力。同时，煤柱的宽高比根据国内外条采的经验，应控制留宽大于采厚的5倍，采宽小于1/4采深。3.3.2确定条带尺寸综合考虑个中条带开采的优劣性以及结合矿井实际条件，决定选用冒落条带开采。1）确定采宽b采出条带宽度b与采深H有关。条带采煤法的基本要求之一是当采出条带开采后，地表不出现波浪形下沉盆地。一般情况下采宽等于或大于三分之一埋深时，地表就要出现波浪形的下沉盆地。为了保证条带开采后地表出现单一平缓的下沉盆地，避免地面出现波浪形起伏，采出条带宽度b一般为采深的1/101/4。受采深条件限制，我国已有的采出条带宽度多在1050m的范围内。目前，随着采深的加大，采出条带的宽度有加大的趋势。bH/4H/9=53130m（采深-520-480m）本着保护地表建筑物的要求，又为了提高采出率，暂取采宽为中间值b=90m。2）确定留宽a目前，国内外有关煤柱强度计算理论有很多种。这次计算使用我国在条带开采煤柱荷载计算中普遍采用的威尔逊理论，先计算煤柱的极限承载能力和实际分担荷载，然后再计算 出煤柱的稳定性安全系数，以评价煤柱的稳定性。 长煤柱承载能力按式(1)计算： (1)式中：P c煤柱承载能力，kNm；r覆岩平均容重，kN/m ；H覆岩厚度，m；a煤柱宽度，m；m煤柱高度，m。煤柱分担荷载按式(2)计算 ： (2)式中，P 煤柱实际承受的裁荷，kNm；H，a同上；B开采煤柱宽度，m。保留条带宽度应满足：a2x0+B=0.01Hh+B式中：B核区宽度，一般取（12h）。当B取2h时，在采深H取500m，h取2.98m时则a7h=21m煤柱安全系数K=PCPD安全系数可取1.32，此处取K=2，则由Pc/PD2即可确定采出条带宽度和保留条带宽度。经过计算，得：综合可得，a取60m采留情况如表2：表2 四采区采留情况开采条带宽度保留条带宽度采出率90m60m603)工作面布置情况图根据四采区煤层赋存情况，将四采区按以上方案的尺寸，沿煤层倾向划分为若干个回采工作面。回采工作面布置情况，见图4图4 条带开采设计图3.3.3条带开采地表沉陷预计在综合考虑上述经验公式计算结果及东欢坨矿地表移动观测站观测成果的基础上，确定本区长壁垮采时的预计参数如下：主要影响角正切为2.56；初次采动下沉系数为0.86；水平移动系数为0.30；1）拐点偏移距的确定：在进行地表移动和变形预计时，拐点偏移距是一个重要的参数，它不仅直接影响到各种移动和变形值的计算精度，而且决定了地表移动盆地的形状和范围。全采时影响拐点偏移距的因素包括上覆岩层岩性、岩层层位、采深、松散层厚度、工作面尺寸、煤层倾角、采厚、采动程度、重复采动、采煤方法和顶板管理方法等。覆岩岩性和采深是影响拐点偏移距的主要因素，随上覆岩层强度的增加而增加，随采深的增加而增加。我国一般的矿区s值约在(0.050.43)H之间。（3）=17.2m2）地表下沉系数垮落开采条件下，当2ab和b1/3H时，条带开采的地表下沉系数可由下式计算：（4）式中：条条带开采的地表下沉系数；a保留条带宽度；b采出条带宽度；H采深；全垮落法处理采空区全部开采的地表下沉系数代入各数值，得条=0.54全 3）主要影响角正切垮落开采条件下条带开采的主要影响角正切可由下式计算。tan条=tan全-0.574lnH+2.34式中：tan条垮落法处理采空区条带开采的主要影响角正切；tan全垮落法处理采空区全部开采的主要影响角正切。由上式可以得出，相同采深条件下，主要影响角正切较小，意味着主要影响半径较大，地表移动和变形指标中的曲率和水平变形值较小，对建筑物的不利影响较小。tan条=tan全-1.23 4）水平移动系数（5）条带开采水平移动系数由式5确定。式中：b条垮落法处理采空区条带开采的水平移动系数；b全垮落法处理采空区全部开采的水平移动系数。由上式可知，与长壁开采相比，采深越大，采用条带法开采的水平移动系数就越小。带入数据得：b条=0.687b全采区条带开采涉及移动与变形的主要参数如表3表3 条采与全采参数对比参数回采率下沉系数水平移动系数主要影响正切角拐点偏移距全采100%0.730.32.5664.73条带开采60%0.390.211.3317.25）地表沉陷预计参数四采区最大值移动和变形值预计地表沉陷预计主要包括最大下沉值、最大水平移动值、最大倾斜值、最大曲率值和最大水平变形值。针对四采区的实际情况，对以上开采方案可能对地表造成的破坏进行预计，计算其最大下沉和变形值。最大下沉值的计算：（6）四采区主采煤层为煤二2和煤二3。查阅煤矿资料，当煤全部采完可得地表最大下沉值为1590mm。最大水平移动值：根据上述参数，可得采用方案1时，当煤全部采完后，四采区地表最大水平移动值可达315mm。最大倾斜值：（7）（8）最大倾斜值与影响半径成反比，与最大下沉值成正比，由式8确定。影响半径r与采深和主要影响角正切有关，可由式9确定。（9）则r=500/1.33=376m根据上述参数，对最大倾斜值进行预计，经计算可知当煤全部采完后，四采区地表最大倾斜值可达2.96mm/m。（10）最大曲率值：对方案进行计算时，当煤全部采完后，四采区地表最大曲率值可达0.009510-3/m。最大水平变形值： （11）针对该方案，当煤11和煤12全部采完后，四采区地表最大水平变形值可达0.922mm/m。个参数数值表4 地表沉陷参数值参数倾斜i/mmm-1曲率K/10-3m-1水平变形/mmm-1数值2.960.00950.922损坏等级由此可知，上述方案基本可靠，对地表建筑物造成的损坏均较小，在该区可以采用，4.条带开采安全技术措施建筑物下采煤的防护措施主要为两方面：一方面在井下采取采矿措施，目的是尽量减少建筑物所在地表的移动和变形值，另一方面对建筑物采取结构保护措施，以增加建筑物承受地表变形的能力。4.1采矿措施开采措施主要有快速开采、长工作面开采、间歇开采、择优开采、协调开采、连续开采、适当调整工作面与建筑物长轴的关系、对称背向开采、干净回采，不残留煤柱、充填法开采、条带法开采等。4.2建筑结构措施采用建筑结构措施的目的在于增强建筑物承受地表变形的能力，使建筑物正常工作。但结构措施有一定的局限性，只有地表变形值在建筑物能承受的范围内时采用才能有效地保护建筑物1)在进行城区压煤开采之前应首先疏浚城区地面和地下各泄水渠道，并在开采时间上稍滞后于周围其它全冒落法回采区的回采时间，以防城区发生内涝。2)先在建筑物较少的城区西部进行开采总结出有关资料和管理经验，为大面积开采城下压煤创造条件。3)在开采过程中，应严格控制煤柱宽度，不得随意缩小煤柱尺寸。4)尽量不在煤柱中穿切巷道，以避免煤柱强度降低。5)开采应保持连续性，不得长期停顿。6)组织专门的维修人员，对开采过程中少量损坏的建筑物及时予以修整。5.结果分析5.1城区压煤开采效益分析对永城市老城区下压煤采用条带法进行开采可有效地处理城下压煤问题，使大量的煤炭资源得以回收，避免了因举城搬迁而带来的经济和社会问题，具有明显的效益。老城区下面所压二2煤和三；煤的设计利用储量为5l72Mt，按采出2586Mt计，用吨煤盈利扣减掉建筑物的维修费用、恢复沱河沉降段河堤标高费用、条带开采自身需增加的部分巷道掘进量和其它不可预见费用，预计城郊矿井城区下采煤量最终可盈利36465万元，经济效益十分显著。经过论证分析和方案比较，设计认为对城郊矿井城区下压煤进行条带开采无论从技术上还是经济上都是可行的，可以达到社会效益和企业自身经济效益两者的统一。参考文献1许家林,煤矿绿色开采M.徐州：中国矿业大学出版社，20112 钱鸣高，石平五.矿山压力与岩层控制M.徐州：中国矿业大学出版社，20033 何满潮，景海河，孙晓明.软岩工程力学M.北京：科学出版社，20034 杜计平，汪理全.煤矿特殊开采方法M. 徐州：中国矿业大学出版社，20035郭文兵，柴华彬煤矿采动损 害与保护 M北京 ：煤炭工业出版社 ，20086 王金庄、郭增长，我国村庄下采煤的回顾与展望，中国煤炭，第28卷第5期，2002年5月。7 钱鸣高，石平五.矿山压力与岩层控制M.徐州：中国矿业大学出版社，2003中国矿业大学2007届本科生毕业设计 第 9页 XXX大学毕业设计任务书学院 矿业工程学院 专业年级 采矿工程 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： 城郊矿4.0 Mt/a新井设计毕业设计专题题目：城郊矿村庄下压煤开采技术研究毕业设计主要内容和要求：以实习矿井城郊矿条件为基础，完成城郊矿4.0Mt/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，撰写一篇关于无轨辅助运输系统在煤矿井下应用的专题论文。完成2011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“Numerical modeling of thawing in frozen rocks of underground mines caused by backfilling”，论文5147个字符院长签字： 指导教师签字：编号：（ ）字 号本科生毕业设计（论文）题目： 城郊矿4.0Mt/a新井设计 城郊矿村庄下压煤开采技术研究 姓名： 学号： 班级： 采矿工程 二 XX 年 六 月英文原文：Numerical modeling of thawing in frozen rocks of underground mines caused by backfillingS.A. Ghoreishi-Madiseha, F. Hassanib, A. Mohammadianc, F. Abbasyba Mechanical Engineering Department, McGill University, Rm 125, Adams Bldg, 3450 University St., Montreal, QC, Canada H3A 2A7b Mining Engineering Department, McGill University, Montreal, QC, Canada H3A 2A7c Civil Engineering Department, University of Ottawa, Ottawa, Ontario, Canada K1N 6N5AbstractThe thawing effect due to backfilling in permafrost mining rocks is investigated. The heat transfer equation in rock and backfill is obtained by considering the effect of phase change, heat generation due to cement hydration and temperature dependent material properties. The governing equations are solved using a finite volume numerical method and the phase change phenomenon is modeled based on the manipulation of specific heat, thermal conductivity and density of rock and backfill. The harmonic mean method was employed to handle the change of thermal properties. The effects of different influential parameters such as cement content of backfill, water content of rock and backfill, thermal conductivity of rock and filling material, and the number of adjacent stopes are investigated. Eventually, using the resulting temperature and phase field, a new parameter regarded as the radius of thawing, is introduced.Keywords: Backfill; permafrost; Thaw; Finite volume; Harmonic mean method1. IntroductionMine backfilling has become an integral part of mining operations used for local or overall support for stability of mine openings or as a platform for mining activities. As a result, the physical and mechanical properties such as strength and other characteristics of Mine Filling Material (MFM) have been under keen theoretical and experimental studies for the past three decades 1. More and more mining facilities are opening in cold regions and are subjected to extreme thermal conditions including mining in frozen environments. As the mining process goes on, extraction of material from the ground results in evacuated underground spaces which are called stopes. Various sequences of stope excavations are proposed for mining entire ore bodies 1,2. As in modern bulk mining, 100% ore extraction is aimed; these stopes cannot be left empty and must be filled so the adjacent stopes can be mined eventually.During the filling operation, a huge amount of backfill material is poured into these stopes. Due to the temperature difference between the fill material and the underground cold rocks, heat is transferred from the fill to the rock causing potential thawing of the rock. In fact, the thawing decreases the mechanical strength of the surrounding or adjacent rocks and it may cause the rocks to fail under in situ stresses resulting in major instability. In addition to the fill-rock temperature difference, cement hydration is another important factor which can also cause thawing. MFM is a blend of tailings, or sand, together with water and binders (small amount of cement which is usually mixed with slag to strengthen the blend).This leads to cement hydration inside MFM with heat generation occurring due to hydration. The resulting hydration heat magnifies thawing and increases the risk of damage. In order to prevent damages caused by thawing, appropriate support systems such as rock bolts are designed and implemented to strengthen the rock mass and prevent its failure. Safe design of mining excavations requires precise information about the extent of the rock mass affected by thawing, but only few studies have been devoted so far to this subject. Kaminski and Moolin3studied the effect of freezing conditions and material composition on the strength of the filling material. Hromadka and Guymon 4 compared the main approaches to the latter subject by trying to categorize various methods of modeling phase change in freezing soils. Thomas and Tart 5 performed a series of studies on freezing and thawing of soils by using a two dimensional finite element analysis. In their studies, they considered a temperature-dependent heat capacity of material which brought in the opportunity of adjusting the thermal properties of material in accordance with experimental observations. However, due to the special characteristics of MFM such as cement hydration heat and thawing, these studies cannot precisely describe the thermal behavior of MFM. One of the few works devoted to the problem of permafrost reaction when in contact with MFM was done by Khokholov and Kurilko 6. They investigated the heat exchange occurring between the fill mass and Kimberlite stones assuming that the latent heat energy of phase change could be related to a change in specific heat capacity of the material during the phase change process. They implemented a 2D finite difference model to determine temperature field in the fill and rock masses. Also, in their approach, the convective heat transfer is considered to have little or no effect due to the impermeability of the frozen porous media. Accordingly, the conductive heat transfer mechanism is supposed to be capable of balancing the local temperature equilibrium between the existing solid and liquid phases of the porous media. A constitutive discussion of the above mentioned assumptions can be found in 7,8.Although dedicated to Kimberlite rock bodies, the model that was developed by Khokholov and Kurilko is applicable to other kinds of rock bodies as long as conduction is the dominant mechanism in heat transfer. Their method can be implemented for inspecting the problem of thawing in rock bodies; studying the effects of different parameters involved in the heat transfer phenomenon and providing useful guidelines for the safe design of mines that utilize MFM and which are excavated in permafrost regions. Thus, one of the main objectives of the present work is to define the extent of influence of various parameters contributing to the thawing in mines constructed within permafrost. Moreover, in Khokholovs and Kurilkos method, two separate physical domains are allocated to rock and MFM and these two domains have been coupled together through imposing boundary conditions. In the present work, in an attempt to simplify the method, a unique physical domain is considered to include the rock and the MFM. The associated unsteady heat transfer equation employed by Khokholov and Kurilko 6 has been descretized using the finite volume method. The thermal properties of the material are considered to be variable and the change of thermal conductance is formulated according to Patankars harmonic mean method 9. By numerically solving the equation, the temperature field is calculated to obtain the thaw-affected regions in rock mass. Having estimated the thaw affected region, a new parameter that is designated the Radius of Thawing is introduced which is the key point for designing rock bolt installations. The effect of different parameters such as initial temperature difference between the fill material and the rock bed, cement content and the different stope geometries are investigated. According to the best of the authors knowledge, this work is the first of its kind which defines critical conditions that engineers should expect to create serious thawing problems in permafrost rock adjacent to underground mine backfilling sites.Fig. 1. The geometry of rock mass and fillings 2. Mathematical modelA rock mass holding a stope inside, shown in Fig. 1a, forms the main geometric cell of this study. Assuming that the depth of the rock mass and the stope are much bigger than the other dimensions,and also considering uniform surrounding boundary conditions, a two dimensional model is appropriate. In order to concentrate on the canonical cases, it has been considered that the dimensions of all the stopes are the same and they are located in an organized manner. Multiple stope geometries can be generated by placing a number of these main cells beside each other. Fig. 1b and c indicates the geometries of, respectively, three and nine stopes inside the rock mass which are studied in the present work. In each case, the outer boundaries of the rock mass are chosen to be sufficiently faraway that extending them further does not affect the interior temperature field. Due to geometrical symmetry, the numerical domain, in which the calculations are done, can be simplified to only the first quarter of the physical domain shown in Fig. 1. As Fig. 1 indicates, the filling material is placed internal to the rock zones.At the initial condition, the rock mass is assumed to be frozen and colder than its melting point. The backfill material which is poured into the stope is warmer than the frozen rock mass and has internal heat generation due to hydration. Consequently, the heat transfer between the rock mass and backfill material is due to both the initial temperature difference between rock and MFM and the heat generation. Furthermore, assuming low permeability of the materials and considering moderate temperature gradients, the main heat transfer mechanism would be conduction. Thus the governing heat transfer equation can be expressed bytCpT=xkTx+ykTy+q （1）(2)where T is temperature, k and r are, respectively, thermal conductivity and the density of the materials, and q is the heat source due to cement hydration. The two dimensional model is valid as long as the temperature gradient in z (third) direction is much smaller than the temperature gradient x and y directions.This condition will be valid when H LW . Here, L, W and H are,respectively, length, width and the height of the physical domain.In order to simplify the formulation, M(x,y) is introduced which indicates whether a point (x,y) is located inside the rock or the MFM. If it is located inside the rock then M(x,y) is 1 and else M(x,y) equals 2. Eq. (2) represents a variable specific heat parameter used to model latent heat energy of phase change.(3)(4)where, Cf 1 , Ct1 , C2 , , Lf , f 1 are, respectively, the specific heat capacity of frozen rock, the specific heat capacity of thawed rock,the specific heat capacity of backfill, the moisture content of backfill, the latent heat of ice and the density of frozen rock.Moreover, it is assumed that hawing happens in the temperature range of T-Tm 0.5Tm, where Tm is the nominal melting point of water andTm,defines the temperature range in which thawing happens. The main idea behind the formulation for heat capacity expressed in (2) is to imitate the latent heat transferred during thawing and freezing of the water content of the backfill material.Also, the thermal conductivity and the density of the materials are considered to be related to temperature as indicated by the following:where kf 1 , kt1 and k2 are, respectively, the thermal conductivity of frozen rock, thawed rock and backfill. Similarly, rf 1 , rt1 and r2 are, respectively, the density of frozen rock, thawed rock and backfill. Regarding the values of density and thermal conductivity of rock during the phase change, average values of the properties of frozen and thawed rock are assumed as described in relationships (3) and (4).The heat generated due to cement hydration is modeled as a time dependent source term. This source term exists only in the filling material and is zero elsewhere. Here, we have taken advantage of the heat generation model developed by Khokholov and Kurilko 6.The boundary conditions depend on the choice of having zero flux or given value. If the symmetric boundary condition is used along a boundary line, then the zero flux boundary condition is considered while a constant boundary temperature is assumed for the non-symmetric boundary condition. The boundary conditions for different boundary configurations are given by the following:where Tb is the boundary temperature which is the temperature of rock zone far away from the stope(s). As for the initial conditions,it is assumed that the rock mass initially has the same deep rock temperature Tb and the filling material has a uniform temperature that is hotter than the temperature of the rock mass i.e.Tx,y,0=Tinti1=Tb Mx,y=1Tinti2 Mx,y=2 (6) where, Tinit1 and Tinit2 are, respectively, the initial temperature of the rock and backfill. The fact that Tinit2 Tinit1 is the initial mechanism for thawing to happen in rock but, as time goes on,it will be diminished if there is no heat generation due to cement hydration inside the MFM.3. Numerical methodThe first step of solving the governing equation is its descretization. Here, the finite volume method developed by Patankar9 is implemented. In this method the temperature at each point of interest (P) is expressed in terms of its neighbor nodes (W, E, Sand N). Accordingly, the discretized equation would be written as follows:aPnTPn=anbTnb+b （7）where aP , anb , TP , Tnb and b are, respectively, the coefficient associated with the point of interest, the coefficients associated with the neighboring points, the temperature of the point of interest, the temperature of the neighboring points and the source term associated with the control volume. The expanded form of Eq. (7) is given byaPnTPn=awTw+aETE+aSTS+aNTN+aPTP+b (8)where, aPn and TPn are, respectively, the coefficient and the temperature of point P in the next time step. Similarly, aP , aW , aE, aS and aN are, respectively, the coefficients associated with the points P, W, E, S and N in the current time step. Moreover, TP , TW ,TE, TS and TN are, respectively, the temperature associated with the points P, W, E, S and N in the current time step. Since, in Eq. (8) the temperature of point P is expressed explicitly in terms of its neighbors temperature, the explicit method is used for discretization in the time domain. The resulting coefficients can be defined as follow: where CP , , kw , ke, ks and kn are all temperature-dependent coefficients. In eq. (9), CP and are associated with the control volume associated with point P, but the thermal conductivities (kw , ke, ks and kn) are related to the thermal conductivity of the links between point P and each of its neighbor nodes. In order to assure heat flux conservation, Patankars harmonic method 9was used to calculate the thermal conductivities. This method provides the ability to model rock and fill as unique domains with variable thermal properties. For instance, according to this method, thermal conductivities are computed as follow:Using Eqs. (2)(10) provides the opportunity to employ them both for rock and backfill without defining boundary conditions between the rock and backfill model zones. In order to have a better understanding the depth to which the rock mass is thawed,the “Radius of thawing”, Rthaw, is introduced. This parameter defines the maximum depth of the thawed zone in the rock mass adjacent to the placed MFM. A positive Rthaw value means that thawing has happened in the rock and a negative Rthaw value indicates that the cold temperature of the surrounding rock has caused freezing inside the filling material. If several filling zones are present in the rock mass, then Rthaw is the maximum amount of the radius of thawing and can be given byRthawt=MaxHit i=1,2N （11）where N is the number of the filling zones present in the rock mass and Hi(t) is the depth of thaw penetration of filling zone number i.A structured Cartesian mesh was employed and a FORTRAN code was developed for carrying out the numerical calculations.4. Results and discussionTo validate the results of the proposed numerical method,three test cases were studied. In the first test case, the results were compared to the results of the analytical solution of a 2D conduction in a homogeneous square-shaped slab of backfill surrounded by constant temperature walls 10. The squareshaped slab of backfill is one meter by one meter in size and its initial temperature is assumed to be 15 while the temperature of the surrounding walls is assumed to be 5 . The results of this study are demonstrated in Fig. 2a. As Fig. 2a shows, the numerical results are in agreement with the analytical solution of zisik 10. The second test case is basically identical to the first one except that it has a constant heat source of 100 W/m3 inside the backfill slab. Fig. 2b shows the result of this test case. It is found that the numerical results agree with the analytical solution of zisik 10. In the third test case, the results of the proposed method were compared to the results of Khokholov and Kurilko 6.The results of this test case are shown in Fig. 3. According to Fig. 3, Khokholov and Kurilko 6 have reported higher center temperatures than the predictions of the proposed numerical method. In order to examine the validity of the results, an energy balance assessment was carried out on the results of 6. In this assessment, the total sensible heat needed to achieve the associated temperature field within the backfill, given in the results of 6,was calculated. It was found that the total sensible heat needed will be 1599 kJ/kg of cement which is 4.77 times larger than the cement hydration heat reported in Khokholov and Kurilko 6(335 kJ/kg of cement). Consequently, one can say that the temperature rise inside the backfill and the rock mass, and the thawing effect due to cementation heat generation, are overestimated in 6.Fig. 2. Resulting center temperature of (a) the first test case and (b) the second test caseIn order to gain a clear understanding of heat transfer and phase change in the filling zone and the rock mass, we begin with a simple rock mass zone having only one stope excavation inside. Typical stope geometries employed will have dimension of L =10 m and W =10 m and the initial temperature conditions will be considered to be Tinit1 =15 and Tinit2 = 10 which resemble the real conditions in permafrost-impacted mines. In order to achieve the thermal properties of backfill and rock, a series of experiments were conducted. The considered values of thermal properties of rock and backfill are given in Table 1. The cement content and the moisture content of the fill material are considered to be 200 kg/tonne of cement and 5%, respectively. Also, assuming the use of Portland cement, the rate of heat generation due to cement hydration in backfill was taken from 6. These authors suggested a heat generation function which is dependent on the temperature of backfill, the cement content of backfill and time .The resulting heat source term was calculated by interpolation between the values given in Table 2 both in terms of time and temperature. Note that the values of heat (generated due to cement hydration) given in Table 2, are in kJ/kg cement. This means that if the backfill includes more cement, more heat will be generated in it during the curing period. All these assumptions will create the simple geometry model that can be used to create a comprehensive interpretation of permafrost generation inside backfill. The numerical model was built on the basis of this model through the following steps.Fig. 3. Comparison of the numerical results and the results of 6.Table1 Thermal properties of rock and filling.Thermal properties/materialBackfillFrozen rockUnfrozen rockSpecific heat capacity (kJ/kgK)1058.79001000Thermal conductivity (W/mK)1.82.32.27Density (kg/m 3)250023002300 Table 2 The values of cement hydration heat generated in Portland cement 6Temperature offilling (K)Time of curing of cement (days)0.250.5123714282787.2514.52963109188209251283122550105146209251293293426710516720927231433531384134188230272341335333130188230272314335 Fig. 4. Temperature field for single stope geometry in different timesAs the first step, an investigation on the size of the physical domain was conducted and the effect of rock mass size on the temperature field was studied. Consequently, it was observed that, as the dimensions of Lb and Wb are increased, their effect on the resulting temperature field and Rthaw becomes negligible.Eventually, it was found that a rock mass domain size of 50 m by 50 m is a proper choice, resulting in a relative difference of 10-6 in comparison to a 40 m by 40 m domain size.In the next step, the suitable grid size was examined. In similar fashion to the procedure carried out in the previous step, the number of nodes, Nx and Ny, were changed and their effects on the temperature field and Rthaw were studied. Finally, Nx and Ny were both chosen to be 200 in order to meet the criteria of a relative difference of 10-6 in comparison to a 150 by 150 grid. Also, a sensitivity study was carried out for determining the time step andt =225 s was selected. Fig. 4 shows the results of the temperature field for this typical case. As can be seen in Fig. 4, the generation of heat inside backfill raises its temperature and diffuses heat from fill zones to the rock mass. However, after 30days, the heat generation effect is diminished and the backfill body is cooled down and eventually frozen. The radius of thawing and the temperature of the center point of the backfill zone are shown in Fig. 5. Note that Rthaw is a parameter that is used to assess the depth of the thaw affected zone of rock. Thus, as it is the maximum value of the depth of thaw affected zone, it may undergo some spontaneous changes due to the extension of the thawing zone in different directions.According to Fig. 5a, during the first day, Rthaw is negative meaning that the backfill initially freezes (even for the case in which it acts as a heat source). This is due to the fact that, according to the employed heat source model (Table 2), the cement hydration heat is initially not powerful enough but gradually strengthens. However, Rthaw increases and reaches a maximum value in approximately 65 days. Afterwards, Rthaw decreases and finally becomes negative meaning that the entire rock zone is frozen again and therefore safe. On the other hand, if there was no cement hydration heat, Rthaw would continuouslydecline until all of the MFM would be frozen. This shows that, in this case, the diffusion of heat from the MFM to the rock mass cannot thaw the rock mass. However, if the initial temperature difference between the MFM and the rock mass was bigger, it could contribute to thawing the rock mass. Fig. 5b shows the temperature profile of the center point of the backfill mass for two cases, these being “with heat source” and “without heat source”. According to Fig. 5b, considering cement hydration, the temperature rises from its initial value to about 29 at the center of the backfill during 28 days. After that, as the cement hydration reaction ends, the temperature will decline and returns to its initial value after almost 123 days.4.1. Effect of cement consumptionFig. 6 shows the effect of cement consumption on Rthaw. When the amount of cement consumed is low (50 and 75 kg of cement per tonne of backfill) the heat generation will not be strong enough to make thawing happen and the resulting Rthaw will be negative. As the amount of cement consumption is increased (to 150 kg of cement per tonne of backfill or more which is the case for most applications in mining operations), more heat is generated inside the backfill mass, and the resulting Rthaw will be positive, promoting deeper backfill thawing and eventually longer will be the time that the rock mass needs to freeze again.4.2. Effect of initial temperatureFig. 7 presents the influence of initial temperature of the fill. When the initial temperature of the backfill increases, the thawed radius becomes larger and it takes longer to cool down. ForT = 5 , the cold spike due to initial heat diffusion is very steep and during the first 20 days Rthaw is negative. However, after 20 days, the effect of hydration heating thaws the rock mass slightly though this rise in Rthaw will diminish after 40 days. As the initial temperature of backfill increases, this spike is weakened and eliminated at T = 25 .The influence of initial temperature of the rock mass is shown in Fig. 8. It is seen that, when the initial temperature of the rock mass is -25 , Rthaw is all negative and no thawing happens in the rock mass. However, as the initial temperature of the rock mass rises, thawing will occur.Fig. 5. (a) Rthaw and (b) temperature in center point of backll, for a single stope geometry mine with and without cement hydration heat.Fig. 7. Effect of initial temperature of backfill on RthawFig. 6. Effect of cem ent content (kg of cement/tone of backfill) on Rthaw4.3. Effect of properties of rock and backfillThe effects of the properties of rock and backfill on the thawing mechanism is studied in this part. Fig. 9 shows how the thermal properties of rock can affect the permafrost. The thermal properties (heat capacity and thermal conductivity) of rock and backfill were measured in accordance to ASTM D 5334 using a needle probe. These experiments were carried out for rock and backfill materials which are often found in Canadian mines and the properties of which are given in Tables 1 and 4. The results are shown for different types of rock material (the properties of which are shown in Table 3). Fig. 9 shows that no thawing happens for the cases of Dolomite and Granite rock materials as opposed to Shale and Kimberlite rock bodies. The physical interpretation of this observation is that, in a material with low thermal conductivity, the heat generated by cementation hydration cannot be diffused and will be stored in the form of latent heat in rock resulting in thawing. In other words, if the thermal conductivity of the rock is higher than 3 W/m K, the thawing effect of backfill will be negligible.Table 3 Thermal properties of different rocksRock type Unfrozen Frozenk（W/mk）q（kg/m）Cp（J/kgK）k（W/mk）q（kg/m）Cp（J/kgK）Shale1.4826008011.52600721Kimberlite2.27230010002.32300900Granite2.86265011052.92650995Dolomite4.93285097552850877 Fig. 8. Effect of initial temperature of rock on Rthaw.Fig. 9. Effect of thermal conductivity of the rock material on RthawSimilarly, the effects of the thermal properties of backfill are shown in Fig. 10, which happen to be opposite to the effects of rock thermal properties; As the thermal conductivity of backfill increases the thawing strengthens. Table 4 shows the thermal properties of studied backfills. It is also seen that thawing happens for all the backfill materials.Fig. 11 demonstrates another important parameter which is the water content of the rock mass. As this figure shows, for the case of rock having 5% water content, the resulting maximum Rthaw is 1.5 times of the case of rock having 10% water content. The reason is that, as the water content of rock increases, more heat energy and longer time is required to thaw the rock. Fig. 10. Effect of thermal properties of filling material on Rthaw.Fig. 11. Effect of rock water content on Rthaw.4.4. Effect of multiple stope geometryIn order to clarify the effect of having multiple adjacent stopes in a mine on thawing of the rock mass, two cases, shown in Fig. 1(cases having three and nine adjacent stopes), were analyzed. In each case the size of the rock mass (Lb and Wb) were chosen to be90 m by 90 m for three and nine stopes cases and the number of nodes were accordingly increased to Nx = Ny = 360. The distance between stopes was chosen to be equal to the stope size(d = 10 m) thus resembling two adjacent primary stopes which are backfilled simultaneously. The resulting temperature field and thaw radius for these cases are shown in Fig. 12. This figure compares the results of single-stope, three-stope and nine-stope cases revealing that a three-stope geometry has almost the same thawing radius as a single-stope but a nine-stope geometry reaches a larger maximum (0.4 m) and cools down more slowly.Consequently, the results of this study recommend that no further excavation should be performed between the two adjacent backfilled stopes during the first 30 days after the filling operation due to the thawing effect, which weakens the rock and may creat damage.Fig. 12. Effect of neighboring backlled stopes on RthawTable 4 Thermal properties of bacfillsbackfill typek（W/mk）q（kg/m）Cp（J/kgK）backfill 11.825001058.7backfill 22.2526001200backfill 32.727001500backfill 43280017005. Summary and conclusionsA finite volume method with harmonic mean interpolation of thermal properties of materials was developed to study the phase change that occurs due to backfilling in frozen hard rock mines. In order to model the latent heat transfer happening in the frozen rock domain, the heat capacity, thermal conductivity and density conditions were assumed to be temperature dependent. The resulting numerical technique that was developed is able to simulate the rock and the backfill zones as one body with no need to impose boundary conditions between them. Using the predicted temperature fields, the depth of the thaw affected zone was computed and the effect of various parameters on it was studied. It was observed that the thawing effect due to the heat generated by cement hydration will dissipate after 30 days. After that time, although there is only heat exchange occurring between the backfill and rock masses, the depth of thawing may continue to change for months after depending on the thermal properties of the rock. Also, it was found that the thawing caused by the initial sensible heat contained in the backfill is negligible compared to the thawing due cement hydration. Moreover, the results show that, if the thermal conductivity of rock is higher than 3 W/m K, there will be little effect of thawing.Table5 Qualitative summary results of backfilling in a typical mine stopebackfill/rockThermal conductivity of backfill (W/mK)Cement consumption (kg of cement/tone of backfill)1.82.252.73300200100Thermal conductivity of rock (W/mK)1.52.32.95：Extreme thawing effect (Rthaw0.15W)：Weak thawing effect0.05W Rthaw 0.15WLittle or no thawing effect (Rthaw LW时这种条件就是有效的（L、W、H分别是该区域的长度、宽度和高度）。为了简化公式，引入一个变量M(x,y)来确定点（x,y）是在岩石还是充填材料中。如果点在岩石中M(x,y)=1，否则M(x,y)=2。(2)式代表一个用于模型比热相变潜热能量的变量参数。（2）式中Cf 1 , Ct1 , C2 , , Lf , f 1分别是冷冻岩石的比热容，解冻岩石的比热容，填充材料的比热容，填充材料的含水量，冰的潜热量和冷冻岩石的密度。另外，假设只有T-Tm 0.5Tm才有解冻发生（Tm是冰的实际融点，Tm表示发生解冻的温度范围）。(2)式中比热容的表达是依据充填材料中的水在冷冻和解冻是潜热的转移确定的。而且，材料的导热系数和密度与温度有关，其关系如下：(3) (4)式中kf1，kf2和k2分别表示冻岩、融岩和充填材料的导热系数。同样，rf1，rt1和r2分别表示冻岩、融岩和充填材料的密度。由于岩石的密度和导热系数中在整个过程中不断变化，（3）式和（4）式冻岩、融岩的参数取平均值。我们认为材料水化热的产生十岁时间变化的变量，改变量只存在充填材料中，其余地方为0.。在这里我们利用了科科里沃和库里尔科开发的产热模型。边界条件的选择取决于选择零通量还是给定值。如果边界线处都是零流量，则认为是对称边界，如果边界温度是常数，就是非对称边界。不同边界的边界条件由下式决定：式中Tb是边界温度，即离采空区无穷远处的岩石温度。初始条件认定岩体最初具有相同的深部温度而且填充材料具有均匀的比岩石温度高的温度，即:Tx,y,0=Tinti1=Tb Mx,y=1Tinti2 Mx,y=2 (6) 式中Tinit1 和Tinit2分别表示岩石和填充材料的初始温度，而Tinit1 大于Tinit2是岩石解冻的基本条件，但是，温差越来越小因为充填材料的将不再有水化热产生。3、数值方法求解控制方程的第一步是解决离散性.。可以采用帕坦克的有限体积法，在这种方法中，各点的温度都由其周围邻点表示（东西南北四个方向）。因此，离散方程可以写成如下：aPnTPn=nbanbTnb+b （7）式中， aP , anb , TP , Tnb 和 b分别表示与目标点的系数,邻近点的系数, 目标点的温度,邻近点的温度和有关的控制源的体积。上式的扩展形式如下：aPnTPn