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专题大采高一次采全高的上覆岩层特性分析 含CAD图纸+文档 凉水 煤矿 4.0 Mta 设计 专题 大采高 一次 采全高 岩层 特性 分析 CAD 图纸 文档

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专题部分大采高一次采全高的上覆岩层特性分析摘要：通过数值模拟研究特殊工程地质条件时大采高工作面煤层采厚与导水裂隙带高度的内在关系，并对模拟结果进行对比分析，得出大采高工作面顶板导水裂隙带高度发育的一些规律。关键词：大采高；顶板；导水裂隙带高度；数值模拟1绪 论1.1 研究目的和意义我国国民经济的快速发展，导致能源紧张问题日益突出。我国是一个富煤贫油的国家，据专家预测，到2030年，煤炭在我国能源构成中的比重仍将占到70%左右。伴随着能源需求的不断扩大，煤炭资源的大规模开采依然在所难免。然而，煤炭作为不可再生能源，如何将其经济效益和社会效益相结合起来，以实现国民经济的可持续发展和社会的和谐发展，已成为我国国民经济发展的焦点。厚煤层是指煤厚大于3.5m的煤层。我国的厚煤层赋存地域广阔，目前已探明的煤炭地质储量10000多亿t，而厚煤层储量占45%左右，厚煤层产量约占总产量的40%50%，厚煤层的合理开采对我国煤炭行业的生产和经济发展有举足轻重的影响。特别是各矿区在投产初期，从提高经济效益出发，优先开采中厚煤层和厚煤层，造成生产接续和资源平衡开采之间的矛盾日益突出，厚煤层的开采越来越突出，厚煤层的开采速度和采出率已成为制约企业发展的一大难题，是一个亟待解决的问题。某矿业集团公司下属的各矿也同样存在着上述矛盾。厚煤层约占公司总产量的1/5左右。因而，近长期来看，厚煤层的回采效率及回收率将是制约枣庄矿业集团公司稳定发展的主要问题之一。某矿业集团公司将厚煤层一次全高开采作为重要课题来研究，积极寻找一种适合于厚煤层开采的高产高效采煤工艺，在厚煤层中实现安全、高产、高效生产。此研究将提升我国厚煤层机械化开采程度和厚煤层回收率，为某矿业集团近长期稳定发展从技术等方面提供有力的保证。某矿业集团公司选择3上405厚煤层工作面做为试验基地。该厚煤层综采工作面的实验成功，为厚煤层一次采全高并实现稳产高产奠定了坚实的基础，为同类条件矿井逐步完善回采工艺，提高安全生产水平和厚煤层资源回收率进行了有益的探索。1.2 国内外研究现状近年来，国内外厚煤层的开采技术方面得到了长足的发展，取得了许多可喜的成果和经验。1.2.1国外技术研究现状国外长壁工作面从一般综采发展到当今的高产高效综采约经历了15a,这一发展过程表明,由于综采设备不断更新换代,采用重型化、强力化、自动化和机电一体化的设备,走生产集中的途径,才使工作面的单产和工效大幅度提高。广泛采用大功率高效能重型成套机电设备，采煤机总功率在1000kW以上,最高已达2285kW,采高已达5m,大修周期23a,可采煤量400600万t；工作面刮板输送机功率已达2250kW,槽宽1200mm,最大输送能力4000t/h,过煤量600万t以上；液压支架普遍采用电液阀控制和高压大流量供液系统,架型向两柱掩护式方向发展,最大工作阻力已达9800kN,移架速度已达68s/架。1.2.2国内技术研究现状我国从1978年起，从德国引进了G320-20/17型、G320-23/45型等大采高液压支架，以及相应的配套设备，与此同时开始研制和试验国产的大采高液压支架和采煤机。经过十多年的努力，现已取得了明显的进展。目前对于厚度3.54.7m的缓倾斜厚煤层一次采全厚的综采成套设备已经实现了国产化，经过工业性试验及多年来生产世界的检验，证明国产设备的性能和质量已达到国外同类产品20世纪90年代的水平；经过各种地质条件的探索和实践，采高为3.54.5m的大采高采煤法，在技术上已经基本成熟，技术经济效益明显，所以，厚煤层大采高一次采全厚综采是一种有发展前途的采煤法。1.3 厚煤层大采高全厚开采技术突破与创新的关键点一般情况下，由于厚煤层大采高全厚开采高度大，工作面维护空间大，煤壁易片帮，顶板易冒顶；更为重要的是用于该煤层全厚开采的机械化装备配套技术，在国内还不成熟，特别是当厚煤层地质条件比较复杂时，断层多，压力大，开采厚煤层的安全程度和回采率低等，严重地制约着我国厚煤层煤炭大采高一次全厚开采技术的效能。目前，我国对厚煤层的开采大部分矿仍采用倾斜分层或放顶煤工艺进行回采，较少矿采用国外进口的成套设备进行大采高综采工艺回采。采用倾斜分层下行垮落采煤方法与一次采全高及放顶煤开采相比较，其掘进率高，增加了掘进费用，工艺也较复杂。特别是网下开采，顶板破碎，上下出口处难以维护，产量小，效率低。煤炭容易自然发火。因其效率低、成本高，存在安全隐患较多，灾害频繁，厚煤层的资源优势未能充分发挥，不利于煤炭行业的发展，目前为落后的回采方式。综采放顶煤的适应性远比倾斜分层强，但是，放顶煤开采煤尘大、回采率偏低、易自然发火，且工作面瓦斯涌出量大，易局部积聚。采用大采高综采进行厚煤层工作面回采，能取得较好的经济效益。但目前设备大多需要进口，初期投资比较大。目前，依靠进口装备一个大采高综采工作面，初期投资至少需23个亿人民币，相当于装备同等规模一个综采工作面初期投资的10倍，如此大的投资制约着大采高综采工艺在我国厚煤层开采过程中的应用。因而只要解决厚煤层综采设备配套及回采工艺方面的技术难点，厚煤层综合机械化回采尤其是一次采全高回采将对提高我国厚煤层的安全生产水平和资源回收率起到至关重要的作用。某矿业集团有限责任公司，借鉴我国中厚及厚煤层综合机械化开采的经验，在厚煤层综采工艺研究及配套设备的研制方面进行了有益的探索，取得了一定的技术突破和创新，主要表现在：（1）某煤业有限公司3上405工作面地质条件大采高开采工艺性进行评价在研究某矿区地质条件对开采影响一般规律的基础上，采用层次分析法对付村矿地质条件开采工艺性进行了综合评估，得出了3上405厚煤层大采高工作面地质条件开采工艺性的综合评价等级，确定了地质条件的优劣程度与开采效益的关系，认为3上405工作面采用一次全厚综采工艺是可行的。为某矿区厚煤层采用大采高综采工艺提供了理论根据。（2）厚煤层大采高综采工艺方式的确定综采工艺方式主要是指工作面的割煤方式及进刀方式。经理论分析和现场实测，最终将循环作业方式确定为：双向割煤、端部斜切进刀方式，不但降低了工人的劳动强度，而且减少了循环作业时间，提高了生产进度和效益。（3）采用关键层理论和RFPA程序对大采高综采工作面的采动覆岩结构特性进行了分析和模拟为研究厚煤层大采高综采工作面的采动覆岩活动规律，并对所设计液压支架的适应性进行评价，分析了大采高工作面的上覆岩层关键层结构效应，并进行了上覆岩层破坏特征数值模拟，揭示了大采高工作面顶板的可控性，为顶板控制提供依据。1.4 拟采取的技术路线课题研究将采用现场调研、理论分析、数值计算、计算机处理及现场工业性试验等综合研究方法，具体技术路线如图1-1所示。研 究 手 段厚煤层大采高全厚开采成套技术及设备研究与应用研 究 内 容厚煤层综采工作面开采条件工艺性评价厚煤层综采工作面设备的选型设计与配套大采高综采工作面工艺方式及工艺参数优化大采高综采采场矿压数值模拟与现场实测分析现场调研理论分析数值计算计算机处理 厚煤层大采高全厚开采工艺应用2 厚煤层一次采全高的开采条件我国各矿区从提高经济效益出发，优先开采中厚煤层和厚煤层，厚煤层的开采速度和效率及其回收率已成为制约企业发展的一大难题，是一个亟待解决的问题。枣庄矿业集团公司也面临同样的问题。为了矿区的稳定持续发展，厚煤层安全高效开采势在必行。因而厚煤层开采的相关回采工艺及配套设备的研究就成为枣庄矿区目前急需解决的问题。为此，首先需对厚煤层开采方法的选择和开采工艺性的地质条件适应性进行评价。2.1 某矿区厚煤层覆存概况截止2003年底，该矿拥有总地质储量15.08亿吨，工业储量8.79亿吨，可采储量5.67亿吨，主要为肥煤、气球、焦煤。某矿业集团公司是一个拥有百年历史的老矿区，开采的煤层多，采煤方法多，采煤工艺多，先后开采的煤层有：二层煤、三层煤、十四层煤、十六层煤、十七层煤。采煤方法主要有：综放、综采、轻型支架放顶煤、轻型支架综采、悬移支架、高档普采、炮采、水采等。到目前为止，某矿业集团公司厚煤层、中厚煤层顶板控制已实现了液压支架化。但该矿业集团公司厚煤层赋存情况比较复杂，不同煤层的顶底板条件差异较大，不易管理，目前几年经常发生顶板伤亡事故。由于该矿业集团老矿井比较多，而矿区内资源有限，随着这几年原煤产量的大幅增加，厚煤层的安全高效回采关系到整个集团公司的原煤产量、安全、整体效益和稳定。由上述可知，该矿区厚煤层煤厚一般在46m，其中可采储量12818万t，约占矿区全部可采煤层储量的20%。各矿在对现有煤层开采的同时，为保证矿井的持续发展都考虑到厚煤层的高效安全开采。为此，该矿业集团公司在其所属的煤业有限公司，选取3上405工作面对厚煤层大采高综采工艺及配套设备进行研究，由于首次进行厚煤层大采高一次全高开采的研究，煤业有限公司对该煤层进行了大采高综采地质条件开采工艺性的评价与研究。2.2 大采高综采工作面地质条件2.2.1工作面位置及井上下关系3上405工作面位于小卜湾村西南3151680m范围内；工作面北端上方有340m宽的疏洪道穿过；疏洪道以南为昭山湖湖区，该面为水体下采煤。井下位置位于东四采区中南部，东距落差1090m的F33断层30-75m，并与407工作面采空区相距230m，西为3上404待掘工作面，西距F16、F17断层10110m不等，北以东四集轨80m保护煤柱线为界，南距井西边界大屯断层118198m不等，见表2-1。表2-1 工作面位置及井上下关系表水平名称-480采区名称东四采区地面标高+3.68+31.79井下标高-167.0392.0地面相对位置位于小卜湾村西南3151680m范围内；工作面北端上方有340m宽的疏洪道穿过；疏洪道以南为昭山湖湖区，该面为水体下采煤。回采对地面设施的影响由于采高在5.1m左右，预计采后地表最大下沉量4m左右，会出现较大幅度的下沉现象，将会对地表鱼塘及芦苇田产生严重破坏。井下位置及相邻关系井下位置位于东四采区中南部，东距落差1090m的F33断层3075m，并与407工作面采空区相距230m，西为3上404待掘工作面，西距F6、F17断层10110m不等，北以东四集轨80m保护煤柱线为界，南距井西边界大屯断层118198m不等。2.2.2煤层3上405工作面煤层埋藏深度为167.0392.0m，本工作面煤层总体呈现单斜构造，煤层走向266336，倾向35666，煤层倾角5.514，平均9。煤层厚度5.195.57m，平均5.37m，厚度稳定，可采性好。回采工作面所采煤层为二叠系山西组3上煤层，黑色，似玻璃光泽，性脆，结构简单，属半光型亮煤，工业牌号：气煤；具有明显规则的线理状及条带状结构，节理发育，贝壳状断口，f=1.52.2，属中硬煤层，见表2-2。表2-2 煤层情况表煤层情况煤层厚度(m)5.19-5.57煤层结构煤层倾角5.5-14537简单(度)9可采指数1变异系数12稳定程度稳定所采煤层为二叠系山西组3上煤层，黑色，似玻璃光泽，性脆，结构简单，属半光型亮煤，工业牌号：气煤；具有明显规则的线理状及条带状结构，节理发育，贝壳状断口，f=1.52.2，属中硬煤层；厚度5.195.57m，平均5.37m，厚度稳定，可采性好。煤层产状：走向266336，倾向35666，煤层倾角5.514，平均9；煤层底板标高-167.0392m，高差225m，西南高东北低，呈单斜构造型式。煤 质情况WAVQCSY工业牌号1.3612.736.156851卡/克85.50.5414.1mm气煤煤质稳定，可选性好，具有低灰、低硫、低磷、结焦性强的特点，是很好的炼焦配煤和优质动力用煤。2.2.3煤层顶底板煤层顶底板条件见表2-3所示。表2-3 煤层顶底板情况表顶底板名称岩石名称厚度(m) 岩性特征老顶细砂岩 3.50灰色，厚层状，细粒结构，成分以石英为主，钙泥质胶结，f=68。直接顶砂质泥岩 1.50黑灰色，致密，泥质结构，性脆，含植物化石及黄铁矿，f=46。伪顶直接底砂质泥岩 1.30灰黑色，砂质泥岩结构，块状结构，含植物化石及小结核，f=46。老底细砂岩 6.93浅灰色，细粒结构，硅质胶结，成分以石英为主，含云母片及星点状黄铁矿，f=68。2.2.4 地质构造本工作面回采巷道所揭露的地质构造情况来看，掘进巷道共揭露断层13条，如表2-4所示。编号为F1F13，落差0.57.2m，其中F6、F7、F9、F10、F11、F13断层对本工作面回采影响较大，尤其是F10、F11断层，由于断层线长，落差大，对生产影响严重，见表2-4。表2-4 断层情况表断层名称走向倾向倾角断层性质断层落差，m对回采 影响F1 10100 60 正断层0.5对末采有一定影响F2 35989 70正断层2.5对末采有一定影响F3 35989 72正断层0.7基本无影响F40790976872正断层1.152.0影响较大F5 72162 60正断层0.8对末采有较小影响F6 80350 66正断层1.4影响较大F7 70160 40正断层2.5影响较大F8 955 58正断层1.8影响较大F9 45135 70正断层2.6影响较大F10 11281 66正断层7.2影响严重F113445124 135 86正断层2.55.5影响严重F12 16575 59 正断层0.6影响较小F13 80350 56正断层3.8影响较大2.2.5水文地质（1）涌水量正常涌水量：10m3/h最大涌水量：100m3/h（2）水文地质情况及防治水措施水文地质情况：影响本面回采的主要水文因素是3上煤层顶板砂岩水，为三层煤开采时直接充水水源，属裂隙承压水，以静储量为主，补给条件差，富水性有不均一性，一般在构造带附近或背斜轴部裂隙带发育形成富水带。本面东邻F33断层3056m不等，该处F33断层落差1090m，使得3上煤层与下盘的三灰(厚度8.910.4m)对口接触或缩小了间距；工作面大采高，大面长，高强度开采，可能导致断层面滑动，存在水患隐患。防治水措施： 加强初采初放期间的防治水工作，加强回采期间的水文观测工作。坚持“有疑必探，先探后采”的探放水原则。回采前对F33断层的导富性进行探查。 根据该面的防治水措施，建立健全排水设施，两道低洼处应建立水仓排水，确保排水能力大于100m3/h，并有备用泵。 制定切实可行的避火路线，做到现场工作人员人人皆知。 轨、运顺两道应设溜水槽排水，并及时清理淤泥等杂物，确保水流通畅。 回采前东四泄水巷应形成泄水能力。 工作面的疏排水系统必须保证畅通无阻，工作面与水仓、水泵之间要布置挡砂设施，排水泵要安装到位，保证工作面达到最大涌水量的疏排水能力。根据经验公式可预计最大涌水量100m3/h，正常涌水量：10m3/h。该工作面属水体下采煤，其可采性依据于2006年4月30日中国矿业大学(北京)资源与安全工程学院所编写的付村煤业公司东四采区水体下开采安全性论证报告。2.2.6影响回采的其它因素影响回采的其它地质情况，见表2-5所示。 表2-5 影响回采的其它地质情况瓦斯瓦斯含量总体不高，但在断层附近瓦斯涌出偏大，存在一定的安全隐患。煤尘煤尘具有爆炸性，爆炸指数为37.4。煤的自燃煤的发火类型为类，具有自然发火倾向，发火期为46天。地温危害工作面温度为23。冲击地压危害初次来压步距为3550m左右，周期来压步距为815m。普氏硬度(f)煤层夹矸直接顶直接底152246462.3大采高综采大采高综采采煤方法是国内、外高产工作面采用的主要方法之一。此种采煤方法采用支撑掩护式或掩护式液压支架及时支撑顶板，和现在中厚煤层所使用的采煤方法基本相似。在近水平、中等硬度、顶板稳定、瓦斯含量较小、采高4.0m左右的条件下，使用国产大采高设备开采已取得了较好的效果（在应用厚煤层大采高的技术和工艺方面，神东、邢台、开滦铁法、西山、徐州、枣庄、晋城等矿区都有效果较好的使用经验；综采工作面日产量可达万吨），全员效率大幅度提高，吨煤成本降低，极大地提高了市场的竞争能力。大采高综采由于回采工艺单一，各方面管理相对简单；且在瓦斯管理、通风安全等方面都优越于放顶煤综采，主要表现在： 工作面过风断面大，放顶煤综采采高一般在3m左右，大采高综采采高为55.5m，大采高综采工作面过风断面增大10m2，增加工作面风量2030m3/s，有利于工作面瓦斯稀释，提高工作面产量。 大采高综采工作面可采用H型通风方式，该种通风方式将避免工作面老塘的瓦斯进入回采工作面，而直接从工作面后面的回风巷道排出，将大大减少工作面瓦斯涌出量。 对于坚硬顶板，可采用顶板注水和深孔爆破相结合的方法处理顶板，其工艺过程较简单。大采高一次采全高综采工艺简单，由于采用重型化、强力化、自动化和机电一体化的设备，使工作面单产和工效得到大幅度提高。与分层开采相比，其掘进率低，减少了巷道掘进维护费用，节省了金属网等材料费用，且易于集中生产，产量大，减少了采掘队组和设备占用费，利于缓和采掘接替紧张的矛盾。在目前情况下，厚度在3.5m5.0m且煤层厚度分布不均、变化较大时应优先采用此种采煤方法。目前对于厚度3.54.7m的缓倾斜厚煤层一次采全厚的综采成套设备已经基本实现了国产化，经过工业性试验及多年来生产世界的检验，证明国产设备的性能和质量已达到国外同类产品20世纪90年代的水平；经过各种地质条件的探索和实践，采高为3.54.5m的大采高采煤法，在技术上已经基本成熟，技术经济效益明显，所以，大采高一次采全厚综采是一种有发展前途的采煤法。但是目前5m以上的厚煤层，采用大采高综采开采厚煤层的工作面成套装备都是从国外进口，国内采用大采高综采的几个矿业集团几乎都是采用进口设备来装备大采高工作面，尚没有研制成完全国产化的成套装备应用于厚煤层一次全高综采。以下是国内应用大采高综采比较成功的神东公司和晋煤集团工作面装备情况。（1）神东矿区工作面装备情况参见表2-6、2-7。表2-6 神东矿区液压支架参数支架型号工作阻力（kN)支护强度（MPa）支护高度（m）重量（t）ZYY6715/21/45KD67150.852.1-4.521.0ZYY7625/22/43KD76250.952.2-4.321.0ZYY8670/24/50KD86701.052.4-5.023.5ZYY7432/22/45KD74320.912.2-4.522.6ZYY8638/24/50KD86381.062.4-5.025.0 表2-7 部分工作面装备情况设备名称生产厂家主要技术特征采煤机美国JOY公司采高2.55.0m，滚筒直径22002500mm，有效截深8501000mm，牵引力617kN，牵引速度015m/min，生产能力20003500t/h，功率1500kw。液压支架德国DBT公司；美国JOY公司支架高度2.14.5m，宽度1750mm，额定工作阻力67157625kN，电液控制系统。刮板输送机德国DBT公司；美国JOY公司电机功率2700kW，运输能力2500t/h，中双链，交叉侧卸。转载机德国DBT公司；美国JOY公司电机功率250、200、300、315kW，运输能力2500、3000t/h。破碎机德国DBT公司；美国JOY公司电机功率250、200、300、315kW，运输能力2500、3000t/h。胶带输送机澳大利亚ACE；美国LAD公司；英国FSW公司。电机功率3315、2400、3375kW，运输能力2500、3000t/h，带宽1200、1400mm，带速3.5、4.0m/s，长度3000、6000m。（2） 晋煤集团寺河矿设计能力400万t/a工作面平均日产原煤1.3万t，最高日产1.6万t。工作面装备情况参见表2-8。同时，目前大采高综采还存在很多局限性，主要在冒顶、底板、煤壁片帮三个方面。如果能成功的克服了上述难题，并能实现设备国产化，则付村矿5m厚煤层一次全高大采高综采实现安全、高产、高效生产是非常有意义的。并可藉此提升我国厚煤层机械化开采程度和厚煤层回收率。表2-8 寺河矿大采高工作面装备情况设备名称生产厂家主要技术特征采煤机德ickhoff公司采高2.26.0m，滚筒直径2500mm，有效截深865mm，牵引速度025m/min，生产能力3000t/h，功率1500kw以上。液压支架德DBT公司支架高度2.555.5m，宽度1750mm，额定工作阻力8200kN，PM-4电液控制系统。刮板输送机德DBT公司电机功率2700kW，运输能力2500t/h，长度250m，中双链，交叉侧卸。转载机德DBT公司电机功率315kW，运输能力2750t/h，长度27.5m。破碎机德DBT公司电机功率315kW，运输能力3000t/h。胶带输送机澳ACE公司电机功率3315kW，运输能力2500t/h，带宽1400mm，带速3.5、长度3000m。综上所述，大采高一次采全厚综采是一种有发展前途的采煤法。付村矿的煤层覆存条件满足一次全厚开采的条件，故选用大采高一次采全厚综采采煤工艺。3 一次采全高采动覆岩结构特征分析为研究厚煤层大采高综采工作面的采动覆岩活动规律，并对所设计液压支架的适应性进行评价，本课题分析了大采高工作面的上覆岩层关键层结构效应，并进行了上覆岩层破坏特征数值模拟，为工作面顶板控制提供依据。3.1 上覆岩层关键层结构效应分析对于采场矿压显现产生影响的关键层，人们习惯称为基本顶或老顶，它破断后形成的“砌体梁”结构将直接影响顶板的稳定性。传统的矿压理论一般仅考虑煤层上方第一层坚硬岩层对采场矿压显现的影响。关键层理论研究表明，当靠近煤层的二层或多层硬岩层间产生复合效应时，影响工作面矿压显现的基本顶将不止一层。就对采场矿压显现的影响而言，关键层理论完全包容了煤层基本顶概念所涉及的各种理论和观点。为研究工作面上覆主关键层以及亚关键层在工作面回采过程中对矿压显现及地表沉降有何影响，就必须判别煤层覆岩中的关键层。在煤系岩层中，由于成岩时间和矿物成份等的不同，使各岩层厚度和力学特性等方面存在着不同程度的差别。一些较为坚硬的厚岩层在采动覆岩的变形和破断中起着主要的控制作用，它们以某种力学结构形式支承上部岩体的压力。而它们的破断又直接影响着采场矿压显现和地表沉陷。同时由于各坚硬岩层的特征不一，因而并不是每一层坚硬岩层都在覆岩的运动中起决定作用。在采场覆岩中存在着多层坚硬岩层时，对岩体活动全部或局部起决定作用的岩层称为关键层。关键层判别的主要依据为其变形和破断特征，即在关键层破断时，其上部全部岩层或局部岩层的下沉变形是相互协调与同步的，前者称为岩层运动的主关键层，后者称为亚关键层。也就是说，关键层的断裂将导致全部或相当部分的覆岩产生整体运动。显然，关键层的断裂步距即为覆岩中部分或全部岩层的断裂步距，从而引起明显的岩层运动和矿压显现。因此，我们将用关键层的破断来分析采场矿压规律。如何判别覆岩中的关键层位置是关键层理论应首先解决的问题。由关键层定义可知，判别覆岩中的关键层位置实则为判别采动岩体中硬岩层的破断顺序。覆岩的破断取决于岩层厚度、岩层的力学性质（如弹性模量E、抗压强度c），只有确定了上述因素，才可对岩层能否破断及上下岩层的破断顺序进行判别。假设开采煤层上覆基岩共有n层岩层，其厚度由下往上分别为h1、h2、hn，对应n层硬岩层共有n层软岩层组，设第1、2、n层软岩层组的分层数分别是m1、m2、mn，其厚度由下往上分别为、，第n层软岩层组上方为表土层，厚度为H，容重为。于是可建立关键层判别计算模型，如图3-1所示。图3-1 关键层判别计算模型具体覆岩条件下，图3-1中硬岩与软岩层组的分层厚度、位置及层数（n值和m1、m2、mn的值）可按刚度法则判别。具体方法为：先确定煤层上方第1层硬岩，然后按以下方法来确定第2层硬岩位置。从第1层硬岩（i=1）开始往上逐层计算值以及值，当下式 (3-1)则不再计算。从第1层硬岩（i=1）往上，第m+1层岩层为第2层硬岩层，第1层硬岩（i=1）与第2层硬岩（i=m+1）间共有m-1层岩层组成第1层软岩层组，即图2-1中m1=m -1。式2-1中，Ei、hi、i分别为各岩层弹模、分层厚度及容重。确定了第2层硬岩层后，从第2层硬岩层开始，按上述方法确定第3层硬岩层位置及第3层软岩层组。以此类推，直到确定最上一层硬岩层，即图3-1中第n层硬岩层为止。由式3-1确定了基岩中硬岩层位置，第1n层硬岩层都有可能成为关键层（亚关键层或主关键层）。要确定第1n层硬岩中哪些层为关键层，还需求得各硬岩层的破断距Li（i=1，2，n）。根据各硬岩层破断距大小判别关键层位置。坚硬岩层在破断前可视为板结构，在一定条件下可简化为梁。考虑到实际开挖存在的损伤效应，老顶关键层按照固支梁力学模型表示，初次来压步距确定计算公式为： (3-2)式中 关键层开挖损伤因子；0.270.45，结合数值和现场实践计算结果一般取0.35；关键层有效抗拉强度；关键层上单位载荷及关键层自重； 当第i层硬岩的厚度hi及岩性一定，其破断距大小，取决于其所受载荷qi。各层硬岩层所受载荷可按下式计算 i=1，2， ，n-1 (3-3)表土层重量将全部作用在最上一层硬岩层上，因此，图3-1所示第n层硬岩层上的载荷为Kz (3-4)式3-3及式3-4中，下标i代表第i层硬岩层；下标j代表从第i层硬岩开始（j0），第i层软岩层组的分层号；，分别为岩层弹模、分层厚度及容重，如E1,0，h1,0，分别为第一层硬岩层的弹模、厚度及容重，E1,1，h1,1，分别为第1层软岩层组中第1层软岩的弹模、厚度及容重。Kz为载荷传递系数；在一定条件下，第i层硬岩层之上的第i层软岩层组的自重可视为全部作用于第i层硬岩层上，此时，式（3-3）及式（3-4）可简化为下列形式 i= 1，2， ，n-1 (3-5) i=n (3-6)根据关键层定义，第i层硬岩层要成为关键层，其破断距Li应大于其下部所有硬岩层的破断距，即满足L iLj i=2，3， ，n j=1，2， ，i-1 (3-7)若第i层硬岩层破断距Li小于第i-1层硬岩层破断距Li-1时，即LiLi-1(i=2，3，n)，则说明第i层硬岩先于第i-1层硬岩破断。第i层硬岩破断后，其所受全部载荷qi将作用在第i-1层硬岩上。此时，作用在第i-1硬岩上的载荷将由qi-1增大为qi-1+qi，应对第i-1层硬岩在载荷qi-1+qi作用下的破断距重新计算。重新计算结果若Li-1li，则取Li-1=Li，说明此时第i-1层硬岩破断受控于第i层硬岩，即第i层硬岩破断前，第i-1层硬岩不破断，一旦第i层硬岩破断，其载荷作用于第i-1层硬岩上，导致第i-1层硬岩随之破断。由于岩层上载荷是由上往下传递作用的，因此，应从最上一层硬岩层(即图3-1第n层岩层)开始逐层往下来判别式(3-7)是否成立，当LiLi-1时重新计算第i-1层硬岩破断距。当基岩厚度较大或硬岩层较多时，手工计算是相当繁杂的。将该方法编成程序，由计算机来实现，只需逐层输入各岩层基本参数，就能自动输出关键层判别的结果。表3-1 3上405工作面上覆岩层关键层判别岩层岩层厚度岩性描述备注砂质泥岩33.0深灰色，含砂质均匀，致密，性脆，局部含菱铁矿石结核及零星状黄铁矿，上部含植物化石碎片，参差状断口。2煤0.35黑色，似玻璃光泽，半光亮型煤，简单结构。砂质泥岩1.0灰色，致密，泥质结构，性脆，含黄铁矿结核。细砂岩1.9灰色，细粒结构，成分以石英为主，呈波状层理。砂质泥岩5.6黑灰色，砂泥质结构，块状构造。细砂岩1.4灰色，细粒结构，成分以石英为主，泥质胶结。砂质泥岩4.4灰白色，砂泥质结构，块状构造，含黄铁矿。中砂岩5.6灰白色，石英长石为主，粒度均匀，分选性好，含白云母，泥硅质胶结。细砂岩3.5灰色，厚层状，细粒结构，呈斜波状层理，成分以石英为主，钙质胶结，f=68。关键层泥岩1.5黑灰色，致密，泥质结构，块状构造，性脆，含植物化石及黄铁矿，f=46。3上煤5.37黑色，似玻璃光泽，半光亮型煤，简单结构，f=1.52.2。砂质泥岩1.3黑灰色，砂泥质结构，块状构造，含植物化石及小结核，f=46。细砂岩6.93浅灰色，细粒结构，硅质胶结，成分以石英为主，含有云母片及星点状黄铁矿，f=68。砂质泥岩0.59灰黑色，含少量植物化石印痕，水平层理明显，f=46。三下煤3.8黑色，玻璃光泽，半光亮型煤，复杂结构，煤层下部含一层00.59m的泥质夹矸，中硬，f=1.52.2。砂质泥岩0.85浅黑色，砂泥质结构，薄层状，f=46。细砂岩8.79深灰色，水平层理，含植物化石碎片及黄铁矿，裂隙较为发育，f=68。粉砂岩3.3灰色，粉砂质结构，水平层理明显。砂质泥岩3.15灰黑色，含黄铁矿菱铁矿结核，水平层理。一灰0.6棕灰色，质不纯，含少量腕足类化石，海百合化石。泥岩1.6深灰色，水平层理，含植物化石碎片和黄铁矿。根据表3-1，确定付村煤业有限公司3上煤层的老顶即细粒砂岩为关键层，且为唯一主关层。3.2 老顶关键层来压步距的理论计算确定3.2.1 初次来压步距综合考虑付村煤业有限公司首采区地质采矿条件和整个井田地煤层覆存状况，本报告中关于支护阻力计算中的煤层厚度按3上煤层最大采高5.1m处理。考虑到实际开挖存在的损伤效应，老顶关键层按照固支梁力学模型表示，初次来压步距确定计算公式为： (3-8)式中 关键层开挖损伤因子；0.270.45，结合数值计算结果取0.35；关键层有效抗拉强度，；关键层上单位载荷及关键层自重；根据关键层理论，我们可以得到： (3-9)式中 ，老顶关键层弹模及厚度； ，第层岩层弹模及厚度； n老顶关键层控制的上覆岩层数（与关键层同步变形）； 载荷层作用在老顶岩层上的单位载荷；Kz覆岩载荷传递系数；考虑到采场载荷的时间传递过程，我们再引进一个载荷传递系数Kz，由此可以合理确定厚松散载荷层老顶关键层岩块的载荷。 Kz除受载荷层本身物理和几何性质的影响为，随工作面推进速度的增大而减小，当推进速度慢到一定程度时，其值较大。其合理的范围应该在0.30.7之间，一般应为0.350.5，参考浅埋煤层的矿压显现规律，在没有相似条件工作面现场测试数据参考的情况下，建议取0.45。经过上述分析，我们就可以在采场的支护阻力计算中，合理确定出老顶关键层（关键层1）的载荷。按照将付村的地质条件，考虑一定的安全系数，计算得出老顶初次断裂长度在38m左右。3.2.2 周期来压步距老顶的主要破坏形式为拉破坏，剪切现象则属老顶基本破断为岩块后的铰接运动行为。由模拟分析可知，老顶出现超前拉裂隙的位置就是顶板周期性破断的位置，破断步距由此确定。按照弹性地基上的半无限长梁理论计算老顶关键层周期来压步距为： (3-10)式中：岩梁悬伸长度；超前破断距离，先设定，再用验证，使此式成立的是岩梁出现拉破坏时工作面的推进步距；式中：，岩梁的抗弯刚度；m弹性地基模量，；，m；，弹性地基（煤层和直接顶）的弹性模量和厚度；按照将付村的地质条件，考虑一定的安全系数，可以得到该矿的周期来时，工作面推进约12m后，老顶在煤壁内超前约4m处断裂，周期来压步距约为16m。3.3 上覆岩层垮落特征分析RFPA2D模拟3.3.1 模型建立根据该矿的地质条件和柱状图建立起来的模型如图3-3所示。模型沿走向方向取300m，垂直方向取95m。计算中对性质相近的岩层作合并处理，在岩层间加入了强度很小的薄弱层作为层理，采用平面应变模型，上边界自由，两端和底边固定约束（力学模型如图3-4所示）。模型中各岩层的灰度代表岩层力学参数(如弹性模量、抗压强度等)的大小，灰度越亮，其值越大（此外，单元的亮暗程度还与单元的破裂程度有关，破裂单元由于应力释放，则颜色变为黑色。由此可以知道整个模型在破裂过程中的微破裂的时间序列和空间分布）。 图3-3 数值计算整体模型 图3-4 力学计算模型工作面从左向右开挖，开挖步距为12m，模拟工作面开挖过程中及停采后顶板应力垮落特征。3.3.3采动履岩垮落特征模拟结果分析 (a) 工作 (b) 工作面推进12m（中间迭代过程） (c) 工作面推进24m (d) 工作面推进24m(e) 工作面推进24m（中间迭代过程）(f) 工作面推进36m (g) 工作面推进48m(h) 工作面推进60m(i) 工作面推进72m(j) 工作面推进84m(k) 工作面推进96m(l) 工作面推进150m 图3-5 模拟工作面推进过程中覆岩垮落情况 图3-5(a)、(b)是工作面推进12m时顶板垮落状态，可以看出，由于工作面推进距离较短，顶板没有太大变化，局部出现裂隙。随着工作面的不断推进，裂隙不断发育，直接顶大面积垮落，垮落高度不断向上发展，约3.5m。工作面推进36m时基本顶已初次垮落，工作面基本顶初次来压。由此确定工作面初次来压步距不大于36m。 工作面推进60m时（图3-5(h)），垮落带高度进一步增大，高度达到15m左右，工作面又一次周期来压，由于顶板各岩层岩性不同，覆岩出现离层和裂隙，并有断裂现象，随着工作面推进有向上发展的趋势。 工作面推进72m时（图3-5（i），垮落带高度进一步增大，高度达到20m左右，工作面又一次周期来压，由于顶板各岩层岩性不同，覆岩出现离层和裂隙，随着工作面推进有向上发展的趋势。 工作面推进96m时（图3-5（k），工作面又一次周期来压，覆岩离层和裂隙随着工作面推进继续向上发展，出现大量裂隙和裂缝。 工作面推进150m时（图3-5（l），覆岩离层和裂隙逐步发展。从模拟过程看，覆岩下沉滞后于工作面一定距离。工作面推进过程中，3.5m的细砂岩基本顶能够形成有承载能力的岩体结构，对覆岩垮落有控制作用。 综合RFPA2D模拟结果，可有如下结论： 工作面初次来压步距为36m左右，周期来压不小于12m； （2）工作面推进过程中，煤层上方厚3.5m的细砂岩基本顶能够形成有承载能力的岩体结构，对上覆岩层的运动起主要控制作用。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： 凉水井煤矿4.0 Mt/a新井设计毕业设计专题题目： 大采高一次采全高的上覆岩层特性分析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，撰写一篇关于大采高一次采全高的上覆岩层特性分析研究的专题论文。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“Effects of frequency and grouted length on the behavior of guided ultrasonic waves in rock bolts，论文4243字符。院长签字： 指导教师签字：翻译部分英文原文Effects of frequency and grouted length on the behavior of guided ultrasonic waves in rock boltsD.H. Zoua, Y. Cui, V. Madengaa, C. ZhangAbstractExperiments were conducted to study the behavior of guided waves in free and grouted rock bolts. Ultrasonic waves with frequencies from 25 to 100 kHz were used as excitation inputs. Tests were rst conducted on free bolts to help understand the behavior of guided waves in non-grouted bolts. The effects of wave frequency and grouted length on the group velocity and attenuation of the guided ultrasonic waves were then evaluated. The test results indicated clear but different trends for the group velocity in the free and the grouted bolts. The attenuation in free bolts was not affected by bolt length and frequency. However, in grouted bolts it increased with frequency and grouted length. It was also found that the two main sources of attenuation are the setup energy loss, which has a xed quantity for a specic type of test setup, and the dispersive and spreading energy loss which varies with frequency and bolt length.2007 Elsevier Ltd. All rights reserved.Keywords: Rock bolts; Guided waves; Attenuation; Amplitude; Group velocity1. IntroductionRock bolts are widely used in underground and surface excavations in mining and civil engineering for ground reinforcement and stabilization. In many applications, rock bolts are grouted in the ground with cement or resin. Testing of the grout quality and monitoring of the bolt tension of rock bolts has long been a challenge in the eld. Conventionally, grout quality is assessed by pull-out test and over-coring. Both methods are destructive and time consuming. The usefulness of pull-out test results as a measure of the grout quality can be limited by the critical length of grout beyond which the steel bolt will fail rst. Therefore, other methods, such as non-destructive testing methods using ultrasonic waves have become attractive. In recent years, research in this area has been very active. It is noticed that properties of guided waves, such as velocity and attenuation, are functions of the input wave frequency. Although the guided ultrasonic wave seems to be a promising method for monitoring rock bolts, research in this area is still in the early stage and many technical problems remain to be solved. In a grouted bolt, wave behavior is not only related to the grout quality but also to the wave frequency. The grouted length and the properties of materials surrounding the bolt may all play an important role.One of the important characteristics of a guided wave is that its velocity not only depends on the material properties but also on the thickness of the material and the wave frequency. Unlike a bulk wave, the guided wave propagates as a packet, which is made up of a band of superimposed components with different frequencies. It is the group velocity that denes the speed at which the envelope of the packet moves along. It has been shown that in a rock bolt, the rate of energy transfer is identical to the group velocity. Our recent research examined the effects of wave frequency and the curing time of grout on the group velocity of guided ultrasonic waves in rock bolts.We found that the wave group velocity is much lower in grouted bolts than in free bolts. The lower the frequency, the lower the velocity. Our test results indicated that the input frequency for rock bolt testing below 100 kHz would provide better resolution and clearer signals. This observa-tion is supported by the results discussed further on in this paper.Attenuation is another important characteristic of a guided wave. In general, attenuation refers to the total reduction in the signal strength. Attenuation occurs as a natural consequence of signal transmission over a distance due to wave energy loss. There have been extensive research and experiments on attenuation of bulk waves. Wave attenuation is dened by an attenuation coefcient. For example, the p-wave amplitude decay can be expressed as a function of travel distance. (1)where Aa is the amplitude at location a, Ab is the amplitude at location b, is the attenuation coefcient, constant, L is the distance from locations a to b, R is the amplitude ratio, R=Ab/Aa.However, there has been little research on attenuation of guided waves, especially in grouted rock bolts. Wave attenuation in grouted rock bolts is very complicated and is often affected by many factors including the grouting material and the grout quality. Each of these factors may cause some attenuation.In general, the observed wave attenuation may have several components, some of which may be frequency-dependent and some frequency-independent. The total attenuation is the sum of the contributions of all inuencing factors 14, and this relationship applies to both bulk waves and guided waves: (2)where is the attenuation coefcient of the ith component caused by the ith factor, is the travel distance affected by the ith factor, is the amplitude ratio after attenuation of the ith component, If is the same for all factors, then weHave or (3)where is the total attenuation coefcient.According to the cause, attenuation may be grouped into the following categories:（a） Dissipative attenuation: An energy loss due to non-elastic resistance of the medium. It increases with thewave travel distance and may become profound over a long distance depending on the material property. This type of attenuation in steel is generally very low compared to that in rocks. As shown later, it can beignored in practice for guided waves traveling in rock bolts due to the low resistance of steel and the short bolt length (13 m).（b） Dispersive attenuation: An energy loss due to deforma-tion of waveform during wave propagation, a char-acteristic that distinguishes guided waves from bulk waves. The phenomenon of wave deformation is calledenergy dispersion.（c） Spreading attenuation: An energy loss which occurs at the interface between the bolt and the grouting material. As a guided wave reaches the interface, not all of the wave energy can be reected at the interface. Part of the energy passes through the interface and is transmitted into the grouted material, a phenomenon called energy leakage.Therefore, it can be reasonably assumed that attenuation in grouted rock bolts consists of two major components;dispersive and spreading attenuation, both of which are frequency-dependent. The total attenuation in grouted rock bolts should thus be the sum of the two components and in future will be referred to as DISP attenuation.It should be pointed out however, that as observed during our laboratory tests, the amplitude decay and the energy loss of guided waves recorded during tests of rock bolts in laboratory are not solely from the DISP attenua-tion. Another important component is the energy loss due to refraction at the contact surfaces between the bolt sample and the equipment. Theoretically, when a wave reaches an interface adjoining a medium which does not transmit mechanical waves (e.g., vacuum or air), no refraction occurs and all energy is reected back.Ina rock bolt test, transducers are attached to the bolt sample, which is in contact with the testing frame (e.g., a table or a rack). It is at these contact surfaces that some energy is inevitably refracted, causing energy loss. This type of energy loss, as shown later, is expected to be constant and is of a xed quantity for a specic type of test setup. In future it will be called setup energy loss. As a result, the recorded amplitude decay and energy loss during rock bolt tests will be greater than what is actually caused by the DISP attenuation.An ongoing research program at Dalhousie University is aimed at studying the characteristics of guided waves in grouted rock bolts. Effects of wave frequency and grouted length on the behavior of guided ultrasonic waves in free bolts and grouted bolts have been studied. The achieved results are strikingly convincing. The details are given below.2. Experiments of guided ultrasonic wave testsAn understanding of the ultrasonic wave characteristics in free bolts (non-grouted bolts) is essential to the study of the behavior of guided ultrasonic waves in grouted bolts. In this research, both free bolts and grouted bolts were tested.2.1. Test samplesThe test samples included two free bolts and three grouted bolts of various lengths. The free bolts were bare steel bars. The grouted bolts were made by casting a cylindrical concrete block around a steel bar to simulate the grouted rock bolts in the eld (Fig.1). In these tests the bolts were not tensioned. The sample sizes and other descriptions are given in Table 1. The two free bolts (samples 1 and 2) were used to study the effects of bolt length and frequency on the behavior of guided ultrasonic waves, particularly the setup energy loss due to equipment setup. The three grouted bolts (samples 35) with varying grouted lengths were used to investigate the effects of frequency and grouted length on the attenuation of guided ultrasonic waves.2.2. Test instruments and experiment descriptionThe instruments used in the study included a Handy-scope HS-3 (a data acquisition device with a wave generator), an amplier, two transducers, and a computer. The equipment setup is illustrated in Fig.2. The HS-3 unit has the capability of generating ultrasonic signals with varying frequencies, as well as receiving and digitizing the received wave signals. Sinusoidal ultrasonic input signals were used to excite the transmitter at the non-grouted end of the bolt. The received signal at the other end was amplied before being digitized. The computer was used to record, display, and process the signals.The transducers used were piezo-electric, types R6 and R15, from Physical Acoustics Corporation. Both ends of the test bolts were smoothed and vacuum grease was used to provide good contact with the transducers.The experiments were conducted by exciting a transmit-ter (R6) with input signals at different frequencies into the non-grouted end of a bolt sample. The signal arriving at the other end was picked up by a transducer (R15) and the whole waveform was recorded digitally. During each test, the input frequency ranged from 25 to 100 kHz.3. Experiment data analysis methodIn the following, rst arrival refers to the rst wave packet that arrived at the receiving end and echo refers to the same wave packet that reached the receiving end for a second time after it was reected back from the input end. The attenuation was estimated by assessing the wave amplitude ratio of the echo over the rst arrival.3.1. Attenuation estimationAs explained earlier, wave attenuation is not only related to the grout quality but also to the frequency and other factors. The amplitude ratio of a wave packet that has traveled some distance has an inverse logarithm relation-ship, as shown in Eq. (1), with the attenuation coefcient.The higher the attenuation, the greater the energy loss, and the lower the amplitude ratio. Therefore the measured amplitude ratio, Rm as dened below, is used as an indirect measurement of attenuation in this study: (4)where A1 is the average amplitude of the rst arrival and A2 is the average amplitude of the echo as dened below.It is understood that good grout quality results in higher energy loss along the rock bolt due to energy leakage and dispersion. It is therefore very difcult to study wave attenuation in grouted bolts because the recorded wave-form is often very weak and is affected by a lot of noises. The received waveform sometimes may not be very clear, making it difcult to identify the boundary between the rst arrival and the echo. This becomes more problematic when the bolt is short or when dispersion is serious. The maximum wave amplitude in this case may be affected by such noises. It is therefore critical to develop a suitable analysis method to analyze the attenuation of ultrasonic waves and to get meaningful results.In this paper, a method to calculate the amplitude ratio using the average amplitude over a time interval is suggested as follows:= (5)where is the time interval centered at the maximum amplitude of a wave packet, is the recorded wave amplitude, i=1 is for the rst arrival, and i=2 is for the echo, k is a material constant.The parameters , , and their denitions are illustrated in Fig. 3. Because this method considers the average amplitude across intervals of equal lengths of time for the rst arrival and the echo, the effects of errors and noises on the maximum amplitude will be minimized. To evaluate the effects of the time interval length and on the accuracy of the results, the amplitude ratios in free boltsthose in which the boundary between the rst arrival and the echo was very clearwere calculated with different time intervals as a percentage of the whole waveforms of the rst arrival and the echo. The results for sample 1 at different frequencies are shown in Fig. 4.Itis clear that if the time interval is too small (e.g., less than 25% of the whole waveform), the amplitude ratio as determined by Eq. (5) varies with the length of the timeinterval. When the time interval is greater than 25% of the whole waveform, the results vary very little and are nearly the same as that at 100% (the whole waveform).In the following, = 100 were used in calculation of the average amplitude for all tests. With an input signal of 25 kHz, this time interval corresponded to 45% f the whole waveform in free bolts, and at 100 kHz, it covered 95% of the whole waveform. It is apparent that although a small part of the whole waveform has not been considered in this method, the calculated amplitude ratio can still reect the total energy loss in a rock bolt. This method however makes it much easier in practice to estimate the energy loss, especially when the boundary between the rst arrival and the echo in grouted rock bolts is difcult to identify because of dispersion.3.2. Group velocity estimationThe wave travel time in the rock bolt is dened as the time lapse from the beginning of the excitation signal, which was recorded from the input end of the bolt, to the rst arrival, which was recorded from the other end of the bolt. However, determination of the beginning of the rst arrival and the echo is often complicated by the dispersion character of the guided wave. Dispersion increases with frequency. The recorded raw waveforms therefore need to be ltered rst by a band lter to narrow the frequency band around each testing frequency 5. This was achieved by using a ltering program designed in Matlab. All the recorded waveforms were ltered using this program to give a narrow band of 75 kHz. The arrival time determined by the ltered waveforms is found to be more representative of the anticipated actual wave travel time at a specic frequency. With the bolt length and the travel time determined using this method, the group velocity of guided ultrasonic waves can be calculated. The calculated group velocity is found to follow different trends in the free and the grouted bolts, as explained later. For partially grouted bolts, the group velocity in the free segment is considered the same as that in the free bolts.4. Effects of frequency and bolt length on the behavior ofguided waves in free boltsExperiments were conducted on free bolts using fre-quencies from 25 to 100 kHz. Fig. 5a) shows the typical waveform recorded in sample 1 at an input frequency of 25 kHz. It was observed during data analysis that with the increase of the input frequency, the travel time of the rst arrival and the echo reaching the receiving end increased slightly, and the wave amplitude reduction of the echo from the rst arrival is almost the same at all input frequencies.4.1. Attenuation in free boltsThe measured amplitude ratio, Rm, determined from the two free bolts (samples 1 and 2) are shown in Fig. 6. It can be concluded from the chart that the total attenuation in the free bolts did not change with frequency. The average amplitude ratio is 0.79 for sample 1 and 0.81 for sample 2. Thus it is also clear that the amplitude ratio is not affected much by the bolt length and that the very small difference for the two bolts is negligible. This conrms that the dissipative attenuation can be ignored for rock bolts because of the short traveling distance. Since there is little or no dispersion in waveforms, nor is there energy leakage to other mediums, the DISP attenuation, which was expected to change with frequency and distance, is negligible in the free bolts.The energy loss for both free bolts was nearly constant and did not change with frequency or bolt length. As discussed earlier, this part of the energy loss has a xed amount, and is mainly caused by setup loss, mostly from refraction at the contact surfaces of the bolt samples with other objects. The setup loss is however expected to change for different test setups.If the amplitude ratio after the DISP attenuation is assumed as R1 and after the setup loss as R2, then the measured amplitude ratio, Rm, according to Eq. (2), will be: (6)As can be seen, the attenuation relationship dened in Eq. (1) applies only to R1, not to the directly measured Rm, since R2 is independent from travel distance.For a free bolt R11.0, the main energy loss will be the setup loss and RmR2. It can be inferred that for grouted rock bolts, the non-grouted free length will have very little effect on the result of attenuation because of its short length and the major energy loss will be in the grouted length. It can also be reasonably concluded from Fig. 6 that the amplitude ratio, R2, after the setup loss (approximately 20%) for the test setup in this research is about 0.8.4.2. Group velocity in free boltsAs indicated above, before estimating the arrival time, the raw waveforms were ltered with a band lter.A typical ltered waveform of sample 1 is illustrated in Fig. 5b), which shows a more well-dened signal than the raw waveform. The determined group velocities for the two free bolts (samples 1 and 2) are shown in Fig. 7 together with the theoretical group velocity solution, which was determined from Achenbachs solution in a steel bar of 19.5 in diameter 3. It can be seen in the chart that the results from the ltered data t well with the theoretical solution in the tested frequency range. As the frequency changed from 25 to 100 kHz; the group velocity dropped by about 10%. The group velocity was apparently not affected by the bolt length.5. Effects of frequency and grouted length on behavior of guided wavesExperiments were also conducted on the grouted rock bolts using frequencies from 25 to 100 kHz. The typical raw waveform for sample 4 at an input frequency of 35 kHz is displayed in Fig. 3. It was observed from the recorded data that the waveforms in grouted bolts showed dispersion, apparently more serious at higher frequency ranges. At the same time, as the input frequency increased the lengths of time for the rst arrival and the echo to reach the receiving end decreased signicantly, following an opposite trend from that observed in the free bolts. The wave amplitude reduction of the echo from the rst arrival also becamemore severe.5.1. Attenuation in grouted rock boltsThe results of the measured amplitude ratio, Rm, for the grouted bolts at different frequencies are shown in Fig. 8.It is already known from the experiment results of free bolts in Fig. 6 that the amplitude ratio after the setup loss, R2,is 0.8 and is independent from frequency. Because the equipment setup and test conditions for the grouted rock bolts are the same as those for the free bolts, it is assumed that the amplitude ratio, R2, is also 0.8 in the grouted bolts. Thus the amplitude ratio R1 after the DISP attenuation can be calculated by re-writing Eq. (6) as R1=Rm/R2. Rm can be calculated from the recorded waveforms following the same procedure as for free bolts.The results of R1 of the grouted rock bolts with different frequencies are shown in Fig. 9. It can be seen that the ratio, R1, of the grouted rock bolts varies inversely with frequency and grouted length. At frequencies less than 65 kHz, R1 decreased linearly with frequency and it also decreased with grouted length. It is noticeable that at frequencies higher than 65 kHz, the data were scattered and the linear trend became unclear. The explanation is that both dispersive and spreading attenuation increased with frequency. The higher the frequency, the greater the energy loss. Hence, the received signal became very weak when the input frequency was above 75 kHz. The weak signal not only introduces more measuring errors, but also aggravates the effects of noises, making the results less reliable.5.2. Group velocity in grouted rock boltsFor the grouted bolts, the results of group velocity calcu-lated from the raw waveform data were totally meaningless. Only after ltering could meaningful results be obtained. The ltering method and the arrival time estimation method are the same as those previously discussed for the free bolts.The group velocity in the grouted length of a partially grouted rock bolt was calculated using the travel time in the grouted length only. The travel time in the grouted length was determined by subtracting the travel time in the free length, which is assumed to have the same velocity as the free bolt, from the total travel time. The measured group velocity in the grouted length for samples 35 are shown in Fig. 7, together with that from the free bolts.It can be seen from Fig. 7 that the results of the three grouted bolts are consistent to each other. The group velocity in the grouted bolts followed an opposite trend as did that in the free bolts; and its value was not affected by the grouted length, but by the frequency. It is interesting to note that at the low frequency end (i.e., 25 kHz), the group velocity in the grouted bolts was about half of that in the free bolts; at frequencies higher than 75 kHz the velocity increase in the grouted bolts slowed down, and at the highfrequency end (i.e., 100 kHz), the velocity was approaching that of the free bolts. In fact, at high frequencies, it was more difcult to separate the grouted length and the free length from the recorded signals. Therefore, frequencies higher than 75 kHz are not recommended for the test.6. Discussions and conclusionsThis research examined the attenuation and group velocity of the guided ultrasonic waves in rock bolts. The test results showed variations with frequency and grouted length. It was determined that due to the short length of rock bolts used in the eld, the dissipative attenuation can be ignored.In free bolts, the dispersive and spreading attenuation along the bolt is negligible and the main source of attenuation is from the setup loss of energy, which reduced the amplitude by 20% in one round trip for the equipment setup in this research. The setup loss is considered to be independent from frequency and bolt length, but depen-dent upon the specic equipment setup. The group velocityin the free bolts decreased by about 10% as the frequency increased from 25 to 100 kHz.In grouted bolts, the setup loss is assumed to be the same as that in the free bolts because the test setup was the same. However, the dispersive and spreading (DISP) attenuation increased with frequency and grouted length, and it was moresevere than that from the setup loss. The amplitude ratio due to the DISP attenuation decreased as the frequency and grouted length increased. The group wave velocity in the grouted length of the test bolts increased steadily as the frequency increased to 75 kHz while the increase slowed down at a higher frequency. However, at 25 kHz, the group velocity wasnearly 50% lower in the grouted length than that in the free bolts. As the frequency approached 100 kHz, the velocity difference between the free bolts and the grouted length was reduced to less than 10%.As indicated earlier, the experiments in this study were conducted using a transmission-through setup (i.e., with sensors on both ends of the tested bolts). This type of setup is not applicable to the eld where only one end of a rock bolt is accessible. The next step of this research will be to conduct similar tests using a transmission-echo setup (i.e., with a sensor at one end only). This will require a different testing device, which is being custom-built for the specic testing requirements. During the next stage of research, tension will also be applied to the bolt samples to study the tension effects. The ultimate goal of this research will be to develop a non-destructive testing device using guided ultrasonic waves for eld monitoring of grouted rock bolts, particularly the grout quality, grouted length, bolt failure, and bolt tension.AcknowledgmentsThis research was supported by a research grant from the Natural Sciences and Engineering Research Council of Canada.中文译文 频率和锚固长度对超声波在锚杆中传播行为的影响D.H. Zoua, Y. Cui, V. Madengaa, C. Zhang 摘要以频率从25至100千赫的超声波作为励磁输入，研究超声波在自由和锚固锚杆中传播的特性。首先对自由锚杆进行实验来了解导波在非锚固时的行为。从波的频率和锚固长度上对群速度和衰减超声导波的影响进行评估。实验结果表明，在自由和锚固锚杆中，群速度有不同的趋势。在自由锚杆中，波的衰减不受锚杆长度和波频的影响。但是，在锚固锚杆中衰减随着频率和锚固长度的增加而增加。同时还发现设置能量损失引起衰减的两个主要来源，一是对某一特定类型的测试体系的一个固定量，二是色散和传播能量损耗随波的频率和锚杆长度的变化而变化。关键词：岩石锚杆；导波；衰减；振幅；群速度1 引言锚杆被广泛应用在采矿和土木工程中的地下和地表开挖后加固和稳定地面。在许多应用中，锚杆用水泥或树脂锚固。测试锚杆锚固质量和监测锚杆预紧力长期以来一直是该领域中的一个挑战。通常用拉拔实验和应力解除法来测试锚固质量。这两种方法都是破坏性和耗时的实验。用拉拔实验结果来衡量锚固质量，受锚杆初次破坏后关键锚固长度的限制。因此，像利用超声波这种非破坏性测试方法已经受到了关注。近年来，这一领域的研究已经非常活跃。导波的性质，如速度和衰减，受输入波频率的作用影响。虽然超声导波是一个很有前景的监测锚杆的方法，但是在这一领域的研究仍尚处于初期阶段，许多技术问题仍待解决。在锚杆中，波的行为不仅与锚固的质量，而且与波的频率有关，也受锚杆周围岩体的特性和锚固长度的影响。导波的一个重要的特征是其速度不仅取决于材料性能，而且取决于材料的厚度及波的频率。导波不像体波，而是由一个束具有不同频率的成分波叠加组成。群速度决定其传播速度，波整体以该速度传播。在锚杆中，能量传递速率与群速度相同。我们最近研究测试锚杆中波的频率和固化时间对超声导波群速度的影响。我们发现群速度在锚固锚杆中低于在自由锚杆中。频率越低，速度越低。实验结果表明，为锚杆实验输入低于100千赫的频率会提供更好的分辨率和更清晰的信号。本文将进一步讨论这个实验结果。导波的另一个重要特点是衰减。一般来说，衰减是指信号强度的减弱。衰减是信号长距离传输过程中波能损失的自然结果。在体波的衰减方面已经有广泛的研究和试验。波的衰减是由一个衰减系数定义的。举例来说，纵波振幅衰减可以表示为一个距离函数。 (1)其中Aa，Bb分别是位置a，b处的振幅；是衰减系数且是常数；L是从a到b的距离；R 是振幅比率，R=Ab/Aa。然而,很少有研究导波的衰减，特别是在锚杆锚固方面。在锚固锚杆中波的衰减是非常复杂并且常常受包括锚固材料和锚固质量在内的多种因素的影响。这些因素都可能造成一些衰减。通常，波的衰减可能有几个部分组成，其中一些随频率变化一些与频率无关。总衰减是所有因素影响的结果，这也适用体波和导波： (2)其中是受第i个因素影响的第i个分量的衰减系数；是受第i个因素影响的距离；Ri是第i个分量衰减后振幅的比；如果对所有的因素都相同，则有 或 (3)其中是所以衰减系数的和。根据起因，衰减可分为以下几类：(a) 耗散衰减：一种由非弹性介质阻碍引起的能量损耗。它随波的传播距离的增加而增加，并可能根据物质的性质在长距离传播时成为很显著的原因。这类型的衰减在钢材中跟在岩石中相比普遍很低，如后面所述，在实践中由于钢的低阻力和锚杆长度(13 m),导波在锚杆中传播时,这种衰减可以被忽视。(b) 色散衰减：一种由于传播过程中波形变形导致的能量损耗。这也是导波在波传播中区别于体波的一个特点。这种波变形的现象称为能量色散。(c) 传播衰减：一种发生在锚杆与锚固材料界面间的能量损失。作为一个导波的到达界面，并不是所有的波能都可以在界面上反射的。一部分能量会穿过界面，并传到锚固材料，这种现象称为能量泄漏。因此，可以合理地假设在锚固锚杆中衰减由两部分组成:色散衰减和传播衰减，这两者都是跟频率密切相关的。锚杆中的总衰减就是这两种衰减的总和，以后将统称为色散衰减。需要指出的是：正如我们在实验中观察到的，在测试锚杆实验室中记录的导波的振幅衰减和能量损失并不仅仅来源于色散衰减。另一个重要组成部分，是在锚杆样品及设备的接触面之间折射的能量损失。理论上说，当一个波到达毗邻另一不传送机械波的界面（例如真空或空气），没有折射发生，所有能量都被反射回去。在锚杆实验中，传感器被放在接触测试框架的锚杆样品上（例如，一张