Instability characteristics of the cracked roof rock beam under shallow mining conditions

To establish the movement relationship for the roof breaking under shallow mining conditions, the mechanical model of the roof rock beam was built, then the structure instability process of the roof rock beam was analyzed. The changing criterion of the vertical displacement was established and the relationship between the deflection and the rotary motion of roof block was determined. Regarding a mining face in Shangwan Mine, the responsing laws of the deflection and horizontal thrust of the roof rock beam were obtained through FLAC3D numerical analysis. The results show that the structure instability of the cracked roof rock beam depends on the interaction between the vertical load and the horizontal thrust.For the roof rock beam, when the vertical load keeps constant, the horizontal thrust fluctuating rises with increasing deflection. The horizontal thrust increases constantly with the deeper buried depth and the smaller span.

Breakability analysis of the elastic rock beam based on the winkler model

Based on the Winkler model, a mechanic model was established with formulas derived concerned with the deformations before and after a roof breakage at places in front of and at the back of the working face. In accordance with the theory for rock beam breakage, the beam breaking position in front of the working face is specified. In addition, the formulas were developed for the velocity of the subsidence at observatory point A in front of the working face when the coal wall serves as the coordinate center and the advance distance at time t as the dynamic coordinate. In the application of the above-mentioned achievements to the practice of Xieqiao Mine and the mines of the Eastern Panji Company of Huainan Mining（Group） Co. Ltd., the results concerned with the velocity with which the roof stratum tends to subside before and after breakage as derived from the mechanic model are well compatible to the results based on in-situ observations and measurements.

Precision blasting excavation of rock face beam in underground hydropower station under complex geological conditions

To deal with the construction difficulties of Xiangjiaba underground hydropower station,such as complex geological conditions,narrow rock bench,high loading,high quality requirements and urgent time limit,the project adopted the concept of precision blasting.The explosive energy and rock mass fragmentation were well controlled by taking reasonable excavation sequence,designing steel pipe drilling frame,the additional techniques of double layer smooth blasting,evenly micro charge,staggered arrangement of boreholes and pre-stressed anchors.These technologies ensured the excavation quality of the rock face beam,achieving successful blasting results:Semi hole ratio was 100%in Ⅱ surrounding rock,99.2%in Ⅲ surrounding rock and 90%~ 97.3%in Ⅳ surrounding rock;underbreak was avoided and the average backbreak was only2.9 cm;the unevenness was 0 ~ 4 cm;the influence depth of blasting and unloading was 0.2 ~ 0.7 cm.

Rock bending creep and disturbance effects

The bending creep and its disturbance effects of red sandstone rock beam and oil shale rock beam were studied by adopting the self-developed gravitation level style rock creep test machine and bending creep test system,and the constitutive equations were established.It is found that fracture morphology of rock beams under no disturbance load is regular,cracking position of fractures is on part of loading concentration,the crack starts from a neutral plane.However,fracture morphology of rock beams under disturbance load is irregular,cracking position of fractures deviates from a neutral plane.Delayed instability of rock beam occurs for some time under constant disturbance load.When disturbance load is beyond a certain range,suddenly instability of occurs rock beam in a certain time.The results show that there is a guiding significance for creep stability in the geotechnical engineering fields.

Earthquake-induced collapse mechanism of two types of dangerous rock masses

As the economy of China develops, an increasing number of key traffic projects have been undertaken in the west of China, where there are high, steep rock slopes. The collapse of dangerous rock masses, especially following a strong earthquake, is one of common geological disasters known in rock slope engineering. Therefore, it is important to study the collapse mechanism of dangerous rock masses induced by an earthquake and the analysis approach of its stability. This study provides a simple and convenient method to determine the collapse mechanisms of two types of dangerous rock masses （i.e. cantilever and upright） associated with the definition and calculation of the safety factor, which is based on the flexure theory of a constant-section beam by combining with the maximum tensile-stress criterion to depict the process of crack propagation caused by seismic waves. The calculation results show that there are critical crack depths in each form of the dangerous rock masses. Once the accumulated depth of the crack growth during an earthquake exceeds the critical depth, the collapse will occur. It is also demonstrated that the crack extension amount of each step is not a constant value, and is closely associated with the current accumulated crack depth. The greater the cumulative crack depth, the more easily the crack propagates. Finally, the validity and applicability of the proposed method are verified through two actual engineering examples.

矿震与冲击地压防治研究进展

矿震与冲击地压是采矿领域亟待解决的热点、难点和瓶颈问题,为了有效控制矿震与冲击地压,综述矿震定义与分类、矿压假说及矿震与冲击地压防治技术,回顾切顶卸压理论及其在中厚金矿采空区处理与卸压开采、中厚及以下煤矿沿空留巷中的应用,并比较其与110工法的差异。据此,给出矿震定义,指出矿震与冲击地压发生的条件类似,针对厚矿体开采提出深埋坚硬顶板控制爆破切槽放顶技术。研究表明:控制爆破切槽放顶技术仍然是未来矿震与冲击地压防治中释放并转移高地压的主要方法,它还可将深埋厚矿体的“砌体梁”简化成弹簧岩梁承载体系。

Cubic ZnO films obtained at low pressure by molecular beam epitaxy

A zinc oxide thin film in cubic crystalline phase, which is usually prepared under high pressure, has been grown on the Mg O（001） substrate by a three-step growth using plasma-assisted molecular beam epitaxy. The cubic structure is confirmed by in-situ reflection high energy electron diffraction measurements and simulations. The x-ray photoelectron spectroscopy reveals that the outer-layer surface of the film（less than 5 nm thick） is of ZnO phase while the buffer layer above the substrate is of ZnMgO phase, which is further confirmed by the band edge transmissions at the wavelengths of about 390 nm and 280 nm, respectively. The x-ray diffraction exhibits no peaks related to wurtzite ZnO phase in the film. The cubic ZnO film is presumably considered to be of the rock-salt phase. This work suggests that the metastable cubic ZnO films, which are of applicational interest for p-type doping, can be epitaxially grown on the rock-salt substrates without the usually needed high pressure conditions.

Stress arch bunch and its formation mechanism in blocky stratified rock masses

Stress arch is a common phenomenon occurring in continuous materials and has also l：een proved to have great influences on the self-stabilization of soils or rock masses after excavation. In this paper, based on UDEC simulation, stress redistribution after excavation is investigated for a kind of special discontinuous material, i.e. blocky stratified rock mass. A layered stress arch system is observed with each stress arch lying over another. This special phenomenon is defined herein as ＂stress arch bunch＂. Effects of dip angle of bedding plane, lateral pressure and joint offset on this stress arch bunch are studied. Its formation mechanism is also discussed based on voussoir beam theory.

软岩地基中新型倒肋式风机基础力学性能有限元分析

目的 提出一种新型倒肋式风机基础,解决软岩地基中采用梁板式风机基础带来的挖方量大、模板支设繁琐、施工成本高、周期长等问题。方法 以2.5 MW风机为例,采用ABAQUS有限元分析软件,建立相同尺寸的倒肋式与梁板式风机基础模型,对比两种基础在极端工况下的倾斜率、水平位移、破坏特征等,并结合挖方量、模板工程量对两者的经济性进行分析。结果 倒肋式基础的水平位移为0.444 mm、倾斜率为0.012 1%,均满足规范要求;倒肋式基础的肋梁受力特征与悬臂梁相似,在基底反力作用下肋梁与墩台连接处承受的剪力及弯矩较大,容易开裂破坏,可通过增加肋梁截面高度改善;倒肋式基础相较于梁板式基础土方挖量可节省54%、模板工程量可节省48%。结论 倒肋式基础充分发挥出了倒置肋梁与软岩地基之间齿槽嵌固的优势,相较于梁板式基础不仅具有更优的抗滑移稳定性和受力性能,而且减少了挖方和模板工程量,经济效益显著。

超长外露锚杆无损检测方法的研究与应用

锚杆无损检测技术是利用声波反射原理检测注浆锚杆的注浆饱满度及其埋设长度的一种方法,目前已在各类支护工程中广泛应用。但当锚杆外露长度过长时,其取得的检测结果误差较大,不能准确地反映锚杆的锚固质量。硬梁包水电站地下厂房岩壁吊车梁锚杆外露长度均超过1 m,其锚杆数量多,对钻孔注浆质量要求高,阐述了对如何准确快捷地实施检测,并进行了研究分析与探讨,所取得的经验可供类似工程借鉴。

Interaction between transverse isotropy rock slope and supporting structure

In order to study the interaction between transverse isotropy rock mass and supporting structure,the laboratory tests for rock sampled from the slope at expressway project were carried out,and the parameters of elasticity for transverse isotropic rock were determined by the uniaxial compression tests for rock sample with different strike of stratification plane.Then,based on the relationship of stress-stain for transverse isotropic rock mass,the analytical model was established for the interaction between transverse isotropic rock mass and frame beam with pre-stressed anchor cable.Furthermore,the conception of the best anchorage-angle in pre-stressed anchor cable was proposed.At last,the parameters of the interaction between transverse isotropy rock mass and frame beam with pre-stressed anchor cable were investigated by finite element method,and the best anchorage-angle in pre-stressed anchor cable was obtained.The rules of the influence of the directivity of stratification plane on supporting structure were determined.The results show that the analytical model and numerical method on the design of pre-stressed anchor cable with frame beam supporting for transverse isotropy rock slope are reasonable and reliable in practical engineering design.

管道作用下急倾斜煤层稳定性分析

近地表荷载与急倾斜煤层老采空区的“活化”有着紧密的关联,采空区覆岩中裂隙带底部的岩块在荷载作用下极易发生回转失稳和滑落失稳,这些岩块对采空区的稳定性起到至关重要的作用,被称为关键岩块,当荷载作用使得关键岩块失稳时,采空区将发生“活化”。基于采空区覆岩“砌体梁”结构力学模型对关键岩块进行力学分析,构建荷载作用下采空区上覆岩土体失稳判断依据,进而对荷载作用下急倾斜煤层上覆岩体稳定性进行定量分析,研究发现:当作用于土体截面处最大摩擦力大于该土体所受最大剪切力时,该块体不会发生滑落失稳;只有关键岩块与岩块之间的平均挤压应力小于岩块在边角处的挤压强度,关键岩块才不会发生回转失稳。将推导结果应用于广东省某急倾斜煤矿,计算结果表明:在茶山煤矿4煤和6煤采空区上方铺设输气管道并不会引起采空区的“活化”;荷载作用下的关键岩块力学分析在急倾斜煤层上覆岩体稳定性中应用效果较好,对实际工程有一定指导作用。

深部开采环境下底板隔水关键层深梁力学分析

【目的】随着矿井开采深度增加,来自高承压岩溶水威胁增大,导致煤层工作面出现涌水、突水等水害现象,分析深部开采环境下煤层底板隔水关键层抵抗水压力强度是解决这一现象的重要内容之一。【方法】为解决此问题,将隔水底板简化为岩梁模型,并运用深梁理论解决深部开采突水预测中的岩梁模型问题,采用理论分析和数值模拟相结合的方法,根据深梁弯曲力学特点,结合前人研究成果,将深梁条分成浅梁,通过弹性力学单根浅梁受力分布形式假定层间挤压应力σy为三次函数,给出深梁弯曲应力求解的条分技术,并将计算结果与弹性力学解、FLAC3D模拟结果进行对比。【结果和结论】结果表明,深梁条分解得到的应力及位移与数值解结果趋势更为接近,计算结果更为精确,相对误差均在10%以内,同时,随着条分层数增加,精度也增加,但提高幅度逐渐降低,因此,工程应用中针对深部岩梁模型条分到一定程度即可;随着高跨比不断增加,精度误差也在增加,说明条分层宽度不宜过大,否则造成误差增加;底板隔水关键层实例表明,当隔水关键层高跨比大于0.2时,为典型的深梁问题,常规弹性力学的最大拉应力求解结果误差较大,相对误差达到40.6%,给正确判定关键层突水危险性带来不利影响,此时采用深梁条分法求解应力精度较高,可为深部煤层底板突水预测研究起到重要的指导作用。

锚杆-围岩结构的耦合振动和减振

锚杆支护是隧道施工中常见的支护手段,而随着施工工况日趋复杂,锚杆与围岩的组合结构也承受着各类动力荷载的影响。针对隧道中单根锚杆的受力特性有较多研究,而对于锚杆和围岩组合体的动力特性研究较少。对锚杆-围岩结构进行整体分析,简化出一种巷道顶板锚杆支护模型,结合动力学双梁理论,建立并求解出模型动力学方程;运用MATLAB软件进行数值模拟,研究不同支护参数下结构的自振特性以及在外荷载作用下的动力响应,提出减振措施;利用有限元软件GTS NX建立二维模型,验证支护体系的安全性。结果表明:锚杆-围岩结构的动力特性与锚固段长度、锚杆间距和锚杆直径有关。在所建模型中,随着锚固段长度与锚杆间距的适当增加,结构动力响应明显减弱;随着锚杆直径的变化,结构动力特性的变化情况较复杂,结构不同部位的动力响应变化趋势差别较大。

深井岩巷空顶区失稳及安全空顶距研究

为解决深井岩巷掘进过程中空顶区冒顶、片帮的安全问题,以吕家坨矿-950四采区回风道为工程背景,综合采用理论分析与数值模拟相结合的方法开展研究。运用卡斯特纳公式计算了巷道开挖之后塑性区半径为3.19 m,以此为基础建立了一端简支一端固支的空顶区岩梁力学模型,推导出了最大空顶距表达式。研究结果表明,-950四采区回风道的安全空顶距为2.6 m;运用GDEM模拟分析了不同工况下围岩的应力和损伤情况,模拟结果表明前方岩壁的支撑作用要明显高于后路锚杆对顶板的支撑作用,Ⅲ型工况下围岩的应力和损伤情况与Ⅱ型工况相差不大,考虑炮孔深度受限,空顶距为2.4 m时较为合适。

四川省大渡河金川水电站地下厂房岩壁吊车梁岩台超挖处理措施及锚杆注浆时机研究

为了解决金川水电站地下厂房岩壁吊车梁岩台超挖严重问题,综合考虑现场地质状况、开挖现状、施工条件以及后续开挖可能进一步加剧围岩劣化等因素,对岩台超挖部分实施混凝土回填,并与岩壁吊车梁同期施工。通过建立岩壁吊车梁和回填混凝土及围岩三维有限元数值模型,计算分析了洞室下部开挖过程中的洞壁应力释放和桥机轮压、受拉锚杆注浆时机对岩壁吊车梁受拉锚杆应力以及壁吊车梁应力影响。结果表明:岩壁吊车梁锚固锚杆应力主要受洞壁应力释放影响,轴向拉应力最大值位于岩体中,桥机轮压影响幅度仅为0.32~3.15 MPa;岩壁梁锚固锚杆不宜与系统锚杆同时注浆。岩壁吊车梁运行状态良好,满足稳定要求。

基于固有频率的错断式坠落危岩体稳定系数计算模型

错断式坠落危岩体的安全稳定程度受后缘裂缝深度控制,基于静力学的稳定系数计算可得到后缘裂隙深度临界值,但静力学计算方法无法得到裂隙深度的实时变化。基于修正Timoshenko梁建立岩梁动力学方程,结合动力基础半空间理论对岩梁的约束刚度及边界条件做深入分析,得到不同裂缝深度条件下危岩体固有频率理论解析。基于数值计算验证固有频率算法的正确性,并得出结论:随裂隙深度增大,固有频率不断降低,固有频率对危岩体后缘裂隙深度变化较为敏感,根据危岩体的固有频率值可反算危岩体后缘裂隙深度。基于固有频率与危岩体后缘裂隙深度之间的关系建立错断式坠落危岩体稳定系数计算模型,并采用室内试验进行验证,得出结论:危岩体固有频率与其后缘裂隙深度近似为负线性相关。基于固有频率的错断式坠落危岩体稳定系数计算模型可为危岩体自动化监测提供有益借鉴。

上薄下厚煤层群上行开采可行性研究

上行开采可有效缓解矿井接续紧张,延长矿井服务年限。以某矿典型的上薄下厚煤层群开采为例,综合采用理论分析、数值模拟等方法对B_(5)煤层上行开采可行性展开研究。结果显示,B_(4)^(2)煤层、B_(5)煤层层间岩层为含单一煤层结构,B_(5)煤层处于在B_(4)^(2)煤层开采后形成的裂隙带范围内,B_(4)^(2)煤层开采后,上覆岩层形成铰接岩梁结构,随着工作面推采,铰接岩梁结构不断向前传递,B_(5)煤层可以保持较好的完整性和连续性。采用4种判别方法对该矿水平采区范围内B_(5)煤层是否具备上行开采的可行性进行验算,明确了B_(5)煤层部分区段具备上行开采的可行性,为高效开采提供了理论依据。

浅埋深大采高工作面矿压显现规律研究

以三道沟煤矿85214工作面为工程背景,对浅埋深大采高工作面矿井的矿压显现规律进行研究,利用理论分析的方法,建立固支梁和悬臂梁模型,确定工作面初次来压步距和周期来压步距分别为104.91和19.90 m。基于覆岩浅埋结构性质,建立短砌体梁和台阶岩梁模型,确定支护阻力分别为5 624和14 461 kN;利用现场试验的方法,对井下支架工作阻力数据实测分析,确定工作面初次来压步距106 m,周期来压步距16.8 m,月平均次数11次,平均支架载荷37.5 MPa,支承压力主要分布于工作面中部区域。研究结果证明了来压步距模型的合理性和有效性,并确定了浅埋深条件下覆岩结构呈现短砌体梁结构和台阶岩梁结构的破断特点,可为矿井生产提供依据。

天台抽水蓄能电站岩壁梁爆破开挖精细化控制技术

岩壁梁具有经济可靠、方便施工、加快进度等优点,在地下厂房的建设中得到广泛使用。以浙江天台抽水蓄能电站中岩壁梁的开挖爆破施工为工程背景,基于现场爆破试验,提出了精细化爆破参数与网路设计方案,总结了现场采用的岩壁梁爆破施工精细控制方法,对比分析了各种施工措施实际应用后的现场效果与监测结果,可供类似工程参考。