System dynamics model of the support-surrounding rock system in fully mechanized mining with large mining height face and its application

Fully mechanized mining with large mining height (FMMLMH) is widely used in thick coal seam mining face for its higher recovery ratio, especially where the thickness is less than 7.0 m. However, because of the great mining height and intense rock pressure, the coal wall rib spalling, roof falling and the instability of support occur more likely in FMMLMH working face, and the above three types of disasters interact with each other with complicated relationships. In order to get the relationship between each two of coal wall, roof, floor and support, and reduce the occurrence probability of the three types of disasters, we established the system dynamics (SD) model of the support-surrounding rock system which is composed of “coal wall-roof-floor-support” (CW-R-F-S) in a FMMLMH working face based on the condition of No. 15104 working face in Sijiazhuang coal mine. With the software of Vensim, we also simulated the interaction process between each two factors of roof, floor, coal wall and the support. The results show that the SD model of “CW-R-F-S” system can reveal the complicated and interactive relationship clearly between the support and surrounding rock in the FMMLMH working face. By increasing the advancing speed of working face, the support resistance or the length of support guard, or by decreasing the tip-to-face distance, the stability of “CW-R-F-S” system will be higher and the happening probability of the disasters such as coal wall rib spalling, roof falling or the instability of support will be lower. These research findings have been testified in field application in No. 15104 working face, which can provide a new approach for researching the interaction relationship of support and surrounding rock.     

Coupling control on pillar stress concentration and surface cracks in shallow multi-seam mining

In order to ensure safe mining and reduce surface damage in shallow multi-seam mining, the failure characteristics of interburden strata with different coal pillars offset distances between pillars in the upper and lower seams, the distribution characteristics of stress concentration in coal pillars, and the development characteristics of stratum cracks and subsidence were investigated by physical and UDEC2 D simulation. Meanwhile, the effect of different coal pillar offset distances on stress concentration of coal pillar and development of stratum cracks were studied. Based on those results, a formula for safe mining and reducing surface damage was established, which provided a theoretical basis for safe and environmentally friendly mining in shallow multi-seam. According to the results, the optimal coal pillar offset distance(the side to side horizontal distance of the upper and lower coal pillars) between the upper and lower coal seams was developed to reduce the stress concentration of coal pillars and surface damage.The results of this study have been applied in Ningtiaota coal mine and have achieved good results in safe and environmentally friendly mining.     

A new cable truss support system for coal roadways affected by dynamic pressure

The support of coal roadways is seriously affected by intense dynamic pressures. This can lead to problems with large deformation of the roof and the two side walls of coal roadways. Rapid convergence of the walls and roof, a high damage rate to the bolts and cables, or even abrupt roof collapse or rib spalling can occur during the service period of these coal roadways. Analyzing the main support measures used in China leads to a proposed new cable truss supporting system. Thorough study of the entire structure shows the superiority of this design for roadways suffering under dynamic pressure. A corresponding mechanical model of the rock surrounding the cable truss system is described in this paper and formulas for calculating pre-tightening forces of the truss cable, and the minimum anchoring forces, were deduced. The new support system was applied to a typical roadway affected by intensive dynamic pressure that is located in the Xinyuan Coal Mine. The results show that the largest subsidence of the roof was 97 mm, the convergence of the two sides was less than 248 mm, and the average depth of the loose, fractured layer was only 6.12 mm. This proves that the new support system is feasible and effective.     

基于模糊层次法的藏式砌体劣化风险权重系数试验标定研究

藏式砌体广泛应用于藏式建筑墙体中,在自然灾害、人为损坏等赋存环境影响作用下,出现了裂缝、倾斜及材料损伤等多种劣化形式。基于科学手段对劣化藏式墙体的健康状况进行合理评估一直是藏式古建砌体保护的难点。基于模糊评价法和层次分析法,对影响藏式砌体墙的几种主要损伤形式进行综合研究,通过参数分析迭代耦合,得到裂缝、倾斜及材料损伤等多种影响因素的权重系数及层次排序,并通过两个砖砌体试验模型进行验证。结合砌体结构安全评价规范,给出砌体结构墙体性能的量化评价标准,解决了利用模糊评价法评估藏式墙体时损伤形式权重系数难以客观确定的问题。     

斜筋配置对单排配筋低矮墙抗震性能影响试验

在低配筋量的单排配筋混凝土低矮剪力墙中配置斜向钢筋,可限制基底施工缝处水平剪切滑移和墙体斜裂缝开展,提高混凝土低矮剪力墙的抗震耗能能力.为探求带斜筋单排配筋混凝土低矮剪力墙的优化配筋设计方法,进行了5个不同配筋设计的剪力墙模型低周反复荷载试验,对比分析了各模型的破坏特征、滞回性能、承载与变形能力、刚度退化规律、耗能能力及钢筋应变发展规律.试验结果表明:对于单排配筋混凝土低矮剪力墙,斜筋可有效控制其剪切变形,使其抗震性能优于不带斜筋的剪力墙;合理配置斜筋,可明显提高混凝土低矮剪力墙的抗震耗能能力,获得性价比较高的抗震墙.     

新型承重围护保温一体化墙体抗震性能试验研究

为实现钢结构装配式住宅承重围护保温一体化的目标,提出一种设置暗支撑的承重围护保温一体化墙体。墙体内部为支撑钢框架,填充发泡水泥等保温隔热材料,外部设置双向钢筋网并浇注砂浆层作为保护层。框架内填充发泡水泥对结构的水平承载力和抗侧刚度有较大影响,以暗支撑设置、墙体高宽比为变化参数,对6榀单层单跨承重围护保温一体化墙体进行低周反复加载试验,得到各试件的水平承载力、抗侧刚度和滞回特性。结果表明：设置暗支撑能够明显提高新型承重围护保温一体化墙体的水平承载力和抗侧刚度;相比纯钢框架,新型承重围护保温一体化墙体具有更高的水平承载力和抗侧刚度,其耗能能力和变形能力也更强;高宽比对墙体抗侧性能影响显著,高宽比越大,墙体的水平承载力、抗侧刚度、耗能能力均越小。给出了新型承重围护保温一体化墙体的水平承载力计算公式,计算结果与试验结果吻合较好。     

后置混凝土翼墙加固框架角柱抗震性能试验

为考察后置混凝土翼墙加固框架角柱的抗震性能,设计制作了6个在相邻两侧面后置混凝土翼墙的试件.这6个在役框架角柱加固前试验轴压比分为0.31、0.36、0.40三档,纵筋采用HRB400钢筋,纵筋配筋率分为1.23%、1.05%、0.82%三档;箍筋采用HPB300钢筋,箍筋配箍率为0.6%.对这6个试件进行低周反复荷载试验,发现加固后的试件平行于受力方向翼墙在远离角柱一侧损伤严重,而角柱和垂直于受力方向翼墙损伤较轻,达到了加固后原柱同时承受竖向荷载和水平地震作用,翼墙以抵御水平地震作用为主并作为耗能元件有效耗能的目的.     

短肢剪力墙节点扭转性能的有限元分析

由于混凝土塑性变形的影响,短肢剪力墙节点在受到扭转作用加剧时,与按弹性理论计算的结果相差较大。因此,利用ANSYS有限元计算软件,模拟在水平低周反复荷载作用下的T型短肢剪力墙节点,通过分析其结构变形、裂缝和混凝土应力情况等研究节点的扭转性能。研究结果表明:在梁端施加水平作用力可以对节点造成扭转破坏,且梁与墙连接处因出现应力集中而最先出现裂缝,裂缝出现后因部分混凝土退出工作,节点的受力性能发生质的改变;在一定范围内,适当增加轴压比可以提高短肢剪力墙节点的耗能能力,增加其延性;对于容易受到扭转作用的短肢剪力墙节点,可以适当加强节点配筋布置以承受全部的外扭作用,避免节点被过早破坏。     

基于折纸理念的新型两边连接钢板剪力墙弹塑性屈曲分析

现有钢板剪力墙难以同时满足力学性能和耗能性能均较高的要求,针对这一问题,作者基于折纸原理,提出了3种由不同类型的折痕单元构成的新型折痕钢板剪力墙。对两边连接条件下受水平侧向荷载作用的折痕钢板剪力墙进行了弹塑性屈曲分析,详细分析了折痕形式对钢板剪力墙极限承载力、初始刚度、延性等弹塑性屈曲性能的影响,并与平钢板剪力墙及压型钢板剪力墙进行了对比。结果表明,折痕形式对钢板剪力墙的各项屈曲性能有较大影响,折痕的引入会显著降低钢板剪力墙的初始刚度,但对极限承载力的削弱程度相对较小,与压型钢板剪力墙相比极限承载力最大削弱12.65%。塑性铰率先出现在钢板剪力墙折痕处,且折痕引导了塑性开展过程。折痕的引入有效避免了钢板剪力墙发生整体面外失稳,提高了板件的延性。3种折痕钢板剪力墙的延性相较于平板和压型钢板剪力墙均有不同程度的提高,最高为平钢板剪力墙的8.2倍、压型钢板剪力墙的5.2倍。C型折痕单元所组成的折痕钢板剪力墙在侧向荷载作用下能够形成完整的折叠变形模式,塑性开展得更为均匀和充分,其对试件延性的提升相较于其他两种折痕钢板剪力墙更大,是其他两种折痕钢板剪力墙的2倍左右,且在地震后期仍具有较高的承载力。带塑性铰引导机制的新型钢板剪力墙具有良好的抗震性能,为结构提供耗能性能的同时持续为结构提供抗侧力,在结构抗震方面具有较好的利用前景。     

影响加筋土挡墙地震稳定性的参数分析

针对现有挡土墙抗震设计影响因素考虑不足等问题,运用拟静力法和水平条分法分析加筋土挡墙的地震稳定性,并研究土体内摩擦角、水平地震力加速度系数、填土粘聚力、挡土墙倾角和滑动体上部荷载等参数对地震稳定性的影响。结果表明:加筋土挡墙的地震稳定性与水平地震力加速度系数和滑动体上部荷载有显著关系,且变化趋势与之成正比;与土体内摩擦角和填土粘聚力的变化趋势成反比;当条件相同时,倾斜加筋土挡墙的地震稳定性比竖直挡墙的稳定性好。     

框架结构填充墙温度裂缝控制试验研究

框架结构填充墙的温度裂缝问题严重影响工程质量,本试验通过增设构造柱和采用多种墙体材料这两种措施对填充墙的温度裂缝的控制进行研究。试验建筑为单开间框架结构,变形测试方法采用电测法;墙体材料选用加气混凝土砌块和页岩空心砖,部分墙体加设构造柱。试验结果表明:加气混凝土砌体墙温度变形比页岩空心砖砌体墙明显偏大,设置构造柱能大大减少填充墙的温度裂缝,说明这两种控制措施都非常有效。     

耗能框架填充墙的设计和实验

设计了一种带缺口的框架填充墙，当框架受动力荷载作用时，这种填充墙主要受水平力的作用，避免了斜向的受压破坏。同时水平力只造成墙体的均匀水平裂缝。实验证明这种填充墙具有较稳定的滞回环，可以产生耗能减震的效果。     

低层装配式墙体水平缝坐浆连接抗剪性能试验研究

为编制低层装配式墙体在一种新型水平连接形式下抗剪承载力计算规范,对51个预制墙体进行了不同条件的试验研究,对其中的15个纯砂浆连接墙体抗剪承载力及破坏形态进行了分析。研究表明,纯坐浆连接墙体受剪破坏具有明显的脆性破坏特征;轴压比的增加,引起砂浆层上下界面摩擦力的增大,导致抗剪承载力的提高;接地梁上表面与墙板下表面粗糙度对试件抗剪承载力有重要影响。最后,通过试验结果推导出了现有文献中承载力计算的相关参数,该计算式将为设有边缘构件的墙体承载力计算提供相关理论依据。     

配筋砌块砌体墙体抗剪性能影响因素的试验研究

主要对采用构造柱-芯柱配筋混凝土小型空心砌块砌体进行抗剪能力的试验研究.由于水平筋及高宽比对配筋砌体剪力墙中抗剪的提升作用是不可忽略的,通过试验研究了不同参数的两组墙体,并分析了水平钢筋与高宽比对配筋砌块砌体抗剪承载能力的影响.试验结果表明,水平钢筋有利于砌体结构抗剪性能的提高;在一定范围内,高宽比越低,抗剪性能越好.     

双肢砌体墙的抗震性能与水平承载力计算模型

双肢砌体墙是将两个独立墙肢联系在一起共同受力的联肢构件，是砌体研究中由构件上升到结构的中间环节。现有双肢墙试验多采用由两片矩形立面墙肢组成的试件，将复杂立面双肢墙的开裂破坏规律、承载力等与单片墙进行对比分析，对于研究结构层面的抗震性能有着重要意义。在单片砌体墙试验基础上，设计3片典型立面形状双肢砌体墙进行低周反复荷载试验，对比分析各双肢墙体的滞回曲线、承载力等抗震性能差异；结合试验现象建立“L”形立面砌体墙转动破坏模式下的水平承载力计算方法，并与试验数据进行对比分析。结果表明：承受不同水平方向荷载作用时，非对称立面形状砌体墙抗震能力具有明显的方向性特征；双肢砌体墙的裂缝开展规律及破坏形态总体上与单肢墙一致；水平承载力计算方法与墙体实际破坏模式有较好的对应性，相对于窗间墙受剪破坏有着更明确的物理意义，承载力计算结果与单片墙和双肢墙试验值均有较高的吻合度。     

半装配式再生混凝土低矮剪力墙抗震性能试验

为研究半装配式单排配筋混凝土剪力墙结构的抗震性能以及再生混凝土在预制剪力墙中的应用效果,设计了4个不同轴压比下工字形半装配式单排配筋普通混凝土和再生混凝土剪力墙试件,试件由底部带预留孔的上层预制剪力墙、带墩头竖向分布钢筋的基础梁、二者之间的坐浆层以及纵横墙交接处的现浇暗柱组成,基础梁顶部伸出的单排竖向墩头钢筋伸入上层预制墙体底部的预留孔中,采用灌浆锚固的方法连接,并进行了低周反复荷载试验,分析了各个试件的破坏特征、承载力、刚度以及耗能等.结果表明:在水平荷载作用下,预制剪力墙与基础梁之间的连接部位出现水平通缝并产生较小滑移,墙身分布着X形交叉斜裂缝;随着轴压比的增大,试件的承载力提高,但延性较差;再生混凝土试件的破坏形态和受力性能与普通混凝土试件相近,再生混凝土可用于工厂预制的结构构件中;半装配式单排配筋混凝土剪力墙构造简单、施工方便,且抗震性能良好,可用于低多层剪力墙结构中.     

Utilising the scientific method to demonstrate that slender beam/column behaviour is the dominant behavioural mechanism leading to roof/rib failure

As per most other earth science engineering problems, the underground coal geotechnical environment and the way in which roof and rib support interacts with the rock mass are complex issues. It is therefore generally recognised that without prudent simplification, the complexity of the problem will overwhelm all current geotechnical methods of modelling, not least for the reason that a rock mass can never be characterised to a level that allows a ‘‘non-simplified" analysis. The fact that numerical models, which are commonly purported to be a ‘‘simulation" tool and the so-called epitome of advanced geotechnical engineering, always need to be ‘‘calibrated" to a known reality is taken to be conclusive proof of this statement. While the problem should not be oversimplified(i.e. the dominant failure mechanisms or critical data input parameters should not be ignored), without question judicious simplification is at the heart of all engineering design, to the point that it has a well-established name –‘‘reductionism". The hypothesis addressed in this paper, is that horizontal and vertical stress-driven slender beam and column behaviour(which includes unstable Euler Buckling) are respectively the dominant(but not only) roadway roof and ribline behavioural mechanism that(if not controlled) can lead to excessive deformation,failure and eventual collapse. As a part of the Scientific Method, a hypothesis can only be tested via real-world observations, measurements and analyses in establishing it is a credible Theory. Utilising the Scientific Method, this paper demonstrates that slender beam/column behaviour is the dominant instability mechanism within a coal mine roof/rib subject to elevated horizontal/vertical stress conditions and therefore, must be representatively accounted for in any credible empirical, analytical, or numerical approach to coal mine roof/rib stability assessment and associated ground support design.     

Preliminary rib support requirements for solid coal ribs using a coal pillar rib rating(CPRR)

Researchers from the National Institute for Occupational Safety and Health(NIOSH) are developing a coal pillar rib rating(CPRR) technique to measure the integrity of coal ribs. The CPRR characterizes the rib composition and evaluates its impact on the inherent stability of the coal ribs. The CPRR utilizes four parameters: rib homogeneity, bedding condition, face cleat orientation with respect to entry direction,and rib height. All these parameters are measurable in the field. A rib data collecting procedure and a simple sheet to calculate the CPRR were developed. The developed CPRR can be used as a rib quality mapping tool in underground coal mines and to determine the potential of local rib instabilities and support requirements associated with overburden depth. CPRR calculations were conducted for 22 surveyed solid coal ribs, mainly composed of coal units. Based on this study, the rib performance was classified into four categories. A preliminary minimum primary rib support density(PRSD) line was obtained from these surveyed cases. Two sample cases are presented that illustrate the data collection form and CPRR calculations.     

地下水浮力对地下建筑结构安全的影响

为研究地下水浮力对地下建筑结构产生的损伤特征和机理,通过一典型工程实例的结构变形和裂缝原因分析,并结合有限元程序对结构变形和变形后刚度变化的模拟计算,对地下水浮力作用下造成的结构变形机理,混凝土梁、柱、墙裂缝特征,以及对结构安全的影响进行研究。研究结果表明：当地下水浮力超出地下建筑自身重量,地下建筑在浮力作用下产生隆起变形和整体上移的趋势,而在周边挡墙处该上移趋势受土体约束,致使各柱、墙竖向变形不一致,导致结构构件开裂甚至局部破坏。损伤后的结构刚度大大降低。结构的总体损伤程度与平面尺寸相关,并受平面短边尺寸的控制,且结构构件损伤呈现周边大于中部的特征。     

螺栓连接装配式墙板抗侧刚度研究

螺栓连接装配式墙板体系具有连接简单、建造快速的优势,工程应用逐渐增多。本文以两种常见的螺栓连接装配式墙板(钢板拼接式螺栓连接和穿缝式螺杆连接)为研究对象,进行了7片墙板的拟静力试验,结果显示：螺栓连接装配式墙板由于水平缝处张开,墙体发生刚性转动,导致抗侧刚度下降;通过理论分析和数值模拟,揭示了螺栓连接装配式墙板水平变形特性,分析了影响墙体抗侧刚度下降的因素,提出了螺栓连接装配式墙板的抗侧刚度计算公式,数值分析与试验结果验证了公式的可靠性;基于参数分析的研究结果,回归了考虑螺栓节点配钢率、墙体的高宽比、轴压比和节点相对位置四个参数在内的干式螺栓连接装配式墙板抗侧刚度降低系数的简化计算公式,该简化公式的计算结果与数值模拟的结果误差在±20%之内,表明预测结果较为准确。