Parameter analysis of anchor bolt support for large-span and jointed rock mass

In order to obtain the optimal parameters of anchor bolt supporting system for large-span and jointed rock mass in Kaiyang Phosphor Mine, it is expensive and unavailable with the method of in-situ experiments. This paper describes a numerical modeling with discrete element method for the supporting effects of different type of anchor bolts. The anchor bolts with variant length of 0.5m, 0.8m, 1.0m, diameter of 10mm, 15mm, 20mm, setting spacing of 3.0m, 2.5m, 2.0m, and setting angle of 10°, 20°, 30°, are simulated respectively. The results show that there exist optimal parameters of anchor bolt support for large-span and jointed rock mass. For the bolt support of the concerning, the optimal length is 2.53.5m, the diameter is 2535mm, the spacing is 0.50.6m, and the setting angle is 105°.

Hydrogeochemical modelling of corrosive environment contributing to premature failure of anchor bolts in underground coal mines

Anchor bolts are commonly used throughout underground mining and tunnelling operations to improve roof stability.However,premature failures of anchor bolts are significant safety risks in underground excavations around the world due to susceptible bolt materials,a moist and corrosive environment and tensile stress.In this paper,laboratory experiments and hydrogeochemical models were combined to investigate anchor bolt corrosion and failure associated with aqueous environments in underground coal mines.Experimental data and collated mine water chemistry data were used to simulate bolt corrosion reactions with groundwater and rock materials with the PHREEQC code.A series of models quantified reactions involving iron and carbon under aerobic and anaerobic conditions in comparison with ion,pH and pE trends in experimental data.The models showed that corrosion processes are inhibited by some natural environmental factors,because dissolved oxygen would cause more iron from the bolts to oxidize into solution.These interdisciplinary insights into corrosion failure of underground anchor bolts confirm that environmental factors are important contributors to stress corrosion cracking.

Prediction of a maximum pull-out load of anchor bolts using an optimal combination model

The mixed model of improved exponential and power function and unequal interval gray GM(1,1)model have poor accuracy in predicting the maximum pull-out load of anchor bolts.An optimal combination model was derived using the optimally weighted combination theory and the minimum sum of logarithmic squared errors as the objective function.Two typical anchor bolt pull-out engineering cases were selected to compare the performance of the proposed model with those of existing ones.Results showed that the optimal combination model was suitable not only for the slow P-s curve but also for the steep P-s curve.Its accuracy and stable reliability,as well as its prediction capability classification,were better than those of the other prediction models.Therefore,the optimal combination model is an effective processing method for predicting the maximum pull-out load of anchor bolts according to measured data.

Anchorage Performance and Interfacial Mechanics Transfer Characteristics of a Composite Anchor Bolt with Different Surface Shape

To solve the deficiency of steel anchor blot in corrosion resistance and flaw of GFRP anchor bolt in fracture resistance, our research group develops a new composite anchor bolt made of steel strands wrapped up with compound fiber resin. To improve the cohesion performance of the composite anchor bolt, pull-out tests of different composite anchor bolts with different groove intervals and depths were made and analyzed. The results show that the pulling resistance of the composite anchor bolt increases with the increase of groove interval and depth, but groove interval and depth have optimal value. Based on elastic mechanics, the cohesion between anchor bolts and anchor bodies and its distribution characteristics caused by axial tension are analyzed and cohesion formula is obtained. By contrast, the experimental result is consistent with the theoretical analysis. Therefore, the surficial change of anchor colts could influence the performance of the composite anchor bolt. The cohesion force and anchorage performance can be improved by changing the surface of anchor bolts. Research results show that the new composite anchor bolt is high-performance material in the civil engineering.

Anchoring mechanism and application of hydraulic expansion bolts used in soft rock roadway floor heave control

Comparing with the resin bolt, the hydraulic expansion bolt has different anchoring mechanism and application advantage. According to the working mechanism of the hydraulic expansion bolt, its anchoring force is expressed in four forms including support anchoring force, tension anchoring force, expansion anchoring force and tangent anchoring force, and their values can be obtained on the basis of each calculation formula. Among them, the expansion anchoring force, which is the unique anchoring force of the hydraulic expansion bolt, can provide confining pressure to increase the strength of rock. Aiming at solving the problem of stability control in the soft rock roadway in Jinbaotun Coal Mine which has a double layer of 40 U-type sheds and cannot provide enough resistance support to control floor heave, the study reveals the mechanism of floor heave in the soft rock roadway, and designs the reasonable support parameters of the hydraulic expansion bolts. The observed results of floor convergence indicate that the hydraulic expansion bolts can prevent the development and flow of the plastic zone in the floor rock to control floor heave. Research results enrich the control technology in the soft rock roadway.

Applied on bolting-cable anchor support of full-seam roadway in weaker thick coal seam

The designing method and the supporting mechanism of both bolt and small cable anchor for full seam roadway in the weaker thick coal seam are systematically analyzed, and the construction technology and the supporting results are briefly summarized.

Vibration Characteristic of Anchoring System of Bolt and Elastic Wave Propagation Law

Based on one-dimension wave theory, the propagation law of elastic wave along the rock bolt, rock medium and their coupling system are researched, and the attenuation law and propagation mechanism of wave in the anchoring system are obtained. Meanwhile, the studies on end reflection and dynamic response under load are also carried out experimentally, the relationship between anchoring length and excited wave length is obtained when the end reflection of holt emerges, and it is concluded that under the condition of bolt loaded, as the load increases, the reflection of the upper interface of anchoring segment weakens while the end reflection strengthens relatively, hence the energy attenuation increases. These results provide some important theory basis for measuring the effective anchoring length of bolt, judging the bonding quality of anchoring end and surrounding rock, and estimating the utmost load force of bolt.

Analysis on the anchor mechanism of the full length resin bolt

The purpose of this paper is to reveal the stress distribution characteristic along the full length anchor bolt. Based on the mechanic model set up, the author calculated the anchor mechanism of the full length resin rock bolt. The stress distribution characteristic is different according to different type of surrounding rock. The conclusion is important to optimize the roadway bolt support design.

锚杆张拉力无损测试原理与技术研究

基于锚杆锚固体系多接触面特征,建造室内模型研究其锚固体系振动特性。通过在锚杆无应力段顶端安装加速度传感器测试时程信号,经快速傅里叶变换获得锚杆无应力段顶端振动频谱图,其频谱图的卓越频率具有良好的可识别性,据此获得其卓越频率与锚杆张拉力、锚杆无应力长度的变化规律,其卓越频率并非锚杆张拉段横向多阶振动频率。以此为基础建立了视锚固螺母为弹性基础的锚杆弹性振动模型、锚固螺母及锚杆相对螺母与球形垫圈接触面转动的刚体振动模型,分别获得其模型频率方程,基于其识别的卓越频率求解频率方程中的刚度参数,室内与现场试验表明其刚度参数—锚杆张拉力具有良好的线性相关性和单调递增关系。进一步室内模型试验表明其刚度参数—锚杆张拉力关系特征与蝶形托盘接触不同介质、不同锚杆张拉段长度不具有明显的相关性。为此提出了锚杆张拉力无损测试原理、方法与实现的技术路线,现场小规模试验表明本文提出的方法具有可靠性。

锚栓屈服型可抬升柱脚节点抗震性能试验研究

为满足结构在震中安全且震后可修复使用的目的,设计了一种锚栓屈服型可抬升柱脚节点,该节点是一种半刚性节点,将柱脚锚栓的一部分作为节点的阻尼器,阻尼器为柱脚提供抗弯能力和可抬升能力,在地震时柱脚节点塑性变形主要集中在阻尼器上,震后通过更换阻尼器即可完成柱脚节点的修复。为此,设计一组普通外露式柱脚节点和锚栓屈服型可抬升柱脚节点进行对比试验,并通过拟静力试验,研究它们在低周往复荷载下的滞回特性、抗弯承载力、刚度退化、耗能能力等抗震性能,同时研究柱脚节点在更换阻尼器前后的抗震性能。研究结果表明:对比普通外露式柱脚节点,锚栓屈服型可抬升柱脚具有更好的耗能能力和变形能力,试件的损伤基本集中在可更换的阻尼器上,耗能模式和损伤机制较为合理。在进行修复后,除初期转动刚度略低于修复前试件外,整体抗震性能基本可恢复至震前水平。另外,该新型柱脚的阻尼器拆卸和更换较为简便。

锚杆倒肋式风机基础受力性能的数值模拟

为了解决风机基础施工成本高、施工难度大等问题,提出了一种新型锚杆倒肋式风机基础。利用有限元分析软件ABAQUS对该新型风机基础与传统梁板式风机基础在极端运行荷载工况下的混凝土应力、钢筋应力、基础位移以及基础倾斜率进行数值模拟分析,并进一步讨论二者的混凝土用量、钢筋用量、土方开挖量。结果表明,锚杆的添加以及倒肋的结构设计使锚杆倒肋式风机基础的受力性能、经济性等方面明显优于传统梁板式风机基础,具有较好的应用前景。

风力发电塔基础预应力锚栓T型法兰连接系统计算方法研究

由于锚固区域基础刚度的影响,风力发电塔基础预应力锚栓组件受力不同于塔筒钢管间锻造法兰连接系统。基于Petersen计算方法的原理,推导出适用于预应力锚栓式风力机基础的计算方法,建立包含锚栓组件在内的单区隔和整体有限元模型研究基础约束刚度的空间效应。通过对单区隔和整体有限元计算所得锚栓拉力的对比发现,基础约束刚度的空间效应可忽略不计;通过对整体有限元模型计算结果和工程算法计算结果的对比,验证了工程算法的精度。

既有隧道不同扩挖宽度下锚杆参数的优化

以黄山洞隧道工程为依托,通过对现场数据的监测和利用有限元分析软件Midas GTS NX进行数值模拟,分析了不同扩挖宽度下隧道拱顶沉降值、周边收敛值和围岩有效应力变化的规律,并改变锚杆的长度和锚杆间距,分析在不同锚杆长度下围岩有效应力、衬砌应力以及锚杆应力的变化规律,确定了不同扩挖宽度下最优的锚杆长度和锚杆间距.研究结果表明:随着扩挖宽度的增加,围岩有效应力由大至小依次为拱脚处压应力、拱腰处压应力、拱顶处压应力和仰拱处拉应力;拱顶处压应力随扩挖宽度的增大而减小,拱腰处压应力随扩挖宽度的增大而增大,但增大趋势不明显;受单侧扩挖方式的影响,扩挖侧的应力大于非扩挖侧;拱脚处受到应力集中的影响,其压应力随着扩挖宽度的增大而增大;扩挖宽度为1.5~2.5 m时的最优锚杆长度和间距分别为2.5 m和1.7 m,扩挖宽度为3.5~4.5 m时二者分别为3.0 m和1.2 m.

缓凝型水泥浆液配合比优化及锚孔浆岩界面特性影响研究

针对预应力锚杆后张法施工中自由段浆液流动性和缓凝效果差的工程难题,提出使用标准型聚羧酸减水剂作为掺加剂以实现水泥浆液缓凝并提高其工作性能,探究其对锚孔浆岩界面特性的影响。采用室内试验、SEM电镜扫描等手段,结合Matlab多目标优化等方法,对掺加减水剂的缓凝型水泥浆液的锚固性能及配合比优化展开研究,得出适用于预应力锚杆自由段的注浆材料及其最优配合比,并与现行规范推荐配合比进行锚孔横断面结石特性对比试验。研究结果表明:1)随着水灰比增大,水泥浆液的流动度和凝结时间增大,体积结石率和抗压强度减小;随着减水剂掺量的增大,水泥浆液的流动度和凝结时间增大,体积结石率减小,减水剂对浆液抗压强度影响较小;2)未掺加减水剂时,浆液结石体致密性随着水灰比的增大而降低,掺加减水剂使得浆液结石体表面局部存在相对较大尺度的孔或孔隙,对宏观结石体强度有一定影响;3)通过Matlab多目标优化方法推荐了缓凝型水泥浆液最优配合比为水灰比0.3,减水剂掺量1.85%,相关性能参数符合规范要求,且流动度与抗压强度较规范推荐配合比分别提升了72.3%和107%;4)浸水围岩会弱化浆岩界面的抗剪强度,因此在锚杆灌浆过程中保证横断面结石率有利于提高浆岩界面的抗剪强度,本文提出的最优配合比浆液抗剪强度优于规范推荐配合比浆液。

基于黏聚力模型的螺纹钢锚杆拉拔数值模拟

为研究螺纹钢锚杆锚固结构变形破坏机理,采用ABAQUS软件建立锚固结构轴对称数值模型,基于黏聚力模型,开展数值试验,获得锚固结构拉拔过程中锚杆变形、荷载以及锚固体位移场分布演化规律。试验结果表明:在相同的拉拔位移下,小肋间距锚杆也能够承受更高的拉拔荷载,表明小肋间距锚杆对巷道围岩变形的承载能力更强;在锚杆拉拔过程中,随着拉拔位移的增加,岩体破坏和离层区域呈倒碗形向岩体深部扩散,当拉拔位移增加至9.06 mm后,岩体锚固段末端处位移增速加大,岩体的最大位移为4.79 mm,出现在锚固段端口处,最终导致锚固段基体破坏;锚杆轴力与锚杆肋间距呈负相关,锚杆的轴力随着肋间距的减小而增加。

基于声发射的含锚固缺陷节理试样单轴压缩破裂机制研究

锚固缺陷会弱化锚杆对节理岩体的支护效果,为探究锚固缺陷对锚固节理试样的锚固效应,对含不同锚固缺陷的锚固节理试样开展了单轴压缩试验,结合声发射、分布式光纤和DIC监测技术,分析了试样在不同破裂演化阶段时的声发射信息,得到了其破裂前兆特征。研究结果表明:锚固缺陷的存在降低了锚固节理试样的单轴抗压强度、峰值应变和声发射能量释放;在加载后期全长锚固节理试样声发射主频的高、低频信号都出现了增长,锚固缺陷试样主要是声发射主频的高频信号增长,且中间缺陷较端部缺陷会出现更高频段的声发射主频;全长锚固节理试样沿节理发生宏观剪切破坏;中间锚固缺陷试样的锚杆对裂纹控制作用较为迟缓,沿着节理发生宏观拉伸破坏;当锚固缺陷在试样一侧时该侧锚杆的变形大于对称侧,节理尖端的反翼裂纹向锚固缺陷一侧发生偏转并与锚固缺陷贯通,最终导致试样发生失稳破坏。持续高能的声发射能量释放,声发射峰值频率分布主频段增加,峰值频率呈降低趋势,声发射b值整体呈波动降低趋势,可作为试样发生失稳破裂的前兆特征。研究成果可为锚杆在节理裂隙岩体中的支护加固提供参考。

波纹钢板套衬加固大断面隧道衬砌力学性能

采用有限元软件建立了江西省某座大断面隧道地层-结构数值计算模型,对波纹钢板套衬加固隧道衬砌的力学性能进行研究。结果表明:波纹钢板套衬分担了部分围岩压力,隧道衬砌的应力出现重分布;波纹钢板套衬与既有衬砌组合结构的承载力随着锚栓数量的增加而增强,建议拱顶至拱肩区间的锚栓间距为2~3 m、拱肩至拱脚位置锚栓间距为1 m;既有衬砌和波纹钢板套衬对围岩压力的承担比呈负相关;考虑经济性和波纹钢板厚度对锚栓受力的影响,建议波纹钢板厚度不超过6 mm。

富水砂层深基坑支护结构模拟分析与优化

基于北京市通州区某深基坑工程,依据降水开挖及支护方案,使用midas GTS NX软件建模研究了在土钉墙-桩锚联合支护下,不同锚杆条件对富水砂层深基坑开挖变形特征的影响,并基于实际施工方案进行支护结构优化。结果表明,桩锚支护中预应力锚杆能够有效加固深层土体,约束其水平位移,显著改善基坑稳定性,相较于无锚杆情况,坡顶和桩顶的水平位移最大值分别减少了60.9%和75.4%;桩锚支护情况下,桩身侧移随桩直径的增大先减小后增大,存在最优桩直径范围,且该范围受到锚杆预应力大小的影响。

动静复合拉拔作用下锚杆结构的破坏机制研究

为研究锚杆结构在动静复合拉拔作用下的破坏机制,基于锚固剂的弹塑性损伤本构模型和锚固界面黏结滑移模型,引入参数“静力比”和变幅正弦式动荷载模型,建立了锚杆结构的数值计算模型。首先以锚杆加载端的荷载—位移曲线为研究对象,通过室内试验进行了模型验证。然后对不同界面强度的多组锚杆结构在复合拉拔作用下的破坏过程、破坏模式和破坏特征等展开了研究,同时对参数静力比的影响进行了分析。结果表明:(1)受锚固界面强度的影响,锚杆结构主要包括:单一破坏模式(锚固界面滑移脱黏)、三段复合破坏模式(锚固剂斜开裂—水平开裂—界面滑移脱黏)和两段复合破坏模式(锚固剂斜开裂—水平开裂)。(2)锚固界面强度较小时,锚杆沿锚固界面完全脱黏。随着界面强度的增大,锚固剂斜向开裂缝倾角越小,斜向开裂区范围越大,但尚未延伸至锚固界面。(3)静力比在70%以下时,锚杆结构的承载力随静力比的提高而逐渐增加,反之则逐渐降低。锚杆结构的极限位移和动载循环次数均随静力比的提高而逐渐降低。(4)复合拉拔作用下锚杆结构的峰值荷载低于其在静力时的值,且峰后承载力下降更为明显。工程应用中,建议增加锚固界面和锚固剂强度,适当降低静力比,减弱动力冲击荷载的作用。

轨道交通桥梁声屏障柱脚节点计算方法研究

声屏障柱脚结构一般采用锚栓连接钢立柱与混凝土基础。此类节点受力方式既不同于钢筋混凝土结构,亦不同于钢结构的螺栓群连接,而钢结构相关设计规范和混凝土设计规范中均未给出此类节点结构受力分析计算办法。本文在轨道交通声屏障柱脚锚栓连接节点结构受力分析中,提出按平截面假定方法分析的计算原理,结合在上海申通地铁集团有限公司科研项目《声屏障风荷载特性研究》中得出的风荷载作用数值,按照计算原理得出的方法,计算了六种不同荷载组合下的柱脚节点受力,并采用有限元仿真分析并行计算,对比二者计算结果以验证该原理和方法,可供相关设计人员计算参考。