Stress analysis of full-length grouted bolt under shear deformation of anchor interface

The bolt anchoring force is closely related to the shear properties of the anchor interface. The shear stress distribution of full-length grouted bolts is analyzed based on the stress-strain relationship among the bolt, grout, rock mass and bond interface,considering the shear properties of the grout and contact interface bonding behavior. In this case, the interfacial shear stress of the grout and rock mass and the bolt axial force are obtained under pull-out and normal working conditions. The results show that the peak shear stress of the interface with the shear deformation of the bond interface is significantly lower than that without it when the pull-out force is applied. When designing bolt parameters of grade IV and V rock mass, the relative deformation between the rock mass and anchor should be considered, with a “unimodal” to “bimodal” shear stress distribution.In the case of a low elastic modulus of rock masses,both the shear stress concentration and distribution range are obvious, and the neutral point is near the bolt head. As the elastic modulus increases, the shear stress concentration and distribution range are reduced, and the neutral point moves towards the distal end. As a result, the optimum length of fulllength grouted bolts can be determined by in-situ pull-out tests and decreases with the increased elastic modulus of the rock mass.

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.

Principles of rockbolting design

This article introduces the principles of underground rockbolting design.The items discussed include underground loading conditions,natural pressure zone around an underground opening,design methodologies,selection of rockbolt types,determination of bolt length and spacing,factor of safety,and compatibility between support elements.Different types of rockbolting used in engineering practise are also presented.The traditional principle of selecting strong rockbolts is valid only in conditions of low in situ stresses in the rock mass.Energy-absorbing rockbolts are preferred in the case of high in situ stresses.A natural pressure arch is formed in the rock at a certain distance behind the tunnel wall.Rockbolts should be long enough to reach the natural pressure arch when the failure zone is small.The bolt length should be at least 1 m beyond the failure zone.In the case of a vast failure zone,tightly spaced short rockbolts are installed to establish an artificial pressure arch within the failure zone and long cables are anchored on the natural pressure arch.In this case,the rockbolts are usually less than 3 m long in mine drifts,but can be up to 7 m in large-scale rock caverns.Bolt spacing is more important than bolt length in the case of establishing an artificial pressure arch.In addition to the factor of safety,the maximum allowable displacement in the tunnel and the ultimate displacement capacity of rockbolts must be also taken into account in the design.Finally,rockbolts should be compatible with other support elements in the same support system in terms of displacement and energy absorption capacities.

锚杆支护对砂泥岩地层铁路隧道仰拱变形及受力的影响

以成渝中线(成都—重庆)某砂泥岩地层隧道为例,采用数值模拟研究锚杆支护参数对仰拱竖向变形、受力的影响。结果表明:在仰拱处施加锚杆能有效提高支护结构与底部岩层的完整性,减小仰拱竖向变形及受力;单个锚杆有效控制面积对仰拱竖向变形、受力有影响,综合考虑推荐锚杆间距×排距为1.2 m×1.4 m,即单个锚杆有效控制面积为1.68 m2方案;随着锚杆长度增加仰拱竖向变形、受力均减小,但锚杆长度大于4.5 m后锚杆长度增加对仰拱变形、受力影响不明显。在依托工程仰拱处施加长4.5 m、间距×排距为1.2 m×1.4 m的锚杆,对仰拱竖向变形、受力的控制效果良好。施加锚杆支护后仰拱竖向变形、受力的数值模拟结果与工程实际监测情况相符。

全长预应力锚注支护下深部巷道控制效果对比研究

本文基于后注浆的全长预应力锚注支护工艺,并通过对FLAC3D软件中内嵌PILE结构单元修正,提出了全长预应力锚注支护数值模拟方法。在此基础上,开展了地应力、原岩强度等级、支护构件长度、布设间距、注浆强化指数与预应力6种因素下巷道围岩控制效果数值模拟对比研究,揭示了各类因素对围岩变形量、塑性区演化的影响规律,构建了全长预应力锚注支护下控制效果敏感性评价指标,将影响因素依次划分为围岩强度、地应力、锚注支护构件设计3个层级,并根据各因素敏感性层级给出了工程措施建议。最后,以现场典型软弱破碎地层巷道为工程依托,研发了具有强度高、可施加预应力等优势的组合式高强注浆锚杆与高强中空注浆锚索。通过现场应用,验证了全长预应力锚注支护可有效增强软弱破碎围岩自承载能力,充分发挥锚固构件的支护潜力,限制巷道围岩变形破坏。

Investigation of the failure mechanism and theoretical model of bolt-reinforced shallow tunnel faces with different bolt lengths

Using fiberglass bolts to reinforce a tunnel face is a practical auxiliary technology for ensuring tunnel face stability in soft ground.The reinforcing effect and the economics of this technology are significantly affected by bolt length.However,to date,the failure mechanism of bolt-reinforced tunnel faces with different bolt lengths has rarely been investigated.To reveal the failure mechanism of bolt-reinforced shallow tunnel faces,in this study,the stability of bolt-reinforced tunnel faces with different bolt lengths was investigated by using laboratory tests and numerical simulations,and a simplified theoretical model for practical engineering was proposed.The face support pressure and failure pattern for different bolt lengths during the face collapse process were obtained,and the influence of bolt length on face stability was clearly revealed.More specifically,the results show that face stability increases with increasing bolt length,and the reinforcing effect of face bolts is governed by the shear failure at the soil-grout interface first in the stable zone of the tunnel face and then in the failure zone.Once the bolt length in the stable zone is larger than that in the failure zone,face stability will not be improved with increasing bolt length;thus,this bolt length is referred to as the optimal bolt length L_(opt).The L_(opt)value is slightly larger than the initial failure range(in the unreinforced condition)and can be approximately calculated by L_(opt)=(1-0.0133u)D(u is the friction angle of the soil,and D is the tunnel diameter)in practical engineering.Finally,a simplified theoretical model was established to analyse the stability of reinforced tunnel faces,and the results are in good agreement with both laboratory tests and numerical simulations.The proposed model can be used as an efficient tool for the design of face bolts.

基于锚杆锚固长度受力全过程力学机理的计算模型研究

在分析锚杆锚固体上剪应力变化基础上,发现锚杆荷载—变形特性与锚固体表面剪应力建立、局部破坏滑移、剪应力消失过程相关。在Mindlin解得到的锚固体上应力分布模型和荷载-位移指数衰减模型的基础上,建立了锚杆受力全过程计算模型。这种模型与锚杆锚固长度相关,能够将锚杆荷载—位移曲线与锚固体表面剪应力变化对应起来。模型分析表明:锚固长度对锚杆的延性作用很大;锚杆荷载—变形曲线不同形态与锚固长度有关。此外,还提出了锚固体表面局部剪应力达到破坏强度时,有效锚固长度的计算方法。

提高PDMS项目法兰连接用螺栓长度的准确性

给出了如何提高三维设计软件PDMS螺栓长度的解决方案,主要通过螺栓连接元件建模标准化、对夹元件建模标准化、螺栓集标准化、螺栓长度标准化、螺栓等级标准化,从而确保PDMS项目螺栓长度的准确。

考虑注浆层剪切变形的全长粘结锚杆应力分析

锚杆锚固力与锚固界面的剪切特性密切相关,基于锚杆-注浆层-围岩以及粘结界面之间的应力应变关系,考虑锚固界面与注浆层的剪切特性,分析了全长粘结锚杆的应力分布特征,得到了锚杆轴力和锚固界面剪应力的分布规律。结果表明:考虑注浆层剪切变形的界面剪应力分布范围相比不考虑时显著增加,峰值显著减小,二者的误差随着围岩弹性模量的增加而降低,其中硬岩条件下二者的差值约为30%;在围岩弹性模量较低时,剪应力集中程度较低,且沿锚杆分布范围较大,故软岩工程中应适当增加锚杆长度;随着围岩弹性模量的增加,界面剪应力分布范围减小,峰值增大,且逐渐向锚杆端部集中,故硬岩工程可适当缩短锚杆长度,并提升界面抗剪强度。

基于旁孔透射法的隧道锚杆长度检测方法

锚杆的锚固长度是隧道围岩支护过程中重要指标,由于锚杆的检测长度长期受到现场施工环境的限制,传统检测方法往往会对锚杆锚固产生损伤,借鉴旁孔投射法原理,利用激振波接收处理器、激振锤、首波接收器、水听器装置组成锚杆检测仪器,通过波传导时间差来计算锚杆的长度,从而对锚杆锚固长度进行检测,并利用数值模拟软件ABAQUS进行数值仿真分析,验证旁孔投射法原理检测锚杆锚固长度的可行性。

索道用地脚螺栓锚固长度研究

文中分析了不同规范中基础锚固长度的规定,采用锚固粘结理论分析与规范中地脚螺栓锚固长度对比相结合的方法,分析了混凝土强度、地脚螺栓的外形、保护层的厚度等条件对锚固长度的影响。通过对比不同规范中地脚螺栓锚固长度的取值范围和情况,评估地脚螺栓的合理锚固长度。研究发现,现有多本规范对地脚螺栓锚固长度的规定不一致,会导致设计中产生一些误区。经过数据对比,提出合理的锚固长度取值,确保地脚螺栓安全可靠。对比了国内外索道工程地脚螺栓的材质及锚固长度取值,提出了基于地脚螺栓锚固机理和规范要求的锚固长度设计取值的原则,为实际工程中提供合理的地脚螺栓锚固长度设计参考。

超大断面扁平结构隧道施工参数优化研究

基于某超大断面扁平结构隧道的上下台阶法施工段,采用数值模拟方法研究在该工程地质条件下台阶长度和锚杆纵距2种施工参数改变带来的影响。利用数值模型对不同台阶长度(分别为30,40,50,60 m)和不同锚杆纵距(分别为1.0,1.5,2.0 m)情况进行研究,对隧洞周边岩体中塑性区、围岩应力和围岩变形情况的分布规律进行分析,结合数值结果和现场监测数据验证了施工现场采用台阶长度为50 m和锚杆纵距为1 m的施工参数较合理。该研究成果可为超大断面扁平结构隧道的开挖和支护施工参数的合理选取提供参考。

Laboratory pull-out tests on fully grouted rock bolts and cable bolts:Results and lessons learned

Laboratory pull-out tests were conducted on the following rock bolts and cable bolts:steel rebars,smooth steel bars,fiberglass reinforced polymer threaded bolts,flexible cable bolts,IR5/IN special cable bolts and Mini-cage cable bolts.The diameter of the tested bolts was between 16 mm and 26 mm.The bolts were grouted in a sandstone sample using resin or cement grouts.The tests were conducted under either constant radial stiffness or constant confining pressure boundary conditions applied on the outer surface of the rock sample.In most tests,the rate of displacement was about 0.02 mm/s.The tests were performed using a pull-out bench that allows testing a wide range of parameters.This paper provides an extensive database of laboratory pull-out test results and confirms the influence of the confining pressure and the embedment length on the pull-out response(rock bolts and cable bolts).It also highlights the sensitivity of the results to the operating conditions and to the behavior of the sample as a whole,which cannot be neglected when the test results are used to assess the bolt-grout or the grouterock interface.

大直径盾构隧道管片连接预埋套筒抗拔性能试验研究

我国大直径盾构隧道工程管片之间多以斜螺栓连接为主,介绍了螺栓连接的特点,通过改变套筒材质聚酰胺的组成成分和螺纹长度、螺牙类型等套筒参数,对斜螺栓连接套筒进行了抗拔力试验研究。结果表明:工程中习惯采用的PA6、圆螺牙的螺纹套筒实际抗拔能力难以达到设计承载要求,螺纹套筒建议采用PA66材质、梯形粗牙形式,且对于M36斜螺栓,套筒长度建议在220 mm及以上。

动静载下全长砂浆锚固玻璃钢锚杆受力及失效特征分析

针对爆破动载作用下玻璃钢锚杆的损伤失效问题,利用FLAC3D软件建立全长砂浆锚固玻璃钢锚杆数值计算模型,研究了预紧力静载和爆破动载下锚杆杆体、杆体与砂浆界面、砂浆与围岩界面的受力及失效特征,同时分析了动载强度、围岩及砂浆强度对锚杆受力的影响规律,并与现有试验结果对比,验证了研究结果的可靠性。研究结果表明:全长砂浆锚固玻璃钢锚杆最大轴向应力随动载强度的增大呈线性增大而随围岩或砂浆强度的增大而减小,且轴向应力分布较金属锚杆更为集中;两个界面剪应力均是沿杆体轴向迅速增大至峰值后快速减小为0,之后黏结性能相对较弱的界面先发生脱黏破坏,脱黏位置剪应力下降至残余黏结强度,同时剪应力峰值向孔底转移;玻璃钢锚杆剪应力分布较金属锚杆更集中,峰值位置更加突出;动载强度越大,破坏界面的脱黏长度和剪应力分布范围越大,而未破坏界面的剪应力峰值位置也会向孔底转移;围岩强度越大或砂浆强度越小,剪切破坏越倾向于发生在杆体−砂浆界面,反之,则越倾向于发生在砂浆−围岩界面。

装配式建筑中梁-墙平面外连接节点承载力研究

目的 为解决困扰梁-墙节点连接的难题,提出一种新型粱-墙平面外连接节点方式——梁靴螺栓连接节点,并对其承载力进行试验研究。方法 根据梁靴的不同锚固长度,制作了3组12个新型粱-墙平面外连接节点试件,并分别进行拉拔和剪切试验,探究不同条件下承载力变化规律。结果 拉拔试验中,随锚固长度的增加,节点的拉拔承载力分别提高了80.12%和122.63%;剪切试验中,随锚固长度的增加,节点的剪切承载力分别提高了40.94%和102.75%。结论 梁靴螺栓连接方式节点能够满足设计要求,并且随着梁靴锚固长度增加,抗拉承载力和抗剪承载力均有提高,极限位移更大,节点的延性也更好。

高应力反复拉压作用下钢板组合单边螺栓钢筋机械连接性能试验研究

针对预制混凝土楼板钢筋直径较小,装配时无法直接使用灌浆套筒完成钢筋连接的问题,提出一种高强钢板组合单边螺栓钢筋机械连接件,仅从楼板表面即可实现钢筋等强连接。为研究钢板组合单边螺栓钢筋机械连接接头在地震作用下的连接性能及工作机理,对2组6个试件分别进行高应力反复拉压试验和单向拉伸试验,重点考察破坏形态、连接钢盖板沿长度方向及宽度方向应变、高强螺栓轴向应变和开槽钢筋应变等。结果表明:相同锚固长度条件下,2组试件的最终破坏模式、极限承载能力无明显区别,但接头变形性能有一定差别,高应力反复拉压试验中极限荷载所对应位移增加约32%,钢筋拉断时位移增加约24%;锚固区钢筋和接头端部钢筋荷载-应变曲线变化趋势无明显区别,高应力反复拉压作用对钢盖板轴向应变和横向应变特征基本无影响;高应力循环作用结束时,高强螺栓压应变增加约30×10^(-6),循环作用对螺栓预紧力的影响较小;试件屈服比、强度比及延性比的均值分别为1.07、1.56和7.92,锚固长度为3 d(d为连接钢筋公称直径)的试件钢筋拔出,可以对连接齿钉的构造进行优化,减小齿钉间距和增加咬合面以提高锚固性能。

复合多层顺倾岩质边坡最优锚固角研究

锚杆支护是一种加固边坡的有效方式,但目前针对复杂多层岩质边坡的锚杆最优锚固角研究较少,且未考虑中间主应力对锚固效果的影响。采用统一强度理论,以全长粘结型锚杆为对象,根据锚杆失效模式及锚固段与围岩的作用方式,推导出复合多层岩体中锚杆的极限抗拔力公式。通过计算不同岩层锚固段微元体的单位长度抗力比,提出了复合多层顺倾岩质边坡的锚杆最优锚固角模型与最优锚固角的确定方法。将该方法应用到三峡库区巴东县一公路边坡工程,结果表明模型计算所得最优锚固角与均匀试验方案确定的最优锚固角一致。新方法计算所得的边坡单位宽度锚杆总长与规范法计算结果相比减少约11.2%,与传统莫尔-库伦理论计算结果相比减少约8.9%。研究结果可为复合多层顺倾岩质边坡的锚固支护设计提供一定的参考和借鉴。

基于数值模拟的柴油机连杆螺纹联接可靠性分析

连杆螺栓是柴油机曲柄连杆机构的关键部件,但是由于螺纹联接的特点,在曲柄连杆工作的过程中极易发生螺纹处应力集中的现象。为了提升柴油机连杆螺纹联接的质量,通过理论分析与数值模拟相结合的方法,基于ANSYS有限元分析软件对连杆大头螺纹联接结构进行数值模拟,分析了不同螺距、螺纹联接长度和螺栓预紧力的应力分布情况,得到了不同因素对螺纹联接结构强度的影响。该研究成果表明,随着螺距的增大,螺纹连接长度的减小以及螺栓预紧力的减小都会导致螺纹联接结构应力过大从而影响螺栓整体结构的可靠性。

锚杆长度对反倾向岩质边坡稳定性影响

以某高速公路层状反倾岩质边坡为实例,采用双弹簧锚杆单元,通过FLAC 3D建立数值分析模型,探讨锚杆长度对边坡稳定性和滑动面的影响规律、锚杆在加固过程中的边坡位移响应,并对边坡锚固及锚杆轴力传递机理进行分析。结果表明,随着锚杆长度增加,边坡安全系数提高,竖向位移和水平位移均减小;锚杆长度变化不会对加固前边坡破坏模式产生影响,其潜在滑动面形状为直线型和折线型;锚杆越长,其轴力越大,且锚固位置在坡底时达到最大值;沿锚杆长度范围内锚杆轴力的分布表现为前端大于后端,先趋于稳定后逐渐减小。