全长黏结型锚杆高频超声导波检测应用研究

分析高频纵向轴对称超声导波在全长黏结型锚杆中传播的特性。在不同频率范围内,锚杆中同一模态的衰减特性及速度差别较大。理论上,在1 MHz以上,高阶纵向轴对称模态在特定频率下的轴向位移集中于杆中心,衰减最小,且能量速度最大,可用于全长黏结型锚杆的质量检测。同时建立实验系统,在1.13～2.85 MHz频率范围内对直径φ22 mm、长度1 m的埋于水泥中的无缺陷锚杆进行了频率扫描,并根据实验结果做出第一次端面回波速度和幅值随频率变化曲线,分别与理论能量速度频散曲线和衰减频散曲线相吻合,并且对埋于水泥中带单缺陷锚杆进行导波检测。研究结果表明导波可用于锚杆长度检测及缺陷定位。最后,将此规律应用于在直径为φ18 mm,长度为2 m的锚杆工程现场检测,检测结果较为理想,验证高频超声导波可以应用于全长黏结型锚杆的无损检测。     

超声导波技术在埋地锚杆检测中的应用研究

分析了超声导波在埋地锚杆中传播的特性。在理论上,对于埋地锚杆,40～90kHz的L(0,1)模态的衰减值在所有模态中最小,传播距离最长;位移模式简单,易于激发;能量速度最大,容易与其他速度较慢模态区别。此段L(0,1)模态可用来对埋地锚杆进行检测。同时建立实验系统,对直径22mm、长2m的埋地锚杆进行检测,实验结果与理论分析相吻合。     

端锚锚杆工作载荷的导波确定法

 使用纵向导波对端锚锚杆的工作载荷进行无损检测。首先分析端锚锚杆工作载荷在锚杆自由段及锚固段的不同分布特征,然后计算纵向导波在锚杆自由段(承受拉应力)中的传播速度。当锚杆变形在弹性范围内时,随着自由段承受拉应力的增大,同一频率纵向导波在锚杆中传播的群速度逐渐减小,并且群速度与拉应力大小呈线性递减关系;对纵向导波在端锚锚杆锚固段上界面的反射情况进行试验研究,结果表明,45～75 kHz频率范围纵向导波在锚固段上界面有明显的反射回波;提出使用纵向导波在锚固段上界面的反射回波及在锚杆自由段的传播时间来确定锚杆工作载荷的大小,由理论分析得到的工作载荷与导波传播时间的关系曲线与试验结果具有相同的趋势。     

锚杆锚固质量无损检测中的激发波研究

采用数值模拟和实验模拟的方法对锚杆-锚固体系中的波动特征进行研究。数值模拟和实验模拟都表明在一般测试激发波的频率范围内锚杆以及锚固体系中传播的波是导波，在不同频率时波的传播速度、波的衰减特性都不同。在锚固锚杆中存在最佳激发波，它能使波传播衰减最小传播距离最长。通过数值模拟的方式找到了对于实验室的锚固锚杆模型能使底端反射清晰可见的最佳激发波。据此定制了实验装置及传感器，实验结果与数值模拟取得了很好的一致性。实验和数值模拟都证明采用最佳激发波可以大人增加锚杆锚嘲质量检测中的测试深度。     

Laboratory testing of a new type of energy absorbing rock bolt

Energy absorbing rock bolts are used as part of rock support systems in underground constructions that are exposed to e.g., rock bursts and detonating explosives. A rock bolt capable of absorbing kinetic energy from these loads must be able to yield with the ground movements and also deform plastically over large distances, at high displacement rates. A new type of energy absorbing rock bolt has been developed and tested in laboratory. The bolt is without a casing and consists of a steel bar that has an inner ribbed-like anchorage section and an outer nut that transfers the load from the rock via a circular disc. When subjected to a dynamic load, the lengthening of the steel bar leads to a decrease in diameter whereby the adhesive bond between bar and grout is lost and the outer end of the bolt is free to yield. The rock bolt is given a very good protection from corrosion when fully grouted in cement. In a laboratory, rock bolts in concrete cylinders were subjected to free fall tests to achieve a loading velocity of 10 m/s. The tests demonstrated that the distribution of plastic strain along the length of a grouted rock bolt is not constant when dynamically loaded. The sections where plastic yielding was allowed were not fully utilized in any of the cases, opposite to that in previous static tests which show almost constant elongation of the bolts. The tests also verified that the load-carrying components of the bolt, the nut and the anchorage, are reliable when dynamically loaded. Elastic and plastic waves will start to propagate through the rock bolt as it is suddenly loaded, resulting in permanent deformation along a section of the bolt. This yield process is demonstrated through a combined graphical and numerical method.     

Non-destructive testing of rock bolts using guided ultrasonic waves

The research outlined in this paper is aimed at the development of a portable non-destructive testing instrument for evaluating the condition of rock bolts. In applications such as coal mine roof reinforcement, the opportunities for rock bolt inspection are currently limited to destructive techniques such as the pull-out test. It is proposed that guided ultrasonic waves can be used to solve this inspection problem, using a pulse-echo test carried out from the free end of the bolt. Suitable test frequencies have been identified through the use of modelling software, and successful laboratory and site trials have been undertaken. The research has shown that the proposed approach is capable of determining the bolt length, and of identifying major defects such as necking, deformation, and loss of resin encapsulation.     

锚杆锚固质量无损检测几个关键问题的研究

对近年来有关锚杆无损检测的研究工作进行总结.通过理论分析和实验研究,对锚杆锚固质量无损检测中的几个关键问题进行较为深入的探讨研究:通过逐渐改变锚杆自由段和锚固段相对长度的方法,研究底端反射的变化规律,得出锚固长度小于3/4首波波长时底端反射不明显的结论;通过对锚固体控制体积的力学分析,用水泥砂浆在不同养护时间内的固化程度和对杆体的握裹强度模拟锚固介质的黏结强度,得出固结波速与锚杆杆体、锚固介质及围岩之间的黏结强度有关的结论;通过对承载条件下锚杆动态响应的分析和实验研究,得出锚固体系的基频和动刚度与荷载呈幂函数增长的规律,以及锚杆的动态响应与锚杆的工作荷载与极限承载能力的相对大小显著相关的结论.研究结果可用于锚杆无损检测的工程实践.     

Effect of grout properties on the pull-out load capacity of fully grouted rock bolt

This paper represents the result of a project conducted with developing a safe, practical and economical support system for engineering workings. In rock engineering, untensioned, fully cement-grouted rock bolts have been used for many years. However, there is only limited information about the action and the pull-out load capacity of rock bolts, and the relationship between bolt–grout or grout–rock and the influence of the grout properties on the pull-out load capacity of a rock bolt. The effect of grout properties on the ultimate bolt load capacity in a pull-out test has been investigated in order to evaluate the support effect of rock bolts. Approximately 80 laboratory rock bolt pull-out tests in basalt blocks have been carried out in order to explain and develop the relations between the grouting materials and untensioned, fully grouted rock bolts. The effects of the mechanical properties of grouting materials on the pull-out load capacity of a fully grouted bolt have been qualified and a number of empirical formulae have been developed for the calculating of the pull-out load capacity of the fully cement-grouted bolts on the basis of the shear strength, the uniaxial compressive strength of the grouting material, the bolt length, the bolt diameter, the bonding area and the curing time of the grouting material.     

The influence of blasting on grouted rockbolts

Field tests and laboratory investigations have been carried out to evaluate the performance of grouted rock bolts subjected to close proximity blasting. The investigations comprised pull-out testing of bolts and vibration measurements on both the rock and the bolts. Laboratory work comprised compressive and flexural testing of the grout and analysis of polished thin sections of specimens consisting bolt, grout and rock. There is no observable decrease in pull-out strength for bolts installed close to the blast (3.4 m), compared to more distant installed bolts (22.0 m). Furthermore, there is no difference in pull-out strength for the bolts with the freshest grout compared to bolts with cured grout, when subjected to blast loadings. Anchorage length of the bolts was 125 mm, which gave an average pull-out strength of 140 kN, or 93 % of steel yielding load. Analysis of polished thin sections of the rock, grout and bolt does not show any variation in crack pattern or crack frequency between bolts with varying distance to the blast or varying curing of the grout when subjected to the blast loadings. Re-pulling of previously pulled bolts shows a healing effect of the grout. None of the tests carried out indicates any decrease of the bolt /grout performance. It can be concluded that fully grouted bolts can be used on or close to the face.     

Non-destructive evaluation of the grouted ratio of a pipe roof support system in tunneling

The pipe roof system is widely used in the New Austrian Tunneling Method (NATM) as the main support system. Thus, the integrity of the pipe roof system influences the tunnel stability. The purpose of this study is to evaluate the grouted ratio of a pipe roof system using a non-destructive method in the laboratory and in the field. In the laboratory tests, four specimens embedded in soils and five non-embedded specimens are prepared with different grouted ratios of 0%, 25%, 50%, 75%, and 100%. The steel pipes are 6 m in length, 60.5 mm in external diameter, and 3.8 mm in thickness. Field tests are conducted with two fully grouted pipes with dimensions of 12 m in length, 60.5 mm in external diameter, and 3.8 mm in thickness. The reflection method of guided waves, which are generated by a hammer impact and are measured using an acoustic emission sensor, is used for the non-destructive testing. Experimental studies demonstrate that the group velocities and the main frequencies of the guided waves decrease as the grouted ratio increases for embedded and non-embedded specimen in soils. The variation of the main frequency, however, is more significant than the variation of the group velocity. In addition, the group velocities and main frequencies of the field specimens are lower than those of the embedded specimens. This study demonstrates that the variations of the group velocity and main frequency may be used effectively to estimate the grout ratio of a pipe roof system in tunneling.     

新型玻璃纤维增强塑料砂浆锚杆的黏结性能试验研究

锚杆广泛应用于隧道、边坡、地下硐室开挖及支护工程中。通过锚杆的支护加固，岩土体的强度和稳定性能够得到显著的改善和提高。传统的钢锚杆在不良地质条件下存在锈蚀严重的缺点，给支护结构的安全性和耐久性带来严重威胁。玻璃纤维增强塑料具有轻质、高强、耐腐蚀等优良特性，是代替钢筋制作锚杆的理想材料之一。在经典拉伸试验模型的基础上，结合锚杆本身的受力特性，建立一种改进的拉伸试验模型，并且根据此试验模型，对直径分别为10，13，16mm的表面经过喷砂和缠绕纤维束处理的玻璃纤维增强塑料锚杆，以及直径为25mm的螺纹钢进行拉伸试验，试样的总数量为24组。试验采用强度等级为C60的混凝土模拟岩体，并采用强度等级分别为41．5，55．5MPa的砂浆作为锚固剂。在试验结果基础上，对玻璃纤维增强塑料锚杆的拉拔破坏模式、临界黏结长度、拉拔承载力、平均黏结强度以及与钢锚杆拉拔性能的比较进行研究讨论，对砂浆锚固玻璃纤维增强塑料锚杆的黏结性能进行系统全面的分析评价，为推广玻璃纤维增强塑料锚杆的工程应用、相关规范的制定，以及进一步研究工作提供一定数据储备和理论支持。     

预应力锚杆作用机制研究

针对预应力锚杆作用机制研究方面存在的问题，根据弹性理论轴对称问题的基本理论和方法，在引入锚杆影响范围内岩体平均轴向应力（平均轴向应变）假设的条件下，推导锚杆在完全黏结条件下界面剪应力分布公式；以此为基础，在考虑界面本构关系情况下，研究界面脱黏段的剪应力分布及脱黏段长度，阐述预应力锚杆的荷载传递特性，从而为预应力锚杆设计提供理论依据。     

A numerical model of fully grouted bolts considering the tri-linear shear bond–slip model

A numerical model of fully grouted bolts is proposed in this study by implementing the tri-linear bond–slip relationship of bolts into the numerical framework presented by Hyett et al. (1996). The bond–slip relationship of bolt–rock interface is simplified and represented by the tri-linear model. The proposed numerical model is characterized by (1) its ability in modeling decoupling mechanism of bolt–rock interface, i.e. the degradation of the interfacial shear bond stress along bolts; (2) its easy implementation in a numerical code. The proposed numerical model is verified with the pullout tests, and good agreements with the experimental results can be observed in terms of axial stress distributions in the bolt, shear stress distributions along the bolt and load–displacement relationship. The proposed model also gives a reasonable prediction on the behavior of bolts installed in the field.     

Structural behavior of tension joint with high-strength bolted split-tee

The strength and behavior of split-tee connections that are applicable to all tensile connections with high-strength bolts have been studied in many countries. The design code of each country (AISC, Eurocode 3) does not consider various field conditions, however, such as the painting of the connection surface, the length of the bolt shank, and the preload. Moreover, the previous studies (Bahaari) that used the link element on the preload of the bolt could not predict the correct behavior of high-strength bolts. In this study, to evaluate the tensile capability of split-tee connections, a total of 20 split-tee specimens with two bolts each were fabricated and tested. The experiment parameters that were used were the thickness of the T-flanges, painting, preload, and the length of the bolt shank. The joint stiffness of split-tee connections was compared with the stiffness equation of Faella et al., and finite-element method analysis with Ansys 8.0 was conducted. Further, to verify the reliability of the highstrength-bolt model, the load-to-bolt stress relation in the experiment test and the analysis results were compared.     

回采巷道锚杆动载响应的数值分析

采用二维快速拉格朗日程序FLAC，对回采巷道锚杆支护(端锚和全锚)进行地震动载模拟分析，得出锚杆轴力随动载作用时间的变化规律，同时发现锚杆安装角对轴力的动载响应有很大影响。在给定的模拟条件下，锚杆一般不会因为地震动载而失效，但锚杆需保留有一定的抗拉强度潜能．端锚和全锚对动载的响应不同，端锚支护巷道受动载的破坏较全锚小，表明动载巷道锚杆支护应采用端锚(或加长端锚)方式。     

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.     

Smart damper using sliding friction of aramid brake lining and self-centering of rubber springs

The purpose of this study is to develop a smart damper with flag-shaped behavior by using the sliding friction of aramid brake lining and the restoring capacity of pre-compressed rubber springs. For this purpose, the friction force of aramid brake lining pressed by bolts was used along with polyurethane rubbers, each with a length of 80 mm, a diameter of 95 mm, and a circular hole of 37 mm. In the experiments, loading frequency and torque force were considered. The loading frequency varied from 0.1 to 2.0 Hz, and frictional force was controlled by variable bolt torque force. The tests were conducted to demonstrate that the clamping force by the bolts could provide normal force to frictional material. The friction force by the aramid brake lining sliding was tested, followed by the pre-compressed rubber springs' behavior. Afterward, a damper combining the two components was tested to verify flag-shaped behavior by using a dynamic actuator, and the damping ratios were evaluated from the hysteretic curves. The behavior of the damper closely matched flag-shaped behavior, resulting in self-centering and energy dissipation capacity.     

顺层岩质边坡锚杆支护机制研究

 全长黏结型锚杆作为一种有效且经济的加固手段,在边坡工程中得到广泛的应用,但其锚固机制尤其是考虑岩体结构特征的锚固理论需要进一步的研究和完善。基于顺层边坡的地质结构特征,考虑边坡岩体与锚杆的相互作用,运用弹性力学和结构力学对全长黏结型锚杆加固顺层边坡的机制进行研究,提出新的锚杆加固顺层边坡的力学模型。分析结果表明,顺层岩质边坡的锚固抗力由锚杆轴力与抗剪力共同提供,锚杆抗剪作用提供的抗滑力与锚杆轴力提供的抗滑力可以用线性关系来描述。运用有限元软件ABAQUS对这一力学模型进行建模,分析这一力学模型的正确性。     

外伸式端板连接蜂窝钢梁-混凝土柱组合节点抗震性能试验研究

通过7个1∶2比例外伸式端板连接蜂窝钢梁-混凝土柱组合节点的低周反复加载试验,研究不同螺栓数目、直径及排列方式的外伸式端板连接蜂窝钢梁-混凝土柱组合节点在各受力阶段的抗震性能和合理的节点构造形式。基于试验数据,分析了节点在反复荷载作用下的破坏形态、滞回曲线、骨架曲线、刚度退化、延性和耗能性能等。试验结果表明：试件的破坏形态和变形与螺栓数目、直径及排列方式有关,外伸端板螺栓连接中螺栓数目多、直径大的节点连接形式的承载力高,抗震性能较好;8个端板螺栓4行2列的排列形式为最合理的抗震节点形式;外伸端板螺栓数量为8个时的延性和耗能性能都能满足抗震的要求。