直锚式涨壳锚杆抗拔特性现场试验研究

普通锚杆在承受拉拔荷载时受力不均匀易发生杆体拔出破坏,因此涨壳式锚杆等新型锚杆逐渐得到了研发应用。本研究在强—中风化和中风化两种场地下,对36mm和52mm直径的普通锚杆和自制涨壳锚杆进行了现场拉拔试验,研究了场地类型、锚杆直径及是否涨壳等因素对锚杆拉拔承载力的影响。并进一步通过构造小波函数对粘结应力随深度变化曲线进行了模拟,探讨了涨壳式岩石锚杆的传力机理。发现涨壳式锚杆由于增加了锚杆端部与岩石之间的嵌固力,改善了锚杆的轴力分布,可以很好地避免杆体拔出破坏,显著提高了岩石锚杆基础拉拔承载力。     

Bearing force mobilisation in pull-out tests on geogrids

This paper presents a study on the mobilisation of bearing forces in geogrids subjected to pull-out solicitation. A theoretical model incorporating the effects of interference between grid bearing members on grid pull-out behaviour is presented and used for the interpretation of the results of large-scale pull-out tests on grids with varying geometrical and mechanical properties. The results obtained in this study show the influence of parameters such as free reinforcement length, test speed and interference between members on the pull-out response of geogrids. It is also shown that the load–displacement curve obtained in pull-out tests is not sufficient for an accurate investigation of soil–grid interaction and bearing force degradation mechanisms must be incorporated in the analysis of grid pull-out response if accurate predictions of pull-out strength and grid deformations are to be made.     

锚杆锚固体与土体界面特性室内测试新方法

为了更真实地反映锚杆受拉时锚固体与土体界面的特性,较准确地获得包含界面剪切残余段的剪应力–位移(?–s)全过程曲线,自行研发了一种锚–土界面摩阻性能测试仪及相应的锚杆拉拔试样制作装置和方法。该测试仪器和测试方法简便易行,可成批模拟多种环境条件进行室内锚杆拉拔试验。利用该仪器完成了4批次27个不同条件的锚固体拉拔试验,深入研究了锚固体养护龄期、拉拔速率等因素对锚–土界面剪切强度特性的影响,提出了一种锚–土界面?–s全过程本构模型。研究结果表明:界面剪切强度在锚固体养护14 d后增长缓慢;锚杆以0.1~2.5 mm/min拉拔时,速率对剪切强度的影响不大;提出的锚–土界面模型计算曲线与试验曲线吻合良好。     

Laboratory investigation into effect of bolt profiles on shear behaviors of bolt-grout interface under constant normal stiffness (CNS) conditions

Rock bolts have been widely used for stabilizing rock mass in geotechnical engineering. It is acknowledged that the bolt profiles have a sound influence on the support effect of the rock bolting system. Previous studies have proposed some optimal rib parameters (e.g. rib spacing); unfortunately, the interface shear behaviors are generally ignored. Therefore, determination of radial stress and radial displacement on the bolt-grout interface using traditional pull-out tests is not possible. The load-bearing capacity and deformation capacity vary as bolt profiles differ, suggesting that the support effect of the bolting system can be enhanced by optimizing bolt profiles. The aim of this study is to investigate the effects of bolt profiles (with/without ribs, rib spacing, and rib height) on the shear behaviors between the rock bolt and grout material using direct shear tests. Thereby, systematic interfacial shear tests with different bolt profiles were performed under both constant normal load (CNL) and constant normal stiffness (CNS) boundary conditions. The results suggested that rib spacing has a more marked influence on the interface shear behavior than rib height does, in particular at the post-yield stage. The results could facilitate our understanding of bolt-grout interface shear behavior under CNS conditions, and optimize selection of rock bolts under in situ rock conditions.     

锚杆荷载传递机理分析的双曲函数模型

假定锚固体与锚杆周围岩 (土 )体之间的剪力与剪切位移呈线性增加关系 ,建立锚杆荷载传递的双曲函数模型 ,获得了锚杆摩阻力和剪切位移沿锚固长度的分布规律及其影响因素。根据埋设于黏性土中 4根灌浆锚杆的现场抗拔试验成果 ,分析了锚杆的荷载传递特性 ,计算与实测结果对比 ,二者较为吻合     

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.     

Numerical modelling of the pull-out of hooked steel fibres from high-strength cementitious matrix,supplemented by experimental results

The paper deals with the numerical modelling of hooked steel fibres embedded in high-strength cementitious matrix. The pull-out of the fibres is first studied by means of accurate three-dimensional models which take into account the non linearities that are present in the physical model. The bonding properties of the fibre–matrix interface considered in the numerical model are based on experimental results of pull-out tests on straight fibres. The results of the numerical model are compared with respect to the results of experimental tests on hooked fibres. Then, the paper studies the effect of different fibre geometries to the load–displacement pull-out curves. It is concluded that fibres having a doubly bended shape have a superior behaviour compared to fibres having a single bended part. Finally, a simplified two-dimensional model is proposed that yield fast results which are similar to the ones obtained by its three-dimensional counterpart.     

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.     

土遗址用变径木锚杆锚固机理数值模拟研究

基于室内拉拔试验的物理模型,利用FLAC3D建立变径木锚杆拉拔数值计算模型,分析了变径木锚杆锚固系统的荷载传递规律、界面剪应力分布和传递规律、浆体土体应力场和位移场,并通过数值试验研究锚孔直径、锚杆直径和锚固长度对锚固效果的影响。研究结果表明:数值试验结果与室内拉拔试验结果较为吻合,证明数值模拟木锚杆拉拔过程的可行性和科学性;木锚杆浆体界面剪应力沿锚固段分布不均,主要集中在锚固段顶端和末端的0.1m范围内,末端界面剪应力呈增大的趋势与其变径的结构特征有关,其变径的特点在一定程度上提高了木锚杆的抗拔力;变径木锚杆同时具有拉力型和压力型锚杆的特征,径向具有剪胀作用;锚固影响因素中锚孔直径、锚固长度对木锚杆抗拔力影响显著,而锚杆直径对其影响相对较小;提出了木锚杆极限抗拔力计算公式。     

Force equilibrium-based finite displacement analyses for reinforced slopes: Formulation and verification

Formulation and verification for a force equilibrium-based finite displacement method (FFDM) using test results of reinforced model slopes subjected to increasing pseudo-static seismic forces are reported. The FFDM requires, in addition to force equilibrium for a sliced potential failure mass, a hyperbolic shear stress–displacement constitutive law for the backfill soils, a hyperbolic pull-out force–displacement constitutive law for the reinforcement, and a displacement compatibility requirement for adjacent soil slices. As a result, the mobilized reinforcement force is an analytical output, rather than an empiricism-based input as required in conventional limit equilibrium analyses. Analytical results from the FFDM also indicated that a brittle failure is associated with the lightly reinforced failure surface; a ductile failure is associated with the heavily reinforced failure surface, regardless of the extensibility of reinforcement investigated in the present study. Good agreements between the measured and the computed slope displacements and reinforcement forces in response to increases in pseudo-static seismic forces suggest that the FFDM can be used as an analytical tool for evaluating displacements of reinforced slopes subjected to pseudo-static seismic loads.     

Performance of identical rockbolts tested on four dynamic testing rigs employing the direct impact method

Impact drop tests are routinely used to examine the dynamic performance of rockbolts.Numerous impact tests have been carried out in the past decades on independently designed,constructed and operated testing rigs.Each laboratory has developed testing procedures;thus,the results are often reported in different ways by various laboratories.The inconsistency in testing procedures and reporting fo rmats presents a challenge when comparing re sults from different labo ratories.A series of impact tests of identical rockbolts was carried out using the direct impact method(i.e.the mass free-fall method) on the rigs in four laboratories in different countries.The purpose of these tests was to investigate the level of consistency in the results from the four rigs.Each rig demonstrated a high level of repeatability,but differences existed between the various rigs.The differences would suggest that there is noticeable equipment-dependent bias when test results obtained from different laboratories are compared.It was also observed that the energy dissipated for the plastic displacement of the bolt was smaller than the impact energy in the tests.The average impact load(AIL) and the ultimate plastic displacement(D) of the bolt describe the ultimate dynamic performance of the bolt.In the case where the bolt does not rupture,the specific plastic energy(SPE) is an appropriate parameter in describing the impact performance of the bolt.Two other relevant parameters are the first peak load(FPL) and the initial stiffness(K) of the bolt sample.The information from this test series will guide the formulation of standardised testing procedures for dynamic impact tests of rockbolts.     

钢结构用自锁式单向螺栓抗拉刚度分析模型

对8.8级和10.9级的M16和M20共4种型号的国产单向螺栓STUCK-BOM进行了轴向拉伸试验,每种型号的单向螺栓采用3种不同厚度连接钢板进行轴向拉伸,得出了各组试验单向螺栓轴向抗拉刚度;对单向螺栓的轴向拉伸过程进行了理论分析,通过理论推导得出了3种轴向变形的理论计算公式,并由此得出了单向螺栓轴向抗拉刚度的理论计算公式;将单向螺栓轴向抗拉刚度理论值与试验值进行比较。结果表明:单向螺栓轴向拉伸存在单向螺栓拔出破坏和单向螺栓螺杆拉断破坏2种破坏模式;单向螺栓的轴向变形可分为螺杆轴向变形、套筒轴向变形以及套筒与锥头间滑移的轴向分量3个部分,其中套筒与锥头间滑移的轴向分量对轴向抗拉刚度起控制作用;单向螺栓轴向抗拉刚度理论值与试验值吻合较好,单向螺栓轴向拉伸理论分析模型具有较好的可靠性。     

Development and application of an interface constitutive model for fully grouted rock-bolts and cable-bolts

This paper proposes a new interface constitutive model for fully grouted rock-bolts and cable-bolts based on pull-out test results.A database was created combining published experimental data with in-house tests.By means of a comprehensive framework,a Coulomb-type failure criterion accounting for friction mobilization was defined.During the elastic phase,in which the interface joint is not yet created,the proposed model provides zero radial displacement,and once the interface joint is created,interface dilatancy is modeled using a non-associated plastic potential inspired from the behavior of rock joints.The results predicted by the proposed model are in good agreement with experimental results.The model has been implemented in a finite element method(FEM) code and numerical simulations have been performed at the elementary and the structural scales.The results obtained provide confidence in the ability of the new model to assist in the design and optimization of bolting patterns.     

锚杆拉剪大变形应变分析

采用基于Ｓ－Ｒ定理的大变形理论,运用拖带坐标描述法,研究了锚杆在节理岩石中的拉剪局部大变形行为,推求了锚杆大变形应变的计算公式,得出了锚杆拉剪应变分量的理论规律,指出可以通过位移量测确定锚杆变形与内力,由多种岩石加锚剪切实验结果证实了理论方法的正确可靠。     

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.     

土钉拉拔接触面的细观模型试验研究与数值模拟

 利用数码可视化跟踪技术和土体变形无标点量测技术,通过室内模型试验,从细观层面对密砂中粗糙土钉拉拔时,钉土接触面的位移场、砂颗粒运动轨迹及剪应变规律进行研究,发现接触面颗粒先竖向运动,而后水平运动,且发生剪胀作用;土钉周围土体剪应变逐渐以径向为主,作用区域上下对称。以室内模型试验为基础,建立土钉拉拔的三维颗粒流模型,从细观力学角度验证室内模型试验中接触面砂土位移场规律,并进一步发现拉拔过程中土钉周围的孔隙率随着与土钉距离的增大逐渐减小,土钉端部处的土体孔隙率等值线为由一点逐渐向外扩散的同心的不规则圆;颗粒接触数在接触面处最小,然后向外逐渐增大等细观发展变化规律。研究成果对于进一步明确土钉拉拔的机制和接触面的发展规律都具有意义。     

Development of a dynamic model for a cone bolt

To ensure safety in underground excavations, it is important that the support systems used are capable of resisting the dynamic loads produced, for example, by rock bursts. In this paper, a dynamic simulation model for a cone bolt is proposed based on an experimental study. Drop weight tests were performed on resin-based cone bolts. These experiments revealed that the bolt has two energy absorption mechanisms: sliding in the resin and plastic deformation. To simulate this behaviour, a two degrees-of-freedom lumped-mass model is proposed. Experimentally, the proportions of sliding and plastic deformation were found to vary significantly from one test to another. To account for this variability, two methods are proposed to determine the value of the parameters governing the sliding of the bolt in the resin, whereas a dynamic force–elongation model is used to simulate the plastic deformation. Comparing the results of a simulation to experimental data proved that the constitutive elements of the model are appropriate to simulate the dynamic response of the cone bolt.     

Deformation-reversal in component-based connection elements for analysis of steel frames in fire

A previous paper covered the principles of practical modelling of common steel beam-to-column connections in frameworks at elevated temperatures, using a component-based approach to represent the main structural actions generally grouped at bolt rows. This is needed for the structural modelling which is a necessary part of performance-based structural fire engineering design based on analysis of a range of natural fire scenarios. This paper extends the treatment of components to the effects of change of temperature during an analysis. This includes the treatment of reversal of displacement, which is essential in order to allow components within the whole model to change their temperatures, even when temperatures are increasing monotonically. Reversal curves, and their Intersection Points with the zero-force axis, are used to link the states of deformation of any component on adjacent force–displacement curves at different temperatures. A desirable feature of this treatment is that it encompasses the effects of cooling after heating, which has been observed in full-scale tests to cause failure of connections as beams contract. A simple sub-frame model including beams, columns and endplate connections, has been analysed using the component-based model, in order to illustrate how the connection and its components behave, and how failure develops when the members and connections are subjected to a heating–cooling sequence.     

An analytical analysis of the full-range behaviour of grouted rockbolts based on a tri-linear bond-slip model

This paper presents an analytical solution for predicting the full-range mechanical behaviour of grouted rockbolts in tension based on a realistic tri-linear bond-slip model with residual bond strength at the grout–bolt interface. The full-range behaviour consists of five consecutive stages: elastic stage, elastic–softening stage, elastic–softening–debonding stage, softening–debonding stage and debonding stage. For each stage, closed-form solutions for the load–displacement relationship, interfacial shear stress distribution and bolt axial stress distribution along the bond length were derived. The ultimate load and the effective anchor length were also obtained. The analytical model was calibrated and validated against two pullout experimental studies. The predicted load–displacement curves as well as the distributions of the interfacial shear stress and the bolt axial stress are in close agreement with test results. A parametric study is also presented, providing insights into the behaviour of the rockbolts.     

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.