风化岩地基全螺纹玻璃纤维增强聚合物抗浮锚杆承载特征现场试验

玻璃纤维增强聚合物（GFRP）抗浮锚杆是一种由树脂和玻璃纤维复合而成的新型材料,与传统的钢筋锚杆相比,它具有比强度高、耐腐蚀性强和抗电磁干扰能力强的优点。基于6根GFRP抗浮锚杆和4根钢筋抗浮锚杆现场足尺拉拔破坏性试验,研究了中风化花岗岩中GFRP抗浮锚杆的承载特征和界面黏结特性。试验结果表明,抗浮锚杆的破坏形式有2种：锚杆和砂浆界面剪切破坏,砂浆和围岩界面剪切破坏。直径为28 mm 的GFRP抗浮锚杆和钢筋抗浮锚杆的极限抗拔承载力均为225 kN,直径为32 mm GFRP抗浮锚杆极限抗拔承载力为250 kN,能够满足工程实际需要;GFRP抗浮锚杆与砂浆（第一界面）的平均黏结强度为1.50～1.54 MPa;GFRP抗浮锚杆砂浆与围岩（第二界面）的平均黏结强度为0.32～0.37 MPa,略低于钢筋抗浮锚杆第二界面的平均黏结强度;直径为32 mm的GFRP抗浮锚杆第二界面平均黏结强度高于直径为28 mm的GFRP抗浮锚杆。在此基础上,进一步分析论证了GFRP抗浮锚杆的破坏机制,为GFRP抗浮锚杆的工程应用提供了理论依据。     

节理岩体锚杆的综合变形分析

在总结国内外对节理岩体中锚杆加固机制的试验研究和理论探讨基础上,综合考虑锚杆的切向和轴向变形能力,建立节理锚固锚杆在剪切荷载作用下的变形模型,将节理锚固锚杆的变形区划分为弹性变形段和挤压破坏段,引入表征挤压破坏段长度的变量,对锚杆与岩体的相互作用机制进行理论分析,推导了剪切荷载与剪切位移和轴向荷载与轴向位移的关系。通过分析锚杆的屈服破坏形式,得到了确定挤压破坏段长度的方法。最后,通过算例分析了挤压破坏段长度与锚杆直径、岩体强度、锚固角度等参数的关系,得到了以下结论：（1）节理锚固锚杆抗剪作用的实质是锚杆调动岩体的抗压强度抵抗节理切向荷载。在抗压强度较高的硬岩中,挤压破坏段局限于节理面附近,锚杆影响范围小;而在抗压强度较低的软岩中,挤压破坏段较大,而且会产生较大的剪切变形,锚杆影响范围较大。（2）锚杆屈服破坏形式与岩质和锚杆直径有关。硬质岩体发生剪切屈服,而较软岩体中容易发生弯曲屈服;小直径锚杆一般直接剪切屈服,而大直径锚杆可能发生弯曲屈服。锚杆屈服破坏后出现塑性铰,挤压破坏段范围在节理一侧约为直径的1～2倍,继续增加剪切荷载,挤压破坏段长度不再增大。（3）随岩质的不同,锚杆锚固节理的最优锚固角变化较大。岩质较硬时,最优锚固角度较小,反之则较大。     

Pull-out behaviour of wood bolt fully grouted by PS-F slurry in rammed earth heritages

This article presents a laboratory and field investigation of pull-out resistance of wood bolts in rammed earth heritages. The laboratory testing involved axial tensile tests of four grout specimens prepared in specially designed moulds using PS-F (Potassium Silicate solution-Fly ash) slurry to investigate the performance of anchors. The field testing involved pull-out tests of three wood anchors installed in rammed earth heritages by gravity grouting. Experiments reveal that the failure mode is the pull-out of bolt from grout and average skin friction resistance of bolt–grout interface is approximately 0.34MPa. Load–displacement curves and elastic–residual displacement derived from cyclic loading indicate such anchor system has strong ductility with small elastic deformation and large residual deformation. Bond collapse firstly occurs at the loaded end and then propagates towards the full bonded length. Bond stress distribution is not uniform along the bonded length. Maximum bond stress distributes at the range from 0.3 m to 0.4 m. Emergence of compressive strain in the interface reveals such anchor system enjoys the advantages of both tensile and compressive anchor types, which significantly differs from results from other regular bolts. The research conclusion makes scientific senses to traditional material and craft in rammed earth heritages.     

An assessment of borehole sealing performance in a salt environment

 Design of plugs for abandonment of boreholes and shafts may be governed by the bond strength between the plug and host rock. This paper presents the results of push-out tests on cement grout plugs in salt. Two types of expandable cement grouts have been tested. The average interface shear strengths ranged from 2 to 12 MPa (290 to 1740 psi). Peak shear stresses at failure, assuming an elastic stress distribution along the interface, were up to eight times higher. Standard deviations commonly reached 20%. Dissolution along the interface was observed, and may have been enhanced by clay inclusions in the salt. This dissolution appears to have reduced bond strengths. Application of the results to the design of plugs for larger openings (for example, shafts, drifts, or boreholes) is discussed. Received: 6 March 1996 · Accepted: 16 July 1996     

扭转导波在锚固锚杆中传播的数值模拟

采用有限元数值模拟的方法研究了扭转导波在锚固锚杆中的传播性质。建立了自由锚杆和锚固锚杆的有限元模型,在锚杆顶端激发20～60 kHz扭转导波信号,计算得到导波在自由锚杆和锚杆锚固段的传播速度值与理论值吻合很好,证明了扭转导波数值模拟方法的有效性。数值模拟结果表明：随着激发波频率的增大,扭转导波在自由锚杆和锚杆锚固段中的衰减值均呈线性递增趋势,导波在锚杆锚固段上界面的反射回波逐渐减弱;扭转导波在锚杆锚固段的衰减值较大,无法在锚杆顶端采集到锚杆底端反射回波信号,所以扭转导波不适用于锚杆长度的检测;随着锚固介质弹性模量的增大,同一频率扭转导波在锚杆锚固段上界面的反射波逐渐增强。通过检测扭转导波在锚杆锚固段上界面的反射回波,可以确定锚固介质弹性模量的大小。     

A mechanical model for conebolts

This paper presents a mechanical model for cone bolts by analysing the cone anchorage function as a wedge-style mechanical anchor. Analytical and numerical methods were employed. The failure of a cone bolt commences with a series of partial shear failure through the grout around the cone, followed by bolt slipping as the actual bearing angle of the bolt decreases to a small value. The theoretical prediction is in good agreement with experimental data in the literature. The effect of the cone’s geometric face angle was also analysed with respect to the bond strength.     

On the stress distribution at the bonding interface between rock and bolt

Rock bolt is a major reinforcement technique for roadways in coal mines in China. Generally, separation of the bonding interface between the rock mass and the bolt may lead to collapse of the bolted rock mass due to stress concentration. In order to establish the stress concentration mechanism on the bonding interface, the distribution functions for shear stress and longitudinal force on the interface are derived using Mindlin's model, and a failure criterion for the interface is proposed. In addition, influencing factors for the stress distribution mode are identified. Both analytical study and numerical simulations by ANSYS have shown that, as the elastic modulus of rock increases, both shear stress and the longitudinal force-concentrating zone move towards the outer end of bolt and decrease gradually from the free surface to the rock mass body. Also, there is an optimizing cement thickness which results in relatively uniform distributions of shear stress and longitudinal force on the interface. It is valuable to investigate the bolt invalidity mechanism as well as reinforcement safety estimation in underground rock engineering design.     

On the Evaluation of Settlement Measurements Using Borehole Extensometers

Borehole extensometers are commonly utilized in field monitoring programs to measure settlement. In order to secure the targets of the extensometer, the borehole is typically backfilled with cement-bentonite grout. In the absence of standards for grout mix designs and due to non-universality of the properties of the backfilling grout, the accuracy of settlement furnished by borehole extensometers may be questionable. A preliminary parametric study was conducted to investigate the influence of grout stiffness on settlement measurements using borehole extensometers. The finite element program ABAQUS was used to model a borehole extensometer installed in an isotropic homogeneous elastic soil layer of a finite depth subjected to a uniform surface surcharge. Effect of the grout?Csoil elastic moduli ratio, soil/grout interface parameters (friction angle and shear strength), and extensometer embedment depth were investigated. Soil/grout interface behavior was assumed to comply with the elastic-perfectly plastic Coulomb friction model. The mechanism of measuring settlement using borehole extensometers was studied. The numerical study revealed that minimum errors in settlement can be obtained if the grout?Csoil elastic moduli ratio is made equal to about 1.0. Depending on the grout?Csoil moduli ratio, larger grout/soil interface friction angle and interface shear strength are generally associated with smaller settlement errors. Compared to fully embedded extensometers, partial embedment yields smaller settlement errors for grout?Csoil moduli ratio significantly above unity. In view of the findings of this preliminary parametric study, it is suggested to adopt the grout?Csoil moduli ratio in conjunction with grout compressive strength as the controlling criterion rather than the grout compressive strength only (current standard of practice). Additionally, it is evident that cement-bentonite grout mix should be carefully designed as part of the settlement monitoring programs to match the expected deformability (stiffness) of the soil mass under consideration. Future laboratory, field and numerical studies are needed to investigate more complex soil stratifications and to evaluate the behavior of various grout mixes.     

拉压分散型锚索锚固机制及工程应用研究

近年来,结合拉力型、压力型以及荷载分散型锚索特点于一体的拉压分散型锚索在工程中有一定的应用,但内锚固段锚固机制以及设计方法研究尚不成熟。基于Kelvin解,分别推导拉力分散型锚索和压力分散型锚索的内锚固段与周围岩土体之间的剪应力解析解,再根据叠加原理得到了拉压分散型锚索内锚固段剪应力简化计算方法;基于理论成果将拉压分散型锚索应用于工程实例中,分别进行了拉压分散型锚索的基本性能试验及与拉力分散型锚索的预应力损失对比测试。通过算例分析结果表明,单元锚固体的两端剪应力较大,中间较小,剪应力的分布特征与现有文献资料模型试验及数值模拟结果相吻合;根据锚索的基本性能试验结果,按照本文计算方法得到了压力段和拉力段剪应力峰值强度,与已有的研究成果根据岩石单轴抗压强度得到的压力型和拉力型锚杆锚固段剪应力峰值强度结果基本吻合;经对锚索预应力损失测试结果分析及工程的长期监测,拉压分散型锚索在工程应用中荷载传递稳定可靠,工程应用效果良好。     

深水注浆锚设计原理及其承载特性试验研究

海洋能源开发不断向深海迈进,大型深水海上平台对锚泊结构的承载力提出了更高的要求。针对传统鱼雷锚承载比不足的问题,提出了一种新型深水注浆锚。锚体带动连接其尾部的注浆管贯入海床,然后在外部注浆设备驱动下向海床注浆,浆液挤压土体并在锚体周围形成注浆固结块,从而大幅增加锚体抗拔力。采用自主设计的海洋锚注浆和拉拔试验系统进行了模型试验,研究了不同注浆量对浆液扩散特性以及锚体承载特性的影响规律。结果表明：浆液可以较好地包裹锚体,浆块呈倒锥形与锚体紧密黏结为一体,共同承受上部荷载,浆块承载比可达 24.6,远高于传统鱼雷锚的 2.4～4.1,从而验证了深水注浆锚的可行性。随注浆量的增加,浆块端部截面积和整体高度增加,注浆锚整体承载力也不断增大。     

顺层岩质边坡锚杆拉剪作用力学性能

锚杆能够显著增强顺层岩质边坡的稳定性.基于顺层边坡结构效应,应用锚杆加固顺层边坡的力学模型,根据结构力学理论和变形协调关系,建立拉剪作用下全长粘结型锚杆加固顺层边坡抗剪计算的理论分析方法.与相关试验数据进行了比较验证,结果表明顺层边坡锚固抗力模型计算结果与试验结果比较一致,验证了理论模型的合理性.讨论了锚杆倾角、锚杆直径、灌浆体强度、结构面内摩擦角、剪胀角等对加锚顺层岩体抗剪性能的影响.分析表明:锚杆锚固抗力模型能够较好地反映锚杆轴力及横向剪切力对顺层岩质边坡的抗剪作用.锚杆倾角越大,锚杆总的抗力呈减小趋势,而锚杆抗力随剪胀角增大而增加;当锚杆倾角等于内摩擦角时,锚杆抗力达到最大;锚杆抗力随锚杆直径增加而增大;当锚杆直径不变时,锚杆抗力随灌浆体抗压强度增大而有所减小.      

弱化节理剪切力学特征的颗粒流模拟研究

在黏结颗粒模型中引入强度弱化因子生成弱化介质材料,进行弱化模型试件的单轴抗压强度试验。结果表明,弱化作用在降低试件单轴抗压强度的同时,还将导致试件弹性模量逐步下降。这一结果符合相关室内试验的研究成果。为进一步对岩石强度弱化模拟方法进行效果检验,利用颗粒流程序内置的FISH语言建立弱化岩石节理直剪试验模型,进行不同法向应力条件下弱化岩石节理的直剪试验。结果表明：弱化节理模型试件表现出类似于真实节理的一系列宏观剪切力学特征;不同壁面弱化程度条件下,节理模型试件的抗剪强度及剪切峰值膨胀角的试验结果与法向应力的依存关系均符合经典的JRC-JCS模型。由此表明,所采用的岩石强度弱化模拟方法可以较好地再现岩石介质的强度弱化效应。通过模型试件内微裂纹发展演化特征的研究表明,壁面弱化作用可导致试件内裂纹发育数目的快速增长、微裂纹分布范围的迅速扩大,以及剪切裂纹发育比例的迅速提高,由此从细观角度揭示了弱化节理面更易于产生宏观剪切破坏的原因。研究成果可以为弱化岩石节理的抗剪强度及大型岩质边坡的稳定性研究提供参考。     

预应力锚索损伤软化精细有限元模型

预应力锚索作为岩土工程的一种主要加固技术已得到日益广泛的应用,但现有的计算方法难以反映岩体、砂浆、钢绞线相互之间的滑移变形等实际情况,计算结果难以体现实际的加固效果。通过研究接触面的特性引入损伤软化概念,建立了包含钢绞线、砂浆、接触面的损伤软化精细有限元模型,并与现场试验进行了对比分析。该模型优点是精细地描述了钢绞线、砂浆和接触面等结构的力学行为,可以反映接触面力学材料损伤软化的过程,更加精确地反映了锚固段的力学变化过程。试验结果对比显示,两者随着荷载不断加大,锚固段接触面上的剪应力峰值由端口往里转移。当端口处于弹性阶段,峰值在端口,呈指数衰减模式;当端口处出现损伤软化,峰值往里转移。计算分析反映的锚固段应力变化规律与试验基本一致。     

压力型锚杆锚固段的应力分布规律研究

根据Kelvin解,推导了压力型锚杆锚固段的弹性黏结应力和正应力分布方程。在推导过程中,考虑了三向应力状态对锚固段黏结应力的提高作用。经过与现场试验实测数据的对比分析,验证了理论计算公式的可靠性。采用软质岩体条件下的参数,对锚固段应力分布进行了计算,总结了岩石条件下锚固段应力分布特点,并分析了各种岩土参数变化对锚固段应力分布的影响,为压力型锚杆的进一步理论研究和工程实践提供了基础。     

锚固的贯通节理岩体剪切破坏特性分析

为了研究节理对锚固岩体力学特征和失稳损伤演化的影响,采用对锚固贯通节理岩体进行室内剪切试验和PFC2D数值模拟的方法,研究不同节理倾角下锚固贯通节理岩体剪切性能的作用机制和破坏模式,研究结果表明:（1）随着节理倾角变化,贯通节理岩体呈现出不同的破坏形式,锚固贯通节理岩体的抗剪强度与剪切位移曲线并不是呈线性增长,而是呈"双驼峰"趋势。（2）锚固体系在剪切试验的过程中,节理面颗粒的接触方位角会发生一定程度的改变,主要集中在锚杆和节理倾角附近。（3）锚固体系在剪切试验的过程中,会因为颗粒间黏结键的断裂生成裂纹,裂纹数生成的越少,其抗剪强度越高,裂纹分为张拉裂纹和剪切裂纹,并且张拉裂纹的数量要远远大于剪切裂纹的数量。研究结论可用于实际工程破坏模式的预测和岩体工程稳定性评价。     

管索组合结构及其力学性能研究

为防止在巷道围岩中锚索发生剪切破断,进一步提高锚索的抗剪强度,自主研发的管索组合结构能更好地提高围岩的抗剪强度及稳定性,该结构主要由C型钢管和锚索组成。在详细介绍了管索组合结构支护结构的基础上,为了更好地研究管索组合结构的力学性能,利用自主研发的新型管索拉剪试验系统分别对不同类型、不同预应力、不同索径的管索组合结构及纯锚索进行了室内力学特性试验,分别从受力?剪切位移曲线特征、支护构件类型影响和支护结构破断模式等方面对比分析了试验结果。结果表明,管索组合结构在剪切过程中经历孔壁岩石自由变形、孔壁岩石压缩C型管、C型管握裹锚索共同变形3个阶段;管索组合结构的剪切破断形式表现为拉伸破断和拉剪复合破断,其峰值剪力与预紧力呈负相关,且与纯锚索相比,管索组合结构的剪切塑性铰的轴向距离较大,管索组合结构的最大剪力、最大轴力以及整体结构变形能力均得到提高,提升率分别达到26.8%、3.5%和7.0%以上。试验结果表明,采用管索组合结构可以有效提高结构面的整体抗剪能力。当围岩发生变形破坏时,锚索与C型钢管的组合结构不仅可以增加整个支护系统的抗剪强度,而且可以同时提高锚索的抗拔能力,从而实现锚索+C型钢管1+1＞2的支护效果,在巷道周围组成有效的围岩承载圈,实现巷道围岩的稳定。     

Numerical Study of Failure Mechanism of Serial and Parallel Rock Pillars

Using a numerical modelling code, rock failure process analysis, 2D, the progressive failure process and associated acoustic emission behaviour of serial and parallel rock samples were simulated. Both serial- and parallel sample models are presented for investigating the mechanism of rock pillar failure. As expected, the numerical results show that not only the stiffness, but also the uniaxial compressive strength of the rock plays an important role in pillar instability. For serial pillars, the elastic rebound of a rock pillar with higher uniaxial compressive strength can lead to the sudden failure of an adjacent rock pillar with lower uniaxial compressive strength. The failure zone forms and develops in the pillar with lower uniaxial compressive strength; however, the failure zone does not pass across the interface of the two pillars. In comparison, when two pillars have the same uniaxial compressive strengths but different elastic moduli, both serial pillars fail, and the failure zone in the two pillars can interact, passing across the interface and entering the other pillar. For parallel pillars, damage always develops in the pillar having the lower uniaxial compressive strength or lower elastic modulus. Furthermore, in accordance with the Kaiser effect, the stress-induced damage in a rock pillar is irreversible, and only when the previous stress state in the failed rock pillar is exceeded or the subsequent applied energy is larger than the energy released by the external loading will further damage continue to occur. In addition, the homogeneity index of rock also can affect the failure modes of parallel pillars, even though the uniaxial compressive strength and stiffness of each pillar are the same.     

锚杆与土体界面渐进破坏的解析解

利用点荷载,作用于半无限空间的Mindlin位移解,考虑锚杆与土体界面的渐进破坏过程,推导出界面摩阻力的微分方程解析解。编制了相应的计算程序,把计算结果和现场试验值进行比较,结果较为吻合,二者的数据都表明,随着锚头拉力的增加,土-锚杆摩阻力峰值逐渐向锚杆末端转移,而锚杆前端则发生部分范围的滑移。然后,利用所求得的解析解,研究了土体弹性模量、锚杆孔径对锚杆摩阻力分布的影响,可见土体弹性模量越大,则界面上的摩阻力越容易达到峰值,从而产生破坏,而锚杆孔径越大,则界面上的摩阻力上升越慢,可延缓破坏过程。     

A simplified analysis of interface failure under compressive normal stress and monotonic or cyclic shear loading

Interface damage and delamination is usually accompanied by frictional slip at contacting interfaces under compressive normal stress. The present work is concerned with an analysis of progressive interface failure using the cohesive crack model with the critical stress softening and frictional traction present at the contact. Both monotonic and cyclic loadings are considered for anti‐plane shear of an elastic plate bonded to a rigid substrate by means of cohesive interface. An analytical solution can be obtained by neglecting the effect of minor shear stress component. The analysis of progressive delamination process revealed three solution types, namely: short, medium and long plate solutions. The long plate solution was obtained under an assumption of quasistatic progressive growth of the delamination zone. In view of snap back response, the quasistatic deformation process cannot be executed by either traction or displacement control. The states of frictional slip accompanied by shake down or incremental failure are distinguished in the case of cyclic loading, related to load amplitude and structural dimensions. The analysis provides a reference solution for numerical treatment of more complex cases. Copyright © 2005 John Wiley & Sons, Ltd.     

节理分布位置对岩体剪切破裂特征影响试验研究

节理分布位置影响岩体综合抗剪强度,并控制“锁固段”型岩质边坡启动和破裂演化。通过模型试件剪切试验,分析了节理分布位置对岩体综合抗剪强度和破裂特征的影响程度。试件模型以水泥砂浆为材料,在剪切面不同位置预制封闭节理,使其成为四周密封、内部节理贯通的模型。在不同法向应力下进行剪切试验,测定综合抗剪强度变化规律和剪切破裂特征。试验结果表明:试样破裂面可分为翼部拉张区、翼部压剪区、端部拉张区三部分,各区面积所占比例随节理位置变化而波动。剪切强度参数也随节理位置变化而规律性波动,且法向应力越大,变化幅度越大。