一种新型载荷试验的研究

针对静载试验要点中三种反力方法的不足，提出了用地锚作为反力的新技术，采用空间组合桁架＋地锚组合结构，通过有限元方法研究了地锚的受力状况，提出了计算极限抗拔力的经验公式，从而在一定的荷载范围内解决原有方法的不足。     

螺旋地锚抗拔力有限元分析

《建筑地基基础设计规范》GB500072002中规定单桩竖向静载荷试验反力装置宜采用锚桩,但是这种方法需要大量的工作和时间,耗费更多的人力和财力。根据《建筑桩基技术规范》JGJ9494关于单桩竖向抗拔静载荷试验中的规定,千斤顶的加载反力装置可根据现场情况确定,因此目前出现了用螺旋地锚作为反力的新技术。该项技术用地锚机将螺旋地锚旋入土层指定标高,通过锚头处螺旋叶片与土层的相互作用,提供竖向反力。极限抗拔力由土的性质、叶片作用的面积及锚固段与土体的作用面共同确定,目前缺乏精确的工程数据计算各阶段的极限抗拔力。本文通过有限…     

抗拔组合式锚板静载反力系统在工程中的应用

传统的基桩静载试验已经不能满足实际工程需要,且试验费时费力,存在着不小的安全隐患。抗拔组合式锚板静载反力系统主要通过锚板、钢箱梁及高强度钢棒连接,可单独用作单桩抗拔静载试验,还可结合锚桩及一定量的配重用作大吨位单桩竖向抗压静载试验。本文基于有限元对锚板装置的初步验算,结合现场试验的验证,从而模拟设计了该反力系统在最大试验荷载下的实际使用工况。该系统通过机械连接代替传统的焊接,解决了在高应力作用下出现开裂的问题,进一步优化该系统,使安装拆卸简单,运输方便,大大节省了工期并降低了施工成本。     

粉土中螺旋锚循环上拔承载特性原位试验研究

螺旋锚因具有较大的抗拔承载力而被广泛应用于杆塔、风轮发电机其等受循环荷载作用结构物的基础。近年来随着极端强风灾害的增多,螺旋锚已被推广应用于输电线路导线防舞动拉索的锚固设备。然而,目前关于循环荷载作用下螺旋锚承载特性的研究较少,没有关于其承载力计算方法的标准。为此,通过对粉土中螺旋锚开展原位单调及循环加载试验研究,探究螺旋锚循环上拔承载性能。结果表明：螺旋锚在50%静态极限承载力循环作用下,土体达到变形稳定时的累计位移均不大于25 mm;双盘螺旋锚在循环上拔荷载作用下的累计位移最小,约为其他单盘螺旋锚累计位移的一半;当螺旋锚承载力不足时,基础变形急剧增大,并伴随地面出现以螺旋锚为中心的辐射状裂纹;在整个试验过程中,循环荷载作用下的螺旋锚荷载-位移骨架曲线始终低于试验锚静载曲线,循环结束后在静载作用下,两者荷载-位移曲线基本重合;螺旋锚的上拔承载力主要由锚杆侧阻和锚盘端阻两部分组成,螺旋锚在循环上拔荷载作用下,锚杆接触界面的剪切带内土体的累积收缩导致法向应力降低,螺旋锚基础的上拔承载力全部由锚盘提供。     

螺旋锚垂直抗拔承载力室内试验研究

通过室内螺旋锚的上拔模型试验,探讨了单节螺旋锚在砂土和粉土中的埋置深度和锚板直径对其上拔承载力的影响.通过受力分析提出了单节螺旋锚上拔破坏的模式及极限抗拔承载力的计算公式,按本文公式计算结果与试验实测值比较一致.     

软土地基机械式抱箍压桩技术及试验研究

针对软土地基条件下输电线路及设备基础沉降问题,结合软土地基与小直径微型钢管桩的技术特点,研发了一种新型机械式抱箍压桩技术,并在输电线路杆塔基础加固纠偏工程中进行了现场试验。试验结果表明,该技术所涉及的压桩反力装置自重轻、占用空间小、操作方便;机械式抱箍能够有效传递压桩力,螺旋地锚抗拔极限承载力计算结果与试验结果吻合较好,可以满足抗拔需要。     

哈大客运专线T1标32mT梁抗拔型静载试验反力架设计和应用

哈大客专线T1标段32m T梁在现场预制,为保证T梁预制质量,检验T梁的承载能力,需要对现场预制的T梁进行静载试验。T梁静载试验采用抗拔型反力架。结合反力架基本原理,进行抗拔桩、连接杆和反力横梁等设计,并通过摩阻力试验验证抗拔桩承载能力。指出了施工中的注意事项,保证反力架有良好工作性能。     

桶形负压试桩反力装置现场试验及工程应用

现有的静力试桩方法主要有堆载法、锚桩反力架法和自平衡法三种,且各自都存在明显的不足。为了弥补传统基桩静载试验的不足,掌握桶形负压反力装置静力试桩法对场地条件的要求及所能达到的效果,选取上部地层为粉质粘土和淤泥质粘土场地进行了现场负压抗拔试验,对各土层所能达到的密封效果、抗拔力大小及持久稳定性进行了对比分析。试验结果表明,抗拔力与土体类型及状态、抽真空时间密切相关,粉质粘土层中的密封效果明显要好于淤泥质粘土,且淤泥质粘土中的密封持续时间也短;结合大量实际工程应用经验,在场地条件适宜、密封措施到位、装置设计和选型合理的条件下,该方法对软土地区低承载力基桩的静力试验是完全可行的,且具有重量轻、安装快、省人力、安全可靠且成本低的优点。     

钢螺杆锚桩受力特性分析及荷载传递机理研究

本文基于广州白云区某扩建项目,采用四组不同钢螺杆充当锚桩搭配反力装置进行基桩竖向静载试验,探究不同桩型的螺杆锚桩在静载试验中的桩身轴力和侧摩阻力分布特征和变化规律,并对其荷载传递机理进行分析,研究结果表明:在相同试验荷载作用下,随着桩长的增加,螺杆锚桩的上拔位移变小,螺杆锚桩的桩侧摩阻力占比增大;同时螺杆锚桩螺旋段的长度占比越大,螺杆锚桩的上拔位移越小;螺杆锚桩桩侧摩阻力的占比越小,桩-土的咬合力分担承载力比例越大。在受上拔力作用下,螺杆锚桩上部直杆段率先发挥效应,同时受到向下的摩阻力作用,桩侧摩阻力的大小与螺杆锚桩的上拔位移有关,随着上拔位移的增加,桩-土间的剪切应力逐渐发挥作用。研究结果对螺杆桩在设计应用及技术推广方面具有积极的意义。     

预应力抗拔灌注桩的轴力分析

本文介绍了预应力抗拔灌注桩的研究意义,同时运用ANSYS软件对预应力抗拔灌注桩单桩进行有限元模拟,分析了在竖向静载作用下单桩的工作性状及桩-土动力相互作用。通过计算分析,分别得出预应力抗拔灌注桩在竖向静载作用下轴力变化曲线;并分别对非预应力抗拔灌注桩和预应力抗拔灌注桩的轴力进行了比较,最后总结了预应力作用对桩的抗拔性能的影响。     

玻璃钢螺旋锚用于稳定膨胀土渠坡的现场拉拔试验和锚筋的破坏形式

介绍了采用玻璃钢螺旋锚锚固河南省邓州市引丹灌区北干渠膨胀土渠道水上渠坡的混凝土框架梁节点和水下渠坡的混凝土板,联合土工格栅、土工泡沫(EPS)用于修复该渠道滑坡试验段(长50 m)的锚杆现场拉拔试验。无灌浆锚杆的拉拔力在30 kN以上(平均36 kN),灌浆锚杆的拉拔力在37 kN以上(平均45 kN)。分析了锚固参数如上覆土层厚度、锚杆钻进长度以及锚固后至拉拔前的时间间隔、灌浆锚杆拉拔时锚具附近锚筋的劈裂破坏等对玻璃钢螺旋锚抗拔力和拉拔位移的影响,并分析了锚固的土类对玻璃钢螺旋锚最大拉拔力的影响。最后通过试验中的观察,总结了玻璃钢锚筋常见的破坏形式。     

Numerical modelling of pullout of helical soil nail

An investigation into the pullout response of helical soil nail using finite element subroutine Plaxis 2D is presented.The numerical modelling of actual pullout response is achieved by axisymmetric and horizontal loading condition.The effect of varying number of helical plates,helical plate spacing and helical plate diameter is studied to understand the pullout capacity behaviour.The failure surfaces for various helical soil nail configurations and their pullout mechanisms are also analysed and discussed.The pullout capacity is found to increase with increase in number of helical plates.The helical plate spacing ratio(s/D_h) and diameter ratio(D_h/D_s) are found to increase the pullout only up to a critical value.The response of helical soil nail using axisymmetric finite element simulation is found similar to the uplift behaviour of helical piles and helical soil anchors.In the absence of literature regarding numerical modelling of helical soil nail,simulation results are validated with uplift responses of helical piles and soil anchors.A good agreement in their comparative study for pullout response is also observed.     

静荷载与循环荷载作用下张紧式吸力锚承载

利用自行开发的电动伺服加载装置,在荷载控制方式下,进行了张紧式吸力锚在最佳系泊点受静荷载作用、受静荷载与循环荷载共同作用时的承载力模型试验。依据试验结果,分析了锚的破坏模式、加载方向与静荷载对循环承载力的影响以及循环承载力随循环破坏次数的变化规律。结果表明,静荷载与循环荷载作用下,如果锚受到的竖向极限抗力小于水平极限抗力,锚的破坏为竖向平移拔出土层的模式;静荷载作用下锚达到极限状态时,系泊点沿系泊方向的位移大约为 0.6 倍的锚径;同一循环破坏次数下, 循环承载力随静荷载比增加而增大,且 锚能承受的循环荷载取决于锚受到的静荷载比;当静荷载比为 0.5 左右时,锚承受的循环荷载最大; 对于同一静荷载比,当加载方向从 30 °变化至 40 °时对循环承载力比随循环破坏次数的变化关系没有 明显影响; 锚的循环承载力随循环破坏次数增加而降低;若锚受到的静荷载比大于 0.5 , 循环破坏次数不大于 1000 ,则循环承载力最多减小至静承载力的 75% 左右。     

岩土锚杆抗拔试验的规范应用与探讨

锚杆抗拔试验在岩土锚固技术中的作用十分重要,也是相关规范中不可缺少的内容。本文通过对现行主要规范（程）锚杆抗拔试验规定的对比分析,在认识目前我国岩土工程技术标准现状的基础上,着重探讨锚杆试验中杆体弹性伸长量的计算意义,锚头位移相对稳定标准的规定以及试验工作中对不同规范的针对性选择问题,力求使锚杆抗拔试验在面对众多试验规...     

Tensile properties and pullout behaviour of AFRP and CFRP rods for grouted anchor applications

Fiber-reinforced-plastic (FRP) rods have been introduced in the market for grouted ground anchors. The resistance to corrosion and chemical attack, high strength-to-weight ratio, and ease of handling of these rods make them a better alternative to steel tendons in some applications of ground anchors. However, to fully utilise FRP rods as tendons for cement grouted anchors, some aspects of their behaviour have to be determined, including tensile properties, tensile capacity, bond strength in cement grout, long-term strength and durability in alkaline environments. In this paper, the tensile characteristics, bond strength and pullout behaviour of AFRP and CFRP rods embedded in cement grout are discussed. The pullout test program involved four types of rods, four types of cement grouts and three types of anchorage tubes with three bonded lengths. The experimental results have shown that the tensile properties of the FRP rods are close to the manufacturers’ data. The surface geometry of FRP rods, the properties of the filling grout and the stiffness of the host medium (anchorage tube) influence the pullout behaviour, pullout capacity and maximum bond stress of cement grouted FRP anchors.     

Investigation of masonry wall fixings subject to pullout load and torque

The experimental investigation into masonry wall fixings is carried out to develop an in-depth knowledge by investigating the factors which lead to a reduction in the effectiveness of scaffolding/brickwork anchors. Since the pullout test of fixings is currently not practical in construction site the research carried out to determine the potential use of torque test as an alternative. The information to assess how various parameters in anchor settings could affect the load bearing capacity of an individual anchor used in scaffolding/brickwork systems is presented in this paper. The correlation between the ultimate pullout load bearing capacity, the maximum torque values, the increments in anchor hole depths and diameters has also been determined. The method, which is described in this paper, can be used to estimate the in situ pullout strength of scaffolding/brickwork anchors by means of the calibration graph between torque and pullout load. The torque in practice can be applied by using a simple torque-meter like tool fits into the fixing and is clamped to it. Paper presents the results and draws conclusions.     

Pullout performance of GFRP anti-floating anchor in weathered soil

Anchors are often used as anti-floating reinforcements in civil engineering structures. However, conventional steel bars present disadvantages concerning corrosion and poor adaptability to aggressive environments. Glass fiber-reinforced polymer (GFRP) components could provide a solution to these problems. In this paper the feasibility of GFRP anti-floating anchors is evaluated. Four full scale pullout tests were performed in moderately decomposed granite (MDG). Bare Fiber Bragg grating (FBG) sensors were embedded into the specimens during the pultrusion process to monitor the stress–strain distribution along their lengths. Based on the results the behavior of the anchors was assessed, including the relationships between the pullout force and the head displacement, the axial strain along anchors and the shear stress at the GFRP-grout interface. The stress distribution of anchors showing interlaminar shear failure was then analyzed based on a maximum shear stress criterion. It was proved that the load transfer mechanism of GFRP and steel anti-floating anchors differs significantly. GFRP anti-floating anchors reach failure due to interlaminar shear failure, while conventional steel anchors generally fail as a result of shear at the grout–soil interface. The test results also showed that the embedded FBG technique is reliable for monitoring the stress–strain state of an anisotropic material.     

不排水黏土中深埋锚板的抗拔承载力

针对不排水均质黏土中深埋条形锚板和圆形锚板,分别构造两种简单的机动容许速度场,利用塑性力学极限分析的上限法求解锚板的极限抗拔承载力。采用非线性有限元方法对构造的速度场和承载力计算结果进行了验证。与现有的相关解答对比可知:本文上限解与已有的上限解或滑移线场解答较吻合。提出的速度场合理、简单,并严格符合机动容许场的要求,便于实际应用,能为工程设计提供参考依据。     

Experimental studies on inclined pullout behaviour of geosynthetic sheet Vis-À-Vis geogrid - Effect of type of anchor and sand

This paper presents the details of an experimental investigation using large-scale inclined pullout apparatus on sheet geosynthetic and geogrid embedded in run-out, I-type, and L-type anchors. The influence of the type of sand on the behaviour of the sheet and the geogrid is also investigated. The results show that in both the sheet and the geogrid, I-type anchor provides approximately 50% and L-type anchor provides 90% higher pullout force than the run-out anchor. The maximum pullout force increases by more than 20% as the inclination of pullout force increases from 0° to 30° for both the sheet and the geogrid.     

玻璃钢螺旋锚的现场拉拔试验

回顾了FRP螺旋锚的基本结构型式,介绍现场拉拔试验的设计,完成了无灌浆和灌浆FRP螺旋锚的现场拉拔试验。无灌浆锚杆的最大拉拔力约在10 kN左右,而灌浆锚杆的拉拔力提高到15～20 kN,且拉拔位移较小。拉拔试验结果与现有拉拔力公式的计算值进行比较,并对螺旋锚的结构和施工提出一些改进意见。