Mechanical responses of anchoring structure under triaxial cyclic loading

Dynamic load on anchoring structures(AS)within deep roadways can result in cumulative damage and failure.This study develops an experimental device designed to test AS under triaxial loads.The device enables the investigation of the mechanical response,failure mode,instability assessment criteria,and anchorage effect of AS subjected to combined cyclic dynamic-static triaxial stress paths.The results show that the peak bearing strength is positively correlated with the anchoring matrix strength,anchorage length,and edgewise compressive strength.The bearing capacity decreases significantly when the anchorage direction is severely inclined.The free face failure modes are typically transverse cracking,concave fracturing,V-shaped slipping and detachment,and spallation detachment.Besides,when the anchoring matrix strength and the anchorage length decrease while the edgewise compressive strength,loading rate,and anchorage inclination angle increase,the failure intensity rises.Instability is determined by a negative tangent modulus of the displacement-strength curve or the continued deformation increase against the general downward trend.Under cyclic loads,the driving force that breaks the rock mass along the normal vector and the rigidity of the AS are the two factors that determine roadway stability.Finally,a control measure for surrounding rock stability is proposed to reduce the internal driving force via a pressure relief method and improve the rigidity of the AS by full-length anchorage and grouting modification.

Mechanical behavior of 2G NPR bolt anchored rock samples under static disturbance loading

The deep mining of coal resources is accompanied by severe environmental challenges and various potential engineering hazards.The implementation of NPR(negative Poisson's ratio)bolts are capable of controlling large deformations in the surrounding rock effectively.This paper focuses on studying the mechanical properties of the NPR bolt under static disturbance load.The deep nonlinear mechanical experimental system was used to study the mechanical behavior of rock samples with different anchored types(unanchored/PR anchored/2G NPR anchored)under static disturbance load.The whole process of rock samples was taken by high-speed camera to obtain the real-time failure characteristics under static disturbance load.At the same time,the acoustic emission signal was collected to obtain the key characteristic parameters of acoustic emission such as acoustic emission count,energy,and frequency.The deformation at the failure of the samples was calculated and analyzed by digital speckle software.The findings indicate that the failure mode of rock is influenced by different types of anchoring.The peak failure strength of 2G NPR bolt anchored rock samples exhibits an increase of 6.5%when compared to the unanchored rock samples.The cumulative count and cumulative energy of acoustic emission exhibit a decrease of 62.16%and 62.90%,respectively.The maximum deformation of bearing capacity exhibits an increase of 59.27%,while the failure time demonstrates a delay of 42.86%.The peak failure strength of the 2G NPR bolt anchored ones under static disturbance load exhibits an increase of 5.94%when compared to the rock anchored by PR(Poisson's ratio)bolt.The cumulative count and cumulative energy of acoustic emission exhibit a decrease of 47.16%and 43.86%,respectively.The maximum deformation of the bearing capacity exhibits an increase of 50.43%,and the failure time demonstrates a delay of 32%.After anchoring by 2G NPR bolt,anchoring support effectively reduces the risk of damage caused by static disturbance load.These results demonstrate that the support effect of 2G NPR bolt materials surpasses that of PR bolt.

Energy mechanism of bolt supporting effect to fissured rock under static and dynamic loads in deep coal mines

The stability control of fissured rock is difficult,especially under static and dynamic loads in deep coal mines.In this paper,the dynamic mechanical properties,strain rate evolution and energy dissipation of fissured and anchored rocks were respectively obtained by SHPB tests.It was found that bolt can provide supporting efficiency-improving effect for fissured rock against dynamic disturbance,and this effect increased quadratically with decrease in anchoring angles.Then,the energy dissipation mechanism of anchored rock was obtained by slipping model.Furthermore,bolt energy-absorbing mechanism by instantaneous tensile-shear deformation was expressed based on material mechanics,which was the larger the anchoring angle,the smaller the energy absorption,and the less the contribution to supporting efficiency improvement.On this basis,the functional relationship between energy dissipation of anchored rock and energy absorption of bolt was established.Taking the coal-gangue separation system of Longgu coal mine as an example,the optimal anchoring angle can be determined as 57.5°–67.5°.Field monitoring showed fissured rock with the optimal anchoring angle,can not only effectively control the deformation,but also fully exert the energy-absorbing and efficiency-improving effect of bolt itself.This study provides guidance to the stability control and supporting design for deep engineering under the same or similar conditions.

Testing and modeling of cyclically loaded rock anchors

The Norwegian Public Roads Administration(NPRA) is planning for an upgrade of the E39 highway route at the westcoast of Norway. Fixed links shall replace ferries at seven fjord crossings. Wide spans and large depths at the crossings combined with challenging subsea topography and environmental loads call for an extension of existing practice. A variety of bridge concepts are evaluated in the feasibility study. The structures will experience significant loads from deadweight, traffic and environment. Anchoring of these forces is thus one of the challenges met in the project. Large-size subsea rock anchors are considered a viable alternative. These can be used for anchoring of floating structures but also with the purpose of increasing capacity of fixed structures. This paper presents first a thorough study of factors affecting rock anchor bond capacity. Laboratory testing of rock anchors subjected to cyclic loading is thereafter presented. Finally, the paper presents a model predicting the capacity of a rock anchor segment, in terms of a ribbed bar, subjected to a cyclic load history. The research assumes a failure mode occurring in the interface between the rock anchor and the surrounding grout. The constitutive behavior of the bonding interface is investigated for anchors subjected to cyclic one-way tensile loads. The model utilizes the static bond capacity curve as a basis, defining the ultimate bond sbuand the slip s1 at τ. A limited number of input parameters are required to apply the model. The model defines the bond-slip behavior with the belonging rock anchor capacity depending on the cyclic load level(τcy/τ), the cyclic load ratio(R= τcy/τcy), and the number of load cycles(N). The constitutive model is intended to model short anchor lengths representing an incremental length of a complete rock anchor.

Experimental study on the stability of plate anchors in clay under cyclic loading

Although the bearing capacity of plate anchors in clay has been studied extensively, the results considering the effects of offshore cyclic loading are relatively rare. In the present study, 1g model tests are carried out to investigate the effect of cyclic loading on the bearing capacity of plate anchors in clay. The ultimate pullout capacity of plate anchors in clay decreases as the accumulated plastic shear strain grows due to the strain-softening of clay under cyclic loading. The load-displacement curves of these tests are presented and the effects of overburden stress and cyclic loading amplitude on the strain-softening behavior are discussed.

Full-scale pullout tests of rock anchors in a limestone quarry focusing on bond failure at the anchor-grout and grout-rock interfaces

Rock anchors are a common safety measure for stabilising large-scale infrastructure,such as bridge towers,retaining walls,rock slopes and windmills.There are four principal failure modes for rock anchors:(a)tensile failure of the steel anchor,(b)anchor-grout interface failure,(c)grout-rock interface failure,and(d)rock mass uplift.Field tests were performed in a limestone quarry.These tests were designed to test failure modes B and C through pullout.In the tests of failure mode B,the shear stress on the anchor-grout interface is the largest at the top of the grout column and attenuates towards the distal end for small loads.The shear stress becomes uniformly distributed when the applied load is approximately 50%of the ultimate pullout load.The anchors designed to test failure mode C were installed with an endplate and had a higher toughness than the straight bar anchors.The shear stress on the grout-rock interface is the largest at the endplate and attenuates upward before slip starts along the interface.When the ultimate pullout load is reached,and the grout column starts to slip,the shear stress is approximately constant.The bond shear strength on the anchor-grout interface was approximately 20%of the uniaxial compressive strength of the grout,and the bond strength of the grout-rock interface was around 5%for that of the grout.The grout-rock interface is likely determined by whichever is weaker,the grout or the rock.

Optimization of Dead Load State in Earth-Anchored Cable-Stayed Bridges

In order to determine the reasonable completed dead load state in earth-anchored cable-stayed bridges,a practical method is proposed. The method is based on the rigidly supported continuous beam method and the feasible zone method,emphasizing on the mutual effect between the self-anchored structural parts and the earth-anchored ones. Three cable-stayed bridge models are designed with the main spans of 1 400 m,including a partially earth-anchored cable-stayed bridge,a cable-stayed-suspension bridge and a fully selfanchored cable-stayed bridge,in which the C50 concrete and Q345 steel are adopted. The partially earthanchored cable-stayed bridge and the cable-stayed-suspension bridge secure lower compressive force in the girder than the fully self-anchored cable-stayed bridge by 25 percent at least. The same is for the material consumption of the whole bridge. Furthermore,the anchor volume is more than 20% lower in the partially earthanchored cable-stayed bridge than that in the cable-stayed-suspension bridge. Consequently,the practical span of cable-stayed bridges can be accordingly extended.

Prediction of a maximum pull-out load of anchor bolts using an optimal combination model

The mixed model of improved exponential and power function and unequal interval gray GM(1,1)model have poor accuracy in predicting the maximum pull-out load of anchor bolts.An optimal combination model was derived using the optimally weighted combination theory and the minimum sum of logarithmic squared errors as the objective function.Two typical anchor bolt pull-out engineering cases were selected to compare the performance of the proposed model with those of existing ones.Results showed that the optimal combination model was suitable not only for the slow P-s curve but also for the steep P-s curve.Its accuracy and stable reliability,as well as its prediction capability classification,were better than those of the other prediction models.Therefore,the optimal combination model is an effective processing method for predicting the maximum pull-out load of anchor bolts according to measured data.

粘土中吸力锚基础的抗扭承载特性研究

文章对粘土中的吸力锚基础承受水平与扭矩组合荷载、垂直与扭矩组合荷载的性能展开了研究。首先通过数值模拟试验,验证了有限元模型的合理性。基于有限元建立了长径比为1的吸力锚基础模型,研究了水平荷载、竖直荷载和扭矩荷载组合作用下的吸力锚基础承载特性。结果表明:在扭矩荷载的作用下,吸力锚基础的水平和竖直承载性能均显著降低,随着水平荷载作用点的下降,吸力锚抵抗扭矩荷载的能力呈现出先增大后减小的趋势;在水平-竖直-扭矩荷载三者组合作用的情况下,随着扭矩荷载的增大,吸力锚极限承载力的下降趋势显著增大,随着荷载方向与水平面夹角增大,吸力锚抵抗扭矩荷载的能力呈现增大趋势。

高频低能冲击扰动下锚固结构渐进失效试验研究

高频低能冲击扰动对巷道围岩及锚固结构造成持续疲劳损伤,是深部巷道趋向失稳的重要诱因,合理构建抗冲击动载巷道锚固支护体系及避免锚固结构失效已经成为深部煤炭开采面临的重要课题之一。采用理论分析、实验室试验、数值模拟等方法,研究了冲击载荷下锚固结构内部应力传递转化机制,阐明了锚固结构累积损伤与渐进失效机理,提出了冲击动载巷道控制准则。结果表明:压缩应力、拉伸应力与压拉快速转换形成的震荡效应是造成锚固结构损伤的三大要素;压缩、拉伸作用下介质抗压强度与不协调变形是导致锚固界面破坏的关键因素,锚固结构在内部法向驱动力作用下损伤累积,切线模量为负或单次动载冲击变形量持续逆势上扬时锚固结构失效,压缩、拉伸、震荡叠加影响下锚固结构预紧力损失及内部损伤存在明显的累积突变效应,内部裂隙以张拉裂隙为主,整体破坏从震荡效应向拉伸效应再向压缩破坏效应逐渐演化。通过提高围岩/锚固剂协调变形能力,增加锚固长度调动大范围岩体承载、保护锚固界面,保持锚固结构承载区抗剪阻滑强度大于动载冲击时内部法向驱动力,同时削弱震荡效应可有效降低锚固结构累积损伤程度。最后提出了降能-高阻-让压的冲击动载巷道控制技术准则,包括远场卸压、近场强支、破碎围岩改性、预紧力维持和让压结构,可为类似条件巷道维控提供指导。

双锚片螺旋锚倾斜拉拔承载特性与承载力计算方法研究

目前对多锚片螺旋锚倾斜拉拔承载特性机制的认识尚不全面,承载力计算方法也还不成熟。采用自制模型试验装置开展了双锚片螺旋锚的多角度倾斜拉拔模型试验,分析了荷载倾角、埋深比对荷载−位移曲线和抗拔承载力因子的影响规律。通过量化水平向和竖向的控制程度分析了两个方向的耦合效应;基于数值模拟标定了锚片间距和荷载倾角对锚片上土压力的影响,提出了锚片上土压力影响系数计算方法,引入考虑位移影响的土压力近似计算方法和p-y曲线法,构建了双锚片螺旋锚倾斜拉拔力学模型,提出了双锚片螺旋锚倾斜拉拔承载力计算方法和相应步骤,并在3个试验案例的计算中取得了较好的效果。所提模型和计算方法的研究思路可推广至其他多锚片的情况,但螺旋锚需满足属于刚性短桩的前提条件。

托顶煤巷道锚固“梁-拱”结构分类及顶板冲击失稳机制

我国煤矿托顶煤巷道冲击地压频发,且冲击动载下顶板灾害尤为严重。为探究托顶煤巷道顶板锚固结构类型和冲击失稳机制,以陕西某矿301工作面回风巷道大面积冲击垮顶为工程背景,运用相似实验、理论分析及数据统计等方法,分析了托顶煤巷道围岩应力、位移和巷表加速度的动载响应特征,研究了顶煤厚度与支护构件影响下顶板锚固结构的分类特征,探究了弹性波下托顶煤巷道的应力响应机制,提出顶板锚固“梁-拱”结构的冲击失稳机制,评估了301工作面回风巷道的抗冲能力,并提出了相应的抗冲支护优化方案。结果表明:①冲击动载下托顶煤围岩应力和位移等监测数据验证了顶板存在内、外层的梁或拱形锚固结构,因顶煤厚度增加,顶板内层锚固结构存在由“梁”向“拱”的转换;②基于顶煤厚度与支护构件相对关系,将顶板锚固结构划分为薄顶煤的“叠加梁-拱”、厚顶煤的“组合梁-拱”和特厚顶煤的“组合拱”,建立了厚煤梁由“梁”向“拱”转化的临界厚度指标;③顶板锚固梁结构和锚固拱结构的冲击失稳机制为动静载荷下分别达到其拉伸、剪切强度极限后破坏,锚固“梁-拱”结构对冲击载荷的放大效应受其尺寸影响明显;④特厚顶煤的“组合拱”结构中内层拱承载强度较低,可增加锚杆长度提升内层拱厚,对应的“组合拱”结构的承载能力上升明显,与抗冲能力评估结果相符。

串联式锚定板抗拔承载特性及影响因素分析

为提高锚定板抗拔承载能力,设计串联式锚定板锚固系统。借鉴侧向受荷桩的“M”法,通过锚固系统受力平衡条件及位移连续性条件,提出串联式矩形锚定板锚固系统抗拔力-位移关系的理论分析方法。基于FLAC3D有限差分软件,建立锚定板锚固系统与土相互作用的数值模拟模型,进行埋设于黏性土中不同尺寸的方形锚定板抗拔承载力室内模型试验。结合室内模型试验及数值模拟结果,通过拟合分析,获得串联式矩形锚定板锚固系统抗拔力-位移关系的近似解析解,将3个工程案例中不同尺寸及埋深的锚定板抗拔力-位移的现场试验结果与理论分析及数值模拟结果对比,验证理论分析方法及数值模拟结果的正确性。探讨串联式方形锚定板锚固系统埋深及相邻锚定板间距对锚固系统抗拔承载力的影响。研究结果表明:当锚定板锚固系统埋深H<5b(b为锚定板边长)时,其破坏模式呈现浅埋锚定板的破坏特征;当埋设深度H≥5b时,其破坏模式呈现深埋锚定板破坏特征。对于串联式锚定板锚固系统,为避免相邻锚定板相互影响而降低锚固系统的抗拔承载能力,相邻锚定板间距应满足L≥3b。

动载作用下锚固体应力波传递及破坏特征研究

为研究动载作用下锚固体的应力波传播规律及破坏特征,利用分离式霍普金森杆(SHPB)对锚固体试件开展了不同预应力及不同冲击次数的冲击试验。研究结果表明:随着预应力增加,锚固围岩中应力波峰值逐渐增加,衰减速度逐渐减小,增大锚杆预应力,锚固自由端拉伸波峰值明显减小;随锚固体试件预应力增加,锚固体轴力损失越快,轴力损失率呈二次线性增加的趋势;预应力较小时,锚固自由端围岩产生裂缝较多,多次冲击下裂缝距离较为接近;随着预应力的增加,自由端头破坏程度减弱;随着预应力增加,拉拔最大位移量越来越小,未受动载作用的原始试件拉拔后未出现明显的破坏;动载作用后,随着预应力增大,锚固端头发生一定程度的劈裂破坏,预应力持续增加劈裂破坏程度越来越弱。

深水FPSO吸力锚建造工艺

以某深水浮式生产储卸油装置(FPSO)的吸力锚建造为例,对吸力锚的钢制筒体、顶盖结构、内部切泥板、铸造吊耳及锚链等主要结构预制安装流程与吸力锚整体装船工艺进行阐述。研究结果表明:深水FPSO吸力锚在建造过程中通过制定合理的施工顺序、严格控制组对尺寸公差和焊接参数等措施,对整个项目的质量管控和工效提升至关重要,也为后期同类大型管状结构物的建造提供了有益的参考。

不锈钢槽式预埋组件受拉性能研究

为研究不锈钢槽式预埋组件在拉力作用下的受力性能,首先对S-CAG-53/34、S-CBG-52/34两种不锈钢预埋槽道进行锚杆中心线和槽道跨中位置受拉静载试验.试验结果表明:不锈钢预埋槽道主要发生槽口卷边屈曲破坏.然后,采用有限元分析软件ABAQUS建立2种不锈钢槽式预埋组件的有限元模型,将数值模拟结果与试验结果对比,验证有限元模型的准确性和适用性.最后,建立50个足尺试件的有限元模型,研究槽口卷边厚度、槽道侧壁厚度、锚杆尺寸、锚杆间距以及相邻荷载对不锈钢槽式预埋组件受拉性能的影响.分析结果表明:增加槽道槽口卷边厚度、槽道侧壁厚度以及减少锚杆间距均能有效提高不锈钢槽式预埋组件的受拉承载力;增加槽口卷边及侧壁厚度会使槽道截面刚度提高,从而提高槽道跨中部位受拉承载力;减少锚杆间距使得槽道受弯承载力增加,从而提升槽道跨中部位受拉承载力.改变锚杆长度对槽道跨中位置受拉承载力的影响较小;在一定间距内同时施加多个荷载,会导致部分锚杆承受较高荷载,对槽道承载力产生影响,但这种影响随着锚杆间距减少逐渐降低.

考虑永久位移的锚索框架减震锚头弹簧组件合理刚度研究

强震作用下预应力框架锚索可能出现内锚段松脱、锚索拉断等震害,在锚头处设置弹簧是一种新型抗震措施,而弹簧刚度的合理选取对改善锚索受力至关重要。建立在锚头处设置弹簧预应力锚索框架的加固基岩-覆盖层边坡三维数值模型,研究边坡在不同峰值加速度、不同持时地震波作用下响应规律,调整锚索-弹簧串联体系等效刚度大小,分析坡体永久位移和锚索轴力减载比随弹簧刚度的非线性变化特征;以控制边坡位移及锚索减载效果为目标,提出弹簧组件的合理刚度确定方法。研究表明:随弹簧刚度降低,缓冲减震作用逐渐显著;坡顶水平加速度受刚度变化影响较小,但当弹簧刚度低于临界值后边坡位移及弹簧变形量急剧增加;以边坡永久位移实际调查经验限值为首要控制条件,结合位移、弹簧峰值行程随刚度变化拟合“直-曲分界点”曲线,以共同确定弹簧刚度下限;同理,依据减载比拟合曲线轴力削减明显区段得出刚度上限,以保证一定工程经济性。针对算例模型取永久位移10 cm、拟合曲线曲率k小于0.002 k max作为直曲分界判断依据,得0.4 g~0.6g强震下弹簧刚度区间为(2.5,3.8)kN/mm,研究方法可为边坡预应力锚固工程抗震设计提供参考。

630MPa热处理带肋高强钢筋机械锚固性能试验研究

为了研究630MPa热处理带肋高强钢筋的机械锚固性能分别采用单侧贴焊锚固与端头塞焊锚板的形式,对2组60个试件进行拉拔试验。研究不同锚固条件下混凝土抗拉强度、锚固长度、钢筋直径、混凝土保护层厚度及配箍率对其机械锚固性能的影响。结果表明:630MPa热处理带肋高强钢筋机械锚固试件具有3种破坏形式,即混凝土劈裂、钢筋拔出、钢筋屈服,端头塞焊锚板试件抗滑移效果更优。试件的机械锚固强度随着混凝土抗拉强度、混凝土保护层厚度、配箍率的增大而增大,随着锚固长度、钢筋直径的增加而减小。基于试验结果建立了630MPa热处理带肋高强钢筋机械锚固强度计算公式,结果表明该公式计算值与试验值吻合较好。

地震荷载下预应力锚固边坡离心振动模型试验研究

预应力锚索作为边坡支护的重要技术,已经在边坡加固中得到了广泛应用,但锚固岩质边坡在地震荷载作用下的响应机制以及锚索受力变形规律还不明确。为此,开展了预应力锚固边坡离心振动模型试验,系统介绍了模型相似设计、模型设计与制作、地震荷载施加等试验关键技术,并以紫坪铺水库泄洪洞进口岩质边坡为原型,开展了简谐地震波作用下的锚固边坡离心模型试验。对试验结果进行了分析,并对该离心振动试验的主要影响因素进行了探讨。研究结果表明:地震作用下预应力锚索发挥了较强的被动支护作用,且越靠近滑面处应力应变响应越明显;边坡竖向位移与应力应变值的响应情况随地震烈度的改变产生明显变化。研究成果可为今后离心振动模型试验的开展提供参考与借鉴。

爆炸作用下超宽自锚式悬索桥动力响应研究

为研究超宽混凝土自锚式悬索桥在爆炸荷载作用下动力响应和毁伤特征,以某超宽混凝土自锚式悬索桥为工程背景,采用数值模拟文法,分析桥面近距爆炸作用下超宽箱梁顶面破口形态、底板竖向位移等动力响应。首先,利用Solidworks软件和Hypermesh软件建立整体桥梁的精细化有限元模型;其次,采用Ansys/LS-DYNA软件和*LOAD_BLAST_ENHANCED(LBE)方法施加爆炸荷载,并结合文献中混凝土构件爆炸试验结果验证计算方法的可靠性;最后,参数化分析不同炸药当量和沿横纵桥向不同爆炸位置工况下桥梁的动力响应。结果表明:当TNT当量为300 kg时,爆心正下方混凝土单元应力达极限值发生失效,形成椭圆形贯穿破口。随着TNT药量的增大,爆心正下方底板中心处的竖向位移峰值不断增大,1 000 kg药量工况下爆炸50 ms后竖向位移达135.9 mm。随着至爆心的距离增大,底板竖向位移减小,且竖向位移的增大速度减缓。吊杆内力变化与相连的箱梁底板竖向位移具有相关性,箱梁底板竖向位移越大,吊杆内力变化达到第一峰的峰值越高。相同爆炸当量工况下,爆心处于横、纵桥向不同位置时,超宽箱梁动力响应和破口形态的区别主要由横隔梁、腹板的支撑和约束作用不同引起。研究结果可为混凝土自锚式悬索桥的抗爆防护与加固提供重要依据。