Simulation of anchor chain based on lumped mass method

In order to develop a anchoring operation simulation system and improve safety during anchoring operations,a relatively accurate mathematical model of anchoring operations needs to be established.In this paper,the stress condition of anchor chain under environmental and subsea geological conditions is further studied and the stress condition of anchor chain is analyzed based on the previous research.In this paper,a quasi-static model based on catenary method is used as the basis of dynamic analysis,and the dynamic model of anchor chain is established based on the concentrated mass method,which fully considers the influence of anchor chain weight,hydrodynamic force,ocean current and interaction with the seabed.The fourth-order Runge Kutta method was used to solve the model numerically,and a calculation procedure was developed.The accuracy of the model was verified by comparing the calculated results with the experimental results,indicating that the constructed anchor chain dynamics model has a high accuracy.

Exploring the feasibility of prestressed anchor cables as an alternative to temporary support in the excavation of super-large-span tunnel

Excavating super-large-span tunnels in soft rock masses presents significant challenges.To ensure safety,the sequential excavation method is commonly adopted.It utilizes internal temporary supports to spatially partition the tunnel face and divide the excavation into multiple stages.However,these internal supports generally impose spatial constraints,limiting the use of large-scale excavation equipment and reducing construction efficiency.To address this constraint,this study adopts the“Shed-frame”principle to explore the feasibility of an innovative support system,which aims to replace internal supports with prestressed anchor cables and thus provide a more spacious working space with fewer internal obstructions.To evaluate its effectiveness,a field case involving the excavation of a 24-m span tunnel in soft rock is presented,and an analysis of extensive field data is conducted to study the deformation characteristics of the surrounding rock and the mechanical behavior of the support system.The results revealed that prestressed anchor cables integrated the initial support with the shed,creating an effective“shed-frame”system,which successively maintained tunnel deformation and frame stress levels within safe regulatory bounds.Moreover,the prestressed anchor cables bolstered the surrounding rock effectively and reduced the excavation-induced disturbance zone significantly.In summary,the proposed support system balances construction efficiency and safety.These field experiences may offer valuable insights into the popularization and further development of prestressed anchor cable support systems.

Mechanical mechanism analysis of tension type anchor based on shear displacement method

Based on the fact that the shear stress along anchorage segment is neither linearly nor uniformly distributed, the load transfer mechanism of the tension type anchor was studied and the mechanical characteristic of anchorage segment was analyzed. Shear stress?strain relationship of soil surrounding anchorage body was simplified into three-folding-lines model consisting of elastic phase, elasto-plastic phase and residual phase considering its softening characteristic. Meanwhile, shear displacement method that has been extensively used in the analysis of pile foundation was introduced. Based on elasto-plastic theory, the distributions of displacement, shear stress and axial force along the anchorage segment of tension type anchor were obtained, and the formula for calculating the elastic limit load was also developed accordingly. Finally, an example was given to discuss the variation of stress and displacement in the anchorage segment with the loads exerted on the anchor, and a program was worked out to calculate the anchor maximum bearing capacity. The influence of some parameters on the anchor bearing capacity was discussed, and effective anchorage length was obtained simultaneously. The results show that the shear stress first increases and then decreases and finally trends to the residual strength with increase of distance from bottom of the anchorage body, the displacement increases all the time with the increase of distance from bottom of the anchorage body, and the increase of velocity gradually becomes greater.

Prestressed tensioning method and its application to testing anchor stress of anchor cables for side-slope stabilization

The anchor stress extent of a prestress anchor cable project has a direct relation with the project safety and performance. Prestressed tensioning method is a kind of nondestructive testing method, by which a reverse stretching load is applied on the external exposure section of anchor cable under construction or in service, and then the elongation variation of stress bars is measured to determine the anchor stress. We elaborated the theory and testing mechanism of prestressed tensioning method, and systematically studied key issues during the prestressed tensioning process of anchor cable by using physical model test, including the composition of tension stress-elongation curve, the variation of anchor stress, the compensation of locked anchor stress, and the judgment of anchor stress, and verified the theory feasibility of prestressed tensioning method. A case study on slope anchor cable of one highway project was conducted to further discuss on the test method, operation procedures and judgment of prestressed tensioning method on obtaining anchor stress, and then the test data of three situations were analyzed. The result provides a theoretical basis and technical base for the application of prestressed tensioning method to the evaluation of construction quality and operation conditions of anchor cable project.

Model test of negative Poisson’s ratio cable for supporting super-largespan tunnel using excavation compensation method

In recent years,there is a scenario in urban tunnel constructions to build super-large-span tunnels for traffic diversion and route optimization purposes.However,the increased size makes tunnel support more difficult.Unfortunately,there are few studies on the failure and support mechanism of the surrounding rocks in the excavation of supported tunnel,while most model tests of super-large-span tunnels focus on the failure characteristics of surrounding rocks in tunnel excavation without supports.Based on excavation compensation method(ECM),model tests of a super-large-span tunnel excavation by different anchor cable support methods in the initial support stage were carried out.The results indicate that during excavation of super-large-span tunnel,the stress and displacement of the shallow surrounding rocks decrease,following a step-shape pattern,and the tunnel failure is mainly concentrated on the vault and spandrel areas.Compared with conventional anchor cable supports,the NPR(negative Poisson’s ratio)anchor cable support is more suitable for the initial support stage of the super-large-span tunnels.The tunnel support theory,model test materials,methods,and the results obtained in this study could provide references for study of similar super-large-span tunnels。

密砂中单盘螺旋锚安装效应对抗拔能力影响的数值分析

目的研究密砂中单盘螺旋锚安装过程中锚周土体变形特性及其对抗拔能力的影响,为螺旋锚基础精细化设计提供技术支撑。方法利用MatDEM软件建立密砂中螺旋锚安装及拉拔过程的数值计算模型,通过与室内模型试验结果对比标定颗粒微观力学参数,进而分析钻入和预埋两种安装方式下不同埋深和盘径的螺旋锚安装效应及上拔承载力。结果当H/d w≤10时,钻入安装的极限上拔力较预埋低,当H/d w>10后,安装方式带来承载力差别不再随埋深增加而增加;随着盘径增大,两种安装方式下螺旋锚的承载能力均表现出增大的趋势,钻入方式下的Q ut比预埋下的Q up降低量从33%增至53%,预埋方式螺旋锚的承载能力高于钻入。结论钻入安装螺旋锚的上拔承载力低于预埋方式的承载力,但当埋深比超过10后,安装扰动对承载力的影响随着深度变化很小;随着盘径增加,安装扰动对极限上拔承载力的影响增大,相较于埋深变化带来的安装扰动差异,盘径变化带来的影响更明显。

岩爆机制及其控制

随着岩体工程向深部发展,开挖引发的围岩大变形和强冲击诱发的动力破坏日益严峻。岩爆作为深部地下工程中常见的一种强动力灾害,被称为岩土工程界的“癌症”,其具有突发性特点,难以有效预报及防治,严重地威胁着施工人员的安全和设备的正常运行。通过对比岩石在真三轴卸荷和单轴压缩这2种应力路径下的储能差异,对岩爆多余能量机制进行探讨。首先,根据岩爆诱发机制的不同,将岩爆分为由应力集中导致的应变型岩爆和扰动诱发的冲击岩爆。然后,模拟开挖诱发的不同类型岩爆的应力路径进而在室内再现各种岩爆现象,并对其机制进行研究,自主研发3套真三轴岩爆模拟试验系统:第1代应变岩爆试验系统、第2代应变岩爆试验系统、冲击岩爆试验系统。同时,在实验室内成功模拟不同类型的岩爆:巷道应变岩爆、巷道交叉点应变岩爆、3个临空面矿柱应变岩爆、矿柱应变岩爆以及动荷载诱发的冲击岩爆。最后,为有效控制岩爆灾害,提出开挖补偿法,并研发具有负泊松比效应的宏观和微观NPR锚杆/索。工程实践证明,NPR锚杆/索能提供高预应力来补偿开挖造成的应力损失,同时具备良好的延展性和吸能效果,可为岩爆灾害的防治提供有效途径。

锚杆倒肋式风机基础受力性能的数值模拟

为了解决风机基础施工成本高、施工难度大等问题,提出了一种新型锚杆倒肋式风机基础。利用有限元分析软件ABAQUS对该新型风机基础与传统梁板式风机基础在极端运行荷载工况下的混凝土应力、钢筋应力、基础位移以及基础倾斜率进行数值模拟分析,并进一步讨论二者的混凝土用量、钢筋用量、土方开挖量。结果表明,锚杆的添加以及倒肋的结构设计使锚杆倒肋式风机基础的受力性能、经济性等方面明显优于传统梁板式风机基础,具有较好的应用前景。

桩撑式支护基坑通用弹性地基梁分析法

弹性地基梁法常用于模拟分析桩撑(锚)式支护基坑在开挖、设撑等施工工况中变形和受力的变化。目前利用该方法对某工况基坑分析时,首先要将整个支护桩在支撑处划分为若干个桩段,然后利用相邻桩段交界处的位移连续条件和受力平衡条件,推导出相应的待定参数方程,之后再利用求出的待定参数分析支护体系(基坑)的变形和受力。由于不同施工工况对应的支撑数和桩段数不同,因此该方法必须根据不同工况重新推导各自的参数方程,从而导致计算过程繁杂,难以形成通用计算公式和方法,也不易编程等问题。通过将支撑与桩段归纳为3种基本连接形式(即支撑分别相连于桩顶、相邻两桩段之间和坑底),本文建立了相邻两个桩段间待定参数的递推公式,进而推导出了适用于内支撑和锚索支撑形式、任意支撑道数、开挖或设撑工况的通用待定参数方程。该方程仅含4个参数,远少于现有方法且易于求解。文中算例结果验证了本文方法的合理性和可行性。

阶段矿房法二步骤采场地压控制研究

在阶段矿房二步骤开采时,为了减小上盘岩移量,常采纳采场中部切槽并向上盘、下盘两侧回采,从而缩短采场暴露时间,以便减小上盘岩移量。当地压达到流变发生的条件后,缩短采场暴露时间并不能有效控制上盘巷道发生岩移破坏。为此,利用三维连续体快速拉格朗日分析数值模拟采场上盘地压,并根据流变理论分析,采纳低松弛预应力大直径钢绞线锚索支护上盘顶板以便减小上盘地压,从而克服发生流变变形的应力条件。结果表明:在上盘岩体上施加支护抗力可减小或消除高地压导致的流变变形;采纳7排7.0 m长的锚索、每排6根支护上盘顶板后大幅度减小了上盘岩移量,但采场第2分层上排锚索及一步骤采场第3分层局部锚索的锚固力超过设计值;采纳8排7.0 m长的锚索、一步骤采场每排7根、二步骤采场每排6根支护上盘顶板后,即使回采底柱,锚索锚固力也不会达到设计值。监测表明,大直径钢绞线锚索支护后上盘岩移量减小到一般不超过6 mm。

含软弱夹层顺层岩质边坡开挖稳定性分析

以都安高速公路某段含软弱夹层顺层岩质边坡为例,采用极限平衡法对开挖后的边坡进行稳定性分析,基于FLAC3D软件模拟分析边坡分级开挖、分级支护过程中的位移、最大剪切应变增量、应力特征及抗滑桩的承载性能。结果表明:严格条分法的安全系数为1.011,强度折减法安全系数为条分法的97.13%,当考虑岩土体变形时,传统计算方法可能会高估边坡自身的稳定性;边坡采用抗滑桩+框架锚索+框架锚杆的联合支护方式,并进行分步开挖及分级支护,对坡体扰动小,支护效果良好,能很好地控制坡体变形,避免边坡因软弱夹层塑性区贯通而发生失稳破坏。

便携式在役锚索预应力检测设备研制及应用

现有的锚索预应力检测设备要求锚索外露段长度>70 cm,不适应于运维期的在役锚索检测,且质量大都在150 kg以上,对于高陡边坡锚索检测显得笨重。为此研制了HRAD-300型便携式在役锚索预应力智能检测仪,可适用于钢绞线外露长度>7 cm的在役锚索预应力检测。检测仪位移量程200 mm,测量误差0.01 mm;测力量程300 kN,测量误差±1%FS,单件质量<15 kg,总质量<40 kg。基于反拉法原理及检测曲线形态,提出锚下有效预应力算法,并编制了相关软件。室内试验表明,检测曲线形态多为拐点不明显型,计算值与原始锁定值基本一致。使用该设备对邛崃市天台山景区凤凰岩不稳定斜坡锚固工程进行检测,结果表明,现场锚索检测曲线多为拐点明显型,具有明显的突变点及陡降;锚索运行状态良好,持续发挥功效,2号锚索预应力损失较为明显,可以采取补偿张拉方式;同一锚索的不同钢绞线存在受力不均的情况。便携式在役锚索预应力检测仪智能、轻便,可为锚固工程健康评价提供数据支撑。

内置式锚箱索塔锚固区索力水平分力分配机理研究

索塔锚固区的受力分析通常采用实体有限元单元进行,然而由于其结构复杂、种类繁多,不易被一般工程设计人员使用。为此,结合某斜拉桥的实际工程案例,分析了内置式钢锚箱锚固体系的传力特点,提出了一种基于平面框架理论的简化计算方法,并利用非线性的分析方法建立了锚固区ANSYS有限元模型以修正公式。结果表明修正前简化公式计算结果与有限元模型计算结果之间的误差在10%左右;考虑到塔壁厚度、索塔计算高度以及锚箱侧板厚度的影响,使用折减混凝土弹性模量的方法来补偿和修正桥塔应力分布,具体的混凝土折减系数使用非线性回归的方法确定。最终将修正公计算式结果与有限元模型计算结果重新进行对比,结果表明,修正后的计算公式与有限元模型计算结果的误差在2%以内,可以较好地分析索塔锚固区的索力分配情况,具有实际工程意义。

川西南公路顺层边坡桩锚组合结构加固分析——以乐西高速ZK9+352~ZK9+526边坡为例

四川盆地周边地形地质条件复杂,公路建设中顺层边坡的工程病害频现。通过工程地质分析和数值计算,基于滑面损伤本构模型,研究顺层边坡支护前后滑面应力、位移和边坡稳定性系数等特征量的变化规律,验证桩锚组合结构加固顺层边坡的适用性;通过施工全周期现场监测,获取边坡深部位移、抗滑桩桩身弯矩和锚索应力的时效特征。结果表明:开挖扰动下顺层边坡具渐进性失稳破坏特征;自坡脚沿滑面向后缘,位移呈指数型平滑递减,剪应力先增大后降低,滑面损伤变量自剪应力峰值位置开始同频衰减;采用桩锚组合结构加固顺层边坡后,滑面位移最大值降低88.62%,最大损伤变量降低84.75%,稳定系数提高25.20%;坡体深部位移、抗滑桩桩身弯矩、锚索应力等监测验证了桩锚组合结构加固的有效作用。

海上浮式风机重力安装式筒形锚承载特性分析

在浮式风电的建设中,可能遇到各种不同的土质条件。对于高渗透性的土体,如粗砂,采用吸力安装的风险较大。根据实际工程的需要,文章提出了重力安装式筒形锚。文章利用有限元方法对重力安装式筒形锚固基础的贯入过程和承载特性进行了分析。分析结果显示,在粗砂地基当中,该锚固基础可以通过自身的重量贯入至设计深度。与普通重力锚主要通过锚底摩擦提供抗滑力不同,重力安装式筒形锚在水平荷载作用下为浅层破坏,在破坏过程中可以调动更多的土阻力,从而有效提高了抗滑能力。该锚固基础形式可以提供超过2000 t的水平承载力,接近常规重力锚的2倍,能够满足浮式风电的承载要求。此种锚固基础为我国海上浮式风机系泊锚型的确定提供了更多的选择。

基于名义应力法与局部应力-应变法的绳轮寿命评估

死绳固定器绳轮在钻井生产实际使用中承受着高强度交变载荷,极易发生疲劳破坏。为准确评估绳轮的疲劳寿命,以JZG18C型死绳固定器为研究对象,结合Goodman等寿命曲线修正的名义应力法和Morrow弹性应力修正的局部应力-应变法,估算死绳固定器绳轮在最大死绳拉力下的疲劳寿命。结果表明:JZG18C型死绳固定器绳轮寿命薄弱位置为传感器支臂过渡圆角处(疲劳寿命安全系数n 1=0.4351),在名义应力法及局部应力-应变法下绳轮薄弱位置处的最小疲劳寿命分别为38194次(3.5年)、37120次(3.4年),2种疲劳寿命评估的理论计算结果与有限元分析得到的疲劳寿命结果分别相差0.38%、2.51%,验证了以名义应力法与局部应力-应变法评估死绳固定器疲劳寿命的可靠性与准确性。

粘土中的螺旋锚上拔承载力模拟试验及设计优化

为深入研究锚盘间距、锚盘外径以及锚盘数量等结构因素对螺旋锚极限承载力的影响。基于螺旋锚基础设计公式,结合数值模拟推断出类圆柱剪切和类单锚盘失效破坏模式,提出并修订了原有设计方法。研究结果表明,螺旋锚的极限承载力受到锚盘间距、锚盘外径和锚盘数量的影响。优化配置可以显著提高螺旋锚的承载力,并且可以节约材料用量。此外,根据破坏模式重新阐述了圆柱剪切和单锚盘失效破坏,有助于进一步理解黏性土壤中螺旋锚的受力行为,为输电线路工程中螺旋锚基础的设计和实施提供了一定的理论参考。

轨道交通桥梁声屏障柱脚节点计算方法研究

声屏障柱脚结构一般采用锚栓连接钢立柱与混凝土基础。此类节点受力方式既不同于钢筋混凝土结构,亦不同于钢结构的螺栓群连接,而钢结构相关设计规范和混凝土设计规范中均未给出此类节点结构受力分析计算办法。本文在轨道交通声屏障柱脚锚栓连接节点结构受力分析中,提出按平截面假定方法分析的计算原理,结合在上海申通地铁集团有限公司科研项目《声屏障风荷载特性研究》中得出的风荷载作用数值,按照计算原理得出的方法,计算了六种不同荷载组合下的柱脚节点受力,并采用有限元仿真分析并行计算,对比二者计算结果以验证该原理和方法,可供相关设计人员计算参考。

基于离散元的岩质高边坡开挖支护数值模拟

为分析岩质路堑高边坡的开挖支护对边坡变形破坏及边坡稳定性的影响,利用离散元数值模拟与原位监测相结合的方法,对开挖适时支护与开挖未支护两种工况进行比较,评价了锚杆支护的效果。结果表明:边坡开挖引起的竖向位移主要集中于开挖面中部;在相同开挖条件下,经适时支护后,边坡开挖面临空向水平位移最大值减小2.50 cm,安全系数提高8.62%,处于基本稳定状态;数值模拟结果与原位监测数据基本吻合,说明离散单元法对于分析岩质边坡稳定性问题的适用性。

某失稳边坡的稳定性及加固效果研究

以某公路失稳边坡为研究对象,采用Bishop法计算了边坡5个代表性剖面的稳定性系数,根据稳定性计算结果提出了“削坡+锚杆格构梁+排水沟+坡面绿化”的边坡治理措施。为验证治理措施的有效性,以稳定系最差的I-I’剖面为例建立三维网格计算模型,利用有限差分法计算了天然工况和暴雨工况下边坡位移量分布结果。数值模拟结果显示,边坡加固前,在天然工况和暴雨工况下的最大水平位移量分别为26.3 mm和28.9 mm,最大竖向位移量分别为19.2 mm和22.1 mm;边坡加固后在天然工况和暴雨工况下的最大水平位移分别为10.7 mm和11.5 mm,最大竖向位移分别为14.3 mm和16.8 mm。在天然工况和暴雨工况下,加固后对比加固前坡面位移分别降低了40.56%和39.83%,坡体位移分别降低了54.37%和58.13%。对比加固前和加固后的坡体位移结果可知锚杆格构梁加固有效抑制了坡体变形。加固后的坡体地表位移监测结果均在安全范围内,表明所提出的边坡加固措施对该边坡具有良好的加固效果。本研究可为类似边坡加固工程提供一定的参考。