大直径钢管桩水平载荷试验研究

文章首次对直径为2800mm 的超大直径钢管桩开展了单桩水平静载试验,研究分析了超大直径钢管桩的桩侧水平抗力、桩身截面弯矩、桩身水平位移与桩基水平荷载之间的变化曲线,得到了不同水平位移时桩周地基反力模量的变化规律,为超大直径桩基水平承载力设计提供了现场试验数据。     

海上大直径钢管桩打桩过程中桩周土强度弱化研究

海上大直径钢管桩打桩过程中,桩周土体受到强烈扰动而发生强度弱化,掌握桩周土体强度弱化规律对于准确预测打桩过程、保证工程安全具有重要意义。为研究土体强度弱化规律,开展了环剪试验模拟打桩对桩周土体的扰动,测试土体强度随剪切速率的变化规律,建立了描述土体强度弱化规律的拟合公式,引入到打桩分析软件中。研究结果表明：土体的强度折减程度不仅与土体本身的性质有关还受到土体的埋深和剪切速率的影响,埋深越深土体强度折减程度越低,剪切速率越高土体强度折减越高,在打桩分析中可采用这里推荐的线性折减方法来模拟不同深度处土体强度的折减规律。     

海上复杂地质条件下大直径钢管桩时效性试验研究

通过对3根海上复杂地质条件下的大直径钢管桩采取高应变初打与不同休止时间复打相结合的试验方法,得到不同休止时间钢管桩承载力、侧阻力及端阻力大小,以此对不同桩侧土及持力层对钢管桩时效性的影响进行了研究。研究结果表明:1)钢管桩承载力时效性现象明显,且随时间增长迅速; 2)钢管桩侧阻力的恢复系数远大于端阻力; 3)桩侧黏性土强度的恢复是钢管桩侧阻力增加的主要原因; 4)砂土层虽提供的侧阻力较大,但其对侧阻力增长的贡献不如黏性土; 5)持力层越硬,端阻力与承载力的恢复性越差。     

黏土中海上风电水平受荷大直径单桩设计方法的思考

文章回顾了目前风电大直径单桩基础水平受荷静力响应分析的p-y 曲线规范方法,结合现有成果探讨了该方法会高估桩侧初始刚度并低估极限承载力的原因。为解决其不足,文章介绍了一种基于土体应力应变关系的p-y 曲线方法,它不但能较为正确地反映桩侧刚度,还能跟踪桩周土体的平均塑性应变的累积。在此基础上探讨了桩基在循环疲劳状态下的规范方法,由于其无法精确反映循环次数和幅值对于桩侧刚度弱化的影响,因此,进一步介绍了基于静力p-y 骨干曲线的滞回曲线构造方法,最后,基于上述分析方法,提出了一些大直径单桩优化设计的建议。     

大直径钢管桩土塞效应的判断和沉桩过程分析

港口工程和海洋工程中出现了越来越多的大直径超长钢管桩。由于这种桩直径较大,土塞的形成对桩的可打入性和承载力有较大的影响。鉴于此,根据大直径和超大直径钢管桩土塞性状的特殊性,考虑了桩直径对侧壁摩阻力、端阻力的影响,引入了尺寸效应系数,重新建立了土塞微分体的静力平衡方程,提出了采用改进的静力平衡法进行土塞效应判断,同时采用波动方程法近似模拟土塞与桩管内壁的相互作用,建立了简化的土塞与桩壁相互作用模型,并用该方法进行实际工程的打桩分析,分析结果表明该方法对土塞效应的判断、打桩过程的预测等与工程实测数据吻合较好。     

大直径海上风电嵌岩钻机的发展现状及关键技术分析

文章简要阐述了海上风电嵌岩单桩市场情况和3种典型嵌岩单桩的施工工艺,介绍了嵌岩钻机的结构组成和主要功能情况,通过对比国内外主要大直径海上风电嵌岩钻机的发展现状和技术特点,提出了适应国内海上风电嵌岩单桩施工的钻机要求和关键技术难度,为进一步发展国产大直径海上风电嵌岩钻机指明了方向。     

海洋平台大直径钢管桩打桩过程有限元分析研究

近年来海上工程的规模越来越大,为了满足工程需要,桩基设计常常采用大直径,大长度的钢管桩。打桩过程是个相当复杂的过程,不仅涉及到几何非线性、材料非线性、边界非线性,而且是个动力过程。有限元法在处理打桩分析方面具有很强的优势,采用PLAXIS对不同条件下的打桩问题进行了动力模拟分析。分析显示在打桩过程中,桩端土体会产生较大的水平位移和竖向位移,桩端土体和靠近桩端的部分土塞内会产生较大的超孔隙水压力。在砂土中,停锤较短时间也会使孔压迅速消散,这也是打桩中间的停锤会造成后续打桩困难的主要原因。     

海上风电钢管桩自平衡法现场试验研究

一种新型钢管桩预装荷载箱法被研发出用于自平衡法海上风电钢管桩基检测试验,并通过现场自平衡试验研究探究了海上打入桩桩基础特性。该方法首次成功应用于海外某海上风电场直径1.4 m的超长大直径钢管桩承载力检测,用于探究其承载特性和桩侧桩端阻力发挥规律。现场试验显示,该新型检测方法达到了预期的测试效果和经济效益,与现有钢管桩自平衡法相比,对土的影响更小,可靠度更高,为类似土层和直径的超长钢管桩承载力试验提供了新的途径。     

p-y曲线对成层土体中大直径单桩的适用性研究

API规范推荐的p-y曲线是由均质土体得到的,并未考虑土层间相互作用,Georgiadis基于柔性桩提出了等效深度法修正p-y曲线,把均质土p-y曲线延伸到了成层土体中。为了研究p-y曲线和等效深度法对于大直径单桩在成层土体中的适用性,取4种典型地质条件:成层砂土、砂土-黏土-砂土、成层黏土和黏土-砂土-黏土,通过L-PILE软件计算了6 m直径单桩基础的p-y曲线、桩顶水平荷载-位移曲线、桩身位移和弯矩。并与ABAQUS建立的单桩基础三维有限元模型计算结果进行比较。结果表明等效深度法对于成层砂土影响不大;对于成层黏土影响较大;对于中间为软弱土层的成层土体,在荷载较大时影响显著,等效深度法计算结果更加接近FEM结果。在成层土体中,p-y曲线应用于大直径单桩对于砂土高估了初始刚度,低估了极限抗力;对于黏土则低估了初始刚度和极限抗力。     

A new look at the phenomenon of offshore pile plugging

Abstract

Open‐pipe piles are widely used for offshore structures. During the initial stage of installation, soil enters the pile at a rate equal to the pile penetration. As penetration continues, the inner soil cylinder may develop sufficient frictional resistance to prevent further soil intrusion, causing the pile to become plugged. The open‐ended pile then assumes the penetration characteristics of a closed‐ended pile. The mode of pile penetration significantly alters the soil‐pile interaction during and after installation. This affects the ultimate static bearing capacity (mainly in granular materials), the time‐dependent pile capacity (in clays), and the dynamic behavior and analysis of the piles.

Following a summary demonstrating the effects of pile plugging, a review of the common view of offshore pile plugging is undertaken. The interpretation of plugging by referring to the average plug length has led to the erroneous conclusion that in most piles significant plugging action does not occur.

Establishment of an analogy between soil samplers and open‐ended piles enabled correct identification of plugging by referring to the incremental changes in plug length. Examination of case histories of plugging of offshore piles revealed that beyond a certain penetration depth‐to‐diameter ratio, most piles are plugged.     

大直径超长管桩打桩过程中土塞性状研究

大直径超长桩的可打入分析是海洋平台打桩施工顺利进行的重要保障,土塞是否闭合的判断对于桩基可打入性分析具有较大的影响,因此,合理准确的土塞判断结果对提高桩的可打入分析的准确性具有重要的意义。以现场静力触探(CPTU)试验数据为依据,采用孔扩张理论推导了基于CPTU测试结果的桩端土的极限承载力计算公式;在求解桩端土体承载力时考虑了管桩与土体的刚度差异,同时考虑到打桩过程中的土体扰动。采用Randolph推荐的方法得到了土塞阻力,将两者进行比较,进而判断土塞的状态。通过实际工程的实测数据,对各个土层的土塞状况进行了判别,并根据判别情况采用波动方程的方法对桩基的可打入性进行了分析,将预测结果和现场的打桩记录进行了比较。计算结果显示,提出的方法与实测结果更为接近,有效地提高了桩的可打入性的预测精度。     

珊瑚礁地质大直径钢管打入桩承载特性研究

马尔代夫中马友谊大桥采用钻孔灌注桩基础,主墩基础施工过程中,将35根大直径钢护筒施沉至中等—强胶结礁灰岩地层,作为钻孔平台的临时桩基础。以主墩大直径钢护筒沉桩记录为依据,并结合高应变动力检测方法,对珊瑚礁地质大直径打入桩的承载性能进行研究。研究结果表明:1)以钙质砂为主的覆盖层侧阻力较小; 2)礁灰岩侧阻力随胶结程度的增加而增大; 3)中等—强胶结礁灰岩可以作为打入桩的持力层,端阻力约占总承载力的70%; 4)打入桩的承载力恢复系数较小,仅为1.1。     

Research on shaft resistance of rock-socketed piles based on the cavity expansion theory

The shaft resistance of rock-socketed piles depends not only on the properties of its surrounding rock, but also on the radial force induced by the load imposed on the top of the pile. This paper deduced a plastic zone of rock around a single pile and obtained the shaft resistance of a rock-socketed pile based on the theories of cavity expansion and shear strength. The research results showed that the magnitude of the radial force in the socketed portion of a rock-socketed pile was related to the pile diameter, Poisson’s ratio, and properties of the surrounding rock. The influence area of rock decreased with increasing pile diameter. The radial force and lateral friction decreased with the increasing relative stiffnesses of the pile and rock. The radial stress on the elastic–plastic interface can be analytically determined based on the rock properties and depth. A field test was used to validate the proposed method, and a good agreement was obtained between the field data and predicted results of the proposed method. The research results in this paper are beneficial to guide actual practice.     

基于实测数据的海上风电结构动力响应分析

地震是危害海上风电结构作业安全的重要环境因素,目前,国内尚未公开发表真实地震响应下,海上风电结构的实测动力响应数据。分析了某地震活动区海上风电结构的实测地震响应,采用随机子空间识别方法进行风机的模态识别,阐述了风机机舱偏航将引起前后、左右两个正交方向振动的耦合,并从理论上证明了利用耦合、解耦数据识别模态参数的差异。结果表明：1）耦合与解耦信号识别的频率、阻尼比完全相同,而耦合信号识别的模态振型与偏航角有关;2）地震作用会对结构产生巨大冲击;3）非地震作用下,风机塔筒前后、左右第一阶弯曲模态为主要模态,地震作用可以激发风机的高阶模态,使得塔筒中上部而不是顶部的振动响应最大。此分析对地震活动区海上风电结构的抗震设计具有一定的参考价值。     

Assessment of CPTU and static load test methods for predicting ultimate bearing capacity of pile

For the static pressure pile, the most important is to determine the standard value of ultimate bearing capacity of single pile. At present, the bearing capacity of pile foundation is usually determined by the cone penetration test (CPT) test. The empirical formula was used in practice, but the effect of excess pore water pressure generated in the penetration on the measured cone-tip resistance and side friction is neglected. In this study, based on the field test results at Fengyu playground at Yancheng Institute of Technology by CPT and CPTU methods, the bearing capacity of pile was predicted by the standardized methods, the LCPC (France method) and CPTU direct prediction methods. The prediction was also compared with the results by the static load test method. The prediction accuracy of the CPTU method was then discussed as well. The results reveal that the accuracy of the CPTU method was the highest, which was consistent with the results obtained by the static load test method. It is the best method and worthy of being applied for predicting bearing capacity of piles in engineering applications.     

Experimental study on stability of sunken large diameter cylindrical structure on sandy seabed during construction period

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