深海石油平台锚桩承载力的研究

目前深海石油平台广泛采用桩基锚固形式,深海锚桩与浅海桩基的受力形式存在较大差异。采用三维有限元软件模拟深海锚桩的受力情况,重点分析深海锚桩在受缆索斜向拉力作用时,不同加载角度和系泊点位对桩基水平承载力和竖向抗拔承载力的影响,可供深海石油平台设计研发参考。     

新型平台基础与土相互作用的有限元分析及试验研究

深卧基础式采油平台采用—种由沉箱及底粱构成的组合式基础,同传统的导管架式平台相比,具有工程上,经济上明显的特色,但其基础与土相互作用的力学机制尚待深入研究。本文介绍深卧式基础与土在垂直及水平荷载作用下的三维非线性有限元分析,以及配合开展的模型实验。计算与实验的结果基本吻合,并都显示了深卧式基础的基本特性及其与土相互作用的基本规律。     

海上风机吸力式桶形基础竖向承载力特性研究

吸力式桶形基础作为一种新型的海上风机基础,正逐渐以单桶或者多桶组合形式被应用于海上风机支撑基础设计中。然而目前对应用于海上风机基础的桶形基础的极限承载力的研究仍存在研究不全面和结果不统一的问题。本文以宽浅型单桶基础为例,采用有限元软件Abaqus对海上风机吸力式桶形基础在饱和黏土地基中的竖向承载特性进行三维有限元分析。考虑桶土接触面分离条件对极限承载力和土体破坏模式的影响,并且对桶形基础长径比、土体的有效重度以及土体不排水抗剪强度分布对桶形基础竖向极限承载特性的影响进行分析。研究成果可以为海上风机吸力式桶形基础设计提供参考。     

水工挡土墙地基承载力特征值修正

在采用载荷试验或原位试验的经验统计关系等确定地基承载力特征值时,考虑的是对应于基本条件下的值;而在进行地基基础设计时,考虑的是承载力极限状态下的标准组合,即采用荷载设计值。针对这一问题,对水工挡墙在水平力作用下基础土体的破坏模式进行了分析,研究埋深和宽度对地基承载力特征值带来的影响。采用引入基础深度修正系数的方法,使挡土墙地基承载力特征值得以提高。     

叉桩和平联撑在高桩码头中抵抗水平力作用分析

当高桩码头承受较大水平力荷载作用时,码头因位移大而存在安全隐患。为此,研究叉桩和平联撑在高桩码头中抵抗水平力作用大小。运用易工水运工程结构CAD集成软件建立高桩排架空间结构模型,计算分析叉桩排架结构在水平力作用下,码头横梁、桩基的内力和位移大小随叉桩的斜度和转角改变的规律,同时对比叉桩和平联撑在高桩码头中抵抗水平力大小。结果表明:叉桩排架结构抵抗水平力产生的位移作用远大于设置平联撑的排架结构。     

绞吸船在软土地质下横移锚抓地力计算方法

大型绞吸船采用三角宽鳍锚作为横移挖掘的定位锚,针对横移锚在软土地质条件下锚抓力受限的问题,采用土体的极限平衡原理进行横移锚受力分析,建立三角宽鳍横移锚抓地力计算方法。经计算分析,在软土地质条件下,影响横移锚抓地力的主要因素为锚冠入土深度、土楔破坏角和锚杆角度。结果表明,锚冠入土越深,锚抓地力越大;锚杆与水平面夹角越小,锚抓地力越大;随土楔破坏角逐步增加,锚抓地力呈先减小、后变大的趋势;土楔破坏角在20°~25°时,横移锚抓地力最小,锚抓力系数为14左右。     

Static and dynamic loading behavior of a hybrid foundation for offshore wind turbines

Considering the deficiencies of the traditional monopile foundation for offshore wind turbines (OWTs) in severe marine environments, an innovative hybrid foundation is developed in the present study. The hybrid foundation consists of a traditional monopile and a wide–shallow bucket. A series of numerical analyses are conducted to investigate its behavior under the static and dynamic loading, considering various loading eccentricities. A traditional monopile with the same steel volume is used as a benchmark. Although the monopile outperforms the hybrid foundation in terms of the ultimate moment capacity under each loading eccentricity, the latter can achieve superior or the same performance with nearly half of the pile length in the design loading range. Moreover, the horizontal load and moment are mainly resisted by the bucket and the single pile in the hybrid foundation respectively. The failure mechanism of both the hybrid foundation and the monopile is excessive rotation. In the rotation angle of 0.05 rad, the rotation center is located at the depth of approximately 0.6–0.75 times and 0.65–0.75 times the pile length for the hybrid foundation and the monopile respectively. The increasing loading eccentricities can lead to increasing moment bearing capacity, increasing initial stiffness and upward movement of the rotation center of the two foundations, while decreasing load sharing ratio of the single pile in the hybrid foundation. Three scenarios are considered in investigating the dynamic loading behavior of the hybrid foundation. Dynamic response results reveal that addition of the bucket to the foundation can restrain the rotation and lateral displacement effectively. The superiority of the hybrid foundation is more obvious under the combined wave and current loading.     

软土地区PHC管桩垂直度检测与施工控制

PHC管桩具有承载力高、施工速率快、质量易控制等优点,在工程实践中得到了广泛应用。管桩地基的一些技术问题随之逐渐显现,其中较突出的一个问题是软土地区成桩垂直度对竖向承载力的影响。介绍了一种管桩施工后垂直度实用检测工艺,两个工程案例的检测结果显示管桩垂直度偏差的倾斜方向和位移量均差异很大,呈现明显随机性。在此基础上,指出软土地区管桩倾斜的主要原因是沉桩施工操作控制不严,次要原因是沉桩后重型机械行驶导致的挤压作用及相邻管桩的挤土效应。根据大量工程实践经验,分析了软土地区管桩垂直度偏差影响因素,并提出了切实可行的控制措施。     

基于水平钢架的全直桩系缆结构优化设计

与传统斜桩结构相比,全直桩结构完全以自身抗弯能力来承受水平荷载,在相同受力条件下存在桩径大、竖向承载力没有充分发挥、工程投资偏高的特点.针对该问题,提出一种新型含水平钢架的全直桩结构,以某工程系缆墩为例,采用空间模型进行计算分析,确定优化结构方案,并在该结构的桩基中间位置利用水平钢架与桩基进行连接.结果表明,增设水平钢...     

Dynamic impedances and load carrying mechanism for skirted foundations

Dynamic impedances of foundations include dynamic stiffness and damping which have important effect on the internal forces in the structure. In some cases, such as offshore wind turbines, the influence of the foundation impedances on the system's natural frequency and overall damping could potentially have a significant effect on the fatigue life of the structure. The vertical, horizontal and rocking impedances of a skirted foundation (also termed bucket foundation in offshore wind industry) embedded in a fully saturated poroelastic seabed are addressed in this paper. The vertical impedance is most relevant for jacket foundations supported on three or four bucket foundations, while horizontal and rocking impedances are applicable for mono-bucket foundations. The dynamic vibration problems are solved semi-analytically with the help of dual integral equations and Green's functions. Numerical results for dynamic impedances are obtained; damping ratio are also obtained to show the importance of radiation damping for bucket foundations, even at very small excitation frequencies. The influence of length-to-radius ratio, Poisson's ratio, permeability of soil, excitation frequency and thickness-to-radius ratio on the impedances are also studied. Besides, the dynamic load sharing among the top plate, bucket shaft and bucket tip is obtained for vertical load, horizontal load and moment to shed light on the carrying mechanism of bucket foundation at dynamic working loads. It is found that for a rigid bucket foundation, even when the length-to-radius ratio is small (e.g. l/a = 1.0), most of the loads are carried by the shaft, while the top plate and tip of the bucket take only a small portion of the loads. The results of this study will be helpful for understanding the load-carrying mechanism of offshore bucket foundations for normal operation conditions.     

深厚软土地基钢管桩静载试验研究

通过对软土地基中1根桩长52.5 m、桩径1 m的钢管桩的压桩试验、拔桩试验和水平静载试验,探讨软土地基中钢管桩工程性状和分布规律。结果表明:软土地基钢管桩水平静载试验的最大弯矩值在泥面以下2倍桩径处,且不随着荷载的增加而改变;软土地基的水平静载试验,按照按泥面位移10 mm进行位移控制时,其m值可取3 500 kN/m~4;软土地基由于侧阻力较小,压桩试验时,传递至桩底的轴力值与桩顶荷载的比例可达30%,而拔桩时,该值为12%左右。     

裙式吸力基础水平承载力影响因素的数值分析

近年来,吸力基础已在各种悬浮结构、海洋平台锚固装置和离岸风电场工程中得到成功应用.重点研究离岸风电场新型裙式吸力基础的水平承载力,分析设置接触面对结构水平位移的影响、裙式基础的尺寸比变化等因素对水平承载力的影响.数值分析结果表明,通过增加裙式基础的高度能有效提高基础的水平承载力.     

尖子山船闸上闸首软岩复合桩基受力特性

为研究船闸分离式闸首复合桩基的受力特性,以尖子山船闸为依托,建立软岩上边墩复合桩基有限元模型,分析边墩位移、变形特征,提出桩顶力简化算法,研究软岩竖向力分担比ξV的影响因素。结果表明:边墩以刚体位移为主,检修期横向转动、竖轴扭转最大,桩基布置宜外密内疏;由于存在破碎带,ξV仅有11.5%;ξV近似与置换率呈双曲线关系、与软岩模量呈幂函数关系,桩间距越小,置换率越大,软岩模量越大,桩岩系数比越小,ξV越大。破碎带固结灌浆处理后,提高了桩基承载力,还使ξV有效提高到26.8%。     

多功能探头静力触探原位测试在跨海大桥建设中的应用

通过将带有测倾斜度、测孔压功能的静力触探技术应用于跨海大桥地基勘察的工程实例,阐述了海上静探施工的操作重点和多功能静力触探测试成果的应用,并与普通探头测试深度数据、钻探分层和桩基载荷试验成果进行了对比、验证。发现依靠带测倾斜度和孔压的探头对地基土分层和深度的校正均起到很大作用,同时通过将静力触探技术应用于海域勘察,可以更直观地估算桩基承载力,判断地基土的工程地质性质。     

SPAR平台锚固基础的有限元分析

SPAR平台是目前应用较为广泛的深海石油平台形式之一,其基础形式主要有吸力锚和桩基。运用有限元分析软件Plaxis 3D Foundation,采用了Mohr-Coulomb弹塑性本构模型,选取具有代表性的吸力锚和桩基进行三维有限元分析,得到了吸力锚和桩基的极限承载力,讨论了二者承载力特性的区别及各自的适用条件。     

绞吸挖泥船大功率挖岩绞刀的荷载分析*

针对绞吸挖泥船在挖岩施工过程中绞刀荷载难以定量确定的问题,建立刀齿的坐标模型,根据施工参数判定刀齿大圈切削状态,利用单齿切削岩石的荷载模型建立绞刀整体的荷载分析模型,计算绞刀在不同转动速度、横移速度、姿态角度和岩层厚度等工况下的横向力、竖向力、纵向力以及绞刀功率情况,每种工况以正刀和反刀两种姿态进行分析。结果表明,无论正刀还是反刀施工,绞刀的转动速度和横移速度都对绞刀的功率消耗产生正相关影响,绞刀的姿态和泥层切削厚度对绞刀荷载的影响最大。     

考虑变荷载和土体非线性的真空预压竖井地基固结解

针对真空预压竖井地基固结问题,考虑地基土体的非线性、涂抹区土体水平向渗透系数呈抛物线变化和荷载随时间变化的影响,推导出真空预压条件下竖井地基固结的一般解。通过退化研究和对比分析,验证了解析解的合理性。基于一般解,得出瞬间加载和线性加载两种特殊加载模式的相应特解。针对特解,编制计算程序,绘制出真空预压竖井地基固结过程曲线。结果表明,土体非线性对固结特性有较大影响,压缩指数与水平向渗透指数比值越大,地基固结速率越慢;初始应力值越大,土体的固结速率越快;线性加载下竖井地基孔压消散速率较瞬时加载慢。     

饱和软黏土中吸力锚的承载能力数值分析*

利用大型通用有限元软件ABAQUS,基于总应力分析法,建立了饱和软黏土中吸力锚的三维有限元数值模型,通过与物理模型试验对比,验证了数值模型的正确性.计算分析了吸力锚的水平承载力特性及其破坏模式、最优系缆深度上的倾斜承载力包络图.通过对有限元结果进行拟合分析,提出了吸力锚承载能力的简化计算公式,公式中考虑了长径比、加载角度和土体不排水抗剪强度的影响.     

Equivalent linear pseudostatic and dynamic modelling of vertically vibrating monopile

To optimize offshore wind turbine (OWT) design, an engineering tool has been developed allowing for a detailed investigation of the effects of nonlinear soil stiffness and damping on foundation dynamics. We have studied the response of a vertically oscillating offshore wind monopile foundation in a realistic soil profile subjected to loads between 1 and 200 MN in the frequency range 0–10 Hz with pseudo-static and equivalent linear dynamic model. The non-linear soil behaviour is modelled with an equivalent linear method with shear modulus reduction and damping curves as input. The tool is verified and validated by comparison with elasto-dynamic model and experiments. With increasing load amplitudes foundation stiffness increases and damping decreases. For large load amplitudes the lower part of the pile foundation contributes more to foundation damping. The results indicate the nonlinear foundation stiffness and damping can be modelled rationally by combining stiffness and hysteretic damping from nonlinear static tools with apparent mass and radiation damping from elasto-dynamic analysis. The tool can be used to compute soil springs and dampers based on laboratory-based soil stiffness and damping.     

水平荷载下桩身稳定性及土体扰动分析

通过数值模拟,对比基桩试验结果和模拟结果,验证计算模型的适用性。计算不同荷载等级下桩身的内力分布情况和位移变化,分析桩身稳定性;对桩周土体的受力状态进行分析,研究水平荷载对桩周土体的扰动情况。研究结果表明:在受到长期性的横向荷载作用时,桩身会受到持续的剪切作用,应定期进行桩身完整性检测;在水平荷载的作用下,基桩周围的土体会受到剪切和张拉作用。