整体卸荷式板桩挡土结构三维有限元数值模拟分析*

整体卸荷式板桩挡土结构是深厚软土地区高桩码头良好的接岸结构形式,采用有限元数值分析方法得到不同桩排距、后排桩间距和开挖深度条件下该类挡土结构前后排桩受力和变形特征并进行研究。结果表明,增加前后排桩间距可以减小桩基的水平变形,并使前后排桩的桩力分布更加合理;改变后排桩间距使前排桩水平和竖向位移均逐渐增大,前后排桩端部弯矩和剪力都增大;开挖深度的增加使结构水平位移增加。     

The uplift capacity of single-plate helical pile in shallow dense sand including the influence of installation

The helical pile has been used to resist the tension for a long time. However, the prediction of the uplift capacity of helical piles including the influence of installation is still a challenge in design. Based on the change in stress according to Mohr-Coulomb failure criterion, a simple theoretical method has been developed, which can calculate the uplift capacity of shallow pre-embedded circular plate anchors and the uplift capacity of helical piles installed by torque and compression. In order to analyse the influence of installation process of a single-plate helical pile on its uplift capacity and verify the theoretical model, a series of model tests have been conducted in dense saturated sand. The single-plate helical piles with different out diameters of helixes have been installed with different installation speeds, and then, the single-plate helical piles have been moved up monotonically. The test results show that the installation speed and the size of the out diameter of the helix have significant influence on the uplift capacity of the helical piles, and the results of the theoretical method have a good fit with the test results. Using this simple theoretical method, the designer can easily predict the uplift capacities of helical piles, which includes the influence of installation.     

Design of a novel drilled-and-grouted pile in sand for offshore oil&gas structures

New offshore oil and gas exploration has placed renewed emphasis on developing structures in relatively complex geological conditions. Due to the damaging nature of impact driving, traditional steel piles used to support jacket structures, are not ideally suited to specific soil types, such as carbonate sands. Drilled and grouted piles are commonly used to support structures in these soil conditions. This paper describes a novel drilled pile, which has been developed specifically to provide a cost effective installation process while maintaining the benefits of grouted piles. The installation process negates the need for temporary casing in weak soils and minimizes the number of offshore operations. In this paper, the installation methodology and post-installation performance of a large scale onshore field trial is described. The installation process was successfully demonstrated with a 1.9 m diameter test pile installed in fine sand to 17.7 m depth in under 3 h. The performance of the pile, as measured in a tension static load test, was shown to compare favorably with existing pile design methods.     

采用X形桩的遮帘式板桩码头结构静力分析

X形桩是一种反拱曲面异型桩,相比于同等截面积的矩形桩和圆形桩,X形桩具有更大的截面周长和惯性矩,受力性能更好。结合京唐港32#泊位遮帘式板桩码头结构,以X形桩代替传统的矩形桩,研究其对结构静力的影响。结果表明:相同桩间中心距时,以X形桩替代后可减小前墙弯矩;在同等桩间净距1.75 m下,两类模型的前墙最大弯矩基本相同。相同荷载作用下,前墙位移主要受桩间中心距影响,X形桩形状影响效应很小;锚碇墙水平位移受桩间中心距和遮帘桩形状的影响均很小。桩间中心距、净距与桩间土体土拱效应直接相关,对前墙弯矩、土压力、遮帘桩弯矩等有显著影响。桩间中心距为4.05 m或桩间净距为1.75 m时,结构内力改善效果较优,可采用该间距的X形桩替代矩形桩,节约工程造价。     

钢管桩桩头剪力键间距优化设计

在码头和深海工程中常采用剪力键连接钢管桩与上部结构,以提高钢管桩的承载力及结构整体性。剪力键的间距是影响钢管桩桩头受力性能的重要影响因素。以桩头带两个剪力键的钢管桩为研究对象,建立8组有限元模型,利用Gebman试验报告中的试验值与数模值进行对比。结果表明:1)试验值与数模值误差较小,且变化趋势一致。2)钢管桩承载力和钢管桩桩头复合刚度随着剪力键间距的增大先增加后减小,剪力键间距介于1. 0D～1. 2D时,钢管桩整体受力性能最好。3)剪力键的最优设计间距始终在1. 0D附近,随着桩径的增加,剪力键的最优设计间距可适当减小。其研究成果为实际工程中钢管桩桩头剪力键的设计提供了重要的参考。     

Simulation of torpedo anchor set-up

Torpedo anchors are used for station keeping of floating offshore platforms and fixing risers to the seabed in deep water. Their main benefit over other anchors is reduction in anchor installation cost via free falling in the water. A torpedo anchor has a steel cylindrical shaft with a conical tip and is ballasted in order to deepen the soil penetration and increase the anchor holding capacity. In order to address the installation effects on the soil strength and consequently the anchor pull-out capacity, first reconsolidation (set-up) of soil next to the anchor after installation is studied by a finite-element (FE) analysis of coupled deformation and fluid flow in porous media. The results of the set-up analysis indicate the rate of dissipation of excess pore-water pressure and soil-strength recovery. These are important considerations in predicting the anchor pull-out capacity at different times after installation. In the absence of a documented complete set of installation and set-up tests, the results are validated qualitatively using available albeit limited field test data.     

异型群桩水流载荷遮掩效应受力分析

中马友谊大桥采用群桩基础，洋流经过群桩时会产生纵向和横向位移。为了探索异型群桩水流载荷计算方法，通过单向水槽模型试验测量单桩、双桩水流载荷，提出异型群桩水流载荷公式，并结合群桩水流载荷试验结果验证计算公式的合理性。结果表明，并列双桩水流载荷随着桩心距增加而减小，桩心距大于5D时，双桩之间干扰效应消失；串联双桩中后桩水流载荷随着桩心距增加而增加，桩心距大于20D时，双桩之间遮掩效应减弱；随着流向角增加，后桩受到的水流载荷呈正弦分布，且随着桩心距变化出现不同趋势。     

振冲碎石桩与CFG桩组合桩型复合地基试验研究

振冲碎石桩主要加固浅层地基,与桩间土构成复合地基,使地基承载力提高、变形减少,并可消除砂土层的液化;CFG桩布置在4根碎石桩的形心,桩端置于相对硬层,对复合地基的承载力和变形起控制作用。对某工程试验区振冲碎石桩与CFG桩组合桩型复合地基加固前后静力触探、动力触探和静载荷试验等进行研究,结果表明组合桩型复合地基中的碎石桩较大程度地提高了CFG桩的单桩承载力和地基承载力,桩距越小,加固效果越好。     

遮帘式板桩码头的遮帘效果及其影响因素分析

为使遮帘桩达到更好的遮帘效果,需要对相关的影响因素进行分析,如遮帘桩与前墙的距离(桩墙间距)、遮帘桩之间的间距(桩间距)。结合工程实例,建立了有限元分析模型,通过计算前墙所受土压力及弯矩,分析了遮帘桩的遮帘效果。进一步利用有限元法分析了桩墙间距与桩间距对遮帘效果的影响。结果表明:当桩墙间距增大时土压力增大,而土压力的增幅减小;桩间距存在临界值,当桩间距小于临界值时土压力的变化很小,当桩间距超过临界值时土压力变化明显。     

组合式深水施工平台设计与施工

为解决码头陡坡裸岩区域的稳桩问题,开展了深水平台稳桩工艺研究,通过理论计算和实践解决了平台结构设计、稳桩临时加固以及稳桩施工中的定位、提升、稳固、沉桩等技术问题,为同类型地质条件的稳桩工艺提供参考依据。     

基于桩间距计算的梯形抗滑桩桩侧角取值

梯形断面竖向预应力锚索抗滑桩是治理水毁滑坡的一种新型抗滑桩结构,桩间土拱特征区别于常规抗滑桩,仍然利用传统抗滑桩土拱受力模型显然不合理。对桩间土拱的形成特征进行了分析,建立了梯形抗滑桩的计算模型,分别推导不同形式的桩间距计算公式,并通过工程应用对比各算法的桩间距;同时,基于桩间距计算的基础,分析桩侧角对桩间距的影响,界定桩侧角的设计取值范围,并探讨较佳角度的取值,为同类工程提供理论参考。     

预制桩承载力时效的人工神经网络预测

分析预制桩单桩承载力时间效应的机理，说明其主要与桩长、桩截面积、土体摩擦角、渗透系数、弹性模量、休止期6个参数有关，建立了考虑时间效应的预测单桩承载力的误差反馈型神经网络模型。该模型充分考虑了桩周土固结对桩承载力的影响，输入层神经元为以上6个参数，物理意义明确且容易确定；训练模式采用共轭梯度法。对34根桩的计算表明该模型预测结果与实测值吻合，说明其是科学有效的。     

海外深水板桩码头连锁式混凝土钻孔排桩施工技术

以巴基斯坦卡拉奇深水港集装箱码头工程为例,对大直径连锁混凝土钻孔排桩在少（无）软质覆盖层海域施工平台的布设,带锁扣钢护筒加工,连锁护筒精确定位、沉设,岩质地层钻孔旋挖,超长、超大直径、超重钢筋笼整体安装等关键施工技术进行阐述,可为同类型板桩码头项目施工提供参考和借鉴。     

桩侧及桩端后注浆对超长桩承载力的影响

以海南省某跨海大桥为工程背景,采用平行对比试验法,以桩侧桩端后注浆及施工桩长为变量,对3根超长灌注桩进行了竖向抗压静载试验,并对试验过程中试桩穿越各土层的分段侧摩阻力及桩端阻力进行测试。通过比对试验结果,分析桩侧桩端后注浆对超长灌注桩承载力性状、荷载传递规律及桩侧、桩端阻力发挥特性的影响。结果表明:进行桩侧、桩端后注浆能显著提高超长灌注桩的承载能力,减小桩基沉降;对于超长灌注桩,桩侧注浆对承载能力的增加效果远远大于桩端注浆;桩侧桩端注浆后,超长桩的荷载传递规律不变,依然是上部侧阻力先于下部侧阻力激发;桩侧注浆处土体表现出与桩体水泥胶结的性质,其抗剪强度较大且随位移增长而增加得更快。     

螺旋钢桩抗拔特性的现场试验研究

根据螺旋钢桩现场抗拔试验中61根试验桩的监测数据绘制Q—S曲线,推算各类桩型的平均极限承载力,分析桩长、叶片数量、叶片间距、首层叶片埋深、叶片直径等参数对螺旋钢桩极限抗拔承载力的影响,试验结果表明螺旋钢桩的极限抗拔承载力随桩长和叶片直径而增加,叶片间距和首层叶片的埋深均存在临界点。分别通过慢速加载法和快速拉拔法测试螺旋钢桩桩极限抗拔承载力,快速拉拔法测得的极限承载力平均值约为慢速加载法极限承载力的2．0倍。     

劲芯搅拌桩的试验研究

劲芯搅拌桩是由搅拌桩和钢筋混凝土芯桩组合而成的新型桩,具有高承载力、低造价、施工便捷等优点,为掌握其荷载传递机理和承载力影响因素,进行了19根桩的荷载试验,包括11根劲芯水泥搅拌桩、4根钻孔灌注桩及4根水泥搅拌桩;并对劲芯搅拌桩进行了有限元分析。研究表明:芯桩对劲芯搅拌桩的荷载传递起关键作用,提高了劲芯搅拌桩的承载力;劲芯搅拌桩的承载力高于水泥搅拌桩和钻孔灌注桩;芯桩的长度、体积含芯率、面积含芯率存在一个最优值;水泥土的固化效应、芯桩的挤土效应和芯桩的荷载传递是劲芯搅拌桩高承载力的主要来源。     

双排桩支护结构在港区护岸工程中的应用

介绍双排桩支护结构应用与瑞安市东山埠渔港下埠港区护岸工程实例,该结构有效地避免基坑开挖对周边建筑物影响。对桩长、排距、粘聚力、内摩擦角及地面荷载等主要设计参数进行阐述,并采用理正深基坑支护计算软件对结构进行稳定性验算,结果表明各指标均满足规范要求。     

在役码头桩基承载力静载试验

传统在役码头的桩基承载力检测需拆除上部结构,使得检测工作量大且工期较长。以某旧码头桩基检测工程为依托,阐述在保持上部结构完整的情况下,快速准确检测桩基承载力的方法。首先通过数值模拟分析上部结构与桩基荷载分担比例,初步确定试验堆载量。同时在码头下部的桩头安装传感器,加载过程中能较精确的测得桩顶的实际荷载。用该方法顺利地对该码头2根桩承载力进行检测,取得了较好的效果。     

曹妃甸30万吨级原油码头超重型钢管桩沉桩施工

曹妃甸30万吨级原油码头桩基采用直径1.8 m钢管桩,桩长64.5～77 m,桩重81.37～94.51 t,桩重为目前国内之最.文章论述了打桩锤、打桩船的选择和打桩锤、打桩船的技术性能;钢管桩节点的布置及受力计算;以及沉桩施工步骤.经优化的沉桩工艺,使超长、超重钢管桩顺利施打完毕,施工质量达到优良水平.     

Parametric study on the effects of pile inclination angle on the response of batter piles in offshore jacket platforms

Offshore jacket-type platforms are attached to the seabed by long batter piles. In this paper, results from a finite element analysis, verified against experimental data, are used to study the effect of the pile’s inclination angle, and its interaction with the geometrical properties of the pile and the geotechnical characteristics of the surrounding soil on the behavior of the inclined piles supporting the jacket platforms. Results show that the inclination angle is one of the main parameters affecting the behavior of an offshore pile. We investigated the effect of the inclination angle on the maximum von Mises stress, maximum von Mises elastic strain, maximum displacement vector sum, maximum displacement in the horizontal direction, and maximum displacement in the vertical direction. The pile seems to have an operationally optimal degree of inclination of approximately 5°. By exceeding this value, the instability in the surrounding soil under applied loads grows extensively in all the geotechnical properties considered. Cohesive soils tend to display poorer results compared to grained soils.