利用等效墩法估算抗拔群桩基础的变形

根据荷载传递理论,提出了一个计算抗拔单桩位移的十分有效的迭代算法及预测抗拔群桩变形的简化分析方法。根据等效墩原理,将抗拔群桩基础简化为单一的墩基础,从而可以将单桩变形研究成果应用于群桩变形分析中。通过与现场试验结果进行比较表明,该方法不但可以大大节省抗拔群桩变形的计算时间,而且计算结果与实测结果也较为相符。     

基于模型试验的静压群桩引起的土体变形分析

以往对沉桩挤土效应的研究主要集中于单桩或双桩,对群桩挤土效应分析较少。基于室内模型试验,分析了群桩压入软土后土体的变形情况,得到了沉桩过程中及压桩后土体侧向位移、竖向变形和土层表面隆起变化的规律。认识到单桩侧向挤土位移随着距桩边距离的增加而以近似对数规律衰减,群桩压入后土体水平侧移和地表隆起是不断累积的,存在着已压入桩的遮帘作用,而且桩施工顺序对土体位移起到了关键作用,应该在实际工程中得到重视。     

群桩效应有限元分析

利用有限元方法,对竖向荷载作用下复合桩基的群桩效应进行了计算分析,讨论了桩长L、桩距与桩径之比Sa/d、桩数n、土类等对群桩效应及群桩效应系数η的影响。结果表明：复合桩基中各个基桩的极限承载力Qu及η随L增大而增大;当Sa/d小于某个数值时,Qu,η随Sa/d增大而增大;当Sa/d大于某个数值时,Qu,η随Sa/d增大而减小。群桩效应及η与土类有关;η存在极大值,随n增多而减小,但减幅不大。     

一种确定导管架平台群桩p-y数据的方法

导管架海洋平台群桩基础的桩头约束是一种弹性约束。针对具有弹性约束桩头的群桩,提出了一种利用非线性地基梁群桩模型,通过迭代计算确定导管架平台群桩p-y数据的方法。该方法首先依据单桩p-y曲线,利用具有弹性约束桩头的群桩模型,计算桩头在总荷载作用下的水平位移;再利用Poulos相互作用系数确定由于群桩相互作用引起的桩头附加水平位移,将总荷载作用下的桩头水平位移与桩头附加水平位移叠加后的结果作为迭代计算的初始桩头水平位移。然后,依据桩头荷载与初始桩头水平位移,通过对单桩p-y数据的标定,确定其修正系数Ym,进而得到与第1次计算对应的群桩p-y数据。在接下来的迭代计算中,利用每次更新后的Ym确定该次计算使用的群桩p-y数据,并据此由群桩计算模型计算桩头位移,通过对单桩p-y数据标定确定相应的Ym,直到第i次与第i-1次计算出的Ym(i)和Ym(i-1)之间相对误差小于允许误差为止。由于该方法考虑群桩效应的p-y数据,且借助具有弹性约束桩头的群桩模型进行分析,从而使计算结果能客观反映具有弹性约束桩头群桩之间的相互作用与变形特性。     

嵌岩桩承载变形特性的数值分析

嵌岩桩的单桩极限承载力高,现场试桩试验加载至极限状态代价和难度均较大,试验取得的数据较难全面反映嵌岩桩的承载变形特性。基于武汉绿地中心嵌岩桩试桩试验成果,采用ABAQUS有限元软件建立桩-土-岩共同作用模型,分析了基岩岩性、嵌岩深径比以及上覆土层厚度等对嵌岩桩承载变形特性的影响。数值计算表明,基于合理的本构模型、合理地参数取值,采用有限元方法对嵌岩桩试桩试验开展模拟分析,可以取得较为合理的拟合结果。基岩岩性、嵌岩深径比、上覆土层厚度对嵌岩桩的承载变形特性均有较大的影响。基岩岩性和嵌岩深度对上覆土层段侧摩阻力的发挥影响不大。嵌岩段的承载力是嵌岩桩总承载力的主要组成部分,但对穿越深厚上覆土层的嵌岩桩,上覆土层段桩侧摩阻力是嵌岩桩总承载力的重要组成部分,不应忽视。     

A modulus‐multiplier approach for non‐linear analysis of laterally loaded pile groups

A modulus‐multiplier approach, which applies a reduction factor to the modulus of single pile p–y curves to account for the group effect, is presented for analysing the response of each individual pile in a laterally loaded pile group with any geometric arrangement based on non‐linear pile–soil–pile interaction. The pile–soil–pile interaction is conducted using a 3D non‐linear finite element approach. The interaction effect between piles under various loading directions is investigated in this paper. Group effects can be neglected at a pile spacing of 9 times the pile diameter for piles along the direction of the lateral load and at a pile spacing of 6 times the pile diameter for piles normal to the direction of loading. The modulus multipliers for a pair of piles are developed as a function of pile spacing for departure angle of 0, 90, and 180sup>/sup> with respect to the loading direction. The procedure proposed for computing the response of any individual pile within a pile group is verified using two well‐documented full‐scale pile load tests. Copyright © 2006 John Wiley & Sons, Ltd.     

层状土中群桩非线性沉降的摄动分析

采用包含一个内变量的连续化St Venant模型,即连续的Masing-Iwan模型,模拟桩-土界面扰动区土体的非线性行为。基于两种分析单桩的荷载传递模型,假设桩-土-桩相互作用为弹性且服从叠加原理,推导出了适用于群桩中基桩的两种荷载传递新模型。采用荷载传递法建立了单桩和群桩的非线性控制方程,提出了近似求解该控制方程的摄动分析法,得出了单桩和群桩的荷载沉降和轴力分布方程。所得结果表明,在低荷载水平下严格趋近于弹性解;而在高荷载水平下,能够反映直到破坏阶段的桩的荷载-沉降特性。通过一个现场试验的理论预测结果与实测数据的对比分析,验证了方法的有效性和适用性。     

基于相互作用系数探讨的群桩简化分析

相互作用系数法是群桩分析的一种有效的数值计算方法,该方法关键在于确定群桩的相互作用系数。传统的弹性分析方法所得的相互作用系数值偏大,计算结果与实测值差距不小;采用考虑土体弹塑性特征和桩土界面接触的三维有限元方法计算相互作用系数可以有效减少弹性方法的计算偏差,在此基础上推导了高承台群桩的简化分析方法。根据ABAQUS平台进行了大量三维有限元计算,分析了荷载水平、桩土模量比、桩距径比和桩长桩径比对相互作用系数的影响;比较了不同方法下相互作用系数的变化规律。通过有限元方法确定的相互作用系数对两群桩工程实例进行分析,计算结果表明该方法最接近于实测结果。     

基于差异沉降和轴向刚度控制的竖向荷载作用下群桩基础优化分析

目前在群桩设计中仍大多数采用均匀等长布桩的方法,这种方法在基础受力、变形等方面存在较大的缺陷。考虑增大群桩轴向刚度和减小群桩基础差异沉降的条件下,将群桩基础位移函数与桩长优化函数相结合,在对基础采取行变换、平面变换的方式下,通过设置不同的桩长比值ξ、连接曲率值η设定不同布桩方案,分析不同方案下群桩基础轴向刚度比、差异沉降比的变化规律;并利用数值模拟法对所得优化结果的可靠性进行验证。此外,针对不同桩土刚度比、不同桩间距对群桩基础的轴向刚度比和差异沉降比进行了参数分析。研究结果表明：不同群桩基础优化变换方式、不同桩长对群桩基础优化结果会产生不同的影响;当优化目的是为增加群桩基础刚度时,应主要考虑行变换的优化方式,当优化目的是为减小基础差异沉降时,应主要考虑平面变换的优化方式;基础轴向刚度比随着桩土刚度比的增加而增大,随着桩间距的减小而增大;基础差异沉降比随着桩土刚度比的增加而减小,随着桩间距的减小而减小。     

A method for the analysis of large vertically loaded pile groups

An iterative method is described for the analysis of vertically loaded pile groups with a large number of vertical piles. The individual pile response is modelled using load-transfer (t–z) curves while pile–soil–pile interaction is determined using Mindlin's solution. The present method not only keeps all the advantages of the so-called ‘hybrid method’, but also makes it possible for practising engineers to solve problems of large non-uniformly arranged pile groups in a time-saving way using a personal computer. Good agreement between the present method of analysis and the direct method is observed. A case history is analysed and the computed response of a large pile group compares favourably with the field measurement. Copyright © 1999 John Wiley & Sons, Ltd.     

水平荷载作用下群桩相互作用的弹塑性数值分析

本文利用三维弹塑性有限元法对水平荷载作用下群桩基础特性进行了分析,讨论了群桩基础水平荷载作用下的承载性状和破坏机理,并探讨了桩距、桩数、桩长、桩径和土质各种因素对群桩效应的影响,指出桩距和桩数是影响群桩效应的主要因素.     

群桩荷载位移特性研究

将杆系结构有限单元法与荷载传递迭代法相耦合,形成一桩基沉降分析计算的混合法。采用近似解析解中Randolph and Wroth’Model与双曲线模型相结合,模拟桩身与桩周介质边界上剪切滑移的非线性。桩间相互作用在采用弹性理论Mindlin方程解答计算,并考虑了桩间“加筋与遮帘”作用。桩周土介质非均质性特征,采用指数函数模拟。分析了刚性承台下群桩桩数、桩长、桩间距和桩土模量比等群桩工作特性的影响。尤其是桩台基础沉降对群桩相互作用影响机制的研究,对桥梁拼接等对桩基础沉降要求严格的工程有重要的借鉴意义。     

Vertical loads effect on the lateral pile group resistance in sand

Vertical loads effect on the lateral response of a 3×5 pile group embedded in sand is studied through a two-dimensional finite element analysis. The soil-pile interaction in three-dimensional type is idealized in the two-dimensional analysis using soil-pile interaction springs with a hysteretic nonlinear load displacement relationship. Vertical loads inducing a vertical pile head displacement of 0.1-pile diameter increase the lateral resistance of the single pile at a 60 mm lateral deflection by 8%. Vertical loads inducing the same vertical displacement applied to a pile group spaced at 3.92-pile diameter increase the overall lateral resistance by 9%. The effect on individual piles, however, depends on the pile position. The vertical load decreases the lateral resistance of the leading pile (pile 1) by 10% and increases the lateral resistances of piles 2, 3, 4, and 5 by 9%, 14%, 17%, and 35%, respectively. Vertical loads applied to the pile group increase the confining pressures in the sand deposit confined by the piles but the rate of increase in those outside the group is relatively small, resulting in the difference in a balance of lateral soil pressures acting at the back of and in front of the individual pile.     

隧道盾构施工引起邻近建筑物及其桩基变形的数值分析

以天津地铁2号线隧道盾构施工为背景,取沿盾构轴线右侧一6层框架居民楼为研究对象,基于ABAQUS软件,建立了隧道和邻近建筑物及其桩基的计算模型,分析盾构施工对邻近建筑物及其桩基础变形的影响。结果表明,隧道盾构施工导致地表沉降,引起框架结构及其桩基变形,框架整体向隧道盾构一侧倾斜。其中框架梁靠近中柱一端沉降较大,而框架中柱及其桩基也较两侧边柱及其桩基的沉降大。同时表明,盾构施工对邻近建筑物及地下桩基变形产生的影响是整体相关的,在隧道盾构施工时应引起相关设计与施工部门的注意。     

Analysis of piled raft with nodular pile subjected to vertical load using a Winkler model approach

An investigation is made to present analytical solutions provided by a Winkler model approach for analysis of piled rafts with nodular pile subjected to vertical loads in nonhomogeneous soils. The vertical stiffness coefficient along a piled raft with the nodular pile in nonhomogeneous soils is derived from the displacement given by the Mindlin solution for elastic continuum analysis. The vertical stiffness coefficients for the bases of the raft and the nodular part in the nodular pile in a soil are expressed by the Muki solution for the 3‐D elastic analysis. The relationship between settlement and vertical load on the pile base is presented considering the Mindlin solution and the equivalent thickness in the equivalent elastic method. The interaction factor between the shaft of the nodular pile and the soil is expressed taking into account the Mindlin solution and the equivalent elastic modulus. The relationship between settlement and vertical load for a piled raft with the nodular pile in nonhomogeneous soils is obtained by using the recurrence equation of influence factors of the pile for each layer. The percentage of each load carried by both nodular pile and raft subjected to vertical load is represented through the vertical influence factors proposed here. Comparison of the results calculated by the present method for piled rafts with nodular piles in nonhomogeneous soils has shown good agreement with those obtained from the finite element method and a field test. Copyright © 2016 John Wiley & Sons, Ltd.     

悬臂排桩支护结构空间变形分析

以矩形基坑悬臂排桩支护结构为研究对象,通过分析现场实测数据和数值计算,归纳出了冠梁和支护桩的空间变形模式,建立了整个支护系统的能量表达式。利用最小势能原理,推导了基坑中部桩顶最大位移的解析解,分析了各主要支护参数对该位移的影响。研究结果表明,桩顶最大位移随坡顶超载和桩间距的增大基本呈线性增大趋势;当嵌固深度系数逐渐增大时,桩顶最大位移也逐渐增大,但趋势渐缓;基坑长度对其影响也较大,当基坑长度超过一定数值后,最大位移值趋于稳定。最后利用所得的研究成果对某基坑进行了验证,并与现场实测结果进行了对比,计算结果能够满足工程要求。     

螺旋群桩基础承载性状试验研究

根据螺旋群桩现场静载试验结果,分析了螺旋群桩基础承载性状的影响因素,讨论了极限荷载下群桩几何参数对螺旋群桩的桩端阻力和桩侧摩阻力的影响。结果表明,螺旋群桩承载性状受到相邻桩的叶片距离以及首层叶片到承台底面间的桩长度影响明显。在叶片桩距比（桩间距比叶片直径）小于2时,螺旋群桩静载试验的荷载-位移曲线呈缓变形,无明显的拐点,群桩破坏属于整体破坏。同时,螺旋桩的叶片有助于减小承台下桩间土变形活动区的高度,增强了桩-土-承台的相互作用,减小了群桩基础沉降量。     

基于最小势能原理的桩锚支护结构空间变形分析

以矩形基坑桩锚支护结构为研究对象,通过分析现场实测数据和数值分析结果,归纳出了冠梁和支护桩的空间变形模式,进而建立了整个支护系统的能量表达式。利用最小势能原理,推导了支护桩桩顶最大位移的解析解,并分析了各主要支护参数对该位移的影响。研究结果表明：桩顶最大位移随着坡顶超载和桩间距的增大而线性增大,但随着锚杆刚度的增大而减小;当基坑深度系数逐渐增大时,桩顶最大位移也逐渐增大,但趋势渐缓;基坑长度对桩顶最大位移的影响也较大,但当其超过临界长度后,桩顶最大位移逼近最大值;同样,锚杆安设也具有临界高度,当处于该位置时,桩顶最大位移达到最小值。最后,利用上述研究成果对广州太平广场花园基坑进行了验证,并与现场监测结果作了对比,计算结果能够满足工程要求。     

Numerical study of group effects for pile groups in sands

The OpenSees finite element framework was used to simulate the response of 3×3 and 4×3 pile groups founded in loose and medium dense sands. Several numerical static pushover tests were conducted to investigate the interaction effects for pile groups. The results were then compared with those from centrifuge study. It is shown that our simulations can predict the behaviour of pile groups with good accuracy. Special attention was given to the three dimensional distribution of bending moment. It was found that bending moment develops in the plane perpendicular to the loading direction. In addition, bending moment data from simulations was used to derive p–y curves for individual piles, which were used to illustrate different behaviour of individual piles in the same group. Copyright © 2003 John Wiley & Sons, Ltd.     

非均匀地基中倾斜桩基竖向承载特性模拟试验研究

群桩基础中设计的倾斜桩基以其横向阻抗能力强等优势在港口、码头以及桥梁基础中得到了较为广泛应用。随着山区及不均匀地基土地区高速公路等基础设施的建设,在滑坡、斜坡变形体和不均匀地基上设计倾斜群桩桥梁基础的情况将会越来越多。由于倾斜桩基受力状态的复杂性,目前倾斜桩基础设计仍参考竖向桩基承载力计算理论,凭借经验进行设计。对此人们虽然做了许多探索,但仍未形成完善的设计计算理论和标准。为此,结合厦深客运专线某特大桥桩基选型研究项目,利用相似材料物理模拟试验,就倾角为0°～12°周边斜桩的群桩基础竖向承载力进行了试验研究。结果表明,竖直桩基的荷载-沉降曲线呈缓变型,倾斜桩基则呈陡降型;就倾斜群桩基础竖向承载力而言,倾斜基桩的合理倾角为8°左右;竖直桩基中角桩轴力最大,边桩轴力次之,中桩轴力最小,倾斜桩基中的中桩轴力最大,角桩轴力次之,边桩轴力最小;倾斜桩基桩身弯矩分布形式与基桩的倾角有关,当倾角达到12°时,桩身将出现反向弯曲段。基桩倾角的不同是导致倾斜桩基和竖直桩基竖向承载特性显著不同的主要原因之一。