海岸带特殊地质条件下双排钢板桩适用性案例分析

双排钢板桩结构是由两排钢板桩、桩间土和拉杆组成的挡土、止水复合结构,由于其较土石围堤占地面积小、施工速度快,较钢板桩整体性好,抗地震和波浪等动力稳定性好,在水利、水运、海岸工程中广泛应用。但由于钢板桩受地质条件影响较大,其使用效果和投入成本不尽相同。本文重点搜集和调查了国内外海岸带工程中使用双排钢板桩的工程案例,分别针对岩溶发育的岩性地基,高渗透性的砂性地基和深厚淤泥质软土地基对双排钢板桩的性能影响和设计约束进行分析。结合原有地质条件和设计资料,采用有限元软件补充计算分析,分析研究在各种不同类型的工程地质条件和水文条件下双排钢板桩的应用效果,总结双排钢板桩在海岸带不同工程地质条件下的适用性。发现在岩溶发育地层施工双排钢板桩需要防止打桩造成垂直度差和岩溶连通性带来的渗漏问题;在砂土地层需要防止钢板桩倾斜变形造成锁扣止水性能劣化,进而导致渗漏水甚至出现流砂;在淤泥地层施工时打入桩施工和桩身止水性能都能得到保证,但可能发生较大桩身整体变形,同时应考虑内侧坑底加固以避免踢脚稳定性破坏。本文的研究对发展海岸带生态工程地质和沿海韧性水工建筑物具有工程指导价值。     

预制静压桩静动载现场试验分析

原位试验是获取桩基设计参数和了解桩基力学性能的最客观、最可靠方法。基于现有疲劳机和千斤顶等试验设备,研制了桩顶静载和动载组合加载装置,为现场静、动载试验解决了一个技术性难题。利用该装置对某工程混凝土预制静压桩进行了模拟交通荷载的现场静、动载试验。通过单桩竖向抗压静载试验和动载试验,分析了静动载对桩身轴力分布、桩身侧摩阻力和基桩沉降的影响及其变化规律。试验结果表明：在静动载作用下桩身侧摩阻力的分布规律基本一致,并且随着振动次数的增加,桩身上部侧摩阻力减小、下部略有增加,但动载循环超过30万次后,侧摩阻力趋于稳定。     

Lateral dynamic response of a pipe pile in saturated soil layer

This paper presents an analytical solution for the lateral dynamic response of a pipe pile in a saturated soil layer. The wave propagations in the saturated soil and the pipe pile are simulated by Biot's three‐dimensional poroelastic theory and one‐dimensional elastic theory, respectively. The governing equations of soil are solved directly without introducing potential functions. The displacement response and dynamic impedances of the pipe pile are obtained based on the continuous conditions between the pipe pile and both the outer and inner soil. A comparison with an existing solution is performed to verify the proposed solution. Selected numerical results for the lateral dynamic responses and impedances of the pipe pile are presented to reveal the lateral vibration characteristics of the pile‐soil system. Copyright © 2015 John Wiley & Sons, Ltd.     

Beam–solid contact formulation for finite element analysis of pile–soil interaction with arbitrary discretization

This paper presents an embedded beam formulation for discretization independent finite element (FE) analyses of interactions between pile foundations or rock anchors and the surrounding soil in geotechnical and tunneling engineering. Piles are represented by means of finite beam elements embedded within FEs for the soil represented by 3D solid elements. The proposed formulation allows consideration of piles and pile groups with arbitrary orientation independently from the FE discretization of the surrounding soil. The interface behavior between piles and the surrounding soil is represented numerically by means of a contact formulation considering skin friction as well as pile tip resistance. The pile–soil interaction along the pile skin is considered by means of a 3D frictional point‐to‐point contact formulation using the integration points of the beam elements and reference points arbitrarily located within the solid elements as control points. The ability of the proposed embedded pile model to represent groups of piles objected to combined axial and shear loading and their interactions with the surrounding soil is demonstrated by selected benchmark examples. The pile model is applied to the numerical simulation of shield driven tunnel construction in the vicinity of an existing building resting upon pile foundation to demonstrate the performance of the proposed model in complex simulation environments. Copyright © 2014 John Wiley & Sons, Ltd.     

Dynamic analysis of piles and pile groups embedded in non-homogeneous soils

A hybrid boundary element formulation for the steady state analysis of piles and pile groups embedded in a soil stratum in which the modulus increases linearly with depth is presented. The piles are represented by compressible columns or flexible beams and the soil as a hysteretic, layered medium. The explicit Green's function corresponding to dynamic loads in the interior of a layered stratum, developed earlier by Kausel is used in the study. The governing differential equations for the pile domain are solved for a distributed periodic loading intensity and those for the soil domain by a system of boundary elements at the pile-soil interface. These are then assembled into a system of algebraic equations by satisfying interface equilibrium and compatibility. The results of the analysis have been compared against those from alternative formulations, e.g. finite elements, and confirm the accuracy of the proposed formulation. Representative results for single piles and pile groups are presented.     

Non-linear soil–structure interaction in disconnected piled raft foundations

Disconnected piled raft foundations are characterised by no structural connection between the upper raft and the underlying piles, mostly playing the role of settlement-reducers. The resulting raft–pile gap is usually filled with a granular interlayer, through which the loads from the superstructure are transferred to the piles.In this paper, the complex interaction mechanisms involving the foundational components (raft, piles and soil) are numerically investigated by means of 3D finite elements analyses, accounting for soil non-linearity. The main features of the soil–structure interaction mechanisms under purely vertical external loads are explored over a realistic range of raft–soil gaps for different pile configurations, in which the number of piles – i.e. their spacing – is varied. Special attention is also devoted to the structural response of the piles in terms of axial and bending internal stress resultants. In particular, while disconnection beneficially affects the structural pile response, increasing the raft–pile gap tends to reduce the overall settlement/stiffness efficiencies.The numerical results being presented are in substantial agreement with the outcomes from literature small-scale experiments and suggest a number of relevant theoretical inferences.     

刚性桩复合地基沉降计算的简化方法

既简便又具有较好精度的刚性桩复合地基沉降计算方法仍是工程实践中迫切需要而又有待于解决的问题,文中提出了一个解决的简化方法。在刚性桩复合地基中,由于桩间土荷载水平不高,将桩间土荷载-沉降曲线近似为线性。当桩的荷载水平不高时,对桩的沉降可按线性考虑,线性关系可按线弹性方程计算得到。若桩可能进入非线性甚至塑性,则假设桩的荷载-沉降曲线满足双曲线规律,可较好地考虑桩的非线性沉降过程。通过计算单桩承载力特征值下的沉降,然后通过双曲线方程特点得到桩的非线性沉降方程。对于有单桩静载试验的情况,提出直接利用单桩试验曲线建立单桩的双曲线方程。最后依据共同作用时桩和桩间土的变形协调条件和静力平衡方程,即可计算其实际基础下复合地基的沉降,从而得到一个刚性桩复合地基沉降计算的简化方法。工程实例表明,简化是方法既简便又具有较好的精度,可为工程实践提供一个有效实用的计算方法。     

群桩基础引发饱和地基振动的近似解析解

建立了饱和半空间-群桩基础耦合动力近似解析模型,其中基桩考虑为欧拉梁,饱和地基采用Biot两相介质动力控制方程,二者在频率-波数域中利用桩-土相互作用点处的饱和地基柔度矩阵进行耦合,并采用快速傅里叶逆变换获得频域解答。分析了饱和地基中群桩基础的动力阻抗及刚性承台上施加简谐振动荷载时群桩基础引起的饱和地基振动响应。研究结果表明,荷载类型、激振频率以及地基渗透系数对饱和地基位移和孔压响应有明显影响。特别的,群桩基础动力阻抗峰值频率会随着地基渗透系数的增加而增大。     

Impedance Functions of Slab Foundations with Rigid Piles

The earthquake resistant design of structures depends upon the soil-structure interaction during seismic excitation. The dynamic behavior of surface foundations and deep foundations has been investigated by several authors (Gazetas in Soil Dyn Earthq Eng 2(1):2–42, 1983; Pecker in Dynamique des sols. Presses de l’Ecole Nationale des Ponts et Chaussées, Paris, 1984; Sieffert and Cevaer in Manuel des fonctions d’impédance. Ouest-Editions, Nantes, 1992, etc.) but the dynamic behavior of pile-reinforced soils has not been sufficiently studied yet. The design of pile-reinforced soils comprises the design of the rigid piles and the design of the earth-platform. The foundation system studied in this article consists of an earth-platform over a soft ground reinforced by deep piles. In order to understand the dynamic behavior of a rigid pile, a series of dynamic tests is conducted on an experimental site. The vertical and horizontal impedances of the slab foundation are obtained with and without rigid piles. The numerical models are developed to interpret these dynamic tests. The numerical and experimental impedance functions are compared in both the vertical and the horizontal directions. A sensitivity analysis on the influence of the physical and geometrical properties of rigid piles on the impedance functions is presented.     

Numerical analysis of the seismic inertial and kinematic effects on pile bending moment in liquefiable soils

In an effort to study the seismic pile moment induced by the combined structure–pile inertial and soil–pile kinematic effects for single piles and pile groups in liquefiable ground, an extensive series of 3D finite element simulations are conducted in this paper. The roles that lateral inertial and kinematic interactions play on the pile moment are found to differ in different soil–pile–structure systems. Inertial structure force and kinematic soil displacement of the same direction could cause pile head moments of the same or opposite directions depending on the rotational constraint at the pile head. Kinematic interaction has a dominating influence on the pile moment for pile foundations with pile head rotation constrained by the existence of a pile cap, while inertial interaction is strongly influential for free-head piles. The coupling of inertial and kinematic interactions depends on the soil–pile–structure system configuration and the magnitudes of the inertial structure force and the kinematic soil displacement. Many current pseudo-static methods for calculating the seismic pile moment through summing a percentage of the kinematic induced moment with another percentage of the inertial induced moment could produce very inaccurate results under certain conditions.     

Negative skin friction on pile groups

A numerical procedure is presented for the downdrag analysis of group piles which penetrate a consolidating upper soil layer to socket into a firm bearing stratum of finite stiffness. The settlement of the consolidating upper soil layer under a surcharge load is estimated using Terzaghi's one-dimensional consolidation theory. Parametric solutions are presented to show the influence of various parameters on the performance of the socketed pile groups in terms of the development of the induced downdrag forces and associated pile head settlements. In general, pile–soil–pile interaction has the beneficial effect of reducing the downdrag forces and settlements of the group piles when compared to the corresponding single pile values, provided that the soil settlements are not so large as to cause full slippage at the interface in all the piles. Reasonable agreement is obtained between the theoretical and experimental results for pile groups subjected to negative skin friction.     

桩基检测方法及其应用

近年随着在软土层上大量建设高层建筑,桩基础被广泛应用,而新的地基处理方法要求对每根桩的质量都须确保,由此一系列经济、快速、可靠的桩检方法应运而生。本文概要地阐述了桩的分类、作用、性能特征和十二种桩检方法,即理论公式法、静荷载法、静力经验公式法、动力公式法、锤击贯入法,机械阻抗法、应力波分析法、水电效应法、球击动测法、基频法、声波及其它测井法、波速动刚度法。指出多种方法综合检测的必要性。     

桩基检测方法及其应用(续)

水电效应法的原理是冲击电流发生装置(电火花振源)在灌满水的桩头上进行高压放电,其放电时间约在10μs内产生可达几吨到几十吨的脉冲作用力作用于桩头使桩产生振动,再用水听器测量桩振动的加速度,测试装置如图13。     

Coupled deformation–seepage analysis of dynamic capacity tests on open-ended piles in saturated sand

Open-ended piles such as tubular piles or I-beams are used as foundations for offshore and nearshore construction. After the pile installation a load test to estimate the bearing capacity of these open-ended piles is necessary. Due to the offshore conditions and the high bearing capacity of the installed piles a static load test is not normally feasible. Therefore, dynamic load tests are carried out where the wave propagation due to an dynamic impact at the pile head is measured. The methods to estimate the bearing capacity from the measured signal of the dynamic tests were derived for solid pile profiles. It is questionable whether these evaluation techniques are applicable for open-ended piles. Hence, the influence of various important system parameters as well as the differences between static and dynamic load tests on open-ended piles is investigated in this paper.     

Analysis of pile‐raft foundations under complex loads in layered soils

Considering there is hardly any concerted effort to analyze the pile‐raft foundations under complex loads (combined with vertical loads, horizontal loads and moments), an analysis method is proposed in this paper to estimate the responses of pile‐raft foundations which are subjected to vertical loads, horizontal loads and moments in layered soils based on solutions for stresses and displacements in layered elastic half space. Pile to pile, pile to soil surface, soil surface to pile and soil surface to soil surface interactions are key ingredients for calculating the responses of pile‐raft foundations accurately. Those interactions are fully taken into account to estimate the responses of pile‐raft foundations subject to vertical loads, horizontal loads and moments in layered soils. The constraints of the raft on vertical movements, horizontal movements and rotations of the piles as well as the constraints of the raft on vertical movements and horizontal movements of the soils are considered to reflect the coupled effect on the raft. The method is verified through comparisons with the published methods and FEM. Then, the method is adopted to investigate the influence of soil stratigraphy on pile responses. The study shows that it is necessary to consider the soil non‐homogeneity when estimating the responses of pile‐raft foundations in layered soils, especially when estimating the horizontal responses of pile‐raft foundations. The horizontal loads and the moments have a significant impact on vertical responses of piles in pile‐raft foundations, while vertical loads have little influence on horizontal responses of piles in pile‐raft foundations in the cases of small deformations. The proposed method can provide a simple and useful tool for engineering design. Copyright © 2013 John Wiley & Sons, Ltd.     

Numerical analysis of axially loaded vertical piles and pile groups

A numerical method, based on a simplified elastic continuum boundary element method, is presented for the settlement analysis of axially loaded vertical piles and pile groups. The soil flexibility coefficients are evaluated using the analytical solutions for a layered elastic half space. Results are presented and compared with existing published solutions for the following cases: (i) piles in homogeneous soil, (ii) piles in finite soil layer, (iii) piles end-bearing on stiffer layer, (iv) piles socketted into stiffer bearing layer, and (v) piles in Gibson soil. Reasonably good agreement is obtained between the present solutions and existing published solutions.     

列车激振荷载下PCC桩复合地基动力分析

PCC桩-网复合地基作为一种新型处理软土路基的结构形式,在软弱土地区高速铁路建设中已获得应用,其在列车激振荷载下的动力特性值得研究。本文确定了合理的列车动荷载加载形式,应用有限元软件ABAQUS建立了轨道-路堤-桩-土复合地基三维动力耦合有限元模型,基于基床、桩、垫层和地基模量参数变化,进行了路堤、桩体以及地基土的动力特性分析。结果表明：PCC桩复合地基动应力响应有别于实心桩,动应力波在管桩中发生反射交叠作用,桩与垫层动力相互作用大于土与垫层动力相互作用。基床表层模量变化对桩-土动力变化影响不大。垫层刚度的增加提高了桩体的动荷载分担比,同时桩顶动应力随着桩与垫层动力相互作用的增强而增大。随着PCC桩模量的提高,动应力在桩体中传播速度加快,动应力增大,使其承担了大部分动荷载,有效地降低了地基土承受的动荷载,同时减弱了上部荷载在复合地基内部影响。随着距离中心桩距离的增大,边桩动应力逐步减小。     

桩筏基础下地基土的荷载传递特性

桩筏基础由桩和筏组成一种联合基础，筏将大部分总荷载传递给桩，同时其本身也承担总荷载的一部分。因此，充分认识桩筏基础对上部荷载向地基土的传递特性是非常必要的。该文提出一个桩筏基础传递荷载的计算模型，模型考虑了桩的布置形式对地基接触压力的影响，同时还考虑了桩的受荷过程中的变化特性，并详细分析了桩与筏之间的荷载分配问题。     

软土地层高承台桥梁群桩基础横向承载特性研究

高承台群桩基础是高速铁路桥梁基础的一种常用形式,受到风、地震等荷载作用影响,常常需要承受较大的横向荷载。采用室内物理模型试验和三维有限元程序ABAQUS对软土地层中单桩、群桩的横向承载特性进行了研究,软土采用修正剑桥黏土本构模型,试验结果与有限元计算结果吻合较好。群桩研究方案包括了桩数的变化以及桩间距的变化。结果表明,群桩基础的基桩平均横向承载力（总承载力/桩数）较单桩基础显著增加,且水平荷载方向桩间距越大,其横向承载力越大;群桩基础基桩受力存在三维空间效应,不同位置基桩受力大小排序为角桩最大,其次为边桩,最小为中间桩,弯矩极值差异可达20%,群桩基础桩周土影响范围距外围基桩边缘净距离约为16D (D为桩径)。桩与桩相互影响效应对群桩水平承载不利,承台约束效应对水平承载有利。探讨了考虑上述两种效应的群桩效应系数计算方法,通过计算验证了该方法在软土地区高承台群桩基础横向承载力计算中的适用性。     

Vertical response of pile raft foundations subjected to tunneling‐induced ground movements in layered soil

A simplified analysis method has been developed to estimate the vertical movement and load distribution of pile raft foundations subjected to ground movements induced by tunneling based on a two‐stage method. In this method, the Loganathan–Polous analytical solution is used to estimate the free soil movement induced by tunneling in the first stage. In the second stage, composing the soil movement to the pile, the governing equilibrium equations of piles are solved by the finite difference method. The interactions between structural members (such as pile–soil, pile–raft, raft–soil, and pile–pile) are modeled based on the elastic theory method of a layered half‐space. The validity of the proposed method is verified through comparisons with some published solutions for single piles, pile groups, and pile rafts subjected to ground movements induced by tunneling. Good agreements between these solutions are demonstrated. The method is also used for a parametric study to develop a better understanding of the behavior of pile rafts influenced by tunneling operation in layered soil foundations. Copyright © 2011 John Wiley & Sons, Ltd.