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1.
This paper describes the development of a boundary element analysis for the behaviour of single piles and pile groups subjected to general three‐dimensional loading and to vertical and lateral ground movements. Each pile is discretized into a series of cylindrical elements, each of which is divided into several sub‐elements. Compatibility of vertical, lateral and rotational movements is imposed in order to obtain the necessary equations for the pile response. Via hierarchical structures, 12 non‐zero sub‐matrices in a global matrix are derived for the basic influence factors. Solutions are presented for a series of cases involving single piles and pile groups. In each case, the solutions are compared with those from more simplified existing pile analyses such as those developed by Randolph and by Poulos. It is shown that for direct loading effects (e.g. the settlement of piles due to vertical loading), the simplified analyses work well. However, for ‘off‐line’ response (such as the lateral movement due to vertical loading) the differences are greater, and it is believed that the present analysis gives more reliable estimates. Copyright © 2000 John Wiley & Sons, Ltd. 相似文献
2.
A simplified method of numerical analysis has been developed to estimate the deformation and load distribution of piled raft foundations subjected to ground movements induced by tunnelling and incorporated into a computer program ‘PRAB’. In this method, a hybrid model is employed in which the flexible raft is modelled as thin plates, the piles as elastic beams, and the soil is treated as interactive springs. The interactions between structural members, pile–soil–pile, pile–soil–raft and raft–soil–raft interactions, are modelled based on Mindlin's solutions for both vertical and lateral forces. The validity of the proposed method is verified through comparisons with some published solutions for single piles and pile groups subjected to ground movements induced by tunnelling. Thereafter, the solutions from this approach for the analysis of a pile group and a piled raft subjected to ground movements induced by tunnelling are compared with those from three‐dimensional finite difference program. Good agreements between these solutions are demonstrated. The method is then used for a parametric study of single piles, pile groups and piled rafts subjected to ground movements induced by tunnelling. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
3.
Yoon Seok Choi Jintae Lee Monica Prezzi Rodrigo Salgado 《Geotechnical and Geological Engineering》2017,35(4):1587-1604
Although the loads applied on piles are usually a combination of both vertical and lateral loads, very limited experimental research has been done on the response of pile groups subjected to combined loads. Due to pile–soil–pile interaction in pile groups, the response of a pile group may differ substantially from that of a single pile. This difference depends on soil state and pile spacing. This paper presents results of experiments designed to investigate pile interaction effects on the response of pile groups subjected to both axial and lateral loads. The experiments were load tests performed on model pile groups (2 × 2 pile groups) in calibration chamber sand samples. The model piles were driven into the sand samples prepared with different relative densities using a sand pluviator. The combined load tests were performed on the model pile groups subjected to different axial load levels, i.e., 0 (pure lateral loading), 25, 50, and 75% of the ultimate axial load capacity of the pile groups, defined as the load corresponding to a settlement of 10% of the model pile diameter. The combined load test results showed that the bending moment and lateral deflection at the head of the piles increased substantially for tests performed in the presence of axial loads, suggesting that the presence of axial loads on groups of piles driven in sand is detrimental to their lateral capacity. 相似文献
4.
《Geomechanics and Geoengineering》2013,8(4):291-298
The buckling behaviour of the 360 × 152 steel H-piles supporting the integral abutments of the Scotch Road Bridge, located in Trenton, New Jersey, has been studied for the cases of single pile and pile bent. Three-dimensional finite-element models for single pile and pile bent have been developed to study the behaviour of these fully embedded piles under axial and lateral loading. An iterative analysis based on extracting the eigenvalues and eigenvectors (mode shapes) that correspond to the pile(s) critical buckling loads has been adopted. The pile(s) and the surrounding sand were modelled using solid continuum elements in the finite-element model. Material non-linearity is accounted for in both the piles and the soil in the base state of the model. A parametric study has been utilized to determine the effect of the geometric and material properties of the pile and the surrounding sand on the predicted critical buckling loads of the piles. The effects of four parameters have been studied: soil stiffness, pile length, type of connection, and combining vertical and lateral loads. The results from the parametric study showed that the variation of the percentage change in the sand stiffness, pile length, and combining vertical and lateral loads with the critical buckling loads of the 360 × 152 H-piles is nonlinear. Furthermore, the parameters studied are more influential in affecting the critical buckling load of a single pile than a pile bent, with the exception of the ‘type of connection’ parameter. 相似文献
5.
This paper focuses on an analysis by the boundary element method (BEM) of the pile-to-pile interaction for pile groups with dissimilar piles of different pile lengths embedded in saturated poroelastic soil. The behaviour of the poroelastic homogeneous soil is governed by Biot’s consolidation equations. The pile–soil system is decomposed into extended soil and fictitious piles. Considering the compatibility of vertical strain between fictitious piles and soil, the second kind of Fredholm integral equations were obtained to predict the axial force and settlement along pile shafts numerically. For the analysis of the interaction factor, two loading conditions for a two-dissimilar-pile system were proposed: (a) only one pile is loaded and (b) each pile is subjected to a load proportional to the pile length. Furthermore, the two-pile system was extended to pile groups with a rigid cap to capture the optimum design where each pile shares the same loading at the pile heads. The optimum results require shortening the peripheral piles and elongating internal piles, and the consolidation effect needs to be considered due to the adjustment of loading distribution among piles. 相似文献
6.
高速铁路超长桥桩承载特性试验研究 总被引：2，自引：0，他引：2
超长桩广泛已应用于土木工程各个领域,但黄土地区超长桩的承载性状和变形特性尚不十分清楚,需要进一步研究。通过对郑西铁路客运专线某特大桥的4根超长桩现场测试项目的资料分析,得出了超长桩桩身轴力及侧阻力的变化规律,对超长桩的承载特性有了更为清晰的了解。试验结果表明,在桩顶竖向荷载作用下,桩身轴力随荷载的增加发生了局部调整,砂性土层的桩侧摩阻力具有增强效应,黏性土层的桩侧摩阻力具有退化效应;单桩竖向刚度随桩顶荷载的增加而减小,单桩竖向刚度降低40 %～70 %。 相似文献
7.
Hasan Ghasemzadeh Mohsen Tarzaban Mohammad Mahdi Hajitaheriha 《Geotechnical and Geological Engineering》2018,36(4):2189-2215
Battered piles are usually used to counteract lateral forces in a pile group. As there is little spacing between piles, they are affected by one another, and there is interaction between them. In this study, pile–soil–pile interaction in a group of battered piles was numerically simulated using finite element analysis. Double and frictional pile groups under static lateral and axial loadings were analyzed separately. The effects of batter angle, slenderness ratio, spacing between piles, pile–soil stiffness ratio, and soil plasticity on interaction factors were computed and presented in curves. 相似文献
8.
In geotechnical practice, it is of considerable importance to assess the behavior of vertical–lateral coupled loading piles in multilayered soil deposits. This study deals with a semi-analytical formulation for the performance of a pile suffering from combined vertical and lateral loads. The emphasis is on quantifying the mobilization of the subgrade reaction provided by the layered soil stratums. In the proposed method, subgrade reactions, correlated with both the accumulative axial load transfer and side resistances depending upon the pile–soil interaction, are abstracted as a series of nonlinear springs in both vertical and lateral directions. On account of this, an alternative transfer matrix method is applied to characterize the pile reaction along the depth under the identified boundary conditions atop the pile; meanwhile, the condition of static equilibrium, between two specific pile segments located at the border of soil layers, is also essential. On this basis, validation of the solution is conducted by comparing with observations from experiments and predictions obtained from other existing methods. In addition, the influence of properties in shallow soil layer and the vertical load on the lateral response of the pile is also discussed. The results indicate a reduction in the lateral displacement and the maximum bending moment within the pile with the increase in the shallow soil stiffness, but a growth with the increase in vertical load due to the “P-Δ effect.” 相似文献
9.
轴向荷载对斜桩水平承载特性影响试验及理论研究 总被引：1，自引：0，他引：1
斜群桩受水平荷载作用时,群桩中的基桩受到径向荷载、轴向荷载和弯矩的共同作用。为研究轴向荷载对斜桩水平承载特性的影响,完成了3根单桩以及1组1×2斜桩的大尺寸模型试验。试验结果表明：轴向拉力作用会降低斜桩的水平刚度和极限承载力;而轴向压力作用则会使其水平刚度和极限承载力提高。基于桩侧浅层土体楔形破坏假定,推导了考虑轴向荷载影响的斜桩水平极限土抗力计算公式,提出了桩侧土抗力的p-y曲线方法,并通过模型试验及现场试验验证其合理性。 相似文献
10.
根据软土地基、非软土地基中长钻孔灌注桩静载荷试验和桩身轴力的测试结果,分析探讨了竖向荷载下长桩的受力性能及沉降特征的一些规律。桩侧土模量较高的非软土地区的长桩静力试桩所测得的结果表明,荷载传递和桩身压缩与软土地区超长桩性状相似,长桩的桩身压缩量相当可观,计算中应予以考虑。极限侧阻力与端阻力不同步发挥,不同深度处的不同土层处基桩的侧阻也不能同步发挥;同时指出相关规范中极限承载力计算公式的不严密之处,并且探讨说明了竖向荷载下的长群桩基础变形性状及沉降计算有待进一步的研究。本项研究对今后超长桩的理论研究和工程设计应用具有一定的借鉴作用。 相似文献
11.
Analysis of kinematic seismic response of tapered piles 总被引：2，自引：0，他引：2
Mahmoud Ghazavi 《Geotechnical and Geological Engineering》2007,25(1):37-44
In the present work, a two-phase analysis is used to assess the lateral movement of a tapered pile due to kinematic seismic
loading resulted from earthquakes. First, the free-field horizontal displacement of the ground due to earthquake is estimated
using available theory of wave propagation. Second, these estimated soil movements are imposed on the taper pile in a closed-form
solution to compute the pile response. The governing differential equation for an arbitrary pile segment is obtained, which
includes the free-field horizontal movement estimated from the first phase. The equation is solved explicitly to obtain the
horizontal deflection. Parametric studies show that tapered piles tend to be more flexible than uniform piles of the same
volume and length under earthquake loading, which is soundly interesting. 相似文献
12.
通过海洋环境条件下大直径管桩的垂直和水平荷载试验,分析了管桩在垂直和水平荷载作用下的受力特点,得到了管桩的垂直极限承载力、侧摩阻力及端承力、轴向反力系数等结果,以及水平荷载作用下桩顶位移和转角关系、弯矩分布、土抗力、水平地基反力系数的比例系数和最大弯矩点等参数。试验结果表明：垂直荷载作用下,极限承载力可达12000kN,在沉桩过程中部分桩有一定程度的闭塞;大直径管桩能够抵抗水平荷载的作用,弹性长桩的受力性质主要受上部土层的影响。根据试验结果计算的水平地基抗力比例系数m值,对本工程及同类地质条件的桩基设计具有参考价值。 相似文献
13.
对土体采用Mohr-Coulomb弹塑性本构模型,用接触面单元模拟桩-土相互作用,利用ABAQUS建立桩筏基础--地基--基坑开挖三维有限元分析模型。对基坑开挖影响下的群桩基础竖向承载性状进行了分析,讨论了桩顶反力分布、桩身轴力、桩侧摩阻力以及开挖引起的桩身水平位移及其弯矩的变化规律,并进行了考虑基坑开挖与不考虑基坑开挖的群桩基础竖向承载性状的对比分析。通过研究,取得了基坑开挖对高层建筑桩筏基础影响的基本认识,这些认识对于改进桩筏基础设计理论有一定的参考意义。 相似文献
14.
成层土中倾斜荷载作用下桩承载力有限元分析 总被引：7，自引：1，他引：6
利用有限元方法对现场单桩水平载荷试验进行模拟,在此基础上,分析了成层土中桩在倾斜荷载作用下其竖向分量的有利作用和横向土抗力分布特点。计算结果表明,在地面下一定范围内,倾斜荷载作用下的桩侧摩阻力比水平荷载作用下的桩侧摩阻力大。在土层分界处土抗力分布有明显的跳跃。达到一定深度后,横向土抗力主要是静止土压力,而由荷载引起的横向土抗力很小。承台能有效减小土体及桩的水平位移。模拟的灌注桩和钢管桩桩顶在地面以上的自由长度较小,竖向分量由于桩身挠曲变形而产生的P-Δ效应较小,所以就算例中的灌注桩和钢管桩而言,荷载倾斜度不大时,荷载竖向分量提高了桩的侧阻并由此增大桩侧土竖向应力,对桩水平承载力总体上起到了有利的作用。 相似文献
15.
The influence of vertical loads on the lateral response of group piles installed in sandy soil and connected together by a concrete cap is studied through finite elements analyses. The analyses focus on the five piles in the middle row of 3 × 5 pile groups. The vertical load is applied by enforcing a vertical displacement equivalent to 2% of the pile diameter through the pile cap prior to the application of the lateral loads. The results have shown that the lateral resistance of the leading pile (pile 1) does not appear to vary considerably with the vertical load. However, the vertical load leads to 23%, 36%, 64%, and 82% increase in the lateral resistance of piles 2–5, respectively. The increase in the lateral pressures in the sand deposit is the major driving factor to contribute the change in the lateral resistance of piles, depending on the position of the pile in the group. The distribution of lateral loads among piles in the group tends to be more uniform when vertical loads were considered leading to a more economical pile foundation design. 相似文献
16.
Three-dimensional (3D) finite element analyses have been performed to study the behaviour of a single pile and 3 × 3 and 5 × 5 pile groups during open face tunnelling in stiff clay. Several governing factors, such as tunnelling-induced ground and pile settlement, axial pile force changes and shear transfer mechanism at the pile–soil interface, have been studied in detail. Tunnelling resulted in the development of pile head settlement larger than the free-field soil surface settlement. In addition, axial force distributions along the pile change substantially due to changes in the shear transfer between the pile and the soil next to the pile, which triggers tunnelling-induced tensile forces in the piles with tunnel advancement. It was found that the relative displacements and the normal stresses at the pile–soil interface drastically affected shear transfer. The extent of slip length along a pile increased as the tunnelling proceeded. The apparent allowable pile capacity was reduced by up to approximately 42% due to the development of tunnelling-induced pile head settlement. Shear stress on the pile was increased for most of the pile depth with tunnel advancement, which was associated with changes in soil stresses and ground deformation, and hence, the axial pile force was gradually reduced with tunnel advancement, indicating the development of tunnelling-induced tensile pile force. The maximum tunnelling-induced tensile force on the pile was approximately 0.33Pa, where Pa is the allowable pile capacity applied to the pile head prior to tunnel excavation. The range affected by tunnelling in the longitudinal direction may be identified as approximately −2D ∼ +(1.5–2.0D), where D is the tunnel diameter, from the pile centre (behind and ahead of the pile axis), in terms of pile settlement and axial pile force changes based on the analysis conditions assumed in the current study. Larger pile head settlements and smaller changes in axial pile forces were computed for piles that were part of groups. It has been found that the serviceability of piles experiencing adjacent tunnelling is more affected by pile settlement than by axial pile force changes, in particular for piles inside groups. The magnitude of the tunnelling-induced excess pore pressure was small and may not substantially affect pile behaviour. 相似文献
17.
Pile group interaction effects on the lateral pile resistance are investigated for the case of a laterally loaded row of piles in clay. Both uniform undrained shear strength and linearly increasing with depth shear strength profiles are considered. Three-dimensional finite element analyses are presented, which are used to identify the predominant failure modes and to calculate the reduction in lateral resistance due to group effects. A limited number of two-dimensional analyses are also presented in order to examine the behaviour of very closely spaced piles. It is shown that, contrary to current practice, group effects vary with depth; they are insignificant close to the ground surface, increase to a maximum value at intermediate depths and finally reduce to a constant value at great depth. The effect of pile spacing and pile–soil adhesion are investigated and equations are developed for the calculation of a depth dependent reduction factor, which when multiplied by the limiting lateral pressure along a single pile, provides the corresponding variation of soil pressure along a pile in a pile row. This reduction factor is used to perform p–y analyses, which show that, due to this variation of group effects on the lateral soil pressures with depth, the overall group interaction effects depend on the pile length. Comparisons are also made with approaches used in practice that assume constant with depth reduction factors. 相似文献
18.
传统的Poulos弹性理论仅适合于均质土中土体侧向位移时桩的性状分析,无法考虑土的层状特性。通过引入层状地基中作用一水平集中力的广义Mindlin解和地面作用有竖向荷载时的应力和位移通解,对Poulos方法进行了改进,使之扩展到多层土中,还用于研究堆载条件下的被动桩变形和受力响应。算例分析表明,改进弹性理论要比Poulos方法更为严密、合理,提高了计算精度,应用范围也更广。 相似文献
19.
软基高桥台桩-土相互作用计算新方法研究 总被引：3，自引：0，他引：3
在软土地基桥台台后高路堤填土会引起下卧软土层产生水平塑流,对桥台桩基产生可观的侧压力。如何计算因软土塑性流动对桩产生的侧压力,是软土地基高桥台桩基设计中尚未解决的难点问题之一。通过分析对比研究,提出应用极限土压力法求解流塑区桥台桩基侧土压力,建立了可以考虑地基土成层特性、桩-土体系参数、侧压力沿深度任意变化的桥台-桩基系统分析力学模型,推导了求解桥台和桩基内力、位移值的新方法,该方法运算过程采用矩阵相乘,适于编程计算,比较一般理论方法和复杂的有限元法,其计算简单,需要的计算参数较少,实用价值更好。结合工程实例,采用MATLAB语言,编写了桥台桩基内力位移计算程序,验证了方法的准确性和可靠性,可供软土地基高桥台桩基设计计算时参考。 相似文献
20.
Wei Dong Guo 《国际地质力学数值与分析法杂志》2016,40(14):1936-1967
This paper develops a three‐layer model and elastic solutions to capture nonlinear response of rigid, passive piles in sliding soil. Elastic solutions are obtained for an equivalent force per unit length ps of the soil movement. They are repeated for a series of linearly increasing ps (with depth) to yield the nonlinear response. The parameters underpinning the model are determined against pertinent numerical solutions and model tests on passive free‐head and capped piles. The solutions are presented in non‐dimensional charts and elaborated through three examples. The study reveals the following:
- On‐pile pressure in rotationally restrained, sliding layer reduces by a factor α, which resembles the p‐multiplier for a laterally loaded, capped pile, but for its increase with vertical loading (embankment surcharge), and stiffness of underlying stiff layer: α = 0.25 and 0.6 for a shallow, translating and rotating piles, respectively; α = 0.33–0.5 and 0.8–1.3 for a slide overlying a stiff layer concerning a uniform and a linearly increasing pressure, respectively; and α = 0.5–0.72 for moving clay under embankment loading.
- Ultimate state is well defined using the ratio of passive earth pressure coefficient over that of active earth pressure. The subgrade modulus for a large soil movement may be scaled from model tests.
- The normalised rotational stiffness is equal to 0.1–0.15 for the capped piles, which increases the pile displacement with depth.