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1.
A numerical analysis of pile driving for tapered piles is presented in this paper. A three-dimensional finite difference analysis for tapered angle and geometry effects has been used on pile driving response of tapered piles. The simulation considers an idealization for pile–soil system in drivability. The vertical pile is assumed to have linear and elastic behavior. It is also assumed that the soil is elasto-plastic material and its failure stage is controlled using the Mohr–Coulomb failure criterion. At the soil–pile contact surfaces along the pile shaft and pile toe, slip is allowed to occur during the driving procedure using interface elements. Quiet boundaries are used to prevent waves traveling in the lateral and vertical directions for the soil. Cylindrical, fully tapered, and semi-tapered piles were analyzed. The results obtained from numerical analyses were compared with those obtained from available laboratory tests and also other available numerical data, resulting in a satisfactory agreement. The results have shown that among piles of the same length and material volume, with increasing the taper angle from zero (representing a cylindrical pile), the driving stresses decrease and the permanent pile toe settlement (set) increases. These are interesting in pile driving and are on the safe side for driven piles and increasing the driving efficiency. It has also been found that the geometry of the pile can generally influence the pile drivability. Generally speaking, tapered and partially tapered piles offer better drivability performance than cylindrical piles of the same volume and length. 相似文献
2.
Simple methods of analysis are developed for computing the dynamic steady-state axial response of floating pile groups embedded in homogeneous and non-homogeneous soil deposits. Physically-motivated approximations are introduced to account for the interaction between two individual piles. It is found that such an interaction arises chiefly from the ‘interference’ of wave fields originating along each pile shaft and spreading outward. For homogeneous deposits the wave fronts originating at an individual pile are cylindrical and the interaction is essentially independent of pile flexibility and slenderness. For non-homogeneous deposits the wave fronts are non-cylindrical and ray-theory approximations are invoked to derive pile flexibility-dependent interaction functions. Results are presented for the dynamic stiffness and damping of several pile groups, as well as for distribution of the applied load among individual piles. For deposits with modulus proportional to depth, the agreement with the few rigorous solutions available is encouraging. A comprehensive parameter study focuses on the effects of soil inhomogeneity and pile-group configuration. It is demonstrated that the ‘dynamic group efficiency’ may far exceed unity at certain frequencies. Increasing soil inhomogeneity tends to reduce the respective resonant peaks and lead to smoother interaction functions, in qualitative agreement with field evidence. 相似文献
3.
打桩引起的地面振动的研究 总被引：1，自引：0，他引：1
为了对打桩引起的地面振动进行研究,应用一维应力波理论建立了粘弹性成层土中等截面弹性桩的力学模型,得到了桩中任意一点处位移的半解析解。利用桩与土的相互作用将桩对土的作用力简化到各土层面上。在复阻尼理论和纳维方程的基础上,利用分层法得到了任意荷载作用下土的位移、速度和加速度的解。从而得到了打桩引起的地面振动的衰减特性。通过实测结果和计算结果的比较说明了该方法的可行性。 相似文献
4.
The influence of inclined piles on the dynamic response of deep foundations and superstructures is still not well understood and needs further research. For this reason, impedance functions of deep foundations with inclined piles, obtained numerically from a boundary element–finite element coupling model, are provided in this paper. More precisely, vertical, horizontal, rocking and horizontal–rocking crossed dynamic stiffness and damping functions of single inclined piles and 2 × 2 and 3 × 3 pile groups with battered elements are presented in a set of plots. The soil is assumed to be a homogeneous viscoelastic isotropic half‐space and the piles are modeled as elastic compressible Euler–Bernoulli beams. The results for different pile group configurations, pile–soil stiffness ratios and rake angles are presented. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
5.
理论计算及实测资料表明,反射波法基桩动测激振信号近似为半周期正弦波,不同激振方式产生的桩顶速度脉冲信号宽度不同,相应频率成分也就不同。桩身内阻尼对不同频率谐波的幅值衰减及频散规律不同,使得不同激振方式产生的复合脉冲在同一桩中会有不同变化规律,为了使不同激振方式测试资料具有可比性,应采用相同频带进行对比。为此利用小波分析的时-频特性,通过对测试信号进行时频分解,就桩身内阻尼对不同频带信号的吸收系数及波速的影响规律进行了研究。对实测资料分析的结果表明,预制桩不同频带信号波速变化不大,但衰减系数随频率增大近似线性增加。 相似文献
6.
The influence of nonlinearity on the dynamic response of cast-in-situ reinforced concrete piles subjected to strong vertical excitation was studied. Forced vibration test of single piles (L/d=10, 15, 20) and 2×2 pile groups (s/d=2, 3, 4 for each L/d) were conducted in the field for two different embedded conditions of pile cap. From the measured nonlinear response curves, the effective pile–soil system mass, stiffness and damping were determined and the nonlinear response curves were back-calculated using the theory of nonlinear vibration. The test results were compared with the continuum approach of Novak with dynamic interaction factor approach using both linear and linear-equivalent numerical methods. Reasonable match between the measured and predicted response was found for linear-equivalent methods by introducing a weak boundary-zone around the pile to approximately account for the nonlinear behaviour of pile–soil system. The test data were used to establish the empirical relationship in order to estimate the extent of soil separation around the pile with soil under vertical vibration. 相似文献
7.
A general methodology is outlined for a complete seismic soil—pile-foundation—structure interaction analysis. A Beam-on-Dynamic-Winkler-Foundation (BDWF) simplified model and a Green's-function-based rigorous method are utilized in determining the dynamic response of single piles and pile groups. The simplified model is validated through comparisons with the rigorous method. A comprehensive parameter study is then performed on the effect of pile group configuration on the dynamic impedances of pile foundations. Insight is gained into the nature of dynamic pile—soil—pile interaction. The results presented herein may be used in practice as a guide in obtaining the dynamic stiffness and damping of foundations with a large number of piles. 相似文献
8.
根据基桩低应变检测的基本原理,对于大型模拟缺陷桩低应变反射波法曲线进行了分析,以便在解释反射波法曲线时作为借鉴,提高基桩质量检测的可靠度。 相似文献
9.
Recent studies have demonstrated that the use of a discretely-spaced row of piles can be effective in reducing the deformations of slopes in earthquakes. In this paper, an approximate strain-dependant Newmark sliding-block procedure for pile-reinforced slopes has been developed, for use in analysis and design of the piling scheme, and the model is validated against centrifuge test data. The interaction of the pile within the slipping soil was idealised using a non-linear elasto-plastic (P–y) model, while the interaction within the underlying stable soil was modelled using an elastic response model in which (degraded) soil stiffness is selected for an appropriate amount of shear strain. This combined soil–pile interaction model was incorporated into the improved Newmark methodology for unreinforced slopes presented by Al-defae et al. [1], so that the final method additionally incorporates strain-dependent geometric hardening (slope re-grading). When combined with the strain-dependent pile resistance, the method is therefore applicable to analysis of both the mainshock and subsequent aftershocks acting on the deformed slope. It was observed that the single pile resistance is mobilised rapidly at the start of a strong earthquake and that this and the permanent slope deformation are therefore strongly influenced by pile stiffness properties, pile spacing and the depth of the slip surface. The model shows good agreement with the centrifuge test data in terms of the prediction of permanent deformation at the crest of the slope (important in design for selecting an appropriate pile layout/spacing i.e. S/B) and in terms of the maximum permanent bending moments induced in the piles (important for appropriate structural detailing of the piles), so long as the slip surface depth can be accurately predicted. A method for doing this, based on limit analysis, is also presented and validated. 相似文献
10.
Based on the theory of tube wave propagation in a fluid-filled borehole, this paper proposes a new method for detecting the integrity of pile foundation and overcomes some limitations of the existing pile integrity tests. The basic principle of detecting the pile integrity by the tube wave, testing equipment and concrete quality evaluation of piles are introduced. The feasibility of the tube wave detection for geological exploration of a bridge pile in a karst development area is verified by field tests. Through some test cases of prestressed high strength concrete pipe piles, cast-in-place piles and rock-socketed piles with defects, the accuracy of the tube wave detection and other methods is compared. Then, some issues of the application of the tube wave for detecting pile defects are discussed. Finally, the content of this paper is summarized, and some suggestions on further research are put forward. 相似文献
11.
工程上广泛采用基于Winkler模型的层状地基反力系数法对桩土水平动力响应进行分析,该方法忽略了地基土剪切作用的影响,与工程实际有一定偏差。另外,对桩土的非线性相互作用和如扩底桩、楔形桩等变截面桩问题常用的传递矩阵法或中心差分法,计算过程较为繁琐。基于Pasternak地基模型和Adomian分解方法,提出一种考虑地基土剪切作用的桩土水平动力相互作用近似计算方法,该方法计算简便且结果精度较高,对变截面桩问题有很好的适用性;并基于该方法,对扩底桩水平动力响应问题和影响因素进行分析。结果指出,扩底半径和上部桩周土弹性模量对扩底桩水平动力响应影响较大,随着扩底半径的增加和桩周土弹性模量的增大,扩底桩水平振动位移幅值逐渐减小。另外,在较低频率的荷载激励下,应考虑土层对桩的剪切作用。 相似文献
12.
13.
针对振动台试验,采用u-p形式控制方程表述饱和砂土的动力属性,选用土的多屈服面塑性本构模型刻画饱和砂土和黏土的力学特性,引入非线性梁-柱单元模拟桩,建立试验受控条件下液化场地群桩-土强震相互作用分析的三维有限元模型,并通过试验结果验证数值建模途径与模拟方法的正确性。以实际工程中常用的2×2群桩为例,建立桩-土-桥梁结构强震反应分析三维有限元模型。基于此,针对不同群桩基础配置对液化场地群桩-土强震相互作用影响展开具体分析。对比发现,桩的数量相同时,桩排列方向与地震波输入方向平行时比垂直时桩基受力减小5%~10%,而对场地液化情况无明显影响;相同排列形式下,三桩模型中土体出现液化的时间约比双桩模型延缓5s,桩上弯矩和剪力减小33%~38%。由此可见,桩基数量增加,桩-土体系整体刚度更大,场地抗液化性能显著,桩基对上部桥梁结构的承载性能明显增强,其安全性与可靠性更高。这对实际桥梁工程抗震设计具有一定的借鉴意义。 相似文献
14.
Nonlinear lateral interaction in pile dynamics 总被引：4，自引：0，他引：4
A model for pile lateral response to transient dynamic loading and to harmonic loading is presented allowing for nonlinear soil behaviour, discontinuity conditions at the pile-soil interface and energy dissipation through different types of damping. The approach is used to establish equivalent linear stiffness and damping parameters of single piles as well as dynamic interaction factors for approximate nonlinear analysis of pile groups. The applicability of these parameters to the pile-group analysis was examined, and a reasonable agreement with the direct analysis was found. The superposition technique may be used to analyze the response of small pile groups. Also, the dynamic stiffness of pile groups is greatly affected by both the nonlinear behavior of the soil and the slippage and gapping between the pile and soil. For a basic range of soil and pile parameters, equivalent linear stiffness and damping parameters of single piles and interaction factors for approximate nonlinear analysis are provided. 相似文献
15.
A quasi-3D method for the analysis of single piles and pile groups is presented. The method includes an equivalent linear constitutive model for nonlinear analysis, an 8-node pile element that simulates the effects of pile volume and energy transmitting boundaries which are especially important for the analysis of high frequency loading of machine foundations. The quasi-3D formulation and equivalent linear model result in orders of magnitude decreases in computational time. The accuracy and reliability of the approximate approach was validated by comparing results with 3D analytical results from MIT and by data from field tests on single piles and pile groups from Taiwan. The computed results compared very favorably with the analytical and field test data. 相似文献
16.
This paper presents theoretical analysis of the parallel seismic (PS) method for evaluating existing piles using the flexural mode wave exited by a horizontal impact on the lateral surface of a pile. A simplified theoretical model of the flexural wave for PS method was established to elaborate the theoretical basis. A correction factor was then obtained and proposed to correct the pile depth obtained from the PS method, thus providing a more accurate estimation. A three dimension (3-D) finite element (FE) model was developed and the existence of the flexural waves on branch F(1, 1) in the pile shaft has been verified. Two time domain methods were used to calculate the flexural wave velocity in the pile. One was based on the pile tip reflection signal using a model where pile head reflection was minimized, and another method used the slope of the upper fitted line in the PS test. The flexural wave velocities from both methods match well with the predicted flexural wave group velocity determined from the dispersion curve of a 1-D rod embedded in the soil. The accuracy in estimation of pile tip depth is improved by applying the correction factor. A series of parametric studies were carried out to demonstrate the effectiveness of using flexural wave for PS test and the correction factor proposed in this study. 相似文献
17.
Khiem T. Tran Michael McVay Rodrigo Herrera Peter Lai 《Soil Dynamics and Earthquake Engineering》2011
A numerical technique is presented to estimate ultimate skin friction of a driven pile using instrumentation installed at the top and bottom of a pile. The scheme is based on an analytical solution of the 1D wave equation with static skin friction and damping along with a genetic algorithm for solution. Specifically, acceleration and strains measured at both the top and bottom of the pile are used to develop an observed Green's function, which is matched to an analytical Green's function, which is a function of secant stiffness and viscous damping. Requiring 1–3 s of analysis time per blow, the algorithm provides a real time assessment of average skin friction along the pile. The technique was applied to four driven piles having ultimate skin frictions varying from 700 to 2000 kN, with the predicted skin frictions generally consistent with measured static load test results. 相似文献
18.
The objectives of this paper are to show practically: (1) the validation of a proposed three-dimensional effective stress analysis for the pile foundations, and (2) the effectiveness of remedial deposits on pile stresses under liquefaction by making comparisons between the results of centrifuge tests and those of the proposed analysis. Two foundation models supported by end-bending piles were studied with improved and unimproved deposits. There exists a good consistency between the numerical and experimental results for excess pore water-pressure ratios ranging from 0 to about 0·9. From the numerical results, the bending moment at the pile top with the improved deposit is about 50 per cent lower than that with the unimproved deposit. However, it was found that the smaller the bending moment develops in the pile with the improved deposit, the larger the compressive and/or tensional axial stresses in the pile. This is due to the predominant excitation of rocking vibration of the foundation. From the analytical and experimental results, it has been found that the remedial method can be a variable means to protect piles from soil liquefaction hazards. However, both axial stress and bending moment produced in piles should be considered in assessing the liquefied seismic capacity of group pile-foundation–structural systems with improved soil deposits. © 1998 John Wiley & Sons, Ltd. 相似文献
19.
A new model named double-shear model based on Pasternak foundation and Timoshenko beam theory is developed to evaluate the effect of a forced harmonic vibration pile to its adjacent pile in multilayered soil medium. The double-shear model takes into account the shear deformation and the rotational inertia of piles as well as the shear deformation of soil. The piles are simulated as Timoshenko beams, which are embedded in a layered Pasternak foundation. The differential equation of transverse vibration for a pile is solved by the initial parameter method. The dynamic interaction factors for the layered soil medium are obtained by the transfer matrix method. The formulation and the implementation have been verified by means of several examples. The individual shear effects of soil and piles on the interaction factors are evaluated through a parametric study. Compared to Winkler model with Euler beam, the present model gives much better results for the dynamic interaction of piles embedded in stiff soil with small slenderness ratios. Finally, the effect of a forced long pile to a short pile embedded in multilayered soil medium is studied in detail. 相似文献
20.
Dynamic response of single piles to seismic waves is fundamentally different from the free‐field motion because of the interaction between the pile and the surrounding soil. Considering soil–pile interaction, this paper presents a new displacement model for the steady‐state kinematic response of single piles to vertically incident P‐waves on the basis of a continuum model. The governing equations and boundary conditions of the two undetermined functions in the model are obtained to be coupled by using Hamilton's principle. Then, the two unknown functions are decoupled and solved by an iterative algorithm numerically. A parametric study is performed to investigate the effects of the properties of the soil–pile system on the kinematic response of single piles. It is shown that the effects of the pile–soil modulus ratio, the slenderness ratio of the pile, and the frequency of the incident excitations are very significant. By contrast, the influence of soil damping on the kinematics of the system is slight and can be neglected. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献