Resistance of soil to a horizontally vibrating pile

The resistance of a soil layer to steady horizontal vibration of an elastic pile is theoretically investigated. The pile is assumed to be vertical and of circular cross-section. The soil is modelled as a linear viscoelastic layer with hysteretic material damping. A closed form solution is obtained for the resistance of the soil layer to the motion. This resistance depends on shear modulus of soil, frequency, pile slenderness, material damping and Poisson's ratio. A parametric study of the effect of these parameters is included. The soil layer resistance is expressed in a form which can be used directly in the solution of the soil-pile interaction problem which is treated in a subsequent paper. The approach also applies for rigid deeply embedded footings.     

Effect of a forced harmonic vibration pile to its adjacent pile in layered elastic soil with double-shear model

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.     

Torsional vibration of a pipe pile in transversely isotropic saturated soil

This study considers the torsional vibration of a pipe pile in a transversely isotropic saturated soil layer. Based on Biot’s poroelastic theory and the constitutive relations of the transversely isotropic medium, the dynamic governing equations of the outer and inner transversely isotropic saturated soil layers are derived. The Laplace transform is used to solve the governing equations of the outer and inner soil layers. The dynamic torsional response of the pipe pile in the frequency domain is derived utilizing 1D elastic theory and the continuous conditions at the interfaces between the pipe pile and the soils. The time domain solution is obtained by Fourier inverse transform. A parametric study is conducted to demonstrate the influence of the anisotropies of the outer and inner soil on the torsional dynamic response of the pipe pile.     

液化土中桩基础动力反应试验研究

本文设计完成了包括三种密度饱和砂土和非液化干砂的多工况桩-土相互作用振动台动力试验,研究液化对土体和桩-承台动力反应的影响。通过试验和分析,得到了液化和非液化土层中土体水平加速度、侧向位移和桩-承台的水平加速度、侧向位移、桩身弯矩等指标的反应过程和模式,对比了液化和非液化条件对这些指标的影响方式,提出了各因素影响大小的分析结果。     

打桩引起的地面振动的研究

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。     

Longitudinal vibration characteristics of a tapered pipe pile considering the vertical support of surrounding soil and construction disturbance

This research is concentrated on the longitudinal vibration of a tapered pipe pile considering the vertical support of the surrounding soil and construction disturbance. First, the pile–soil system is partitioned into finite segments in the vertical direction and the Voigt model is applied to simulate the vertical support of the surrounding soil acting on the pile segment.The surrounding soil is divided into finite ring-shaped zones in the radial direction to consider the construction disturbanc...     

单桩水平及水平-摇摆耦合振动分析

采用Novak薄层法,分析了单桩的水平及水平-摇摆耦合振动。然后,引进Novak和韩英才的边界层理论,全面分析和对比了匀质弹性、匀质粘弹性和非匀质粘弹性地基中单桩的动力阻抗,考察了各种因素对单桩动力阻抗的影响程度。在推导单桩水平动力阻抗的过程中,采用克雷洛夫函数和初参数法求解单桩的水平振动微分方程,从而能够方便地考虑桩长和桩底土对单桩动力阻抗的影响。计算表明,当桩的长径比较小时,桩底土对单桩动力阻抗有重要的影响。     

Soil-pile interaction in horizontal vibration

Interaction between soil and an elastic pile vibrating horizontally is theoretically examined. The soil is modelled as a linear, viscoelastic layer overlying rigid bedrock. The pile is assumed to be vertical and point bearing. This study utilizes the definition of soil resistance presented in a preceding paper.¹ A direct solution is developed which yields closed form formulas for pile displacement, stiffness and damping. A parametric study clarifies the role of the parameters involved, illustrates the interaction between the soil and the pile and shows the stiffness and damping properties of the soil-pile system for typical values of the governing parameters.     

Numerical and test study on vertical vibration characteristics of pile group in slope soil topography

Topography effects on the vertical vibration responses of pile group are revealed though numerical analysis and model tests.First,a series of model tests with different topography of ground and bedrock are conducted.The results indicate that displacement amplitude of the pile head in sloping ground topography is larger than in horizontal ground.Differential displacement at various positions of the pile cap is observed in non-horizontal topography.Afterwards,a numerical algorithm is employed to further explore the essential response characteristics in group piles of different topography configurations,which has been verified by the test results.The lengths of the exposed and frictional segment,together with the thickness of the subsoil layer,are the dominant factors which cause non-axisymmetric vibration at the pile cap.     

Generalization of the Rayleigh-Tikhonov stationary geothermal problem for a horizontal layer

The Rayleigh-Tikhonov generalized stationary geothermal problem is formulated and solved exactly for a set of homogeneous horizontal infinite plane-parallel layers located in a lower half-space. The known solutions follow as particular cases of the solutions found. The results obtained in this work are usable for 1-D approximations of many important problems of geophysics, tectonophysics, and geology.     

基于API规范的液化土层桩基p-y曲线修正计算公式

基于小型振动台拟静力试验和往返动荷载试验,将得到的静力p-y曲线及滞回曲线与基于静力方法提出的API规范方法进行对比研究,指出了采用目前API规范中的折减系数方法进行液化土层中桩基横向承载力计算时与实际不符并导致工程设计无法接受的原因。进行四种不同相对密度可液化土中大型振动台桩?土?承台动力相互作用大型振动台试验,考虑到API规范方法在工程中的广泛应用性和可接受性,在不改变其基本模式前提下,提出其中土体初始模量和极限土阻力两个修正参数,以地震波输入下的振动台试验对构建的公式进行验证,结果较为吻合。     

群桩的回转及水平动力刚度和阻尼

视群桩为弹性组合杆件,将弹性半空间理论的V.A.Baranov薄片分解为组合薄片,并利用Bara-nov函数的精确解和M.Novak对单桩的近似解,提出了群桩的回转及水平动力刚度和阻尼系数的计算公式。该公式直接计算群桩的回转及水平动力参数,体现了群桩的动力本征特性,无需工程经验修正或群桩效率修正。理论计算结果与几个工程现场实测值对比,两者吻合较好,能满足工程精度。     

Field vibration mitigation by honeycomb WIB for pile foundations of a high-speed train viaduct

Environmental vibrations from recent high-speed trains are becoming a special concern in the civil and environmental engineering field since they can give detrimental effects to residents, sensitive equipments and high-tech production facilities in the vicinity of train tacks. Herein, aiming at the vibration mitigation for a specific high-tech industrial area, the low-frequency vibrations from a train viaduct are targeted over an anticipated range. A theoretically designed innovative countermeasure, called honeycomb wave impeding barrier (WIB) for a wave impeding barrier, is introduced and its effects are investigated by computer simulation. The present WIB is based on the wave dispersion phenomenon that can modulate the incoming wavelengths into the shorter wavelengths, creating an apparent wave cut-off characteristic in the wave field across WIB installation area. The shorter wavelengths are further impeded due to the impedance ratio of the WIB walls and in-fill materials and absorbed by the in-fills more. The three-dimensional FEM simulation demonstrates a dramatic reduction effect that is difficult to achieve by conventional measures.     

Determination of rock magnetization in a horizontal layer from the external magnetic field

The inverse problem of magnetometry is solved for a horizontal layer. Model masses are magnetized nonuniformly. The magnetization vector is a function of two horizontal coordinates. The components of this vector are determined from data on the external magnetic field.     

Dynamic response of a tunnel buried in a saturated poroelastic soil layer to a moving point load

The dynamic response of a tunnel buried in a two-dimensional poroelastic soil layer subjected to a moving point load was investigated theoretically. The tunnel was simplified as an infinite long Euler–Bernoulli beam, which was placed parallel to the traction-free ground surface. The saturated layer was governed by Biot’s theory. Combined with the specified boundary conditions along the beam and saturated poroelastic layer, the coupled equations of the system were solved analytically in the frequency–wavenumber domain based on Fourier transform. The time domain responses were obtained by the fast inverse Fourier transform. The critical velocity of the considered structure was determined from the dispersion curves. The different dynamic characteristics of the elastic soil medium and the saturated poroelastic medium subjected to the underground moving load were investigated. It is concluded that, for coarse materials or fine materials subjected to the high-velocity loading, models ignoring the coupling effects between the pore fluid and the soil skeleton may cause errors. The shear modulus and the permeability coefficients of the saturated soil as well as the load moving velocity had significant influence on the displacement and pore pressure responses.     

Flexible support of a pile embedded in unsaturated soil under Rayleigh waves

Under the action of Rayleigh waves, pile head is easy to rotate with a concrete pile cap, and pure fixed-head condition is rarely achieved, which is a common phenomenon for it usually occurs on the precast piles with insufficient anchorage. In addition, the propagation characteristics of Rayleigh wave have been changed significantly due to the existence of capillary pressure and the coupling between phases in unsaturated soil, which significantly affects the pile-soil interaction. In order to study the above problems, a coupled vibration model of unsaturated soil–pile system subjected to Rayleigh waves is established on the basis that the pile cap is equivalent to a rigid mass block. Meanwhile, the soil constitution is simplified to linear-elastic and small deformations are assumed to occur during the vibration phase of soil–pile system. Then, the horizontal dynamic response of a homogeneous free-field unsaturated soil caused by propagating Rayleigh waves is obtained by using operator decomposition theory and variable separation method. The dynamic equilibrium equation of a pile is established by using the dynamic Winkler model and the Timoshenko beam theory, and the analytical solutions of the horizontal displacement, rotation angle, bending moment and shear force of pile body are derived according to the boundary conditions of flexible constraint of pile top. Based on the present solutions, the rationality of the proposed model is verified by comparing with the previous research results. Through parametric study, the influence of rotational stiffness and yield bending moment of pile top on the horizontal dynamic characteristics of Rayleigh waves induced pile is investigated in detailed. The analysis results can be utilized for the seismic design of pile foundation under Rayleigh waves.     

Dynamic response of a flexible plate on saturated soil layer

An analytical approach is developed to study the dynamic response of a flexible plate on single-layered saturated soil. The analysis is based on Biot's two-phased theory of poroelasticity and also on the classical thin-plate theory. First, the governing differential equations for saturated soil are solved by the use of Hankel transform. The general solutions of the skeleton displacements, stresses, and pore pressures, derived in the transformed domain, are subsequently incorporated into the imposed boundary conditions, which leads to a set of dual integral equations describing the corresponding mixed boundary value problem. These governing integral equations are finally reduced to the Fredholm integral equations of the second kind and solved by standard numerical procedures. The accuracy of the present solution is validated via comparisons with existing solutions for an ideal elastic half-space. Furthermore, some numerical results are presented to show the influences of the layer depth, the plate flexibility, and the soil porosity on the dynamic compliances.     

Artificial neural network application to estimate kinematic soil pile interaction response parameters

Six artificial neural network (ANN) models are developed to predict various response parameters of kinematic soil pile interaction. These responses include (1) kinematic response factors for free and fixed head piles in homogenous soil layer to derive foundation input motion (2) normalized bending moment at fixed head of pile in homogenous soil layer (3) normalized kinematic pile moment at the interface of two soil layers of sharply different soil stiffnesses. These ANN models represent simple solutions that can be implemented in a simple calculator capable of matrix operation and bypass the site response analysis and the complex wave diffraction analysis. The data required for ANN training is generated using beam on dynamic Winkler formulation (BDWF). Fifty percent of the data is used to train the ANN models while remaining 50% is used to test the ANN models. The trained ANN models show good agreement with BDWF results.     

Performance-based seismic assessment of a large diameter extended pile shaft in a cohesionless soil

The seismic behavior of a large diameter extended pile shaft founded on a dense sandy site is investigated in this paper. First, a deterministic analysis is conducted including both nonlinear dynamic analysis(NDA) and pushover analysis to gain insights into the behavior of the pile and make sure an appropriate modeling technique is utilized. Then a probabilistic analysis is performed using the results of NDA for various demands. To this end a set of 40 pulse-like ground motions are picked and subsequently 40 nonlinear dynamic and pushover analyses are performed. The data obtained from NDA are used to generate probabilistic seismic demand model(PSDM) plots and consequently the median line and dispersion for each plot are computed. The NDA and pushover data are also plotted against each other to find out to what extent they are correlated. These operations are done for various engineering demand parameters(EDPs). A sensitivity analysis is done to pick the most appropriate intensity measure(IM) which would cause a minimum dispersion in PSDM plots out of 7 different IMs. Peak ground acceleration(PGA) is found to be the most appropriate IM. Pushover coefficient equations as a function of PGA are proposed which can be applied to the pushover analysis data to yield a better outcome with respect to the NDA. At the end, the pacific earthquake engineering research(PEER) center methodology is utilized to generate the fragility curves using the properties obtained from PSDM plots and considering various states of damage ranging from minor to severe. The extended pile shaft shows more vulnerability with a higher probability with respect to minor damage compared to severe damage.