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.     

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.     

General elastic analysis of piles and pile groups

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.     

Analysis of piles subjected to lateral soil movements using a three‐dimensional displacement approach

An analytical approach using the three‐dimensional displacement of a soil is investigated to provide analytical solutions of the horizontal response of a circular pile subjected to lateral soil movements in nonhomogeneous soil. The lateral stiffness coefficient of the pile shaft in nonhomogeneous soil is derived from the rocking stiffness coefficient that is obtained from the analytical solution, taking into account the three‐dimensional displacement represented in terms of scalar potentials in the elastic three‐dimensional analysis. The relationship between horizontal displacement, rotation, moment, and shear force of a pile subjected to lateral soil movements in nonhomogeneous soil is obtainable in the form of the recurrence equation. For the relationship between the lateral pressure and the horizontal displacement, it is assumed that the behavior is linear elastic up to lateral soil yield, and the lateral pressure is constant under the lateral soil yield. The interaction factors between piles subjected to both lateral load and moment are calculated, taking into account the lateral soil movement. The formulation of the lateral displacement and rotation of the pile base subjected to lateral loads in nonhomogeneous soils is presented by taking into account the Mindlin equation and the equivalent thickness for soil layers in the equivalent elastic method. For lateral movement, lateral pressure, bending moment, and interaction factors, there are small differences between results obtained from the 1‐D and the 3‐D displacement methods except a very flexible pile. Copyright © 2015 John Wiley & Sons, Ltd.     

A simplified analysis method for piled raft foundations subjected to ground movements induced by tunnelling

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.     

Analysis of rectangular piles subjected to lateral loads in nonhomogeneous soil using a Winkler model approach

An analytical approach using a Winkler model based on two lateral soil displacement components in a three‐dimensional soil is investigated to provide analytical solutions of horizontal response of a rectangular pile subjected to lateral loads in nonhomogeneous soil. The two lateral displacement components of a soil surrounding the rectangular pile are represented by the Fourier series of displacement potential functions in the elastic three‐dimensional analysis. The lateral stiffness coefficient of the rectangular pile shaft in nonhomogeneous soil is derived from the rocking stiffness coefficient taking into account rocking rotation of a rigid pile shaft. The relationship between horizontal displacement, rotation, moment, and shear force for the rectangular pile subjected to horizontal loads in nonhomogeneous soil is obtainable in the form of the recurrence equation. The formulation of lateral displacement and rotation for a rectangular pile subjected to lateral loads on the pile base in nonhomogeneous soil is proposed by taking into account Mindlin's equation and the equivalent thickness for soil layers in the equivalent elastic method. The difference of lateral behavior between square and circular piles subjected to lateral loads is insignificant. The effect of aspect ratio of the rectangular pile on the lateral behavior is great for the lower stiffness ratio between pile and soil and the larger length–equivalent diameter ratio. The effect of the value of Poisson's ratio of soil on lateral stiffness coefficient is relatively small except Poisson's ratio close to 0.5. The comparison of the results calculated by the current method for a rectangular pile subjected to lateral loads in nonhomogeneous soil has shown good agreement with those obtained from the analytical methods and the finite element method. Copyright © 2015 John Wiley & Sons, Ltd.     

Numerical analysis of the response of battered piles to inclined pullout loads

This paper presents a three‐dimensional finite element analysis of the response of battered piles to the combined lateral and vertical pullout loads. Analyses are carried out using an elastoplastic constitutive law based on the non‐associated Mohr–Coulomb criterion. The influence of the contact condition at the pile–soil interface is also investigated. Analyses show that the load's inclination with regard to the pile's axis affects both the lateral and axial response of the battered piles. Analyses also show that the pullout capacity of battered piles is affected by the pile's inclination regarding the vertical axis as well as the load's inclination regarding the pile's axis. The investigation of the influence of the contact condition at the soil–pile interface shows that the possibility of sliding at the soil–pile interface affects the response of battered piles subjected to loads with low inclination regarding the pile's axis. Copyright © 2008 John Wiley & Sons, Ltd.     

基于两阶段法的堆载对公路桥梁桩基础影响分析

首先基于布西奈斯克解,将表面作用有集中荷载时半无限弹性体的应力变形解在荷载作用区域利用复合辛普森公式进行数值积分,得到了表面处于不同形式的分布荷载作用下土体自由场水平及竖直方向应力和变形的计算公式。结合有限差分法及Mindlin位移解分别推导出弹性地基中桩顶作用有集中荷载时单桩桩、土单元的位移,两者结合便得到主动桩的分析方法。通过将堆载作用下的土体自由场位移施加于桩上把上述自由场分析及主动桩分析结合起来,推导出堆载作用下被动单桩的竖向和水平向承载特性的分析方法。选取地表附近作用有矩形均布荷载的计算工况,通过与有限元计算结果的对比验证了所提出的分析方法的正确性;将所提出的方法计算结果与某处工程案例中实测数据结果进行对比,分析表明利用该方法分析堆载对邻近桩基的水平及竖向影响是合理可靠的。     

Numerical analyses of uplift behavior of pile foundation for transmission line structure in frozen soil regions北大核心CSCD

Pile foundation is one of the most commonly used and suitable foundations to support transmission line structure, especially in seasonally frozen soil regions and permafrost regions. Axial compression is the controlling condition in the design of foundations for such structures as bridges and buildings, while uplift and overturning will control the design of transmission line structure foundations. This paper presents an extensive overview of previous studies including experimental (e. g., laboratory model test and full-scale field load test), analytical/theoretical (e. g., limit equilibrium and limit analysis based on plasticity)and numerical(e. g., finite difference and finite element methods). The review indicates that study on the uplift behavior of pile foundation in frozen soil is relatively limited, particularly in the case of combined effect of axial uplift and lateral loading. Interaction between pile and frozen soil and mechanism of load transfer along the pile shaft and around the pile tip still remain unclear. Therefore, this paper implements finite difference analysis within FLAC3D to investigate the behavior of pile foundation in frozen silty clay and gravelly sand under axial uplift behavior and the effect of ground condition and lateral loading on the uplift behavior. Because of the axisymmetric condition of the problem studied, only half of the model is simulated. The chosen domain of the medium is discretized into a set of quadrilateral elements and the pile is discretized by the cylinder element. The interaction between the soil and pile is considered according to interface elements. Mohr-Coulomb criterion is adopted to model the soil behavior (perfectly elastic-plastic), while the pile is simply considered as a rigid body. The soil parameters such as Young’s modulus, cohesion and internal friction angle used for numerical analyses are determined by laboratory tests and estimated according to the empirical correlations with in-situ tests. The present numerical modeling is verified with the results from field loading tests on pile foundations in Qinghai-Tibet ±550 kV transmission line project. On this basis, parametric studies are carried out to uncover the behavior of pile in frozen soil. It is observed that pullout is the dominant failure mechanism of pile and the uplift load-displacement curve clearly exhibits an asymptote, consisting of initially linear elastic, nonlinear transition, and finally linear regions. These results are consistent with the observations in a few previous studies. In addition, larger uplift capacity of pile foundation in freezing period and gravelly sand is gained (about 20%). Lateral loading increases the deflection and therefore, decreases the uplift capacity of pile foundation. For the convenience of using the results obtained in practice, the values of uplift factor for pile foundation in silty clay and gravelly sand are provided. Finally, it should be noted that the method used, and the results obtained in the current work could be useful for engineers and designers, at least providing them some qualitative evidence for pile design in seasonally frozen soil regions and permafrost regions. This is important and necessary to ensure the safety of construction in such regions. Meanwhile, numerical analyses in the current work can be a benchmark example for subsequent research studies. © 2022 Science Press (China).     

Three dimensional elasto‐plastic interface for embedded beam elements with interaction surface for the analysis of lateral loading of piles

This paper presents a numerical formulation for a three dimensional elasto‐plastic interface, which can be coupled with an embedded beam element in order to model its non‐linear interaction with the surrounding solid medium. The formulation is herein implemented for lateral loading of piles but is able to represent soil‐pile interaction phenomena in a general manner for different types of loading conditions or ground movements. The interface is formulated in order to capture localized material plasticity in the soil surrounding the pile within the range of small to moderate lateral displacements. The interface is formulated following two different approaches: (i) in terms of beam degrees of freedoms; and (ii) considering the displacement field of the solid domain. Each of these alternatives has its own advantages and shortcomings, which are discussed in this paper. The paper presents a comparison of the results obtained by means of the present formulation and by other well‐established analysis methods and test results published in the literature. Copyright © 2016 John Wiley & Sons, Ltd.     

Approximate computer analysis of pile groups subjected to loads and ground movements

This paper describes the development of an approximate approach for the analysis and design of piles subjected to axial and lateral loading and also to vertical and horizontal ground movements. The analysis involves a number of simplifications in order to make it feasible to implement. For example, it considers the behaviour of a ‘representative’ pile in a group to characterize the behaviour of all piles in the group, and adopts approximations to derive free-field interaction factors from the conventional interaction factors for direct loading. The analysis has been implemented via a computer program called EMbankment PIle Group (EMPIG) and has the ability to incorporate the following features:

• 1. single piles or pile groups,
• 2. applied vertical, lateral and moment loading on the pile cap,
• 3. the effects of axial and lateral soil movements caused by embankment construction,
• 4. a layered soil profile,
• 5. non-linear axial and lateral response of the piles.

Comparisons between solutions from EMPIG and other independent programs suggest that it is capable of providing results of adequate accuracy for practical design purposes. The analysis has been used to investigate the effects of pile rake on a typical bridge abutment group. The presence of raked piles can have a detrimental effect on group behaviour, especially in the presence of ground movements. Large lateral deflections can be generated and axial forces and moments in the piles are increased. Comparisons are also made with the results of centrifuge model tests on abutment pile groups. Copyright © 1999 John Wiley & Sons, Ltd.     

Skin friction features of drilled CIP piles in sand from pile segment analysis

Numerical pile segment analysis is conducted in this study with an advanced soil model to investigate the skin friction behaviour of a drilled Cast‐In‐Place (CIP) pile installed in sand. Although the interface between the sand and pile is considered rough, thin elements adjacent to the pile are used to include effects of localized shear. Unit weights of fluid concrete and accompanied changes in stress are considered as the effects of pile installation. Changes in effective stresses are the most prominent effect due to pile installation with a change in direction of the major principal stress from the vertical to the radial direction. Shear behaviour of the sand at the interface during the early shear stage is related to the contractive tendency of the sand at small strain levels. Changes in the stress field around the pile with little changes in volumetric strain take place during the early shear stage. Stress redistributions during the early shear stage depend on the direction of the major principal stress before shear. Results of the pile segment analyses for drilled CIP piles show good agreement with design methods. Parametric studies are used to characterize the effects of sand density and pile diameter on the skin friction behaviour of drilled CIP piles. Copyright © 2007 John Wiley & Sons, Ltd.     

被动桩侧土体位移场的透明土模型试验

常规室内模型试验中,土体侧向位移作用下桩身变形特性能够获得,而桩周土体内部的位移很难量测。因此,结合透明土材料、粒子图像测速(PIV)技术和光学测量系统,设计了侧向位移作用下被动桩桩周土体变形测量试验系统。通过非插入式测量,得到桩不同埋置深度下桩周土体的位移场。试验结果表明:相同侧向位移模式下,桩埋置深度越大,桩对桩前土体的遮拦效应越明显,中间与两侧土体的相对位移越大。基于模型试验的结果建立了数值模型,参数敏感分析表明土体侧向位移形状对桩前土体位移遮拦效应的影响程度依次为矩形、抛物线形和三角形,且遮拦效果随着桩径的增加而更加明显。     

An analysis method for the influence of tunneling on adjacent loaded pile groups with rigid elevated caps

Tunnel excavation could influence the working performance of adjacent pile foundations. How to accurately predict the tunneling‐induced pile responses is becoming an important issue in urban areas. Previous methods tend to neglect the influence of working loads on the tunneling‐induced pile responses. In this paper, a two‐stage analysis method is proposed to study the behavior of pile groups with rigid elevated caps subjected to tunneling‐induced ground movements, in which the pile–pile interaction, coupling of longitudinal and lateral deformation, and influence of working loads are considered. This method is validated by comparing the results with those from a general pile analysis program, GEPAN, centrifuge test data and field measured data. Thereafter, a series of parametric studies is carried out. The results show that the influence of working load on tunneling‐induced pile responses is significant. Three different features of the pile responses will take place for different depth ratios. With the increase in soil stiffness, the tunneling‐induced axial force increases linearly, whereas the bending moment increases nonlinearly. For soils with high stiffness, the maximum bending moment increases linearly with the ground loss ratio within the range of 0–5%; but for soils with low stiffness, this tendency becomes obviously nonlinear. Copyright © 2010 John Wiley & Sons, Ltd.     

Embedded beam element with interaction surface for lateral loading of piles

This paper presents a numerical formulation of a three dimensional embedded beam element for the modeling of piles, which incorporates an explicit interaction surface between soil and pile. The formulation is herein implemented for lateral loading of piles but is able to represent soil–pile interaction phenomena in a general manner for different types of loading conditions or ground movements. The model assumes perfect adherence between beam and soil along the interaction surface. The paper presents a comparison of the results obtained by means of the present formulation and by means of a previously formulated embedded pile element without interaction surface, as well as reference semi‐analytical solutions and a fully 3D finite element (FE) model. It is seen that the proposed embedded element provides a better convergence behavior than a previously formulated embedded element and is able to reproduce key features of a full 3D FE model. Copyright © 2015 John Wiley & Sons, Ltd.     

土体水平位移对邻近既有桩基承载性状影响分析

城市建设中经常会遇到由于堆载或基坑开挖所引起的土体水平位移现象,土体水平位移的作用会使邻近建筑物的桩基础产生附加内力或变形,并可能导致邻近桩基的破坏而发生工程事故。针对此类问题,基于Winkler地基模型以及桩-土变形协调条件,建立单桩水平位移控制方程,根据内力与位移的微分关系,采用两阶段方法进行求解。结合典型的工程事故,通过参数分析,研究土体水平位移对邻近桩基承载性状的影响程度。分析表明,基坑工程围护墙体的稳定和开挖深度对邻近桩基的安全有着重要影响,并提出了近期发生在上海的某小高层楼房整体倒覆事故的一种可能原因。     

软土中已打入桩对土体位移的遮帘作用研究

采用侧向移动土中桩的理论分析结果以及有限元数值模拟,较为系统地分析了沉桩工程中已打入桩对土体侧向位移及地表隆起的遮帘作用,结果表明已打入桩对土体侧向位移的总体遮帘作用并不显著。采用不同切向劲度系数的接触面单元以模拟已打入桩间隔时间长短对地表隆起的遮帘效应,结果表明：打入桩间隔期较短时,已打入桩对地表隆起的遮拦作用主要体现在对土体位移的“水平阻隔”上,土体沿桩土界面发生流动向上隆起;而间隔期较长时,桩土间存在有较大的摩阻力而限制了土体的位移,此时已打入桩对地表隆起的遮拦作用体现在竖向摩阻力对土体隆起的“抑制”上。     

A study of the effect of driving on pre‐bored piles

A finite element model for pile‐driving analysis is developed and used to investigate the behaviour of pre‐bored piles, which are then driven the last 1.25 or 2.25 m to their final design depth. The study was conducted for the case of saturated clays. The model traces the penetration of the pile into the soil and accommodates for large deformations. The non‐linear behaviour of the clay in this study is predicted using the bounding‐surface‐plasticity model, as applied to isotropic cohesive soils. The details of the 3‐D numerical modelling and computational schemes are presented. A significant difference was observed in the pile displacement during driving, and in the computed soil resistance at the pile tip, particularly at the earliest driving stages. No difference in soil resistance at the soil pile interface along the pile shaft was detected between the pre‐bored piles whether driven 1.25 or 2.25 m. Copyright © 2002 John Wiley & Sons, Ltd.     

Thermal analysis of energy piles in sand

The present work investigates the behaviour of geothermal energy piles in sand subjected to thermal loading and the resulting soil-structure interaction, numerically using the finite element software Abaqus and user-defined material subroutines for soil. The stress-strain response of sand has been simulated using CASM constitutive model based on critical-state soil mechanics. Detailed parametric sensitivity studies have been carried out to understand the effects of different end conditions of the pile, relative densities of the soil, coefficients of lateral earth pressure of the ground, lengths and diameters of the pile, thermal loads, coefficients of friction at the pile-soil interface, critical-state friction angles of soil, thermal conductivity of soil, specific heat of soil and thermal conductivity of the pile on the stress response of soil, deformation of the pile and soil, and strains in the pile. The results show that negative shear stress is generated in the soil at the pile-soil interface. In the pile with both ends restrained the lateral earth pressure coefficient in soil increases due to high radial strain generation. Moreover, the lateral earth pressure coefficient in soil increases with the increase in the thermal load, the coefficient of friction at the pile-soil interface and the critical-state friction angle of the soil.     

A non‐linear coupled finite element–boundary element model for the prediction of vibrations due to vibratory and impact pile driving

This paper presents a non‐linear coupled finite element–boundary element approach for the prediction of free field vibrations due to vibratory and impact pile driving. Both the non‐linear constitutive behavior of the soil in the vicinity of the pile and the dynamic interaction between the pile and the soil are accounted for. A subdomain approach is used, defining a generalized structure consisting of the pile and a bounded region of soil around the pile, and an unbounded exterior linear soil domain. The soil around the pile may exhibit non‐linear constitutive behavior and is modelled with a time‐domain finite element method. The dynamic stiffness matrix of the exterior unbounded soil domain is calculated using a boundary element formulation in the frequency domain based on a limited number of modes defined on the interface between the generalized structure and the unbounded soil. The soil–structure interaction forces are evaluated as a convolution of the displacement history and the soil flexibility matrices, which are obtained by an inverse Fourier transformation from the frequency to the time domain. This results in a hybrid frequency–time domain formulation of the non‐linear dynamic soil–structure interaction problem, which is solved in the time domain using Newmark's time integration method; the interaction force time history is evaluated using the θ‐scheme in order to obtain stable solutions. The proposed hybrid formulation is validated for linear problems of vibratory and impact pile driving, showing very good agreement with the results obtained with a frequency‐domain solution. Linear predictions, however, overestimate the free field peak particle velocities as observed in reported field experiments during vibratory and impact pile driving at comparable levels of the transferred energy. This is mainly due to energy dissipation related to plastic deformations in the soil around the pile. Ground vibrations due to vibratory and impact pile driving are, therefore, also computed with a non‐linear model where the soil is modelled as an isotropic elastic, perfectly plastic solid, which yields according to the Drucker–Prager failure criterion. This results in lower predicted free field vibrations with respect to linear predictions, which are also in much better agreement with experimental results recorded during vibratory and impact pile driving. Copyright © 2008 John Wiley & Sons, Ltd.