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1.
A series of centrifuge shaking table model tests are conducted on 4?×?4 pile groups in liquefiable ground in this study, achieving horizontal–vertical bidirectional shaking in centrifuge tests on piles for the first time. The dynamic distribution of forces on piles within the pile groups is analysed, showing the internal piles to be subjected to greater bending moment compared with external piles, the mechanism of which is discussed. The roles of superstructure–pile inertial interaction and soil–pile kinematic interaction in the seismic response of the piles within the pile groups are investigated through cross-correlation analysis between pile bending moment, soil displacement, and structure acceleration time histories and by comparing the test results on pile groups with and without superstructures. Soil–pile kinematic interaction is shown to have a dominant effect on the seismic response of pile groups in liquefiable ground. Comparison of the pile response in two tests with and without vertical input ground motion shows that the vertical ground motion does not significantly influence the pile bending moment in liquefiable ground, as the dynamic vertical total stress increment is mainly carried by the excess pore water pressure. The influence of previous liquefaction history during a sequence of seismic events is also analysed, suggesting that liquefaction history could in certain cases lead to an increase in liquefaction susceptibility of sand and also an increase in dynamic forces on the piles. 相似文献
2.
Chunyang Liu Hoda Soltani Kanthasamy K. Muraleetharan Amy B. Cerato Gerald A. Miller Sri Sritharan 《Acta Geotechnica》2016,11(6):1431-1444
Presented in this paper are results of two centrifuge tests on single piles installed in unimproved and improved soft clay (a total of 14 piles), with the relative pile–soil stiffness values varying nearly two orders of magnitude, and subjected to cyclic lateral loading and seismic loading. This research was motivated by the need for better understanding of lateral load behavior of piles in soft clays that are improved using cement deep soil mixing (CDSM). Cyclic test results showed that improving the ground around a pile foundation using CDSM is an effective way to improve the lateral load behavior of that foundation. Depending on the extent of ground improvement, elastic lateral stiffness and ultimate resistance of a pile foundation in improved soil increased by 2–8 times and 4–5 times, respectively, from those of a pile in the unimproved soil. While maximum bending moments and shear forces within piles in unimproved soil occurred at larger depths, those in improved soil occurred at much shallower depths and within the improved zone. The seismic tests revealed that, in general, ground improvement around a pile is an effective method to reduce accelerations and dynamic lateral displacements during earthquakes, provided that the ground is improved at least to a size of 13D × 13D × 9D (length × width × depth), where D is the outside diameter of the pile, for the pile–soil systems tested in this study. The smallest ground improvement used in these tests (9D × 9D × 6D), however, proved ineffective in improving the seismic behavior of the piles. The ground improvement around a pile reduces the fundamental period of the pile–soil system, and therefore, the improved system may produce larger pile top accelerations and/or displacements than the unimproved system depending on the frequency content of the earthquake motion. 相似文献
3.
A simplified method of numerical analysis has been developed to estimate the deformation and load distribution of piled raft foundations subjected to vertical, lateral, and moment loads, using a hybrid model in which the flexible raft is modelled as thin plates and the piles as elastic beams and the soil is treated as springs. Both the vertical and lateral resistances of the piles as well as the raft base are incorporated into the model. Pile–soil–pile, pile–soil–raft and raft–soil–raft interactions are taken into account based on Mindlin's solutions for both vertical and lateral forces. The validity of the proposed method is verified through comparisons with several existing methods for single piles, pile groups and piled rafts. Workable design charts are given for the estimation of the lateral displacement and the load distribution of piled rafts from the stiffnesses of the raft alone and the pile group alone. Additionally, parametric studies were carried out concerning batter pile foundations. It was found that the use of batter piles can efficiently improve the deformation characteristics of pile foundations subjected to lateral loads. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
4.
Zheng Li Panagiotis Kotronis Sandra Escoffier Claudio Tamagnini 《国际地质力学数值与分析法杂志》2018,42(12):1346-1365
Batter piles are widely used in geotechnical engineering when substantial lateral resistance is needed or to avoid the interference with existing underground constructions. Nevertheless, there is a lack of fast numerical tools for nonlinear soil‐structure interactions problems for this type of foundation. A novel hypoplastic macroelement is proposed, able to reproduce the nonlinear response of a single batter pile in sand under monotonic and cyclic static loadings. The behavior of batter piles (15°, 30°, and 45°) is first numerically investigated using 3D finite element modeling and compared with the behavior of vertical piles. It is shown that their response mainly depends on the pile inclination and the loading direction. Then, starting from the macroelement for single vertical piles in sand by Li et al (Acta Geotechnica, 11(2):373‐390, 2016), an extension is proposed to take into account the pile inclination introducing simple analytical equations in the expression describing the failure surface. 3D finite element numerical models are adopted to validate the macroelement that is proven able to reproduce the nonlinear behavior in terms of global quantities (forces‐displacements) and to significantly reduce the necessary computational time. 相似文献
5.
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
6.
旋喷群桩复合地基承载特性的数值分析 总被引：2，自引：0，他引：2
旋喷桩加固软土地基在各种地基处理工程中得到了广泛应用。对旋喷桩的研究多数集中在其施工工艺的改进上,或者针对单桩的承载特性进行研究,而对旋喷群桩的承载特性则研究不多。根据工程实际情况,采用基于MIDAS-GTS的三维有限元分析技术,通过改变旋喷群桩的布置方式、桩弹性模量、桩长、桩径、桩距等设计参数及桩-土接触面等参数对旋喷群桩复合地基承载特性的影响进行了研究。研究表明：旋喷桩加固软土地基主要减小了地表至桩底深度范围内土体的竖向沉降,对桩底下方的土体沉降基本无影响;提高旋喷桩桩径及材料强度会提高复合地基承载能力;不同旋喷桩布置方式、桩-土之间是否设置Goodman接触面单元对地基承载能力基本无影响。 相似文献
7.
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
8.
砂土地基斜桩水平承载特性p-y曲线法 总被引：2，自引：0，他引：2
基于Reese建议的砂土p-y曲线,提出了适用于斜桩水平承载特性分析的修正p-y曲线及相应的有限元分析方法。根据桩前土体受力特点,假设桩前浅层土体达到极限破坏状态时桩侧被动破坏区为一个三维楔形体,采用极限平衡分析方法导出了斜桩桩侧极限土抗力表达式,对比研究了斜桩倾角、桩-土界面摩擦系数等因素对极限土抗力的影响规律,并给出了斜桩初始地基反力模量确定方法。在此基础上,修正Reese提出的直桩p-y曲线,提出了砂土地基中斜桩p-y曲线确定方法。利用虚功原理,导出了斜桩水平承载特性分析的有限单元列式,编制相应的分析程序,通过算例验证了方法的合理性和有效性。最后,采用修正的p-y曲线法对一离心机模型试验进行了模拟分析,结果表明,计算与试验结果吻合得很好 相似文献
9.
通过模型试验研究了竖向荷载作用下砂土中斜桩的荷载传递性状,分析了桩身倾角及长径比对斜桩桩身轴力、弯矩、剪力、桩侧摩阻力及端阻比的影响。试验结果表明：在桩顶竖向荷载作用下,斜桩桩身轴力均小于相应直桩桩身轴力,桩身倾角越大,轴力沿深度衰减得越快,桩长径比越大,轴力沿深度衰减得也越快;斜桩桩身最大弯矩随桩身倾角及长径比的增加而增加,最大弯矩出现的深度与桩身倾角无关,只与长径比相关;不论桩身倾角及长径比的大小,斜桩桩身最大剪力均出现在桩顶截面处,桩身最大剪力随着桩身倾角的增加而增大;桩身倾角越大,斜桩最大摩阻力越大,长径比越大,斜桩最大摩阻力越小,斜桩最大摩阻力出现在桩顶下1/4～1/5桩长处;斜桩端阻比随着桩顶竖向荷载的增加而增大,随着桩身倾角及长径比的增加而减小。 相似文献
10.
This article derives the closed‐form solutions for estimating the vertical surface displacements of cross‐anisotropic media due to various loading types of batter piles. The loading types include an embedded point load for an end‐bearing pile, uniform skin friction, and linear variation of skin friction for a friction pile. The planes of cross‐anisotropy are assumed to be parallel to the horizontal ground surface. The proposed solutions are never mentioned in literature and can be developed from Wang and Liao's solutions for a horizontal and vertical point load embedded in the cross‐anisotropic half‐space. The present solutions are identical with Wang's solutions when batter angle equals to 0°. In addition, the solutions indicate that the surface displacements in cross‐anisotropic media are influenced by the type and degree of material anisotropy, angle of inclination, and loading types. An illustrative example is given at the end of this article to investigate the effect of the type and degree of soil anisotropy (E/E′, G′/E′, and ν/ν′), pile inclination (α), and different loading types (a point load, a uniform skin friction, and a linear variation of skin friction) on vertical surface displacements. Results show that the displacements accounted for pile batter are quite different from those estimated from plumb piles, both driven in cross‐anisotropic media. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
11.
Goit Chandra Shekhar Saitoh Masato Igarashi Takumi Sasaki Shun 《Acta Geotechnica》2021,16(4):1231-1245
Physical-scaled model testing under 1 g conditions is carried out in obtaining the vertical response of fixed head floating-inclined single piles embedded in dry sand. Practical pile inclinations of 5° and 10° besides a vertical pile (0°) subjected to static and dynamic vertical pile head loadings are considered. To account for the effects of soil nonlinearity as well as the soil–pile interface nonlinearity on the response of piles, a range of low-to-high magnitude of pile head displacements is considered for the static case while a varying amplitude of harmonic accelerations for a wide range of frequencies is considered for the dynamic case. Experimental results are obtained in the form of pile head stiffnesses and strains generated in the pile under both the static and dynamic loadings. Results suggest that the nonlinear behavior of soil as well as the nonlinearity generated at the interface between the soil and the pile as the result of applied loading considerably affect the response of piles. The soil–pile interface nonlinearity that governs the slippage of pile shows a clear influence on the pile head stiffnesses by providing two distinct values of stiffnesses corresponding to the push and the pull directional movement of piles; the two values are significantly different. Axial and bending strains generated in the piles show expected dependency on the amplitude of applied loading; the pile head-level bending strain increases almost linearly with the increase in the angle of pile inclination.
相似文献12.
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
13.
This paper evaluates the potential of two machine learning approaches i.e. Support vector machine (SVR) and Gaussian processes (GP) regression to model the oblique load capacity of batter pile groups. Linear regression was used to compare the performance of both SVR and GP based regression approaches to model the oblique load. Data set used consists of 147 samples obtained from the laboratory experiments. Out of the total sample size, 105 randomly selected samples were used for training whereas remaining 42 were used for testing the models. Input data set consist of angle of oblique load, pile length, sand relative density, number of vertical piles, number of batter piles where as oblique load was considered as output. Two kernel functions i.e. Polynomial and radial based kernel function were used with both SVR and GP regression. A comparison of results suggest that radial basis function based SVR approach works well in comparison to GP and linear regression based approaches and it could successfully be employed in modelling the oblique load capacity of batter pile groups. Parametric analysis and sensitivity analysis suggest that loading angle, pile length and number of batter pile were important in prediction of oblique load. 相似文献
14.
The plugging of pipe piles is an important phenomenon, which is not adequately accounted for in the current design recommendations. An open-ended pipe pile is said to be plugged when the soil inside the pile moves down with the pile, resulting in the pile becoming effectively closed-ended. Plugging is believed to result in an increase in the horizontal stresses between the pile and the surrounding soil, which results in an increase in skin friction. A total number of 60 model pile tests are carried out to investigate the behavior of plugs on the pile load capacity and the effects of plug removal. Different parameters are considered, such as pile diameter–to–length ratio, types of installation in sands of different densities, and removal of the plug in three stages (50, 75, and 100 %) with respect to the length of plug. The changes in the soil plug length and incremental filling ratio (IFR) with the penetration depth during pile driving show that the open-ended piles are partially plugged from the outset of the pile driving. The pile reached a fully plugged state for pressed piles in loose and medium sand and partially plugged (IFR = 10 %) in dense sand. For driven piles, the IFR is about 30 % in loose sand, 20 % in medium sand, and 30 % in dense sand. The pile load capacity increases with increases in the length of the plug length ratio (PLR). The rate of increase in the value of the pile load capacity with PLR is greater in dense sand than in medium and loose sand. Based on test results, new empirical relation for the estimation of the load carrying capacity of open-ended piles based on the IFR is proposed. 相似文献
15.
分析了刚性桩复合地基中垫层、桩及桩间土的共同作用机理,考虑复合地基中桩、土变形协调,提供一种计算复合地基桩土应力比的方法;在此基础上研究复合地基中垫层模量、桩端持力层模量、桩土相对刚度比、桩长径比、面积置换率等因素对复合地基桩土应力比的影响,分析刚性桩复合地基的承载特性。 相似文献
16.
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
17.
Asskar Janalizade Choobbasti Meysam Saadati Hamid Reza Tavakoli 《Arabian Journal of Geosciences》2012,5(6):1307-1315
The performance of pile foundations in liquefiable soil subjected to earthquake loading is a very complex process. The strength and stiffness of the soil decrease due to the increase in pore pressure. The pile can be seriously destroyed by the soil liquefaction during strong earthquakes. This paper presents the response of vertical piles in liquefiable soil under seismic loads. A finite difference model, known as fast Lagrangian analysis of continua, is used to study the pile behavior considering a nonlinear constitutive model for soil liquefaction and pile?Csoil interaction. The maximum lateral displacement and maximum pile bending moment are obtained for different pile diameters, earthquake predominant frequencies, Arias intensities, and peak accelerations. It is found that the maximum lateral displacement and the maximum pile bending moment increase when the predominant earthquake frequency value decreases for a given peak acceleration value. 相似文献
18.
Harry G. Poulos 《国际地质力学数值与分析法杂志》1999,23(10):1021-1041
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.
19.
A modulus‐multiplier approach, which applies a reduction factor to the modulus of single pile p–y curves to account for the group effect, is presented for analysing the response of each individual pile in a laterally loaded pile group with any geometric arrangement based on non‐linear pile–soil–pile interaction. The pile–soil–pile interaction is conducted using a 3D non‐linear finite element approach. The interaction effect between piles under various loading directions is investigated in this paper. Group effects can be neglected at a pile spacing of 9 times the pile diameter for piles along the direction of the lateral load and at a pile spacing of 6 times the pile diameter for piles normal to the direction of loading. The modulus multipliers for a pair of piles are developed as a function of pile spacing for departure angle of 0, 90, and 180sup>/sup> with respect to the loading direction. The procedure proposed for computing the response of any individual pile within a pile group is verified using two well‐documented full‐scale pile load tests. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
20.
This work presents analytical solutions to compute the vertical stresses for a cross‐anisotropic half‐space due to various loading types by batter piles. The loading types are an embedded point load for an end‐bearing pile, uniform skin friction, and linear variation of skin friction for a friction pile. The cross‐anisotropic planes are parallel to the horizontal ground surface. The proposed solutions can be obtained by utilizing Wang and Liao's solutions for a horizontal and vertical point load acting in the interior of a cross‐anisotropic medium. The derived cross‐anisotropic solutions using a limiting approach are in perfect agreement with the isotropic solutions of Ramiah and Chickanagappa with the consideration of pile inclination. Additionally, the present solutions are identical to the cross‐anisotropic solutions by Wang for the batter angle equals to 0. The influential factors in yielded solutions include the type and degree of geomaterial anisotropy, pile inclination, and distinct loading types. An example is illustrated to clarify the effect of aforementioned factors on the vertical stresses. The parametric results reveal that the stresses considering the geomaterial anisotropy and pile batter differ from those of previous isotropic and cross‐anisotropic solutions. Hence, it is imperative to take the pile inclination into account when piles are required to transmit both the axial and lateral loads in the cross‐anisotropic media. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献