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1.
In the present study an analytical procedure based on finite element technique is proposed to investigate the influence of vertical load on deflection and bending moment of a laterally loaded pile embedded in liquefiable soil, subjected to permanent ground displacement. The degradation of subgrade modulus due to soil liquefaction and effect of nonlinearity are also considered. A free headed vertical concrete elastic nonyielding pile with a floating tip subjected to vertical compressive loading, lateral load, and permanent ground displacement due to earthquake motions, in liquefiable soil underlain by nonliquefiable stratum, is considered. The input seismic motions, having varying range of ground motion parameters, considered here include 1989 Loma Gilroy, 1995 Kobe, 2001 Bhuj, and 2011 Sikkim motions. It is calculated that maximum bending moment occurred at the interface of liquefiable and nonliquefiable soil layers and when thickness of liquefiable soil layer is around 60% of total pile length. Maximum bending moment of 1210 kNm and pile head deflection of 110 cm is observed because of 1995 Kobe motion, while 2001 Bhuj and 2011 Sikkim motions amplify the pile head deflection by 14.2 and 14.4 times and bending moment approximately by 4 times, when compared to nonliquefiable soil. Further, the presence of inertial load at the pile head increases bending moment and deflection by approximately 52% when subjected to 1995 Kobe motion. Thus, it is necessary to have a proper assessment of both kinematic and inertial interactions due to free field seismic motions and vertical loads for evaluating pile response in liquefiable soil. 相似文献
2.
可液化场地微型桩的地震响应分析是确保工程安全和优化抗震设计的前提。应用动态离心机试验和三维有效应力数值分析方法,研究了微型单桩桩台的侧向变形和加速度、不同埋深桩身弯矩、可液化场地的加速度及超孔隙水压力等响应特征。首先开展了相对密实度为57%饱和土层、输入波是频率为1 Hz和峰值加速度为1.516 m/s2正弦波的微型桩40 g动态地震响应离心机试验,进而应用基于多重剪切机构塑性模型和液化前缘状态面概念的三维有效应力分析方法,反演了试验结果,并进行了对比分析,结果表明,数值模拟与离心机试验结果吻合,液化场地特性控制着建于其中微型桩的地震响应特征,微型桩桩台的水平变形和残余变形可达78、30 mm,桩身最大弯矩和最大残余弯矩呈现向桩身底部迁移特点,同时表明,基于动态土工离心机试验和数值分析相结合的研究方法,分析可液化场地微型桩地震响应特性是有效可行的,研究结论为可液化场地微型桩的抗震设计提供了可靠的依据和参考。 相似文献
3.
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
4.
Adel Javdani Naeini A. J. Choobbasti M. Saadati 《Arabian Journal of Geosciences》2013,6(11):4487-4497
The significance of liquefaction-related damage to pile foundations has been clearly demonstrated by the major earthquakes occurring during past years. The current project investigates the seismic behaviour of a single pile in the three-layered soil of the Babol City centre site (located in Babol City, Mazandaran Province, Iran). The site soil consists of sandy and clayey soils modelled based on the data collected from drilled boreholes. Numerical analysis was performed using Flac2D finite difference program. Three different natural ground motion records are considered, and the influence of each earthquake on the bending moment and lateral displacement of the simulated pile is investigated. In addition, the effect of vertical surcharge on the settlement of the pile during the earthquakes is investigated. Results illustrate that the maximum bending moment has occurred on the interface of liquefiable and non-liquefiable soil layers. 相似文献
5.
结合淤泥土地基中的三洋港挡潮闸工程,研究水泥土桩增强灌注桩水平承载特性的效果,在现场进行水平静载荷试验。试验时,为量测钢筋应力,在钻孔形成灌注桩时将钢筋计焊接在钢筋笼的不同高程,测得在施加水平荷载时桩身的应力分布情况,从而得到弯矩的分布;将土压力盒埋入桩侧土体中,测试在水平荷载下桩周土体的土压力分布规律。试验结果表明,打设水泥土桩能够控制灌注桩水平位移的发展,并能提高灌注桩水平承载能力;灌注桩桩身弯矩值和桩周土体的土压力的分布情况都呈现先增加后减小的变化规律,并且都主要集中在上部桩体和土体中,其最大值约为泥面以下3 m左右的位置;水泥土桩的打设能够有效地减小桩身弯矩值,并且可以减弱底部反弯矩的出现;打设有水泥土桩的灌注桩桩周土体能够提供更大的土压力。另外,灌注桩的水平承载力受上部土体的影响较大,即提高上部土体的物理力学性质可以有效增大灌注桩水平承载力。 相似文献
6.
为研究桩-土-断层耦合作用下桩基动力响应特性,利用振动台试验选取0.35g地震动峰值加速度时4种类型地震波,研究断层上下盘桩基加速度响应、桩顶相对位移、弯矩及桩基损伤情况。试验表明：断层上盘桩基各项参数明显大于断层下盘,呈现出上盘效应;桩顶峰值加速度大于桩底峰值加速度,上部土层对输入地震波具有滤波作用;桩顶加速度响应相较于桩底具有滞后性;桩顶峰值加速度与桩顶加速度放大系数α在输入El-Centro波时最大;上、下盘α 差值在输入Kobe波时最大;弯矩和桩顶相对位移峰值在输入Kobe波时最大;弯矩在土层分界面处较大,输入不同地震波时弯矩峰值均未超过桩身抗弯能力;提出了强震区近断层桩基可根据验算内容选取合理地震波进行验算的抗震设计建议。 相似文献
7.
大面积堆填或开挖时深厚软土地层内部常产生较大滑移,这为该类地层中考虑桩土作用的抗滑桩分析带来较大困难。考虑深厚软土的滑移性状,针对既有悬臂桩法计算存在的问题进行修正,滑动面上部桩身受荷段的桩身荷载采用等腰三角形分布且极值点为极限侧土压力,设滑动面下部桩身锚固段上侧桩周软土为理想弹塑性以考虑软土大位移条件,下侧为弹性状态,并通过位移叠加原理对传统方法求解产生滑动面不连续的缺陷进行修正。通过现场桩侧堆载试验验证,修正悬臂桩法的弯矩和位移计算结果较好,桩顶位移误差小于3%,桩身最大弯矩误差小于10%。所提方法有助于深厚软土地层抗滑桩的设计和计算。 相似文献
8.
在开挖、降雨或地震等外部因素作用下,边坡土体很容易进入局部或瞬态大变形乃至失稳滑动,使抗滑桩产生附加位移及弯矩。基于两阶段分析方法,采用Winkler模型模拟抗滑单桩与土之间的相互作用,建立单桩水平位移控制方程组,根据内力与位移的连续条件得到考虑不同土体侧移模式下求解桩身响应的矩阵解析表达式,并采用现场监测数据及Poulos弹性理论进行验证,证明该方法是合理可行的,并通过参数分析土体侧移对抗滑桩水平承载性状的影响程度。分析结果表明,土体侧移模式包括最大侧移值、分布形状及重心、侧移势等,对抗滑桩的挠度和弯矩均有显著影响,在工程设计中应予以充分重视。 相似文献
9.
隧道开挖会降低邻近桩基承载力,如何更为合理评价桩基水平附加响应是需要解决的问题。基于Pasternak双参数地基模型和三折线弹塑性荷载传递模型,采用两阶段分析法,并考虑侧向土体作用及地基土层的非均质特性,提出了更符合实际的单桩水平反应简化分析方法。通过与Winkler地基梁法及边界元法的对比分析,验证了方法的合理性。结合对单桩水平反应的多种影响因素进行参数分析,通过各因素相应的修正系数来对基准工况中单桩最大水平反应进行修正,得到计算工况中单桩的最大水平位移和最大弯矩。分析结果表明,桩基水平位移计算时可忽略侧向土体作用,而弯矩计算时应予以考虑;桩基计算工况的最大水平位移 最大弯矩 与平均地层损失比 呈现线性关系,而与隧道半径R、隧道轴线深度H、桩距隧道中心线距离x及桩身柔度系数 均呈现非线性关系。 相似文献
10.
Flexural response of piles under liquefied soil conditions 总被引：1，自引：1，他引：1
The paper pertains to the development of a generalized procedure to analyze and predict the flexural behavior of axially and
laterally loaded pile foundations under liquefied soil conditions. Pseudo-static analysis has been carried out taking into
consideration the combined effect of axial load and lateral load. Based on the available literature effect of degradation
on the modulus of subgrade reaction due to soil liquefaction has been incorporated in the analysis. The developed program
was calibrated and validated by comparing the predicted behavior of the pile with theoretical and experimental results reported
in literature. The predicted behavior has been found to be in excellent to very good agreement with the theoretical and observed
values in the field, respectively. The present study highlights the importance of considering the axial load from the superstructure
along with the inertia forces from the superstructure and the kinematic forces from the liquefied soil in the design of pile
foundations in liquefiable areas. The significance of densification of the soil in the liquefiable areas and presence of an
adequate top non-liquefied soil cover causing appreciable reduction in deflection and bending moment experienced by the piles
has been highlighted. 相似文献
11.
An efficient analytical approach using the finite element (FE) method, is proposed to calculate the bending moment and deflection response of a single pile under the combined influence of lateral and axial compressive loading during an earthquake, in both saturated and dry homogenous soil, and in a typical layered soil. Applying a pseudo-static method, seismic loads are calculated using the maximum horizontal acceleration (MHA) obtained from a seismic ground response analysis and a lateral load coefficient (a) for both liquefying and non-liquefying soils. It is observed that for a pile having l/d ratio 40 and embedded in dry dense sand, the normalized moment and displacement increase when the input motion becomes more severe, as expected. Further increasing of a from 0.1 to 0.3 leads to increase in the normalized moment and displacement from 0.033 to 0.042, and 0.009 to 0.035, respectively. The validity of the proposed FE based solution for estimating seismic response of pile is also assessed through dynamic centrifuge test results. 相似文献
12.
This study used model pile load testing and numerical analysis to investigate the experimental analysis results of pile and soil responses for lateral load testing due to the flexural yielding of a pile, and to examine the applicability of the distributed plastic hinge model to the numerical simulation of inelastic pile response. A lateral load test on an aluminum model pile in sand was conducted as an analysis case. The pile was loaded to a large lateral pile-head displacement, a displacement under which some of the pile sections yielded and thus the pile had inelastic flexural deformation. The test results showed that before the pile yielded, the depth of maximum moment increased with increasing load due to soil nonlinearity; after the pile yielded, the depth of maximum moment varied less and the plastic region expanded upward and downward around this depth with increasing pile displacement. In deducing the responses of the pile and soil for the pile-soil system, the actual nonlinear flexural rigidity of the pile section built based on the bending test was essential to retrieve rational ones. In addition, the distributed plastic hinge model was shown to be effective to model the inelastic pile responses and capture the development of plastic zones in the pile. 相似文献
13.
软土地层中当桩顶水平荷载较大时,采用传统m法计算容易低估桩身弯矩与挠曲变形,有必要针对该问题提出相关计算方法。将地基土体简化为理想弹塑性体,假定桩身某一深度处存在土体的弹塑性变形临界点,临界点以上的土体进入塑性变形状态,而临界点以下的土体仍处于弹性变形状态,分段建立桩身挠曲微分控制方程,得到水平受荷单桩简明弹塑性计算方法。现场单桩实测和参数敏感性分析结果表明：采用简明弹塑性计算方法得到的桩身最大弯矩较传统m法计算精度提高38.1%;桩身最大水平位移计算精度提高22.3%;桩顶边界条件对桩身水平位移与弯矩沿桩身的分布规律影响显著;桩身最大弯矩和水平位移对土体的极限抗力系数及其形状参数较敏感,设计中宜按下限值选取。 相似文献
14.
轴向和横向荷载作用下单桩的受力变形分析是桩基研究的重点内容之一。单桩在水平荷载作用下会产生一定的水平位移与弯矩,而此时作用轴向荷载会使得桩体出现一定的压曲与附加弯矩,以致轴横向荷载作用下的单桩受力变形与单独作用水平荷载或轴向荷载的单桩存在较大的区别。故本文基于能量法,首先分别建立轴横向荷载作用下单桩的受力变形能量方程以及桩周土体能量方程,然后考虑桩土变形协调与一定的桩土相互作用,基于最小势能原理得到单桩变形控制微分方程,并采用幂级数法进行求解,最终得到轴横向荷载作用下单桩受力变形分析的幂级数解答。通过编程计算,将本文方法计算结果与试验结果、数值分析结果、规范法计算结果进行对比分析,验证了本文方法的合理性和可行性。在此基础上,基于本文解答进行了影响参数分析,结果表明:桩体长径比、桩土弹性模量比、桩周土模量深度变化系数均对轴横向受荷单桩的桩身水平位移与最大弯矩值有一定的影响,其中桩周土模量深度变化系数以不小于0.6为宜。 相似文献
15.
为探明不同类型地震波作用下软弱土层差异厚度对单桩动力响应特性的影响,采用振动台试验,开展了不同软弱土层厚度变化下桩基础的加速度、水平位移、弯矩动力响应变化特性及桩基损伤分析。试验结果表明：地震波作用下,桩周土体的约束作用受软弱土层厚度的影响显著。桩身加速度在软弱土层中的放大效果最为显著,桩顶加速度放大系数与软弱土层厚度呈正相关;桩顶水平位移在软弱土层厚度最大时达到最大;桩身弯矩最大值出现在软弱土层中,随其厚度增大而增大。不同土层厚度下,桩身弯矩最大值均小于抗弯能力设计值,桩基完整性较好。桩基础抗震设计计算时,应重点加强桩基础在软弱土层中的抗震能力,并选择多种地震波进行抗震验算。 相似文献
16.
四川输电线路经过的山区场地中,碎石土地基分布普遍,而碎石土是一种介于岩石和土体之间特殊的岩土体,水平受荷碎石土桩基础在不同含石量下水平承载特性具有较大的差异,现行规范给出的地基水平抗力系数的比例系数m值取值范围较为宽泛。研究碎石土地基在不同含石量下桩-土水平作用特性与m值取值是输电线路塔桩基设计中有待解决的问题。通过室内单桩水平静载试验,得到了不同含石量的碎石土地基对桩顶位移、桩身内力、地基水平抗力系数的比例系数m值的影响,以及不同含石量下m值的变化趋势。对比分析得到试验特征规律,研究桩身弯矩、剪力曲线与桩侧土压力曲线,不同含石量条件的m值变化趋势。结果表明:随着碎石土地基含石量提高,桩身最大弯矩值呈非线性增大,且最大弯矩值约在埋深0.3 m截面位置处;碎石土含石量的提高,地基土水平抗力会有所增大,桩侧土压力零点位置也会有所提高;m值随着含石量的提高而增大。含石量每提高10%,m值约增大1.15~1.40倍,该项研究可作为地基水平抗力系数的比例系数m值取值的一个参考。 相似文献
17.
为研究液化场地中群桩在强震作用下的动力响应特征及桩侧土抗力-桩土相对位移（p-y）曲线规律,依托海文大桥实体工程,基于振动台模型试验,开展了0.15g～0.35g地震动作用饱和粉细砂土层不同埋置深度下的砂土孔压比、桩身弯矩及p-y曲线动力响应研究。结果表明：地震动强度达到0.25g时,不同埋置深度下的饱和粉细砂土层孔压比均大于0.8,产生液化现象,且随埋置深度增加,孔压比增长时刻明显滞后;不同埋置深度下,桩身弯矩最大值均位于液化土层和非液化土层分界面处;同一埋置深度时,随地震动强度的增大,p-y曲线所包围的面积逐渐增大,其整体斜率逐渐变小,说明桩-土相互作用动力耗能逐渐增大,桩周土体刚度逐渐减小;随埋置深度增加,p-y曲线所包围的面积逐渐减小,其整体斜率逐渐增大,说明桩-土相互作用动力耗能逐渐减小,桩周土体刚度逐渐增大。因此,液化场地桥梁群桩抗震设计时,应综合考虑液化土层与桩基础的相互位置关系,确保桩基础在液化土层与非液化土层分界处的抗弯承载能力。 相似文献
18.
饱和砂土地基上抗滑桩加固边坡的动力离心模型试验研究 总被引：5，自引：1，他引：4
动力离心模型试验是研究可液化地基上抗滑桩加固边坡地震动力响应的有效手段之一。使用铜质抗滑模型桩,采用黏度为50 cs的甲基硅油做为孔隙流体,通过抽真空法制作了饱和地基上的加固边坡模型。进行动力离心模型试验,研究了地震作用下饱和砂土地基中动孔压、边坡变形与土体加速度和抗滑桩弯矩的响应特征。试验结果表明,地震作用导致的动力附加弯矩相当于震前静力弯矩的87 %,说明地震作用与地基液化导致的附加弯矩不容忽视,该结论可为边坡进行抗震设计与稳定分析提供有意义的参考。 相似文献
19.
为了研究地震作用下预应力管桩的抗震性能和提高预应力管桩的延性设计水平,通过进行预应力管桩振动台试验,了解有限桩基形式下振动特性,建立预应力管桩振动分析数值模型,模拟振动试验全过程。改变桩数量和输入不同地震波加速度峰值,探讨各种桩基础形式在地震作用下的反应及抗震性能。分析结果表明,对于4桩基础,在3倍桩径的位置出现桩身反向位移,在2.5倍桩径处出现桩身负弯矩,在4～9倍桩径的区域范围内会出现开裂弯矩,在5倍桩径的位置出现弯矩最大值,在15倍桩径位置之下开始桩身弯矩急剧减小,分析结果可为预应力管桩抗震设计、制造、施工提供可靠依据。 相似文献
20.
This article revisits the influences of axial load on the lateral response of single pile with integral equation method. The problem is formulated by decomposing the pile soil system into an extended elastic soil and a fictitious pile, the former of which is analyzed by making use of the fundamental Mindlin's solution for a concentrated horizontal load whereas the latter is modeled by the conventional beam bending theory. According to the rotation compatibility condition between the fictitious pile and the extended soil, a Fredholm integral equation of the second kind is established with the shear strain and rotation angle of the fictitious pile being the basic unknowns. The bending moment and displacement distribution along the pile are subsequently obtained. Comparison with existing solutions validates the accuracy and applicability of the present formulation. The results of parametric analysis indicate that the influences of axial load on the lateral response of single piles could be significant, and in general, the bending moment and horizontal displacement distributions along the pile increase considerably with the increase of axial load. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献