共查询到20条相似文献，搜索用时 31 毫秒
1.
A. J. Choobbasti A. Zahmatkesh R. Noorzad 《Geotechnical and Geological Engineering》2011,29(5):675-684
Stone columns (or granular piles) are increasingly being used for ground improvement. This study investigates the qualitative
and quantitative improvement in soft clay by stone columns. Finite element analyses were carried out to evaluate the performance
of stone columns in soft clay. A drained analysis was carried out using Mohr–Coulomb’s criterion for soft clay, stones, and
sand. The interface elements were used at the interface between the stone column and soft clay. Analyses and calculations
were carried out to determine equivalent parameters of soil/columns system. The bearing capacity ratio (BCR) of the soil has
been estimated for homogeneous and heterogeneous soil. The results have shown that the values of BCR for homogeneous soil
are obviously higher than those for heterogeneous soil. 相似文献
2.
水平旋喷桩施工引起周围土体变形分析 总被引：1，自引：0，他引：1
水平旋喷桩施工期间,大量高压流体注入土层,引起土层内部产生较大的膨胀作用,致使周围一定区域的土体发生变形。水平旋喷桩施工引起土体变形可以归结为压力膨胀和体积膨胀共同作用的问题。依托单根水平旋喷桩施工的现场实例,建立了水平旋喷桩施工引起土体变形的数值模型。将水平旋喷桩施工引起的土体变形问题简化为圆孔的膨胀问题,可以统筹考虑注浆压力和注浆流量的影响。首先需要确定注浆压力的影响半径和注浆流量引起的体积膨胀比,然后可以通过数值模型计算膨胀引起的土体变形。数值分析结果与现场实测值的对比表明,当注浆压力影响半径为成桩半径的6倍时,数值计算结果与现场实测值吻合较好。 相似文献
3.
Consolidation and deformation around stone columns: Numerical evaluation of analytical solutions 总被引：1，自引：0，他引：1
Coupled finite element analyses of the consolidation and deformation around stone columns have been performed to assess the accuracy of different analytical solutions. The numerical model reproduces the hypotheses of the closed-form solutions. In the model, a rigid load is applied to a unit cell formed by a fully penetrating column and its surrounding soil, and simple elastic or elasto-plastic soil models are used. The surface settlement, the dissipation of the pore pressure and the vertical stress concentration on the column are studied. These soil responses are accurately estimated with closed-form solutions that properly include the radial and plastic strains in the column. However, the surrounding soil does not yield for usual conditions, which reasonably justifies the elastic soil behavior assumed in the analytical solutions. The differences between drained and consolidation analyses are also evaluated. Comparing the numerical results with the closed-form solutions illustrates the implications of the assumptions of each approach. 相似文献
4.
Stone columns in soft soil improve bearing capacity because they are stiffer than the material which they replace, and compacted stone columns produce shearing resistances which provide vertical support for overlying structures or embankments. Also stone columns accelerate the consolidation in the native surrounding soil and improve the load settlement characteristics of foundation. In this paper, the finite element method is utilized as a tool for carrying out analyses of stone column–soil systems under different conditions. A trial is made to improve the behaviour of stone column by encasing the stone column with geogrid as reinforcement material. The program CRISP-2D is used in the analysis of problems. The program allows prediction to be made of soil deformations considering Mohr-Coulomb failure criterion for elastic–plastic soil behaviour. A parametric study is carried out to investigate the behaviour of standard and encased floating stone columns in different conditions. Different parameters were studied to show their effect on the bearing improvement and settlement reduction of the stone column. These include the length to diameter ratio (L/d), shear strength of the surrounding soil and, the area replacement ratio (as) and others. It was found that the maximum effective length to diameter (L/d) ratio is between (7–8) for Cu, between (20–40) kPa and between (10–11) for Cu?=?10?kPa for ordinary floating stone columns while the effective (L/d) ratio is between (7–8) for encased floating stone columns. The increase in the area replacement ratio increases the bearing improvement ratio for encased floating stone columns especially when the area replacement ratio is greater than (0.25). The geogrid encasement of stone column greatly decreases the lateral displacement compared with ordinary stone column. 相似文献
5.
碎石桩复合地基性状的弹塑性分析 总被引：3，自引：2，他引：1
基于双剪统一强度理论,利用复合地基中碎石桩与桩周土的竖向位移相等、侧向变形协调与连续的条件,通过弹塑性理论对碎石桩复合地基在竖向荷载作用下的应力、应变状态进行了弹塑性分析,探讨了权系数b的取值方法;讨论了b的大小对复合地基承载及变形性状的影响,并推出了作用在复合地基上的荷载、碎石桩所分担的荷载及加固区压缩量与桩周土的塑性区半径的关系的系列解析算式;提出了对于碎石桩复合地基的设计应该实行承载力和沉降双重控制的设计思想。为验证该方法的可行性,将模型试验的结果与计算结果进行了对比,结果表明该方法对碎石桩复合地基的设计具有指导意义。 相似文献
6.
格型钢板桩结构有限元数值分析 总被引：2，自引：0，他引：2
以有限元软件ABAQUS作为分析平台,建立波浪荷载作用下格型钢板桩结构稳定性及应力分析的三维弹塑性有限元分析模型。格型钢板桩采用壳体单元模拟,在相邻板桩之间设置铰接连接器模拟板桩之间的相对转动;土体采用Mohr-Coulomb本构模型模拟,在格型钢板桩与其内、外土体之间设置接触面单元模拟它们之间的滑移、张裂和闭合。结合某实际工程,研究结构的破坏模式、失稳特性和应力分布特性,分析参数变化对结构稳定性和环向拉力的影响,并对格内土体的剪切变形进行分析,建议格型钢板桩锁口拉力的验算断面。结果表明,铰接连接器的设置对于结构稳定性影响不大,但对环向拉力有一定影响;格内土体的剪切变形主要发生在格体中轴处,符合太沙基法结论。 相似文献
7.
C.Y. Lee 《Computers and Geotechnics》1991,11(4):295-313
This paper presents a simple discrete layer approach for the settlement analysis of axially loaded piles and pile groups. The soil profile may be arbitrarily layered and underlain by either a stiff or rigid stratum. The pile-soil-pile interaction is determined using a modified form of Mindlin's solution for finite soil depth. Good agreement between the present approach and more rigorous finite element and boundary element approaches is observed for the analysis of piles and pile groups embedded in finite soil layers. Settlement predictions obtained from the present approach also agree reasonably well with measurements from a number of published pile tests. Although the emphasis of this paper is on linear elastic solutions, it can easily be extended to include non-linear response. 相似文献
8.
为了完善碎石桩复合地基固结理论,通过假设从桩体排出的水量等于流入桩体的水量与桩体体积变化之和以及地基扰动区土体水平渗透系数呈线性变化,并考虑上部荷载逐渐施加,推导了考虑桩体体积变化的碎石桩复合地基超静孔压及固结度解析解。当加载时间趋于零时,本文解可退化为瞬时加载情况下的解;当加载时间及桩径同时趋于零时,本文解可进一步退化为Terzaghi一维固结解,这证明了本文解的正确性。通过与已有解的比较,对地基固结性状进行了分析。结果表明,加载过程对地基固结度影响显著,加载历时越长,固结越慢;在各种条件下,不考虑桩体固结变形时地基固结始终比考虑桩体变形时快,并且其影响随着加载历时变小、桩径比变小、桩土模量比变小、桩土渗透系数变小而逐渐增大,这说明在实际工程固结计算中不考虑桩体固结变形是偏于不安全的。 相似文献
9.
The axial and lateral load–displacement response of single piles and pile groups during the secondary consolidation (creep) phase of deformation is obtained by idealizing the soil as a linear viscoelastic material. The boundary element method is used to model the soil halfspace and the piles, which are assumed to behave elastically, are idealized as beam-columns. By using the correspondence principle, the problem is solved in the Laplace transform domain and the final solution is obtained by numerical inversion of the transformed data. The salient features of the viscoelastic response are identified in several non-dimensional plots which encompass the spectrum of geometrical and material parameters commonly encountered in practice. The results of the analysis compare favourably with the limited data available in the literature. 相似文献
10.
路堤荷载下柔性桩复合地基沉降实用计算方法 总被引：5，自引：0，他引：5
根据等应变假设得到的复合地基加固区复合模量计算公式与实际路堤荷载下柔性桩桩土间的非等应变事实不符,因此,路堤荷载下复合模量法计算的沉降量多小于实测值。通过二维有限元方法分析了路堤荷载下复合地基变形特性。采用分层总和法反算加固区复合模量,提出了复合模量计算修正方法;并通过参数分析得到了各主要影响因素对复合地基加固区变形特性的影响;对比桩体设置前后下卧层变形差异,对下卧层沉降计算方法进行修正。由此建立了有限元方法与工程实用的分层总和法之间的联系,将有限元方法实用化,分别得到了路堤荷载下柔性桩复合地基加固区和下卧层的沉降实用计算方法。实例计算证明了所推荐方法的有效性。 相似文献
11.
Settlement of the surrounding soil due to surcharge placement may give rise to negative skin friction developed in piles. In this paper, a simple discrete element approach using subgrade reaction method is proposed to analyse negative skin friction on single piles. The pile is embedded in a two-layer soil where the upper soil layer undergoes consolidation while the lower soil layer acts as a stiffer bearing stratum. Two different and uncoupled deformation modes, one at the pile shaft and the other at the pile toe have been assumed in the determination of the soil stiffness. The effects of a compressible bearing stratum and embedment length of the pile in the bearing stratum are considered in the analysis. This simple approach is verified by comparison with rigorous methods of modelling the soil as an elastic continuum. Three reported case histories are analysed and the computed results are shown to be in reasonable agreement with the field measurements. 相似文献
12.
针对变截面群桩基础高墩的几何特性,将桥墩与群桩基础简化为空间整体,在考虑桥墩变截面特性及桩土相互作用的基础上,提出群桩基础变截面桥墩分析模型;将分析模型分解成群桩基础的刚体变形与桥墩的弹性变形两个部分,分别基于能量法与有限单元法求解相应的自振频率,并采用Southwell频率合成法,将整体计算模型表示成两个部分的合成,从而导出变截面桥墩的自振频率,通过算例证明该方法的实用性,并分析了桥墩参数对自振频率的影响,获及了一些定性的结论。结果表明,变截面高墩自振频率的计算分析中,桩-土相互作用的影响不容忽视,考虑桩土相互作用和桥墩本身的非线性更符合工程实际。 相似文献
13.
Settlement evaluation of soft clay reinforced with stone columns using the equivalent secant modulus 总被引：3，自引：2，他引：1
A method is proposed to evaluate settlement of soft clay reinforced with stone columns. Finite element analyses were carried out using 15-noded triangular elements with PLAXIS. A drained analysis was carried out using Mohr?CCoulomb??s criterion for soft clay, stones, and sand. The stress due to column installation has been considered in the analysis. At the interface between the stone column and soft clay, interface elements have been used. The settlement ratio (SR) of the soil has been estimated using the equivalent secant modulus. The results are compared with those available in the literature, and the advantages of the numerical analysis were highlighted. Based on the results of this analysis, the SR decrease with compaction surrounding soft soil, but decrease of SR is mainly due to a stiffer column material in soft clay. 相似文献
14.
A plane strain yield design approach to stability analysis of a column‐reinforced soil foundation under inclined loading 
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下载免费PDF全文 The ultimate bearing capacity problem of column‐reinforced foundations under inclined loading is investigated within the framework of static and kinematic approaches of yield design theory. The configuration of a native soft clayey soil reinforced by either a group of purely cohesive columns (lime‐column technique) or a group of purely frictional columns (stone‐column technique) is analyzed under plane strain conditions. First, lower bound estimates are derived for the ultimate bearing capacity by considering statically admissible piecewise linear stress distributions that comply with the local strength conditions of the constitutive materials. The problem is then handled by means of the yield design kinematic approach of limit analysis through the implementation of several failure mechanisms, allowing the formulation of upper bound estimates for the ultimate bearing capacity. A series of finite element limit load solutions obtained from numerical elastoplastic simulations suggests that the predictions derived from the kinematic approach appear to be more accurate than the estimates obtained from the static approach. Comparison with available results obtained in the context of yield design homogenization demonstrates the accuracy of the proposed direct analysis, which may therefore be viewed as complementary approach to homogenization‐based approaches when a small number of columns is involved. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
15.
振冲碎石桩地基有限元分析的复合模型研究 总被引：2，自引：0，他引：2
从振冲碎石桩的变形、受力机制出发,提出相应的假设条件,利用弹性力学和Biot固结理论建立了可以考虑固结问题的振冲碎石桩复合的平面有限元分析弹性复合模型,并编制相应的有限元分析程序APOSE。通过算例考证了APOSE的可靠性和有效性,APOSE程序可以用于分析研究振冲碎石桩地基、砂井地基等类似复合地基沉降变形和固结问题。 相似文献
16.
在引入围桩-土耦合式抗滑结构的基础上建立数值分析模型;通过分析该抗滑结构中围桩-土的应力、应变分布规律,详细探讨围桩-土整个结构的耦合效应特征。进一步开展模型试验,测试并分析围桩前、后土压力和桩身弯矩分布特征,论证了围桩-土耦合式抗滑结构的作用机制。最后,分析了桩后距离、不同深度及不同土体强度参数对土拱效应的影响。得到：（1）围桩与桩内土体耦合呈现出4种应力拱形态：紧邻围桩后为扩肩型拱、围桩间双曲线型拱、围桩间凸向桩外的抛物线型拱、围桩间凸向桩内的抛物线型拱;（2）相邻围桩采用约4倍桩径间距、正六边形布置并顶部用圈梁固结、锚固一定深度可形成一种耦合式抗滑结构。该结论对于该新型抗滑结构的推广应用具有一定的指导意义。 相似文献
17.
考虑桩土效应的双排桩模型及参数研究 总被引：1，自引：0，他引：1
双排桩作为一种新型的深基坑支护结构,目前尚无简单而有效的设计方法。首先,借助Winkler地基梁基本思想,在忽略桩土竖向摩擦效应及空间效应的前提下,对双排桩支护结构力学机制进行分析,建立了考虑桩土效应的双排桩平面杆系有限元模型。接着围绕双排桩平面杆系有限元模型的关键参数土压力分布及弹性抗力系数展开了研究,针对连梁拉力将使传统的坑后土体滑移面临界距离增加特征,利用滑动比例系数法获得了土压力分配规律;针对弹性抗力系数正分析取值不确定性,提出了采用位移反分析优化方法获得弹性抗力参数的取值。最后,根据杆系有限元及反分析中位移最优准则函数的求解步骤,分别编制了doublerowpile及doublerowpileparameter计算程序,并进行了相应的工程计算,工程计算结果表明,计算位移与监测位移趋势一致,计算内力符合规范要求,且能较准确获得弹性抗力系数取值。 相似文献
18.
In order to gain a better understanding of pile-soil interaction under lateral loading, this paper presents a numerical analysis which combines the infinite and finite element method. Interest is focused on the group effect on ultimate lateral soil resistance. Firstly, a single isolated pile is analysed and reasonably good agreement is found between existing analytical solutions and results obtained by the present method. A limited parametric study is also presented and some parameters influencing the ultimate lateral soil resistance are identified. The analysis of pile groups is then considered and it is shown that the group effect tends to reduce pile capacity when the spacings between piles are within the practical ranges. The extent of the reduction depends on the arrangement of piles within the group. 相似文献
19.
为全面考虑路堤荷载下搅拌桩复合地基的桩土非等应变特性,将路堤、桩体、桩间土及下卧土层整体考虑,在总结前人试验结果基础上提出简化的桩土应力比和桩土差异沉降两阶段模型,改进了现有的桩顶平面处的桩土应力比计算方法。根据实际的应力状态计算桩侧摩阻力,计算桩土荷载分担,进而得到桩体和桩间土沉降。通过各子系统界面处的位移和应力边界条件考虑其相互作用,得到了路堤荷载下搅拌桩复合地基总沉降计算模型。对比淮盐高速公路试验段搅拌桩复合地基的实测沉降、文中模型以及传统复合模量法计算结果,验证了该模型的正确性,结果表明模型计算沉降与实测数据吻合,较常规的复合模量法计算结果更接近实测值。 相似文献
20.
Column consolidation and deformation are considered by assuming that the quantity of water flowing through the disturbed soil zone into the column is not equal to that flowing out from the column and the difference between them is equal to the volume change of the column. In addition, three patterns of distribution of the horizontal permeability of soil in the disturbed zone are also considered to account for the disturbance effect of columns construction on the surrounding soil. These three patterns include the constant distribution pattern (Pattern I), the linear distribution pattern (Pattern II) and the parabolic distribution pattern (Pattern III). By incorporating the aforementioned characteristics into the analyses, the governing equations containing two variables (i.e. the average excess pore-water pressures within the column and within the entire foundation at any depth) for the consolidation of a composite foundation are derived. The solutions of the governing equations are then obtained using a new initial condition derived from the assumption of equal strain and the equilibrium condition. On the basis of the solutions for excess pore-water pressures, the average degree of consolidation of a composite foundation is obtained and discussed. Finally, a comparison is made of some available solutions. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献