水流冲刷条件下群桩基础力学性质数值模拟

分析了群桩基础桩-土相互作用的主要特征,对三维问题进行分析并简化,建立桩-土非线性作用问题的有限元求解模型,并对不同工况进行数值计算。根据数值模拟计算所得位移、应变和应力结果,分析不同荷载组合下基桩受力特点和承台受力变形特征,为群桩基础设计考虑土与基础结构协调作用提供依据。     

有限棱柱法对单桩与土相互作用系统的弹塑性分析

用有限棱柱单元法对采用长桩的单桩与土相互作用系统进行了三维弹塑性分析，并开发出一种可模拟半无限空间地基土边界条件的无限棱柱元．计算中考虑了承台对地基土的约束作用及桩土之间的竖向相对位移，地基土的本构模型采用修正剑桥模型．分析了集中荷载作用下摩擦长桩与土相互作用系统，得到了合理的荷载－沉降曲线及桩侧摩阻力的分布曲线，为长桩的研究与设计提供了一种有效的计算方法     

水平偏心受荷群桩的非线性分析（英文）

目的:群桩基础在近海建/构筑物及桥梁中广泛应用,而风、浪、船舶撞击等在群桩基础中产生的水平和扭转荷载往往影响群桩基础的安全。本文旨在提出一套能够计算水平和扭转荷载联合作用下的群桩非线性响应简化分析方法。创新点:1.采用广义p乘子法考虑群桩中各桩水平变形导致的桩-土-桩相互作用;2.建立基于瞬时转动中心的基桩桩头位移关系和承台平衡方程。方法:1.通过理论分析给出基桩桩头位移之间的关系,建立承台平衡方程;2.采用荷载传递模型(p-y和τ-θ曲线)模拟桩周土体非线性响应;3.采用广义p乘子法考虑群桩中各桩水平变形导致的桩-土-桩相互作用,并采用耦合因子计算基桩中推-扭耦合响应;4.通过迭代方法求解各基桩p乘子和群桩响应。结论:1.多组算例均表明本文提出的群桩非线性分析模拟能够较准确地模拟群桩响应,尤其在承台位移较大的情况下;2.广义p乘子能够有效地模拟群桩效应的主要部分;3.模型中的简化公式能够应用于实际工程问题分析。     

桩土相互作用及单桩承载力确定模拟研究

以灌注桩桩土相互作用的原位试验为基础,结合苏嘉杭高速公路具体土层结构、性质特点,采用有限单元法对软土地区的砼灌注桩桩土相互作用进行仿真模拟,研究桩土相互作用、荷载的传递规律、桩土相对位移与桩侧摩阻力的关系,通过桩载试验资料对比,得出三维有限元法的模拟结果与实测值相近.在此基础上,根据侧摩阻力最大值发挥不同步这一特点和桩土相互作用的实质及荷载传递规律,提出一种新的单桩极限承载力计算公式.     

桩土相互作用及单桩承载力确定模拟研究

以灌注桩桩土相互作用的原位试验为基础,结合苏嘉杭高速公路具体土层结构、性质特点,采用有限单元法对软土地区的砼灌注桩桩土相互作用进行仿真模拟,研究桩土相互作用、荷载的传递规律、桩土相对位移与桩侧摩阻力的关系,通过桩载试验资料对比,得出三维有限元法的模拟结果与实测值相近。在此基础上,根据侧摩阻力最大值发挥不同步这一特点和桩土相互作用的实质及荷载传递规律,提出一种新的单桩极限承载力计算公式。     

双向简谐波荷载作用下群桩力学性状分析及其受力性能

为研究双向简谐波荷载作用下群桩的力学性状及其受力性能,采用PLAXIS有限元软件建立相应的数值模型,分析了群桩基础在双向简谐波荷载作用下内力、位移响应情况,探究了桩周土体的动应力应变关系,进而对其在循坏水平荷载作用下的受力性能进行探讨。研究结果表明,与水平静载作用相比,桩基在循坏水平荷载作用下的承载能力有所降低;桩顶荷载-位移曲线出现“滞回圈”,基桩产生“疲劳效应”;桩周土抗力的变化使得各排桩内力分配不均匀;桩周土体的动应力应变关系呈现滞后性、非线性及累积性。     

荷载倾角对光伏支架微型桩承载特性影响的试验与数值模拟研究

依据卵石土地区华能海南州光伏项目现场试桩竖向抗拔和水平静载试验数据,采用三维连续介质拉格朗日法有限差分软件(FLAC^3D)建立计算模型,通过模型分析光伏微型短桩及支架体系在不同荷载倾角下的承载特性。结果表明：光伏微型单桩竖向位移的增长率随着荷载倾角的增大逐渐变缓,水平位移增长率逐渐变快;荷载倾角位于15°～75°范围内,光伏支架体系竖向位移在加载前期增长趋势相同;光伏支架体系的倾斜荷载-桩顶水平位移曲线均呈缓变型,极限水平荷载随荷载倾角的增大而减小;由于光伏支架体系的整体性,荷载倾角位于15°～30°范围内时合位移由竖向位移和水平位移共同决定,建议在工程设计时采用倾角在此范围内的光伏支架,以保证其良好的抗拔性能。     

水平循环荷载下单桩沉降的离心机试验研究（英文）

目的:探究单桩在水平循环荷载作用下的沉降行为。创新点:1.采用离心机模型试验,研究水平循环荷载作用下单桩的沉降规律;2.揭示了水平循环荷载作用下单桩的沉降机理。方法:1.利用自主研发的伺服加载系统,在100g条件下对单桩施加水平循环荷载,并采用数字图像关联处理技术分析单桩的沉降规律;2.同时针对两个重要参数(即竖向荷载和水平位移幅值)开展正交试验,明确两个参数对桩体沉降的影响。结论:1.在水平循环荷载作用下,桩侧摩阻力将会损失,不平衡力传向桩端,从而让桩体发生沉降;2.作用在桩顶的竖向荷载越大,或水平位移幅值越大,桩沉降越大;3.在水平循环荷载作用下,端承桩抗沉性能优于摩擦桩。     

路堤荷载下混凝土芯水泥土搅拌桩工作特性研究（英文）

研究目的:研究混凝土芯水泥土搅拌桩在路堤荷载下的荷载传递规律和变形控制机理。创新要点:评价路堤荷载下混凝土芯水泥土搅拌桩的地基处理效果,测量混凝土芯的竖向应力变化规律和复合地基桩土荷载分担特点,并分析填土过程中混凝土芯水泥土搅拌桩复合地基的固结规律。研究方法:通过埋设沉降板、分层沉降管、测斜管、土压力盒、孔隙水压力计以及钢筋应力计,在路堤填筑过程中对混凝土芯水泥土搅拌桩复合地基进行了长期现场试验。重要结论:1.混凝土芯水泥土搅拌桩复合地基的总沉降、工后沉降以及深层水平位移控制效果均较好,优于普通水泥土搅拌桩复合地基;2.混凝土芯水泥土搅拌桩复合地基的桩土应力比以及荷载分担比均大于普通水泥土搅拌桩复合地基,能有效减小土体表面的荷载量,对于控制沉降有一定的效果。3.在路堤这种柔性荷载作用下,混凝土芯水泥土搅拌桩上部会出现一定的负摩擦阻力,存在一个"中性点"。4.混凝土芯水泥土搅拌桩复合地基的固结速率较快,能有效控制由于主固结引起的长期沉降。     

受推桩静力特性模型试验研究

本文采用模型桩进行了桩在几种水平荷载作用下桩的静力特性的试验研究,得到了桩身弯矩、桩头位移及土抗力系数等参数的一些变化规律。并进行了《m》法、《c》法及《k》法的计算比较,得出在砂土中《m》法稍优于其它两种方法。     

弹性承台下沉降控制复合桩基的变分法研究

在刚性承台下桩筏基础变分计算方法的基础上，采用弹性薄板单元，引进弹性承台，给出了计算方法并考虑了承台刚度变化对复合桩基工作性状的影响。应用本方法对一工程算例进行计算分析，结果表明承台刚度的变化对桩土分担比有显著影响。     

路堤荷载下挤密螺纹桩复合地基沉降现场试验

对新建兴泉铁路黄塘车站挤密螺纹桩复合地基的桩、土沉降及应力进行监测,分析了路堤荷载下桩、土沉降及差异沉降变化规律,桩土应力比与差异沉降关系。结果表明:桩、土沉降及差异沉降均随路堤填土高度的增加而呈线性增大;桩顶和桩间土应力随路堤填土高度的增加均不断增大,且桩顶应力大于桩间土应力;桩土应力比随着桩土差异沉降的增加先增加后减小,最终趋于稳定。结合修正的Terzaghi土拱理论提出了简化桩土应力比随桩土差异沉降变化曲线。现场试验分析结果有助于完善挤密螺纹桩复合地基设计理论,为工程实践提供一定的参考。     

Three-Dimensional Representations of Contour Maps

Contour map learning may require three-dimensional representation of the area depicted by a contour map. The purpose of the study was to test the hypothesis that participants created three-dimensional mental representations of contour maps when asked to generate a cross-section profile of the map terrain from one point on the contour map to another. Gender differences in cross-section performance were also investigated, and it was hypothesized that males would perform better than females in a contour map cross-section test. Participants studied a series of contour maps or landsurface maps (three-dimensional drawings of an area), and answered two cross-section questions per map. Following the cross-section test, participants were given an incidental recognition test for the previously studied maps, either in a contour map format or a landsurface map format. Males recognized the landsurface maps corresponding to the contour map cross-section questions answered correctly better than contour map cross-section questions answered incorrectly, whereas females did not. This finding suggested that males, but not females, formed three-dimensional representations of the contour maps. There were no gender differences in performance on the contour map cross-section test, but males achieved higher recognition scores than females when the cross-section stimuli were contour maps. It was concluded that multiple spatial and verbal processing strategies can be used successfully to solve a contour map cross-section test, but that three-dimensional spatial processing may be more efficient than other forms of processing for long-term memory of contour maps.     

Bearing capacity and load transfer mechanism of a static drill rooted nodular pile in soft soil areas

The static drill rooted nodular pile is a new type of pile foundation consisting of precast nodular pile and the surrounding cemented soil. This composite pile has a relatively high bearing capacity and the mud pollution will be largely reduced during the construction process by using this type of pile. In order to investigate the bearing capacity and load transfer mechanism of this pile, a group of experiments were conducted to provide a comparison between this new pile and the bored pile. The axial force ofa precast nodular pile was also measured by the strain gauges installed on the pile to analyze the distribution of the axial force of the nodular pile and the skin friction supported by the surrounding soil, then 3D models were built by using the ABAQUS finite element program to investigate the load transfer mechanism of this composite pile in detail. By combining the results of field tests and the finite element method, the outcome showed that the bearing capacity of a static drill rooted nodular pile is higher than the bored pile, and that this composite pile will form a double stress dispersion system which will not only confirm the strength of the pile, but also make the skin friction to be fully mobilized. The settlement of this composite pile is mainly controlled by the precast nodular pile; meanwhile, the nodular pile and the surrounding cemented soil can be considered as deformation compatibility during the loading process. The nodes on the nodular pile play an important role during the load transfer process, the shear strength of the interface between the cemented soil and the soil of the static drill rooted pile is larger than that of the bored pile.     

Analytical model of vertical vibrations in piles for different tip boundary conditions: parametric study and applications

In this paper,a model named fictitious soil pile was introduced to solve the boundary coupled problem at the pile tip.In the model,the soil column between pile tip and bedrock was treated as a fictitious pile,which has the same properties as the local soil.The tip of the fictitious soil pile was assumed to rest on a rigid rock and no tip movement was allowed.In combination with the plane strain theory,the analytical solutions of vertical vibration response of piles in a frequency domain and the corresponding semi-analytical solutions in a time domain were obtained using the Laplace transforms and inverse Fourier transforms.A parametric study of pile response at the pile tip and head showed that the thickness and layering of the stratum between pile tip and bedrock have a significant influence on the complex impedances.Finally,two applications of the analytical model were presented.One is to identify the defects of the pile shaft,in which the proposed model was proved to be accurate to identify the location as well as the length of pile defects.Another application of the model is to identify the sediment thickness under the pile tip.The results showed that the sediment can lead to the decrease of the pile stiffness and increase of the damping,especially when the pile is under a low frequency load.     

Analytical model of vertical vibrations in piles for different tip boundary conditions: parametric study and applicationsx

In this paper,a model named fictitious soil pile was introduced to solve the boundary coupled problem at the pile tip.In the model,the soil column between pile tip and bedrock was treated as a fictitious pile,which has the same properties as the local soil.The tip of the fictitious soil pile was assumed to rest on a rigid rock and no tip movement was allowed.In combination with the plane strain theory,the analytical solutions of vertical vibration response of piles in a frequency domain and the corresponding semi-analytical solutions in a time domain were obtained using the Laplace transforms and inverse Fourier transforms.A parametric study of pile response at the pile tip and head showed that the thickness and layering of the stratum between pile tip and bedrock have a significant influence on the complex impedances.Finally,two applications of the analytical model were presented.One is to identify the defects of the pile shaft,in which the proposed model was proved to be accurate to identify the location as well as the length of pile defects.Another application of the model is to identify the sediment thickness under the pile tip.The results showed that the sediment can lead to the decrease of the pile stiffness and increase of the damping,especially when the pile is under a low frequency load.     

A semi-analytical method for the analysis of pile-supported embankments

In this paper, a semi-analytical method for the analysis of pile-supported embankments is proposed. The mathematic model describes the cooperative behavior of pile, pile cap, foundation soil, and embankment fills. Based on Terzaghi??s 1D consolidation theory of saturated soil, the consolidation of foundation soil is calculated. The embankments with two different types of piles: floating piles and end-bearing piles are investigated and discussed. The results of axial force and skin friction distributions along the pile and the settlements of pile-supported embankments are presented. It is found that it takes a longer time for soil consolidation in the embankment with floating piles, compared with the case using end-bearing piles. The differential settlement between the pile and surrounding soil at the pile top is larger for the embankment with end-bearing piles, compared with the case of floating piles.     

预应力混凝土板桩-冠梁协同支护作用机理

以湖岸支护工程为例,基于有限元模拟研究了支护结构内力及变形、地表沉降、基坑隆起以及土压力分布情况,探讨了桩顶锚固形式和板桩嵌固深度,得到板桩-冠梁协同支护体系工作机理。 研究表明:板桩-冠梁协同支护体系的桩土协同作用机制与有锚板桩相似,桩体变形呈现中部鼓出状,主动土压力呈R 形分布;桩顶冠梁锚固以及桩底嵌固作用是影响板桩支护性能的重要因素,板桩最佳嵌固深度比为0.69~0.79。 研究成果可为相关板桩支护的设计和工程应用提供参考借鉴。     

一种基于二次变换运动预测的有损分割图轮廓编码

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