Bearing Behaviors of Stiffened Deep Cement Mixed Pile

A series of investigations were conducted to study the bearing capacity and load transfer mechanism of stiffened deep cement mixed (SDCM) pile. Laboratory tests including six specimens were conducted to investigate the frictional resistance between the concrete core and the cement soil. Two model piles and twenty-four full-scale piles were tested to examine the bearing behavior of single pile. Laboratory and model tests results indicate that the cohesive strength is large enough to ensure the interaction between core pile and the outer cement-soil. The full-scale test results show that the SDCM piles exhibit similar bearing behavior to bored and cast-in-place concrete piles. In general, with the rational composite structure the SDCM piles can transmit the applied load effectively, and due to the addition of the stiffer core, the SDCM piles possess high bearing capacity. Based on the findings of these experimental investigations and theoretical analysis, a practical design method is developed to predict the vertical bearing capacity of SDCM pile.     

路堤荷载下混凝土芯水泥土搅拌桩工作特性研究

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士荷载分担特点,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,能有效控制由于丰崮结引起的长期沉降。     

某大楼人工挖孔桩荷载传递及承载性状试验研究

根据某大楼2根无扩底人工挖孔桩灌注的静载试验,通过埋设在桩中不同土层位置的混凝土应变传感器在各级加载下所测得的数据,分析了桩端阻力、桩侧摩阻力的发挥规律和桩的变形规律,研究了人工挖孔桩的承载特性和荷载传递机理.试验结果表明,对嵌入软质岩有一定深度的人工挖孔桩,其桩的荷载传递性状呈现为摩擦桩的特点.根据这一特点,建议在人工挖孔桩设计前应对桩进行承载力试验,当桩端嵌入岩层一定深度时可不设计扩大头.     

微型桩水平承载特性的现场试验与数值模拟分析

水平承载微型桩在工程现场的静载试验,对比了不同桩长、不同抗弯刚度微型桩的水平承载特性,在实验研究基础上,对桩径、桩身模量等主要因素对微型桩水平承载特性影响进行的数值分析,得出结论:通过合理选择微型桩桩长、桩径以及桩身插设钢管等,可以提高水平承载微型桩的承载能力。     

开发端承力的桩型──沉管灌注夯扩桩

通过对大量静载试验成果的统计，证明花岗岩残积上中夯扩桩在承载能力与造价上的优势。通过计算探讨夯扩桩扩头成形规律性和成形条件，并对偶然出现的桩顶质量问题提出改进措施。     

倾斜桩的承载能力及其利用

通过结合某工程事故处理中进行的系列基桩静载试验与分析,确定不同倾斜率的基桩的竖向承载力,并将这一成果应用于处理实践.工程实践表明,科学地确定并利用倾斜桩的竖向承载力将产生显著的经济效益.     

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.     

新规范下长短深层搅拌桩在工程中的应用分析

以惠州一建筑工程为例, 分析了新规范下长短深层搅拌桩在高层建筑中的应用, 对影响深层搅拌桩在高层建筑中应用的几个关键问题进行了论述, 并采用Ansys 系统对桩体的受力进行了分析, 并讨论了垂直荷载沿桩体的分布规律。     

后注浆桩技术应用研究

结合工程实例,通过对泥浆护壁钻孔灌注桩采用后注浆技术,明显增强单桩竖向承载力事实的分析,得出了以下结论:把后注浆技术引用到桩基工程中,采取对桩端及桩侧实施压力注浆措施,解决桩底沉渣和桩侧泥膜影响桩基承载力的问题,从而达到增强桩基承载力、缩短工期、减少工程造价的目的。     

Influence of reaction piles on test pile response in a static load test

This work presents a new analytical method to analyze the influence of reaction piles on the test pile response in a static load test.In our method,the interactive effect between soil and pile is simulated using independent springs and the shear displacement method is adopted to analyze the influence of reaction piles on test pile response.Moreover,the influence of the sheltering effect between reaction piles and test pile on the test pile response is taken into account.Two cases are analyzed to verify the rationality and efficiency of the present method.This method can be easily extended to a nonlinear response of an influenced test pile embedded in a multilayered soil,and the validity is also demonstrated using centrifuge model tests and a computer program presented in the literature.The present analyses indicate that the proposed method will lead to an underestimation of the test pile settlement in a static load test if the influence of the presence of reaction piles on the test pile response is neglected.     

超长钻孔灌注群桩承载特性的实验研究和数值分析

采用离心机模型试验和三维有限元模型对天兴洲大桥的超长嵌岩钻孔灌注群桩进行了分析.离心机试验中,根据相似理论,不同的原型材料用不同的指标进行模拟,细砂、桩身、承台分别以天然密度、抗压刚度、抗弯刚度作为指标进行模拟.对土体未开挖阶段、钻孔阶段、混凝土灌注阶段和养护阶段的应力场进行了详细的讨论,并应用ANSYS进行了分析.根据2种方法得到的结果,从荷载沉降曲线、桩身轴力分布和侧向摩阻分布等方面,对比分析了加载和卸载条件下超长钻孔群桩的承载特性.结果表明,有限元计算模型与离心机试验模型沉降观测的结果吻合得很好;桩顶反力的分布规律复杂,与承台的自身刚度、相应的假定和分析方法有关;轴力随着深度先稍微增加,后逐渐减少,并且在岩层中减少的速度远比砂土中快.     

后压浆技术在PHC管桩工程中的应用

从后压浆技术的概念提出及其机理分析入手。结合实际桩基工程中后压浆技术的应用与现场检测。探讨后压浆技术在PHC管桩工程事故处理和加固等方面的机理作用及效果。通过注浆前后试验结果对比。阐明后压浆技术能提高持力层地基承载力及桩侧摩阻力，改善桩身质量和桩的荷载传递性能。使桩基综合承载力大幅度提高，并缩短工期。     

小截面静压预制桩承载力预测及取值探讨

采用双曲线法、调整双曲线法和指数法对某小区住宅楼3根试验桩的静载试验结果进行单桩极限承载力预测，并将预测结果与理论计算结果进行对比，分析结果表明：盲目套用《建筑桩基技术规范》JGJ94-94中有关预制桩承载力指标来计算桩的极限承载力是不科学的，其指标也不适合小截面静压预制桩。结合桩基施工终压力和每延米压桩耗能的对比分析，表明桩的竖向极限承载力与终压力存在一定的比例关系但与压桩耗能不存在比例关系。     

预制小桩径桩单桩承载力探析

分析了预制桩静载试验实测资料,发现桩侧摩阻力和桩端阻力在试验过程中发挥了作用,说明沉桩施工对桩周土和桩端土层的挤密作用,提高了单桩承载力。建议小桩径桩,根据现场静载试验确定单桩竖向承载力作为设计取值的依据,以充分发挥单桩承载力,降低基础造价,提高经济效益。     

Static load test and load transfer mechanism study of squeezed branch and plate pile in collapsible loess foundation

As a special geological phenomenon, the character of collapsible loess foundation is collapsible when penetrated by water. This character leads to the soil losing load bearing capacity largely and may lead to foundation failure. Pile is a popular foundation used in collapsible loess. The squeezed branch and plate pile is a new type of pile developed in recent years and has not be used in a project before. In this paper three squeezed branch and plate piles are tested in collapsible loess after immersion processing. The results may be used for reference in similar construction project, and to provide theoretical references for de- signing of the squeezed branch and plate piles in engineering practice.     

卵石层中采用高频振动锤施打PHC管桩效果分析

以一高频液压振动锤施打PHC管桩的施工实例，说明在以卵石为持力层的场地中可采用高频液压振动锤进行PHC管桩的沉桩施工；通过对桩的施工顺序、入土深度和单桩静载试验结果的差异情况分析，表明高频振动对无粘结粒状土层的深层振实效果非常明显，振动后卵石层桩端阻力得到明显的提高，但会存在工后桩长差异较大的现象。     

竖向荷载作用下群桩效应的数值模拟研究

群桩效应是桩基理论中的一个重要问题。文章利用大型通用有限元程序ANSYS,进行数值模拟研究,主要分析群桩与单桩在桩侧摩阻力、承载与位移等方面的不同,同时对群桩基础中不同部位桩的应力场位移场进行更深入的研究,为揭示群桩基础的作用机理提供了技术支持。     

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。     

长短桩、变径桩桩间相互作用系数数值研究

采用三维数值方法,建立长短桩、变径桩双桩模型,通过大量的数值计算,分析桩顶荷载水平、桩距径比、不同桩长、桩端土模量比及不同桩径对相互作用系数的影响。分析表明,在线弹性变形阶段,桩-桩相互作用系数近似为恒定值,与桩顶荷载水平无关,进入塑性变形之后,则逐渐减小直至极限状态时趋于0;长短桩桩长比及桩端土模量比对短桩-长桩相互作用系数影响大,而对长桩-短桩相互作用系数影响小;变径桩相互作用系数仅与受荷桩桩径有关;并提出了针对长短桩、变径桩的简化计算公式,为实际工程提供参考。     

某桩筏基础细长桩单桩承载性能浅析

结合三根静载试验桩的试验数据,采用载荷传递法,利用迭代计算方法,编制计算程序对三根试验桩进行计算分析。通过对三根试验桩的计算数据与试验数据进行对比,获得两种不同类型的桩(嵌岩桩和非嵌岩桩)在载荷沉降变化趋势,桩身侧摩阻力与桩端阻力的分配,以及桩身轴力变化等方面的规律。