利用挤密砂桩处理挤土效应引起的桩位偏移

挤土桩在沉桩过程中会产生明显的挤土效应 ,应用圆柱孔扩张理论可推导出桩周土体在打桩过程中产生的径向位移。挤土效应也可用来处理桩位的偏移 ,通过合理布置桩数和排数 ,使桩产生需要的反向位移。工程实例表明 ,理论计算与实测结果吻合程度较好     

静压桩沉桩挤土效应控制措施探析

为减小静压桩在施工过程中对周围市政道路、建筑等环境所产生的影响,需要采取合理的沉桩挤土效应措施。以杏林华铃花园三期工程(9#~13#楼)工程为例,分析了静压桩挤土效应对具体的挤土效应表现形式,从设置应力释放孔、降水井、控制打桩进度、防挤沟、沉桩施工顺序等方面提出措施进行有效控制。     

管桩水泥土复合桩群桩挤土效应现场试验研究

管桩水泥土复合桩作为一种新型桩,近年来使用越来越广泛。为研究该复合桩在群桩施打过程中产生的挤土效应,结合现场试验,对打桩过程中产生的径向应力及超孔水压力进行分析,并对比施工前后场地内静力触探结果,试验成果表明:沉桩过程中挤土效应的影响范围约为12倍管桩桩径,超孔压在施工后24h内消散完毕,打桩后场地径向有效应力提高了1.85~2.92倍,复合桩所在土层侧壁阻力提高了2.05~2.45倍。     

挤土桩对砂土地基挤密效应及液化状态变化的机理研究

为研究打桩对砂土地基挤密效应及液化状态的变化,根据土塑性力学的基本原理,本文用空穴球形扩张和源-源影射的方法,推得了挤土桩打桩结束后土体内产生各点应力的理论计算公式,取得了打桩后离桩越近,土体被挤密的程度越大,砂土比粘土更容易挤密,并且挤密的范围更大以及桩径越大,土体挤密程度越大,影响范围也越大等基本规律,并由此预估砂土地基标贯锤击数及液化状态的变化。文章用工程实测结果与其进行了对比。     

桩长、桩型及打桩的速率、顺序等因素对挤土的影响

预制桩打入时的挤土作用会使附近已打好的桩及原有建筑物或周围其他设施产生破坏。挤土程度的大小除了与桩的截面积及某处与桩间的距离有关外,还与桩长、桩型、打桩速率及打桩顺序有较大关系。本文即讨论上述因素对挤土影响的定量关系。     

PHS预应力混凝土空心方桩对桩间土挤密效应试验研究

依托工程实例,通过对打桩前后桩间土的物理力学性质指标、标准贯入试验的对比分析,研究了PHS预应力混凝土空心方桩对桩间土的挤密效应。试验表明,挤密效应可消除地基土液化,使桩间土的工程性质得到明显改善,提高强度,降低压缩性。桩间土的物理力学指标、标准贯入试验指标较打桩前均有不同程度的提高。挤密效应对粉土、砂土较为敏感,粘性土相对较弱。挤密效应与桩间土的粘粒含量、塑性指数呈负相关,粘粒含量、塑性指数越大,挤密效应越弱。     

减少锚杆静压桩挤土效应方法及预防措施

锚杆静压桩为挤土型桩,压桩过程中产生的挤土效应明显,产生的挤压作用使桩区及附近的土体产生向上隆起和水平位移,桩体上抬、偏位时有发生.论文阐述了锚杆静压桩在基础加固过程中采取PHC管桩的压桩效应,对挤土效应进行了较详细地理论计算分析,得到桩塑性区半径解析表达式.提出了现有的减少沉桩挤土效应的设计和施工两方面的工程预防措施...     

静压桩挤土效应近期研究述评

介绍了现场实测、室内试验研究、理论分析和有限元数值模拟三种静压桩挤土效应的研究方法,并对静压桩挤土效应的进一步研究提出了一些建议,以减少静压桩施工过程中所产生的挤土效应对周围工程环境造成的影响。     

软粘土地基中挤土桩沉降时效性分析

位于饱和软粘土地基中的挤土桩。由于沉桩过程中地基土产生挤土效应及超静孔隙水压力，同时随着超静孔隙水压力的消散，桩周地基土产生再固结沉降。在研究沉桩过程中超静孔隙水压力的形成及消散规律的基础上，研究了桩周地基土再固结沉降的变化规律；从桩土相互作用的原理出发，研究了在桩周地基土再固结沉降的作用下，工程桩基沉降的计算方法。研究表明：由于桩周地基土的再固结沉降作用，工程桩基产生较大的沉降量，其值远大于垂直荷载作用下的桩基沉降；由于桩周地基土的再固结，桩基沉降随着时间的推移而增长。     

桩尖角对PHC管桩沉桩挤土位移影响的有限元分析

文章基于某长江大桥管桩基础工程项目,利用ABAQUS软件对锤击法PHC管桩沉桩的挤土位移进行了数值计算,研究了不同桩尖角对PHC管桩沉桩贯入过程挤土位移的作用。研究结果表明:桩尖角不同,沉桩过程中产生的竖向挤土位移不同,其大小与地表土体挤出高度存在负相关,当沉桩贯入3m深后,对桩顶地表土体的位移几乎没有影响;改变桩尖角大小对径向挤土位移无明显作用。     

Performance analysis of a jacked-in single pile and pile group in saturated clay ground

When a pile is installed into saturated clay ground, the “setup” effect may occur due to ground consolidation, which changes pile performance. Although this phenomenon has been observed both in the field and laboratory, its numerical simulation is still challenging. In this work, pile installation effects on the behaviors of jacked-in piles were investigated through three simulation techniques by a three-dimensional finite element analysis program, PLAXIS 3D. A constitutive model called the soft soil creep model was used to describe the soil behavior based on soil parameters obtained from laboratory tests. The behaviors of single piles were first investigated with or without the consolidation process after pile installation to evaluate the pile setup effect. Then, a pile group comprising 4 piles was analyzed using the consolidation process to verify the applicability of the three simulation techniques. The calculated results were compared with the corresponding experimental results. The calculated results using three techniques generally agreed well with the experimental results in terms of initial stiffness and pile shaft resistance. Both the measured and calculated results indicate that ground consolidation caused by pile installation significantly increases the pile bearing capacity and especially, the pile shaft resistance. Therefore, the pile setup effect can be reasonably simulated by the three proposed techniques.     

Interaction between pile foundation and soil

Problems of interaction between a single long pile (more than 20 m) or a group of long piles as component parts of a pile foundation and soil are discussed on the basis of a new geomechanical model. The settlement of a pile or group of piles is caused primarily by shear deformations of a soil mass of limited area and depth, and also as a result of deformations of the mass beneath the lower ends of the piles. __________ Translated from Osnovaniya, Fundamenty i Mekhanika Gruntov, No. 2, pp. 2–7, March–April, 2007.     

考虑时间效应的群桩负摩阻力模型试验研究

基桩负摩阻力是桩基础设计中必须考虑的重要问题之一,但是针对考虑土体固结时间效应的群桩负摩阻力研究却相对较少。进行了在地面堆载固结条件下,黏性土层中3×3群桩负摩阻力性状的室内模型试验研究,测得了不同桩间距(3d,4d,6d)条件下各位置桩(角桩、边桩、中心桩)的桩侧负摩阻力、桩端阻力以及桩周土体分层沉降随固结时间的变化情况,分析了桩身下拽力和中性点位置随时间的变化规律;并进行了同等条件下单桩及2×2群桩(4d)试验作为比较分析。试验结果表明,群桩中桩侧负摩阻力引起的下拽力和中性点位置都存在明显的时间效应和群桩效应,其数值与基桩数、基桩的布置位置及桩间距等因素有关;在本文试验情况下,当桩–土相对位移达到2 mm时,桩侧负摩阻力将达到其最大值的80%～90%。     

碎石桩加固地基力学机理分析

对碎石桩复合地基的加固机理进行了分析,揭示了碎石桩加固地基土体的效应主要包括:挤密、置换和固结等效应,并分析了扰动区渗透系数变化的碎石桩固结特性,以指导碎石桩施工实践。     

软土地区偏斜预应力管桩的处理

通过软土地区偏斜预应力管桩实例，分析造成该工程管桩偏斜的原因，根据管桩的地质情况和偏斜度的不同，采用在管桩桩芯孔内灌注钢筋混凝土桩芯或灌注钢管混凝土桩芯、新增锚杆静压桩的不同方法进行加固处理，取得了较好的效果。     

透水管桩抗弯性能试验研究

透水管桩通过在桩身预留透水孔,联通土体,释放超静孔隙水压力,可加速沉桩过程桩周土的固结,有效减小沉桩挤土效应;但是,预留孔不可避免地会破坏桩身结构的完整性,为了探讨开孔对透水管桩抗弯抗裂性能的影响,开展了普通管桩与透水管桩的抗弯试验,记录了各桩的开裂弯矩、破坏弯矩以及不同弯矩作用下的桩身挠度与裂缝宽度,探讨了开孔对透水管桩抗弯抗裂性能的影响。研究表明,相对普通管桩,透水管桩跨中挠度更大,开裂弯矩降低,但仍满足规范要求;在相同弯矩作用下,透水管桩裂缝宽度小于普通管桩;在以相同裂缝宽度(1.5mm)作为极限状态判断标准的条件下,透水管桩的破坏弯矩大于普通管桩,透水管桩拥有优于普通管桩的抗弯性能。     

Interaction between inclined pile groups subjected to harmonic vibrations

Vertical and inclined piles are used in seismic areas where they could be subjected to oblique harmonic vibration loads. The effect of closely spaced battered piles on the pile–soil–pile interaction has not yet been fully recognized. A simple analytical method, based on the elasto-dynamic theory by Novak and his associates, is used in the present study to characterize vertical and inclined isolated cylindrical piles subjected to inclined harmonic vibrations. The free field movement of the ground in the vicinity of the piles is determined using an approximate approach based on the interference of the cylindrical wave field originating along each pile shaft and spreading radially outward. In calculating the interaction factor between two battered piles, an analysis has been carried out to demonstrate the effect of the presence of a neighboring pile (receiver) while the first pile (source) is loaded. In this situation, it has been found that the movement of the source pile head is decreased when a receiver pile is present. Also, the effects of the pile–pile distance, the group geometry, the length of the piles, and the inclined angle for each or all of the piles have been studied and the corresponding results will be presented.     

Uplift tests of jet mixing anchor pile

The jet mixing anchor pile is a new kind of supporting technology for foundation pit engineering in soft clay. The engineering features of jet mixing anchor pile as well as the difference between it and normal anchor bolt are introduced. The uplift tests of 4 jet mixing anchor piles are presented in detail to obtain the ultimate bearing capacity and load–deformation relationship of the piles. Load-transfer analysis, which is rarely applied in the analysis of uplift piles, is carried out on the piles with a hyperbolic calculation model. The load transfer method focuses on the interface between pile and soil, with which the non-linear behavior, the bearing capacity and the engineering features of the anchor piles can be fully studied. The calculated load–displacement curves of the piles have close agreement with that of the pullout tests, indicating that the proposed analytical solution is reasonable and feasible in predicting the bearing capacity of the piles. Thus, with this study, the supporting stiffness of the anchor pile can be predicted in the design stage of the foundation pit engineering, which is very important and meaningful in practical engineering. The decay curve of shear stress of soil surrounding the pile is derived with the load-transfer method, through which the minimum transverse space of each two piles can be decided against the pile group effect. Engineers can optimize the length and spacing of group piles through this.     

考虑桩基剪切效应的盾构开挖对邻近桩基水平向变形分析

盾构隧道开挖将引起土体卸荷,会对邻近既有桩基产生不利影响,为探究既有桩基在邻近盾构开挖下的水平向响应规律,针对已有研究的不足,提出了一种在邻近盾构开挖下能考虑桩基剪切效应的计算桩基水平向响应的简化算法。首先既有桩基被视为置于Pasternak双参数地基上的铁木辛柯梁,然后由两阶段法建立起考虑桩基剪切效应的桩基水平向变形控制微分方程,利用有限差分法解得附加荷载作用下的桩基水平向变形解析解。通过离心试验、监测数据的对比,验证了该方法的合理性。并在给定的桩土参数下,把同时考虑桩基剪切和弯曲变形的解析解与只考虑桩基弯曲变形的退化解进行对比,发现较之于欧拉–伯努利梁法,盾构对桩基扰动程度的影响,扰动越大,剪切效应体现越明显,由铁木辛柯梁法计算的位移值与弯矩值更接近实测数据。     

变刚度悬臂式双排抗滑桩水平推桩模型试验研究

双排抗滑桩常用于加固大型滑坡,其中悬臂式双排抗滑桩由于施工便利,受到工程界广泛重视。已有研究表明,后排桩承受的滑坡推力大于前排桩,是困扰设计的重要问题。文章借鉴变刚度调平设计原理,通过改变前后排桩间距实现前后排桩刚度的调整,设计了变刚度悬臂式双排抗滑桩支护形式,并进行了室内水平推桩模型试验,得到桩顶及坡顶位移、桩身弯矩以及滑体内土压力分布。结果表明：水平推桩模式下,桩顶位移和桩身弯矩随荷载增大而增大,模型边坡沿着滑动面破坏,根据桩顶的荷载-位移曲线,双排桩在推力作用下的发展过程被划分为三个阶段;适度增大前排桩的桩间距并不会明显降低双排抗滑桩的临界荷载;采用变刚度调平设计悬臂式双排抗滑桩,前排作用被充分调动,前后排最大弯矩差值变小;双排抗滑桩存在明显的三维土拱效应,在推力方向上被划分为后排桩后土拱效应、桩排间土拱效应、前排桩前土拱效应,在深度方向上,滑体中部土拱效应与滑体下部有所不同;适度扩大前排桩的间距,桩排间土体保持稳定,未见土体绕流现象,桩排间土拱效应作用明显。