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1.
砂土海床中大直径单桩水平承载与变形特性 总被引：5，自引：0，他引：5
通过室内三轴固结排水剪切试验等获得典型剪胀性砂土的力学参数,在此基础上利用有限元软件ABAQUS,开展了近海大直径单桩基础在水平荷载作用下的三维有限元数值分析,揭示了加载过程中桩周土的应力路径,探讨了桩周土内摩擦角、剪胀角及桩土接触面特性等对三维数值分析结果的影响,得到了离心模型试验的验证,进而提出了砂土海床中大直径单桩基础的合理数值分析模型及参数取值方法,并建议风机大直径单桩基础水平承载力确定以变形作为控制标准。在此基础上,利用该数值分析模型分析了现有桩基承载力和变形分析方法对超大直径单桩的有效性,并提出了采用数值分析来确定基础的临界埋深的确定方法。 相似文献
2.
A simplified method of numerical analysis has been developed to estimate the deformation and load distribution of piled raft foundations subjected to vertical, lateral, and moment loads, using a hybrid model in which the flexible raft is modelled as thin plates and the piles as elastic beams and the soil is treated as springs. Both the vertical and lateral resistances of the piles as well as the raft base are incorporated into the model. Pile–soil–pile, pile–soil–raft and raft–soil–raft interactions are taken into account based on Mindlin's solutions for both vertical and lateral forces. The validity of the proposed method is verified through comparisons with several existing methods for single piles, pile groups and piled rafts. Workable design charts are given for the estimation of the lateral displacement and the load distribution of piled rafts from the stiffnesses of the raft alone and the pile group alone. Additionally, parametric studies were carried out concerning batter pile foundations. It was found that the use of batter piles can efficiently improve the deformation characteristics of pile foundations subjected to lateral loads. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
3.
S. S. Chandrasekaran A. Boominathan G. R. Dodagoudar 《Geotechnical and Geological Engineering》2010,28(5):603-617
This paper presents the results of two-way cyclic lateral load tests carried out on model pile groups embedded in soft marine
clay. The tests are conducted on 1 × 2, 2 × 2 and 3 × 3 pile groups having length to diameter ratio (L/D) of 15, 30 and 40
with the spacing to diameter ratio (S/D) of 3, 5, 7 and 9. The experimental results are presented in the form of load–deflection
curves and bending moment profiles. Cyclic group efficiency, critical spacing, critical cyclic load level and cyclic p-multipliers are evaluated. It is found that the lateral capacity of the 3 × 3 group reduces by about 42% after 50 cycles
of loading. The cyclic p-multipliers of 3 × 3 pile group are found to be 0.41, 0.25 and 0.29 for leading, intermediate and rear rows respectively.
The test results are compared with the numerical analysis carried out by p–y method using GROUP program. The analysis carried out with experimentally evaluated p-multipliers predicts load—deflection and bending profiles of pile groups reasonably well, but underestimates the depth to
maximum bending moment by about 15%. 相似文献
4.
针对浮式海洋结构采用的桩基础,考虑土的循环软化效应,将软土的循环强度与Mohr-Coulomb屈服准则相结合,基于拟静力弹塑性分析建立了循环波浪载荷作用下斜向抗拔桩循环承载性能的计算模型,确定了斜向上载荷作用下抗拔桩的循环承载力,并与单调加载作用下的斜向抗拔桩的极限承载力进行了对比,进一步探讨了桩长、桩径、桩体模量及载荷循环次数等因素对斜向抗拔桩循环承载力的影响。研究结果表明：循环波浪荷载的作用导致了斜向抗拔桩土体循环强度的分布不均匀,从而降低了地基的循环承载力。斜向抗拔桩的动态极限承载力随循环次数的增加而降低,随桩长、桩径及桩体模量的增大而增大。 相似文献
5.
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
6.
Pile foundations are frequently subjected to cyclic lateral loads. Wave and wind loads on offshore structures will be applied in different directions and times during the design life of a structure. Therefore, the magnitude and direction of these loads in conjunction with the dead loads should be considered. This paper investigates a loading scenario where a monotonic lateral load is applied to a pile, followed by two‐way cycling in a direction perpendicular to the initial loading. This configuration is indicative of the complexity of loading that may be considered and is referred to in the paper as ‘T‐shaped’ loading. The energy‐based numerical model employed considers two‐dimensional lateral loading in an elasto‐plastic soil, with coupled behaviour between the two perpendicular directions by local yield surfaces along the length of the pile. The behaviour of the soil–pile system subjected to different loading combinations has been divided into four categories of shakedown previously proposed for cyclic loading of structures and soils. A design chart has been created to illustrate the type of pile behaviour for a given two‐dimensional loading scenario. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
7.
抗滑桩加固斜坡软弱地基路堤的数值模拟 总被引：2，自引：0，他引：2
在路堤荷载作用下,斜坡软弱地基易产生侧向变形过大、滑塌失稳等病害。路堤下坡脚处采用钢筋混凝土抗滑桩,以有效限制地基侧向变形,是斜坡软弱地基路堤的核心设计原则。采用三维快速拉格朗日有限差分法,经与室内土工离心模型试验成果对比、校核,建立抗滑桩加固斜坡软弱地基路堤的精细化数值分析模型,研究抗滑桩桩距、桩长、桩身弹性模量、桩身横截面尺寸及桩位等设计参数对其内力、变位的影响。研究表明：下坡脚处实施抗滑桩可显著约束斜坡软弱地基侧向变形;需综合考虑桩身受力、经济性、施工等因素确定合理的桩距;桩长应深入滑移面以下,但随着桩长的增长,加固效果增长不明显;随着桩身弹性模量、桩身横截面尺寸的增加,抗滑桩的加固效果得到一定提高;抗滑桩宜设置在下坡侧路堤边坡的中部。 相似文献
8.
针对取自南沙群岛的钙质砂,通过室内模型试验对钙质砂中单桩轴向抗拔承载特性进行研究,讨论了地基相对密实度与桩基埋深对于其抗拔承载力的影响特征。结果表明,在一定范围内,增大地基相对密实度和埋深均能显著提高桩基的承载能力;降低相对密实度或埋深不仅会降低其承载能力,也会增加其在同级荷载下产生的变形;模型桩的桩身轴力从桩顶随深度增加而逐渐降低至0;相对密实度的增加不仅能提高极限桩侧摩阻力的大小,还会在一定程度上影响桩侧摩阻力的分布形式;0.1倍的桩径可以看作是模型桩出土破坏的临界位移量。 相似文献
9.
Many structures (including transmission-line towers, bridges, tall buildings and coastal structures) are founded on piles, which are designed to transmit both vertical and horizontal forces, and resulting moments, to the load bearing strata. The design of such foundations for large lateral repeating loads (e.g. caused by wind, wave action, earthquake) and lateral earth pressures is a challenging task. This paper presents an experimental study that investigates the use of concentric rings (CRs) of small diameter (displacement) piles (SDPs) surrounding a monopile installed in dry sand, with the intention of limiting its rotation (lateral displacement) under repeated lateral loading. The test results showed that the rotation of the monopile, investigated for a range of different repeated lateral loading schemes, was reduced by 35?75% on account of the densification of the sand achieved during installation of the SDPs and also the lateral confinement they provided to the sand located within the CRs. Significant increases to both the cyclic stiffness and load carrying resistance of the monopile under lateral loading are documented with the inclusion of the SDPs. Further experimental as well as numerical studies are necessary to validate this novel technique and to optimise the geometrical size and network pattern of the SDPs and the CRs. 相似文献
10.
沿海地区深基坑设计施工都十分重视其抗浮问题,在深基坑开挖前掌握抗拔桩对于基坑隆起和围护结构变形及受力规律十分重要,其研究成果对于节约工程成本和保证基坑施工安全具有重要的指导意义。以港珠澳大桥侧接线拱北海关隧道明挖段为依托,首先建立抗拔桩与土体的硬接触模型,并验证该模型对于抗拔桩模拟的合理性,采用极差分析法研究底板不同桩长和桩径加固对基坑围护结构稳定性的影响规律。分析结果表明,增大桩长可更有效地减小地表沉降,增大桩径可更好地控制连续墙的变形,增大桩长和桩径都可以很好地控制坑底隆起。 相似文献
11.
静钻根植桩是在水泥土中插入预应力管桩而形成的复合桩。为了认识其在水平荷载作用下的变形性能,实施了3组共6根桩的水平静载试验。第一组是? 600～? 750 mm静钻根植桩（SDRP）,第二组是 800～? 900 mm静钻根植桩,第三组是? 1 000 mm的钻孔灌注桩,第二组与第三组属于几何尺寸十分接近而组成材料不同,第一组与第二组属于组成材料相同而几何尺寸不同。对比水平力-水平位移、水平力-水平位移梯度以及水平变形比后发现,弹性阶段钻孔灌注桩的水平承载性能优于静钻根植桩,而弹性阶段以后则逐渐相反;静钻根植桩变形复原能力强于钻孔灌注桩;桩在弹性阶段的变形量与截面抗弯刚度成近似线性关系;如果只考察弹性阶段,为提高水平承载能力宜将静钻根植桩改为同直径的钻孔灌注桩,不宜单纯扩大静钻根植桩的桩径。 相似文献
12.
为了考察路堤荷载作用下桩网结构路基桩土间的荷载分担与传递、垫层筋带拉力的组成与分布,选择某新建铁路桩网结构路基试验工点进行了现场试验,测试了地基变形、路堤基底压力、孔隙水压力、桩身轴力和格栅拉力等数据。测试数据表明：①地基沉降以压密下沉为主,路基结构稳定,软土较厚一侧地基变形较大;②当桩、土间沉降差与桩间净距的比值为5.93%时,土拱效应完全发挥,之后增加的路堤荷载完全由桩承担;③桩间土竖向附加应力在加固区内沿深度呈K型分布;④筋带拉力沿路基横向呈M型分布,软土较厚一侧拉力较大;⑤筋带拉力由路堤荷载作用下的桩间筋带张力与路堤横向滑移引起的筋带拉力两部分组成,设计筋带时二者均需考虑。 相似文献
13.
The fatigue life of offshore wind turbines strongly depends on the dynamic behaviour of the structures including the underlying soil. To diminish dynamic amplification and avoid resonance, the eigenfrequency related to the lowest eigenmode of the wind turbine should not coalesce with excitation frequencies related to strong wind, wave and ice loading. Typically, lateral response of monopile foundations is analysed using a beam on a nonlinear Winkler foundation model with soil–pile interaction recommended by the design regulations. However, as it will be shown in this paper, the guideline approaches consequently underestimate the eigenfrequency compared to full-scale measurements. This discrepancy leads the authors to investigate the influence of pore water pressure by utilising a numerical approach and consider the soil medium as a two-phase system consisting of a solid skeleton and a single pore fluid. In the paper, free vibration tests are analysed to evaluate the eigenfrequencies of offshore monopile wind turbine foundations. Since the stiffness of foundation and subsoil strongly affects the modal parameters, the stiffness of saturated soil due to pore water flow generated by cyclic motion of monopiles is investigated using the concept of a Kelvin model. It is found that the permeability of the subsoil has strong influence on the stiffness of the wind turbine that may to some extent explain deviations between experimental and computational eigenfrequencies. 相似文献
14.
Integrating ground heat exchanger elements into concrete piles is now considered as an efficient energy solution for heating/cooling of buildings. In addition to the static load of buildings, the concrete piles also undergo a cycle of thermal deformation. In the case of single energy pile, calculation methods already exist and permit to perform a proper geotechnical design. In the case of energy pile group, the thermo‐mechanical interactions within the group are more complex. Very few experimental results on the energy pile group are available so that numerical analysis can be an interesting way to provide complementary results about their behavior. This paper deals with a numerical analysis including a comparison between a single energy pile and an energy pile group with different boundary conditions at the pile head. In order to take into account the stress reversal induced by the thermal expansions and contractions, a cyclic elastoplastic constitutive model is introduced at the soil–pile interface. The analysis aims to give some insights about the long‐term cyclic interaction mechanisms in the energy pile group. Based on this qualitative study, some guidance can be brought for the design of energy piles in the case where group effects should be considered. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
15.
本文针对静力荷载作用的情况,对比了4种黏土中水平受荷大直径单桩的设计方法,包括基于p-y弹簧模型的API规范方法,以及新近发展的基于p-y弹簧模型的Zhang et al.(2017b) 、基于双弹簧模型的Wang et al.(2020) 方法以及基于三弹簧模型的Fu et al.(2020) 方法。考虑两种大直径单桩常用的长径比(L/D=5和10),通过与三维有限元结果比较,对现有设计方法进行了对比,分析了不同参数对预测结果的影响。结果表明:(1)对于大直径单桩的水平位移和转角,现行API规范的预测值最大,而Wang et al.(2020) 方法预测值最小; (2)Fu et al.(2020) 方法不仅考虑了桩底剪力及桩身摩擦造成的分布力矩,还能够有效捕捉初始剪切模量与土体延性对水平响应的影响,还因此具备其余方法所不具备的优势; (3)采用Fu et al.(2020) 方法时,桩土界面粗糙系数α越大,桩身位移与转角越大,且长径比越小影响越显著,而与桩身分布力矩有关的缩放系数ξp2的影响则相对有限,当L/D≥10时其影响可以忽略。 相似文献
16.
The finite element interpretation is discussed of two load tests carried out on instrumented vibro-piles in a granular deposit. A first back analysis, aimed at assessing the improvement of the mechanical characteristics of soil induced by the vibratory construction process, highlights an apparent contradiction between the experimental variation of the axial load along the pile and the numerical results. This suggests introducing as a free variable, in addition to the elastic and shear strength parameters of the granular soil, also the increase of the nominal diameter of pile caused by vibrations. The second back analysis provides some insight into the variation of the diameter with depth and leads to an acceptable interpretation, from the engineering standpoint, of the load tests. On these bases a quantitative comparison is presented between the calculated load–settlement diagram of the vibro-pile and that of a “standard” pile constructed without vibrations in the same granular deposit. 相似文献
17.
波浪、船舶等长期水平循环荷载作用下,桩基将不可避免地产生附加应力和变形。针对饱和黏土地层,开展离心模型试验研究了船舶系泊水平荷载作用下单桩和群桩的变形特性。发现水平循环加-卸载诱发了桩周土体的塑性变形,进而导致桩身产生了不可恢复的水平位移和弯曲变形。随着循环荷载的增加,单桩和群桩的桩顶最大水平位移和残余水平位移均同时增加,但残余水平位移明显小于最大水平位移。单桩的桩顶残余水平位移与最大位移比值介于0.17～0.22;群桩的桩顶残余水平位移与最大水平位移比值介于0.30～0.84。水平循环加-卸载作用下,桩身残余弯曲应变明显小于最大弯曲应变。单桩的残余弯曲应变与最大弯曲应变比值介于0.13～0.50;群桩的桩身残余弯曲应变与最大弯曲应变比值介于0.23～0.82。群桩前桩的残余和最大弯曲应变明显大于后桩,前桩与后桩的最大弯曲应变、残余应变比值分别高达3.2和3.1。因此,前桩要采取合理的加固和保护措施,以确保桩基长期服役的安全性。 相似文献
18.
利用三维弹塑性有限元模型,对水平荷载作用下现浇薄壁管桩(简称PCC桩)受力特性进行数值模拟和分析,并与试验结果进行比较,验证了模型的合理性。利用该模型对桩长、桩径以及桩身相对刚度等影响桩受力特性的主要因素进行分析,结果表明：桩径一定的情况下,桩长对桩的破坏形式有很大的影响,弹性桩与刚性桩临界点的长径比为8左右,且弹性桩的受力主要集中在桩的上部,约为0.3倍桩长;桩径对侧向位移和弯矩都有很大影响,桩径越大,桩侧向位移越小,而最大弯矩值越大,且最大弯矩点下移;在一定程度上,提高桩体强度,有利于提高桩的抗水平变形能力,但当增加到一定程度时,效果并不十分明显。 相似文献
19.
干湿交替对砂岩力学特性影响的试验研究 总被引：5，自引：0，他引：5
由于地下水位的升降等原因,岩体经常处于干湿交替状态,这对岩体工程的长期稳定性不利。以红砂岩为研究对象,进行了干燥－饱水干湿交替作用后的常规单轴和三轴压缩试验研究,获得了砂岩应力-应变曲线,分析了其变形破坏特征。相对于没有经过干湿交替作用的干燥试件,经过不同次数的干燥－饱水交替作用后,砂岩的弹性模量、单轴和三轴抗压强度、黏聚力、内摩擦角等都有不同程度的降低。各力学指标的总体变化趋势是在第1次饱水之后均有较大幅度的下降,此后,随着干湿交替作用次数增加其降低的幅度逐渐减小,干湿交替作用使岩石的延性增强。在围压作用下,砂岩的峰值强度均随着围压的增大而增大,干燥试件强度的围压效应要比多次干湿交替作用后的试件显著。 相似文献