共查询到19条相似文献，搜索用时 161 毫秒
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某港口堆场地基上部5．0m系吹填而成，地表下18m范围均属软土，经真空预压初级加固后地基承载力仅在80—90kPa，局部区域上部淤泥土层土性指标较差，含水量大于50％，地基承载力不足60kPa。为了使地基达到230kPa的承载要求，设计采用深层搅拌法加固超软弱地基。通过现场成桩工艺试验和检测表明，桩身水泥土强度在90d龄期时大于1．80MPa，单桩承载力标准值大于150kN，以φ600桩径、桩长13．5m、置换率为0．308和φ500桩径、桩长13．5m、置换率为0．267两种方案布置的复合地基承载力标准值均超过了230kPa的设计要求。试验结果表明，深层搅拌法在港口超软弱地基土应用只要施工工艺适当，完全可以使地基承载力提高2—3．5倍以土，从而节省大量的工程投资。 相似文献
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CFG桩网复合地基广泛应用于处理软土地基。采用土工离心模型试验研究某码头堆场超大荷载下CFG桩网复合地基的变形和桩土应力特性,试验模拟了地基、CFG桩、树根桩、加筋垫层、防尘网和轨道梁基础、矿石堆载等,分析了超大荷载作用下复合地基表面变形、桩顶轴力、桩间土压力、桩土应力比的变化规律。试验结果表明,复合地基的沉降速率在稳定控制标准之内,沉降量满足堆场使用要求,防尘网基础和轨道梁基础水平位移和沉降均很小,桩土应力比为25.2~43.8,CFG桩网复合地基在350 kPa荷载作用下是稳定安全的,达到了预期加固效果。 相似文献
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工程中常涉及到地基承载力特征值fa及桩端阻力qpa,作为同量纲的地基指标,对同一土层后者往往要比前者高得多。运用梅耶霍夫地基极限承载力理论,分析了随基础埋深的加大地基土破坏形式的变化,对浅基础及桩基础破坏形式、地基承载力特征值fa与桩端承载力特征值qpa作了对比。研究结果将有利于建立及区别地基承载力特征值及桩端端阻力特征值的物理概念,对实际工程具有指导意义。 相似文献
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《中国海洋大学学报(自然科学版)》2016,(1)
CFG桩在地基处理工程中已越来越广泛应用,针对大型炼厂工程地基处理的复杂性,开展了CFG桩施工前后的标准贯入、重型动力触探及施工后的单桩和复合地基静载荷试验,基于标准贯入和重型动力触探试验结果分析了CFG桩对桩间土的影响。以单桩和复合地基载荷试验结果对大型油罐CFG桩复合地基承载能力进行了评价,并与理论估算进行了对比。此外,建立了CFG复合地基的三维有限差分模型,对桩身6m以下不同厚度的软土夹层对CFG桩复合地基的影响进行了详细分析,进一步验证现场试验结果,得出一些结论。标准贯入和重力动力触探试验结果揭示CFG桩对桩间土未有明显的挤密效应;静载荷试验结果表明,CFG桩复合地基承载力能达到设计要求;现场试验和数值模拟结果揭示桩身10m以下软土夹层不会明显影响复合地基的承载特性。 相似文献
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离岸深水全直桩码头承载性能有限元分析 总被引：1，自引：0，他引：1
全直桩码头是适于软土地基上离岸深水海域的新型高桩码头结构型式,其承载机理与传统高桩码头存在较大差异,且软土地基循环软化效应显著。建立全直桩码头结构与地基相互作用三维弹塑性有限元模型,基于二次开发采用拟静力法对土体循环软化效应进行模拟。通过有限元模型研究全直桩码头的承载特性与破坏模式,并探讨水平极限承载力的影响因素。研究表明水平荷载作用下,基桩的塑性破坏是结构失稳的控制因素,地基土体的承载力对结构水平极限承载力不起决定性作用;竖向荷载作用下,结构竖向极限承载力由地基土体强度决定。研究范围内入土深度对结构水平极限承载力影响不大,但桩壁厚度减小或考虑土体软化后,结构水平极限承载力明显降低。设计中,增加入土深度可有效减小土体软化引起的水平极限承载力降低程度,且应考虑结构腐蚀和土体软化对水平极限承载力的双重降低效应,为钢管桩预留足够的腐蚀富裕量。 相似文献
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浅谈挤密碎石桩的施工方法 总被引：1，自引：0，他引：1
挤密碎石桩施工法是一种振动成桩法,即先用桩管振动成孔,然后填入足够数量的碎石,最后振动密实成桩体。通过振动、挤密的成桩过程,将原地基土振动夯实,桩体与桩间土形成复合地基,达到既处理可液化地基又增强地基的效果。介绍了挤密碎石柱的施工方法和质量检测方法。 相似文献
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Study of the Bearing Capacity at the Variable Cross-Section of A Riser-Surface Casing Composite Pile
Reducing the cost of offshore platform construction is an urgent issue for marginal oilfield development.The offshore oil well structure includes a riser and a surface casing.The riser,surface casing and oil well cement can be considered special variable cross-section piles.Replacing or partially replacing the steel pipe pile foundation with a variable cross-section pile to provide the required bearing capacity for an offshore oil platform can reduce the cost of foundation construction and improve the economic efficiency of production.In this paper,the finite element analysis method is used to investigate the variable cross-section bearing mode of composite piles composed of a riser and a surface casing in saturated clay under a vertical load.The calculation formula of the bearing capacity at the variable section is derived based on the theory of spherical cavity expansion,the influencing factors of the bearing capacity coefficient Nc are revealed,and the calculation method of Nc is proposed.By comparing the calculation results with the results of the centrifuge test,the accuracy and applicability of the calculation method are verified.The results show that the riser composite pile has a rigid core in the soil under the variable cross-section,which increases the bearing capacity at the variable cross-section. 相似文献
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为了研究桩长对海底防沉板—桩复合基础在水平、弯矩和扭转荷载作用下承载特性的影响,以我国南海水深200 m的某工程实例为研究对象,利用Flac3D有限差分仿真软件建立了计算模型。研究了桩长为4 m、6 m和8 m的防沉板—桩复合基础在水平、弯矩和扭转荷载作用下的极限承载力和荷载传递机理。结果表明,桩长超过6 m时复合基础的水平承载力显著增长,在水平加载过程中,防沉板总是先达到极限状态而破坏,桩基础的贡献在加载后期体现,且桩长为4 m、8 m时,桩基础与防沉板的连接处弯矩最大;随着桩长的增加,复合基础的抗弯承载力大幅提高,桩基础对复合基础的抗弯承载力贡献增大,当桩长超过8 m,桩长的增加对提高复合基础的抗弯承载力意义不大;在弯矩加载过程中,桩长对于防沉板、桩基础的荷载分配有显著影响,桩长为4 m时,外荷载主要由防沉板承担,当桩长超过4 m时,外荷载主要由桩基础承担;当扭转荷载不超过2 100 k N·m时,防沉板承担主要荷载,直至防沉板达到极限状态而发生旋转,随后桩基础的承载力逐渐发挥;对于桩长为6 m、8 m的复合基础,其极限状态根据防沉板适用性准则确定。 相似文献
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AbstractCement soil mixing piles are an effective treatment method for marine soft clay. To investigate the static and dynamic characteristics of the composite soil with cemented soil core, a series of experiments are carried out by using the cyclic simple shear test. The result shows that, the static shear strain showed strain hardening, cemented soil core can improve static shear strength of composite soil, vertical stress can enlarge reinforcement of cemented soil core. The tendency of strain development of composite soil with different area replacement ratios under cyclic loading is the same as that of pure clay, existing critical cyclic stress ratios corresponding to different area replacement ratios. In addition, improving area replacement ratio can increase cyclic strength. At same time, adding of cemented soil core does not change shape of hysteresis curve compared with it for clay either. Moreover, cemented soil core can also obstruct stiffness softening. Through regression analysis of the experimental data, relationship between cyclic number and soil softening index is proved to be linear. The results can give a reference for the dynamic characters of the marine soft clay foundation with cement soil mixing piles. 相似文献
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利用室内半模试验和颗粒流数值模拟,揭示多层砂土地基扩底桩单桩抗压承载特性及变形特征。结果表明,通过对比分析极限承载力与H_h/D(持力层厚度与扩大头直径之比)的关系可以看出,单桩的抗压极限承载力随H_h/D逐渐增加,当H_h/D超过2.0时,极限承载力基本不再增加,此时的单桩抗压极限承载力稳定在300.01~303.25 N,是H_h/D=0.5时极限承载力(183.83 N)的1.65倍。扩大头下部土体发生局部压缩-剪切破坏,破坏面从扩大头底面边缘向斜下方扩展,在水平方向影响范围达到最大后逐渐向桩内侧收缩;荷载作用越大,地基破坏区域越大,相应的极限抗压承载力也越大;持力层厚度增加,扩大头分担的荷载比例增大,分担的荷载达到稳定需要的桩顶位移也越大,H_h=0.5 D试验扩大头分担的荷载比例稳定时为60%,对应的桩顶位移约为29 mm;桩顶位移达到33 mm后,H_h=1.0~3.0 D试验稳定在63%~65%之间;通过细观颗粒流理论对砂土移动特性的研究发现,持力层厚度从0.5 D增大至2.0 D,破坏面的起始扩展角度从31°增大至42°。数值模拟研究结果与模型试验数据吻合效果良好,证明该方法分析多层砂土地基扩底桩单桩抗压荷载传递机理是可行的。 相似文献
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螺旋桩芯劲性复合桩（helix stiffened cement mixing pile,简称HSCM桩）是一种新型复合桩,其成桩工艺会对桩身及其承载性能有较大影响。为验证HSCM桩在软黏土中同步旋进注浆工艺的可行性,并研究其成桩参数对抗压承载性能的影响,设计了2组缩尺模型试验,包括不同叶片数量与钻进速度的HSCM桩与对比螺旋桩。通过在高岭土制备的软黏土中成桩,并进行抗压承载性能及桩身几何尺寸测试,分析HSCM桩的成桩参数与水泥土桩身间的关系。试验结果表明：同步旋进注浆工艺能够在螺旋桩周围形成倒圆台状的水泥土桩身,水泥土桩身的平均黏结直径约为叶片直径的1.17～1.35倍;适当增加叶片数量能够使水泥与土体充分拌和,提高水泥土桩身的完整性与连续性,以改善HSCM桩的成桩质量;钻进速度大幅提高会导致注浆量不足,减小水泥土桩身的黏结直径与刚度;试验条件下HSCM桩的抗压极限承载力是螺旋桩的3.83～3.93倍,桩径扩大提高了侧摩阻力,注浆工艺加固并提高了土体强度,弥补了叶片在旋进过程中扰动土体造成强度降低的问题。 相似文献
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近海海床表层多为软黏土或淤泥质土,为探究海床表层软土对海上风电宽浅式筒型基础承载特性的影响,以中国广东某海域风电场为背景,通过有限元分析的方法,研究竖向、水平、弯矩荷载作用下软土层厚度和土体强度对基础极限承载力、破坏模式以及筒基土压力分布的影响。研究结果表明:当软土层厚度小于H/2(H为筒裙高度)时,单向荷载作用下宽浅式筒型基础极限承载力随软土层厚度的增加呈线性减小的趋势;当软土层厚度大于H/2后,承载力降低速率逐渐增大。表层软土的存在,使得塑性区范围缩小,软土层内土体塑性破坏更加明显。竖向荷载作用下,随软土层厚度的增大,筒顶承载先减小后增大,筒内侧摩阻力先增大后减小;水平荷载和弯矩作用下,筒侧被动土压力的降低是引起软土覆盖地基中基础承载能力降低的主要因素。 相似文献
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针对海相软土地区螺旋钢管桩承载力低与腐蚀问题,提出一种新型压力注浆螺旋钢管桩,并设计5根足尺试验桩,进行现场抗拔承载性能试验,研究螺旋叶片直径与排布方式对成桩直径与桩基抗拔承载性能的影响.结果表明,成桩直径与螺旋叶片直径呈正相关,在每节延长段钢管末端设置螺旋叶片利于提高水泥土柱完整性,使成桩直径更为饱满,提高桩基的抗拔承载性能.将试验结果和现行规范抗拔极限承载力计算结果进行对比,计算结果约为实测平均值的94％,在此基础上提出压力注浆螺旋钢管桩抗拔承载力计算参数修正建议,为后续的设计提供参考. 相似文献
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Jun Wang Zhi Zhou Hongtao Fu Yuanqiang Cai Xiuqing Hu 《Marine Georesources & Geotechnology》2013,31(7):870-879
AbstractLand reclamation has increased significantly in the eastern coastal areas of China. The increased exploitation of offshore resources has made cast-in-situ piles more preferable in these regions. However, precise prediction of axial forces and shaft resistances of piles is particularly difficult because geological conditions are complex after the foundation is treated by vacuum preloading. In this study, two groups of cast-in-situ piles, each of which consisted of two piles installed in soft soil in Oufei Project, Wenzhou, China, were compared by conducting tests using the slow static loading method to evaluate the influence of applying vacuum preloading to deal with soft soil foundation on the vertical bearing capacities of the piles. Two piles were located in an untreated area, while the other two were located in a vacuum preloading treating area. All the piles had the same length and diameter. In addition, the axial forces and shaft resistances of piles were calculated based on the measured strains. The field tests revealed that the ultimate bearing capacities and shaft resistances of test piles were significantly improved compared to those of the piles in untreated area. The experimental results presented in this study are expected to be highly beneficial for practical engineering. 相似文献