共查询到19条相似文献，搜索用时 171 毫秒
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在沉桩位置处设置预钻孔是工程中减小扩孔挤土效应的常用有效措施。针对邻近斜坡的沉桩挤土问题,假定土体为线弹性模型,采用镜像方法,将桩体的贯入模拟为一系列球形孔连续扩张过程,在已有文献的基础上进一步推导出邻近斜坡设有预钻孔时的沉桩挤土位移表达式。结果表明,受斜边非轴对称位移边界的影响,远离斜边自由边界一侧的挤土位移不如靠近斜边自由边界一侧明显;斜边自由倾斜边界越陡（即参数 越小）,斜坡挤土位移越大;随着边界角度 的增大,斜边倾斜边界对沉桩挤土位移的影响逐渐减弱;预钻孔的孔深和孔径对减小邻近斜坡沉桩挤土位移有较大的影响,二者的结合能更有效地减少挤土位移的范围和深度。 相似文献
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楔形桩是一种可以有效提高桩侧摩阻力的纵向变截面异形桩,然而针对该变截面桩沉桩效应特性方面的研究却相对较少。基于透明土材料和粒子图像测速技术（简称PIV）,开展静压楔形桩沉桩模型试验,测得沉桩过程中桩周土体的位移场变化规律;沉桩过程中桩周土体位移场由激光射入透明土材料,与透明土材料之间的相互作用产生的独特散斑场,通过CCD（charge-coupled device）电荷耦合元件相机成像处理而获得。同时进行了等截面桩的沉桩模型试验,并对等混凝土材料用量情况下楔形桩和等截面桩的沉桩效应进行对比分析。最后,将此试验结果与基于常规试验手段的静压楔形桩沉桩模型试验和圆孔扩张理论计算结果进行对比分析,验证了基于透明土材料的静压楔形桩沉桩模型试验的准确性和可靠性。研究结果表明,基于透明土材料和PIV技术可以有效地开展静压楔形桩沉桩模型试验研究;楔形桩静压施工过程中对桩周土的影响范围约为等混凝土用量等截面桩的1.2倍。 相似文献
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挤土型桩的挤土效应一直是工程界研究和关注的热点问题之一。结合南京长江四桥北接线段现浇X形桩软基处理工程,首次开展现浇X形混凝土桩（简称X形桩）沉桩过程现场试验,测得不同X形横截面方向、不同距离及深度处的水平位移、侧向土压力以及孔隙水压力的分布规律,研究X形桩挤土效应规律。研究结果表明,最大水平位移发生在桩顶,距离5倍等效桩径处的土体水平位移可以忽略不计;随着桩中心距的增加,挤土压力和孔隙水压力逐渐减小,并且尖角方向的挤土压力大于凹弧方向的挤土压力。现场试验数据为X形桩的布置形式以及桩间距的选择提供有力的设计参考依据。 相似文献
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《岩土力学》2017,(10):2873-2880
基于圆孔扩孔理论,考虑挤密砂桩挤密过程中砂桩本身的挤密体积变化,建立了砂桩桩身压缩模量的计算方法。采用Mohr-Coulomb屈服准则计算桩周土屈服区范围,同时结合桩间土的e-p曲线压缩理论,提出了基于扩孔理论的桩周土平均压缩模量计算公式,从而提出了考虑埋深影响的分层桩土应力比计算方法。结合越南河内-海防高速公路实际工程进行了计算分析,随着套管直径增大(0.5~0.6 m),挤密砂桩和桩周土的压缩模量都变小,但平均桩土应力比增大,从2.56增大至2.72,这符合《复合地基技术规范》中对于无实测资料时,桩间土强度低时桩土应力比取大值,桩间土强度高时取小值的规定。桩土应力比理论计算结果处于规范建议取值2~3之间。说明理论方法合理可靠,从而提高了挤密砂桩设计的科学性。 相似文献
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变径桩在桥梁桩基和软土地基处理得到了一定程度的应用,对其承载特性和工作机制的研究十分必要。通过室内大型模型试验,对大直径变截面单桩的荷载与沉降关系、桩侧摩阻力分布形式、桩身内力和桩端、变截面处的破坏模式等问题进行了探讨,试验结果表明,在桩顶截面相同的情况下,变截面桩竖向承载特性受变截面比影响显著,变截面比越小,竖向极限承载力越小。模型试验P-S曲线不存在最优变截面比,变截面比设计受桩横向受力特性的控制。变截面处土体挤土效应的发挥是以牺牲桩顶位移为代价,在只有到达一定桩身位移时,才体现明显的挤土效应,使承载力提高。 相似文献
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Y型沉管灌注桩是在传统圆形桩基础上通过改变截面形状以增大桩土接触面积、增加侧摩阻力进而增加承载力的一种新桩型。由于桩身截面的特殊性,在振动沉管的过程中Y型沉管灌注桩截面不同处对土有不同程度的挤压作用,其侧摩阻力分布性状比圆形桩复杂,若将Y型桩侧摩阻力看作沿桩身矩形分布、沿桩周均匀分布与实际不符,工程经验亦表明其不适。通过孔扩张理论与Y型截面的解析方程相结合,推导Y型桩侧摩阻力沿桩周及桩身的不均匀分布模型,同一截面最大侧摩阻力为最小侧摩阻力的1.24~1.75倍,同时分析外包圆半径R、模板弧度θ、桩长L对侧摩阻力的影响。将侧摩阻力沿Y型截面周边的9个区间积分,然后沿桩长积分,得到Y型桩总侧摩阻力,结合端阻力模型计算了Y型桩单桩极限承载力,与静载试验数据吻合。 相似文献
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在软土地区进行预制桩沉桩施工时，往往由于挤上效应造成邻近建筑物产生破坏。本文结合工程实例，提出通过采用取土卸压孔减少被保护建筑附近的挤土位移，结合信息化施工手段，是一种解决沉桩挤土效应的有效方法。本文还对土体位移监测成果进行了分析。 相似文献
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表面约束下的沉桩挤土效应数值模拟研究 总被引：6，自引：0，他引：6
采用数值方法对表面约束下的沉桩挤土效应进行了研究。以道路约束为例，讨论了不同宽度道路以及道路与浅基础共同约束时，对沉桩挤土引起的地表隆起及水平位移的影响，得出若干有参考价值的结论。 相似文献
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A novel analytical approach for predicting the noncylindrical pile penetration‐induced soil displacement in undrained soil by combining use of cavity expansion and strain path methods 
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下载免费PDF全文 Since development of cavity expansion theory and strain path method, almost all the conventional analyses of pile penetration problem have been based on circular cross section penetrometer. However, noncylindrical pile (with noncircular cross section) is also required in geotechnical engineering such as rectangular cross‐sectional pile, X‐sectional cast‐in‐place concrete pile, H‐shaped steel pile, prefabricated vertical drains, and flat dilatometer. This paper presents a novel and general analytical approach for capturing the soil deformation mechanism around the pile with arbitrary cross section. The penetration problem is simulated by a new 2‐dimensional (radial and circumferential) cavity expansion model. Based on the theoretical framework of strain path method, the kinematics (velocity field) of the noncylindrical cavity expansion is reduced to solve the Laplace equation with arbitrary velocity boundary conditions by using the conformal mapping technique. Then, solutions for the strain and displacement, which could consider the large deformation effect, are obtained by the integration of the strain rate and velocity along the streamline. The analytical solution is validated by comparing the degenerate solution of this study with conventional circular (cylindrical) cavity expansion theory. Subsequently, typical numerical examples for the deformation mechanism of elliptical and rectangular cavity expansion are presented to prove the advantage of the proposed new solution particularly in capturing the noncylindrical symmetric displacement field. A brief application of the proposed new analytical solution to the interpretation of the smear effect of prefabricated vertical drain installation confirms its useful in geotechnical engineering. 相似文献
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This paper presents a simplified analytical model: the X-shaped cylindrical cavity expansion method (XCEM), which can be used to interpret and predict the displacement, stress, and excess pore pressure caused by the X-section cast in place concrete (XCC) pile installation in soft soil. Analytical solutions for the displacement and strain field are obtained with a streamlined solution, base on the strain path method (SPM). The stress and excess pore pressure can then be subsequently determined with the assumption of the elastic-perfectly plastic soil behavior. A positive agreement was found when the theoretical prediction of the displacement, stress, and excess pores pressure was compared against the field measurements. The proposed XCEM improves the conventional cavity expansion method (CEM) and offers a framework for understanding the non-circular cross-section penetrator problem, which is different from the conventional circular penetrator problem. 相似文献
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对于传统矩形截面抗滑桩的受力而言,由于混凝土抗压不抗拉的力学性质,使截面受拉区的混凝土没有发挥出最大效用。通过对矩形截面形状的改变,即把受拉区面积减小和受压区面积增大,进一步利用了混凝土在截面中的抗压性能,使得抗滑桩截面的抗弯承载力和抗弯刚度都得到了提升,并通过计算,验证了此说法。截面形状的改变,也使得桩间土拱受力发生了改变,即从以前的一个土拱,变为了由一个主要拱和一个次要拱来共同承担,对桩间土拱效应有一定增强。通过对矩形截面和特殊截面抗滑桩的数值模拟对比分析,论证了桩间土拱效应在截面改变后得到增强的观点,也表明特殊截面抗滑桩降低了土体从桩间滑出的可能性,可为抗滑桩的传统设计提供理论参考。 相似文献
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Field studies have shown that the driving of a displacement pile into cohesive soil generates large excess pore pressures in the vicinity of the pile. These pore pressures are often larger than the effective overburden pressure and facilitate the installation of the pile. The subsequent increase in bearing capacity of the pile is largely controlled by the dissipation of the excess pore pressures and a consequent increase in the effective stresses acting on the pile. The paper presents a closed formanalytical solution for the radial consolidation of the soil around a driven pile, assuming that the soil skeleton deforms elastically. This assumption is examined in the light of the predicted effective stress changes in the soil and is shown to lead to, a realistic model for the decay of pore pressure near the pile with time after driving. Although the solution may be applied to any initial distribution of excess pore pressure, attention is focussed on that due to the expansion of a cylindrical cavity in an ideal elastic, perfectly plastic soil. The resulting logarithmic variation of excess pore pressure with radius is considered to be close to that generated around a pile as a result of driving. In addition to giving estimates of the time needed for a driven pile to achieve its maximum strength, the solution may also be used in the analysis of pressuremeter tests to provide in-situ measurements of the coefficient of consolidation of the soil. 相似文献
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The conventional approach in the design of laterally loaded piles with rectangular cross section involves the simplification of converting the rectangular cross section of the pile to an equivalent circular cross section. An analysis to determine the response of laterally loaded rectangular or circular piles in elastic soil is presented in which this simplification is not required. The analysis is based on the solution of differential equations governing the displacements of the pile–soil system derived using energy principles. The pile geometry and the elastic constants of the soil and pile are the input parameters to the analysis. Using this analysis, comparisons are made between the response of rectangular and circular piles in elastic soil. Based on the proposed solution scheme, a user-friendly spreadsheet program (LATPAXL) was developed that can be used to perform the analysis. In addition, simple equations obtained by regression analysis of the pile head deflection and bending moment profiles are proposed. Examples illustrate the use of the analysis. 相似文献
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Analysis of rectangular piles subjected to lateral loads in nonhomogeneous soil using a Winkler model approach 下载免费PDF全文
下载免费PDF全文 Hiroyoshi Hirai 《国际地质力学数值与分析法杂志》2015,39(9):937-968
An analytical approach using a Winkler model based on two lateral soil displacement components in a three‐dimensional soil is investigated to provide analytical solutions of horizontal response of a rectangular pile subjected to lateral loads in nonhomogeneous soil. The two lateral displacement components of a soil surrounding the rectangular pile are represented by the Fourier series of displacement potential functions in the elastic three‐dimensional analysis. The lateral stiffness coefficient of the rectangular pile shaft in nonhomogeneous soil is derived from the rocking stiffness coefficient taking into account rocking rotation of a rigid pile shaft. The relationship between horizontal displacement, rotation, moment, and shear force for the rectangular pile subjected to horizontal loads in nonhomogeneous soil is obtainable in the form of the recurrence equation. The formulation of lateral displacement and rotation for a rectangular pile subjected to lateral loads on the pile base in nonhomogeneous soil is proposed by taking into account Mindlin's equation and the equivalent thickness for soil layers in the equivalent elastic method. The difference of lateral behavior between square and circular piles subjected to lateral loads is insignificant. The effect of aspect ratio of the rectangular pile on the lateral behavior is great for the lower stiffness ratio between pile and soil and the larger length–equivalent diameter ratio. The effect of the value of Poisson's ratio of soil on lateral stiffness coefficient is relatively small except Poisson's ratio close to 0.5. The comparison of the results calculated by the current method for a rectangular pile subjected to lateral loads in nonhomogeneous soil has shown good agreement with those obtained from the analytical methods and the finite element method. Copyright © 2015 John Wiley & Sons, Ltd. 相似文献
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注浆成型螺纹桩为一种利用施工工艺创新,结合钻孔灌注和二次注浆技术的新型螺纹抗拔桩型,目前已在软土地区开展应用。为了对其受力承载特性深入研究,使该桩型得到广泛推广,通过数值分析方法对其抗拔性能和承载机制进行了三维有限元数值模拟。首先,通过数值模拟桩-土界面室内大型直剪试验得到了有限元分析需要的桩-土接触面参数,而后将得到的参数带入注浆成型螺纹桩抗拔三维有限元数值模型,通过计算得到了不同距径比S/D（即螺距与桩径的比值）螺纹桩的抗拔荷载-位移曲线和轴力分布,并观察了抗拔过程中桩周土体塑性变形的发展。数值分析表明,螺纹桩与桩周土体的机械咬合作用增大了桩侧摩阻力,从而使桩体极限抗拔承载力较等截面圆桩提高约2～5倍;同时,其承载能力与桩体的S/D有关,当S/D取最优时,荷载-位移曲线的初始切向刚度最大,极限承载力最高,桩周土体形成的连续拱形破坏区域最大。 相似文献