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1.
The pile-to-pile interaction was obtained for vertically loaded piles embedded in homogeneous poroelastic saturated soil. Deduced from Biot’s theory, the fundamental functions of the quasi-static development for the force, displacement and pore pressure were acquired in cylindrical coordinates. The pile–soil system was decomposed into extended soil and fictitious piles, and the compatibility condition was set up between the axial strain of the fictitious piles and the corresponding average strain over the extended soil. This approach results in the governing equations, which consist of the Fredholm integral equations of the second kind and the basic unknowns of the axial forces along the fictitious pile shaft. The axial force and settlement along the pile shaft were calculated based on the axial forces of the fictitious piles. The interaction between the piles was investigated under different consolidation conditions through a two-pile model, and two pile interaction factors were obtained. Stemming from the two-pile analysis, numerical analyses on the settlement of the pile groups were conducted to probe pile interaction with consolidation. The conventional solutions for the single-phase soil-pile problem seem to underestimate the interaction factor if the consolidation effect is taken into account as pile settlement continues. The pile-to-pile interaction can also aggravate the percentage of consolidation settlement (PCS), and as the pile number increases, the value of the PCS will also increase. Several key factors, such as the pile stiffness, pile slenderness ratio and pile spacing, are investigated to better understand the impact of consolidation on pile analysis. 相似文献
2.
为探讨桩侧地基土反力对高承台嵌岩灌注桩桩身屈曲稳定的影响,假定地基反力系数呈更为复杂的幂分布,基于弹性地基梁理论建立桩土体系总势能方程,采用最小势能原理,导出了桩身屈曲临界荷载与稳定计算长度的解析解,并据此获得了地基反力系数分布模式、桩身自重及桩侧摩阻力等对桩身屈曲稳定的影响规律。工程应用分析结果表明,考虑地基反力系数为一般幂分布时,桩身屈曲分析结果更趋合理。 相似文献
3.
Recent study indicates that the response of rigid passive piles is dominated by elastic pile–soil interaction and may be estimated using theory for lateral piles. The difference lies in that passive piles normally are associated with a large scatter of the ratio of maximum bending moment over maximum shear force and induce a limiting pressure that is ~1/3 that on laterally loaded piles. This disparity prompts this study. This paper proposes pressure‐based pile–soil models and develops their associated solutions to capture response of rigid piles subjected to soil movement. The impact of soil movement was encapsulated into a power‐law distributed loading over a sliding depth, and load transfer model was adopted to mimic the pile–soil interaction. The solutions are presented in explicit expressions and can be readily obtained. They are capable of capturing responses of model piles in a sliding soil owing to the impact of sliding depth and relative strength between sliding and stable layer on limiting force prior to ultimate state. In comparison with available solutions for ultimate state, this study reveals the 1/3 limiting pressure (of the active piles) on passive piles was induced by elastic interaction. The current models employing distributed pressure for moving soil are more pertinent to passive piles (rather than plastic soil flow). An example calculation against instrumented model piles is provided, which demonstrates the accuracy of the current solutions for design slope stabilising piles. Copyright © 2014 John Wiley & Sons, Ltd. 相似文献
4.
基于厦深铁路潮汕车站地基处理加固工程,完全参照原型的软土地基地层分布情况,设计了两种不同桩间距下的超大面积深厚软土桩-网复合地基物理模型试验,对荷载传递机制与不同桩间距下桩体荷载分担比、桩土应力比及地基沉降规律等进行了系统研究。结果表明,桩身轴力沿着桩身高度往下先逐渐增大到某一深度后又逐渐减小,随着桩间距增大,桩承担上部荷载的方式由摩擦桩逐渐向端承桩变化;随着桩间距增大,桩身中性点下移,桩身最大负摩阻力出现的位置下降,且其值减小;桩间距对桩-土应力比有显著影响,而对桩体荷载分担比影响较小;不同桩间距下,两桩中心桩间土与桩顶差异沉降均小于4桩中心桩间土与桩顶差异沉降;随着路堤填土荷载增加,土工格栅表现为拉应变逐渐增大,拉应变曲线刚开始比较平缓,后逐渐变陡,增大的速率先慢后快。 相似文献
5.
大厚度黄土地基中大直径长桩、超长桩的应用急剧增多,但黄土地基中超长桩的承载变形机理、侧阻和端阻的发挥性状与普通桩差别较大。采用研制的黄土相似材料填筑模型,分别进行超长单桩和群桩竖向抗压静载试验,分析桩顶荷载作用下荷载-沉降、桩身轴力、桩侧阻力、桩端土体塑性区发展变化规律。研究结果表明:超长单桩在竖向荷载作用下,荷载主要由桩侧阻力承担,桩侧阻力由上向下逐步发挥,属纯摩擦桩,单桩破坏形式为刺入破坏,桩端土体塑性变形影响范围约为1.1 d。与单桩相比,超长群桩基础桩端承载力有较大幅度的提高,桩身轴力衰减深度范围有所减小,侧阻力沿桩身逐渐增大,桩端土层的影响范围约为1.25 d,与超长单桩的影响范围较为接近。本文的研究方法和结果可为大厚度黄土地区超长桩基的承载特性研究提供参考。 相似文献
6.
A simplified analysis method has been developed to estimate the vertical movement and load distribution of pile raft foundations subjected to ground movements induced by tunneling based on a two‐stage method. In this method, the Loganathan–Polous analytical solution is used to estimate the free soil movement induced by tunneling in the first stage. In the second stage, composing the soil movement to the pile, the governing equilibrium equations of piles are solved by the finite difference method. The interactions between structural members (such as pile–soil, pile–raft, raft–soil, and pile–pile) are modeled based on the elastic theory method of a layered half‐space. The validity of the proposed method is verified through comparisons with some published solutions for single piles, pile groups, and pile rafts subjected to ground movements induced by tunneling. Good agreements between these solutions are demonstrated. The method is also used for a parametric study to develop a better understanding of the behavior of pile rafts influenced by tunneling operation in layered soil foundations. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
7.
This paper presents a procedure to assess the mobilized pile side and tip resistance versus pile head and tip settlement under axial load in clay soil. The load transfer ( t– z) curve is evaluated at any point on the loaded pile based on the combined pile tip/side resistance–displacement mechanisms along the length of the pile. Unlike current methods that assume the pile settlements as a percentage of the pile/shaft diameter, the presented technique determines the side and tip resistance of the pile and the associated pile settlement under existing load based on the current stress/strain level in the surrounding soil up to failure (excessive settlement). The technique employs the concepts of the elastic theory and Ramberg–Osgood characterization of the stress–strain behavior of the clay soil. Case studies are also presented to exhibit the capabilities of the proposed procedure. The good agreement between measured and calculated load transfer curves along the pile and pile tip resistance versus pile head, side, and tip displacements shows the consistency of the proposed procedure. A computer code is developed to employ the presented technique. 相似文献
8.
Unlike conventional grouted micropiles, screw micropiles have been recently introduced to the foundation industry. Full-scale field tests of screw micropiles were carried out at a cohesive soil site. The screw micropiles have a diameter varying from 76 to 114 mm and a length varying from 1.6 to 3 m, and spiral threads welded on the lower half of the steel tubular shaft. Site investigation from cone penetration tests (CPT) and laboratory testing implies that the soil was medium to stiff, low plasticity clay. Six axial monotonic and three axial cyclic load tests were performed on three micropiles. One micropile was instrumented with strain gauges to investigate the shaft load distribution during loading. The axial cyclic loading was intended to simulate cyclic inertia load during vertical ground motions. Results showed that the micropiles behave as frictional piles during monotonic tests; the unit shaft resistance and adhesion coefficient were calculated and compared with results in the literature. The end installation torque was estimated using CPT shaft resistance and was shown to agree reasonably with the measured torque. Under axial cyclic loading, the micropiles underwent small cumulative displacements and the magnitude of the displacement decreased with increasing pile length and diameter. Cyclic loading redistributed the load transfer along different segments of the micropile. Negative skin resistance was observed along the smooth pile shaft when the pile underwent decreasing axial loading. 相似文献
9.
This article revisits the influences of axial load on the lateral response of single pile with integral equation method. The problem is formulated by decomposing the pile soil system into an extended elastic soil and a fictitious pile, the former of which is analyzed by making use of the fundamental Mindlin's solution for a concentrated horizontal load whereas the latter is modeled by the conventional beam bending theory. According to the rotation compatibility condition between the fictitious pile and the extended soil, a Fredholm integral equation of the second kind is established with the shear strain and rotation angle of the fictitious pile being the basic unknowns. The bending moment and displacement distribution along the pile are subsequently obtained. Comparison with existing solutions validates the accuracy and applicability of the present formulation. The results of parametric analysis indicate that the influences of axial load on the lateral response of single piles could be significant, and in general, the bending moment and horizontal displacement distributions along the pile increase considerably with the increase of axial load. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
10.
针对夯实水泥土桩的施工方法,在桩身埋设特制的应变传感器,测定桩身应变,进而计算桩身轴力,由此得出桩侧摩阻力,在此基础上分析夯实水泥土桩荷载传递规律及侧摩阻力的分布特征。结果表明,由于夯实水泥土桩体强度的限制,荷载沿桩身的传递限定在浅层一定范围内,桩身变形、轴向荷载、桩侧摩阻力分布主要发生在此范围内,而且变化梯度较大。 相似文献
11.
A simplified method of numerical analysis has been developed to estimate the deformation and load distribution of piled raft foundations subjected to ground movements induced by tunnelling and incorporated into a computer program ‘PRAB’. In this method, a hybrid model is employed in which the flexible raft is modelled as thin plates, the piles as elastic beams, and the soil is treated as interactive springs. The interactions between structural members, pile–soil–pile, pile–soil–raft and raft–soil–raft interactions, are modelled based on Mindlin's solutions for both vertical and lateral forces. The validity of the proposed method is verified through comparisons with some published solutions for single piles and pile groups subjected to ground movements induced by tunnelling. Thereafter, the solutions from this approach for the analysis of a pile group and a piled raft subjected to ground movements induced by tunnelling are compared with those from three‐dimensional finite difference program. Good agreements between these solutions are demonstrated. The method is then used for a parametric study of single piles, pile groups and piled rafts subjected to ground movements induced by tunnelling. Copyright © 2005 John Wiley & Sons, Ltd. 相似文献
12.
The axial capacity of novel spun-cast ductile iron (SCDI) tapered pile fitted with a lower helical plate is investigated. Seven instrumented piles, five SCDI tapered and two steel straight shafts, were installed in sand soil using mechanical torque. The piles were tested under axial compressive loading and their ultimate capacities were determined. To assess the cyclic loading effect on the piles performance, two load sequences were adopted: four piles were subjected to monotonic loading, and three were subjected to initial cyclic loading followed by monotonic loading. The installation torque was monitored and the resulting capacity-to-torque ratio was compared to the literature reported values. Tapered helical piles displayed a stiffer response and yielded higher capacities compared to the straight ones. Strain gauges were used to evaluate the piles load transfer mechanism, and demonstrated increased shaft resistance due to the pile taper. The taper helped compact the sand within the zone adjacent to the pile, originally disturbed by the helix penetration, hence increased the soil strength and stiffness. These effects were prominent for larger ratio of shaft/helix diameter. Finally, 3D finite element analyses were conducted to evaluate the axial performance of the system and demonstrated its enhanced frictional resistance. The experimental and numerical results confirmed the superior performance of the proposed system in sands. 相似文献
13.
Three-dimensional (3D) numerical analyses have been carried out to study the behaviour of a single pile to adjacent tunnelling in the lateral direction of the pile. The numerical analyses have included comparisons between the current study, previous elastic solutions and advanced 3D elasto-plastic analyses. In the numerical analyses, the interaction between the tunnel, the pile and the soil next to the pile has been analysed. The study includes the axial force distributions on the pile, the relative shear displacement between the pile and the soil, the shear stresses at the soil next to the pile and the pile settlement. In particular, the shear stress transfer mechanism along the pile related to tunnel advancement has been analysed by using interface elements allowing soil slip. It has been found that existing solutions may not accurately estimate the pile behaviour since several key issues are not included. Due to changes in the relative shear displacement between the pile and the soil next to the pile with tunnel advancement, the shear stresses and axial force distributions along the pile change drastically. Downward shear stress develops at the upper part of the pile, while upward shear stress is mobilised at the lower part of the pile, resulting in a compressive force on the pile. A maximum compressive force of about 0.25–0.52 Pa was developed on the pile, solely due to tunnelling, depending on the pile tip locations relative to the tunnel position, where Pa is the service pile loading prior to tunnelling. The majority of the axial force on the pile developed within ±2D in the transverse direction (behind and ahead of piles) relative to the pile position, where D is the tunnel diameter. In addition, mobilisation of shear strength at the pile–soil interface was found to be a key factor governing pile–soil–tunnelling interaction. The reduction of apparent allowable pile capacity due to tunnelling was dependent on the pile location relative to the tunnel position. Some insights into the pile behaviour in tunnelling obtained from the numerical analyses will be reported and discussed. 相似文献
14.
This paper presents an analytical solution for determining the dynamic characteristics of axially loaded piles embedded in elastic-poroelastic layered soil of finite thickness. The interface between the elastic and poroelastic soil coincides with the groundwater table level, which is explicitly taken into account in the solution. The pile is modelled as elastic one-dimensional rod to account for the effect of its dynamic characteristics on the response of the soil-pile system. The solution is based on Biot's poroelastodynamic theory and the classical elastodynamic theory, which we use to establish the governing equations of the soil and pile. Accordingly, the pile base resistance, shaft reaction, and the complex impedance of soil-pile system are obtained using the method of Hankel integral transformation. Following the validation of the derived solution, we identify the main parameters affecting the vertical dynamic impedance of the pile via a parametric study. The presented method poses as an efficient alternative for quickly estimating the dynamic characteristics of axially loaded piles, without having to resort to complex numerical analyses. 相似文献
15.
The torsional response of a pile exhibits features which are a mixture of those for axial and lateral response. At low load levels, the response is dominated by interaction with the upper soil layers and by the pile rigidity itself, similar to laterally loaded piles. However, failure will generally occur by the whole pile twisting, and so the latter part of the response incorporates the integrated effect of all soil penetrated by the pile, as is the case for axial loading. In view of the above, solutions for the torsional response of pile must endeavour to incorporate accurate modelling of the soil stiffness profile, and also pay appropriate attention to the gradual development of slip (relative twist) between pile and soil. The paper presents analytical and numerical solutions for the torsional response of piles embedded in non-homogeneous soil, where the stiffness profile follows a simple power law with depth. The solutions encompass: (1) vertical non-homogeneity of soil expressed as a power law; (2) non-linear soil response, modelled using a hyperbolic stressstrain law; (3) effect of relative slip between pile and soil for non-homogeneous stiffness and limiting shaft friction; (4) expressions for the critical pile slenderness ratio (or length) beyond which the pile head response becomes independent of the pile length. The solutions are developed using a load transfer approach, with each soil layer acting independently from neighbouring layers, and are expressed in terms of Bessel functions of non-integer order, and as simple non-dimensionalised charts. The solutions are applied to two well-documented case histories in the latter part of the paper. 相似文献
16.
Most analytical or semi‐analytical solutions of the problem of load‐settlement response of axially loaded piles are based on the assumption of zero radial displacement. These solutions also are only applicable to piles embedded in either a homogeneous or a Gibson soil deposit. In reality, soil deposits consist of multiple soil layers with different properties, and displacements in the radial direction within the soil deposit are not zero when the pile is loaded axially. In this paper, we present a load‐settlement analysis applicable to a pile with circular cross section installed in multilayered elastic soil that accounts for both vertical and radial soil displacements. The analysis follows from the solution of the differential equations governing the displacements of the pile–soil system obtained using variational principles. The input parameters needed for the analysis are the pile geometry and the elastic constants of the soil and pile. We compare the results from the present analysis with those of an analytical solution that considers only vertical soil displacements. The analysis presented in this paper also provides useful insights into the displacement and strain fields around axially loaded piles. Copyright © 2011 John Wiley & Sons, Ltd. 相似文献
17.
The plugging mechanism of infinitely-long open-ended piles is examined using numerical simulation of the wave propagation inside the soil plug and pile. It is shown that the key parameters for the plugging mechanism are the pile radius, the shape of the impact load, the shear wave velocity of the soil inside the pile, and the friction at the pile–soil interface. Consequently, the tendency of the pile to plug during driving can be assessed prior to the driving process by consideration of these key parameters. Existing one-dimensional models for the shaft response of open-ended piles are discussed and an improved model is presented. The differences between using one-dimensional models and finite element models to simulate the plugging process are examined. The differences are found to vary with the key parameters. Pile-in-pile and lumped-mass one-dimensional models are found to give satisfactory performance for some parameter combinations, while for others an axisymmetric finite element model must be used. © 1998 John Wiley & Sons, Ltd. 相似文献
18.
This paper describes the main features related to lateral displacements with depth after successive lateral loading–unloading cycles applied to the top of reinforced-concrete flexible bored piles embedded in naturally bonded residual soil. The bored piles under study have a cylindrical shape, with 0.40-m in diameter and 8.0-m in length. Both bored piles types (P1 and P2) include an embedded steel pipe section in their center as longitudinal steel reinforcements: pile type P1 has another 16 steel rods as steel reinforcement to concrete while pile type P2 has no further steel reinforcement. Pile type P1 has three times as much stiffness (EI) and four and a half times the plastic moment (My) than pile type P2. A similar load–displacement performance was observed at initial loads as for small displacements of both piles. At this initial loading stage, the response of the reinforced concrete piles is a function of the soil characteristics and of a linear elastic pile deformation. During this stage, piles can even be understood as probes for evaluating soil reactions. For larger horizontal displacements, after the concrete section starts undergoing large deformations, approaching the ultimate bending moment, pile behavior and consequently the load–displacement relation starts to diverge for both piles. For pile P1 the values of relevant lateral displacements are extended to about 2.5-m in depth, while for pile P2 lateral displacements are mostly constrained to about 2.0-m in depth. Measurements of horizontal displacements of pile P1 against depth recorded with a slope indicator show that, after unloading, lateral loads at distinct stages (small and near failure loads), exhibits a much higher elastic phase of the system response. An analytical fitting model of soil reaction is proposed based on the measured displacements from slope indicator. The integration of a continuous model proposed for the soil reaction agrees fairly well with the measured displacements up to moments close to plastic limit. Results of load–displacement show that the stiffer pile (P1) was able to mobilize twice as much lateral load compared to pile P2 for a service limit displacement of about 20 mm. The paper shows results that enable the isolation of the structural variable through real scale pile load tests, thus granting understanding of its importance and enabling its quantitative visualization in examples of piles embedded in residual soil sites. 相似文献
19.
利用有限元方法对现场单桩水平载荷试验进行模拟,在此基础上,分析了成层土中桩在倾斜荷载作用下其竖向分量的有利作用和横向土抗力分布特点。计算结果表明,在地面下一定范围内,倾斜荷载作用下的桩侧摩阻力比水平荷载作用下的桩侧摩阻力大。在土层分界处土抗力分布有明显的跳跃。达到一定深度后,横向土抗力主要是静止土压力,而由荷载引起的横向土抗力很小。承台能有效减小土体及桩的水平位移。模拟的灌注桩和钢管桩桩顶在地面以上的自由长度较小,竖向分量由于桩身挠曲变形而产生的P-Δ效应较小,所以就算例中的灌注桩和钢管桩而言,荷载倾斜度不大时,荷载竖向分量提高了桩的侧阻并由此增大桩侧土竖向应力,对桩水平承载力总体上起到了有利的作用。 相似文献
20.
采用双曲线模型模拟桩土界面上的力学行为,利用剪切位移法反映剪应力在土层中的传递,考虑群桩之间的相互作用,建立了热?力耦合作用下能量桩群桩基础工作特性的简化分析方法。该方法能反映桩土界面上的非线性、桩顶的约束条件和能量桩位置的影响,可直接计算所有桩的位移和轴力。与现有方法相比,计算得到的双桩相互作用因子更加合理。通过与文献中试验数据的对比表明,若只有局部桩经历温度变化,能量桩运行过程中各桩之间存在差异变形,基础出现倾斜,桩顶荷载发生重分布。所建立方法计算方便,能合理模拟能量桩群桩基础的主要工作特性,可用于大规模能量桩群桩基础的设计计算。 相似文献
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