High-strain dynamic model of large-diameter pipe piles with soil plug for vertical vibration analysis

A rigorous analytical model is developed for simulating the vibration behaviors of large-diameter openended pipe piles(OEPPs)and surrounding soil undergoing high-strain impact loading.To describe the soil behavior,the soil along pile shaft is divided into slip and nonslip zones and the base soil is modeled as a fictitious-soil pile(FSP)to account for the wave propagation in the soil.True soil properties are adopted and slippage at the pile-soil interface is considered,allowing realistic representation of largediameter OEPP mechanics.The developed model is validated by comparing with conventional models and finite element method(FEM).It is further used to successfully simulate and interpret the behaviors of a steel OEPP during the offshore field test.It is found that the variation in the vertical vibrations of shaft soil along radial direction is significant for large-diameter OEPPs,and the velocity amplitudes of the internal and external soil attenuate following different patterns.The shaft soil motion may not attenuate with depth due to the soil slippage,while the wave attenuation at base soil indicates an influence depth,with a faster attenuation rate than that in the pile.The findings from the current study should aid in simulating the vibration behaviors of large-diameter OEPP-soil system under high-strain dynamic loading.

A theoretical analysis of vertical dynamic response of large-diameter pipe piles in layered soil

Considering the viscous damping of the soil and soil-pile vertical coupled vibration,a computational model of large-diameter pipe pile in layered soil was established.The analytical solution in frequency domain was derived by Laplace transformation method.The responses in time domain were obtained by inverse Fourier transformation.The results of the analytical solution proposed agree well with the solutions in homogenous soil.The effects of the shear modulus and damping coefficients of the soil at both outer and inner sides of the pipe pile were researched.The results indicate that the shear modulus of the outer soil has more influence on velocity admittance than the inner soil.The smaller the shear modulus,the larger the amplitude of velocity admittance.The velocity admittance weakened by the damping of the outer soil is more obvious than that weakened by the damping of the inner soil.The displacements of the piles with the same damping coefficients of the outer soil have less difference.Moreover,the effects of the distribution of soil layers are analyzed.The results indicate that the effect of the upper soil layer on dynamic response of the pipe pile is more obvious than that of the bottom soil layer.A larger damping coefficient of the upper layer results in a smaller velocity admittance.The dynamic response of the pipe pile in layered soil is close to that of the pipe pile in homogenous soil when the properties of the upper soil layer are the same.

A Theoretical Analysis of the Bearing Performance of Vertically Loaded Large-Diameter Pipe Pile Groups

This paper aims to present a theoretical method to study the bearing performance of vertically loaded large-diameter pipe pile groups.The interactions between group piles result in different bearing performance of both a single pile and pile groups.Considering the pile group effect and the skin friction from both outer and inner soils,an analytical solution is developed to calculate the settlement and axial force in large-diameter pipe pile groups.The analytical solution was verified by centrifuge and field testing results.An extensive parametric analysis was performed to study the bearing performance of the pipe pile groups.The results reveal that the axial forces in group piles are not the same.The larger the distance from central pile,the larger the axial force.The axial force in the central pile is the smallest,while that in corner piles is the largest.The axial force on the top of the corner piles decreases while that in the central pile increases with increasing of pile spacing and decreasing of pile length.The axial force in side piles varies little with the variations of pile spacing,pile length,and shear modulus of the soil and is approximately equal to the average load shared by one pile.For a pile group,the larger the pile length is,the larger the influence radius is.As a result,the pile group effect is more apparent for a larger pile length.The settlement of pile groups decreases with increasing of the pile number in the group and the shear modulus of the underlying soil.

Case analysis of piled raft socketed in weak rock

Piles socketed in soft rock were traditionally regarded as end bearing piles, and the loads transferred from superstructure were assumed in design to be shouldered totally by the piles. This paper was designated to deal with the interaction between the piles socketed in weak rock and surrounding soil through field measurement. The pile head reaction and ground pressure under piled raft foundation were monitored, respectively. The analysis of the data measured in situ shows the characteristics of the pile embedded in weak rock are similar to that of friction pile to some extent. The rock socketed pile, together with the surrounding soil, shoulders the weight of the superstructure. It is suggested that soil bearing should be considered in designing the soft rock socketed piles, which can make the design more economical.

An Approach to Stability Analysis of Embedded Large-Diameter Cylinder Quay

The large-diameter cylinder structure, which is made of large successive bottomless cylinders placed on foundation bed or partly driven into soil, is a recently developed retaining structure in China. It can be used in port, coastal and offshore works. The method for stability analysis of the large-diameter cylinder structure, especially for stability analysis of the embedded large-diameter cylinder structure, is an important issue. In this paper, an idea is presented that is, embedded large-diameter cylinder quays can be divided into two types, i.e. the gravity wall type and the cylinder pile wall type. A method for stability analysis of the large-diameter cylinder quay of the cylinder pile wall type is developed and a method for stability analysis of the large-diameter cylinder quay of the gravity wall type is also proposed. The effect of significant parameters on the stability of the large-diameter cylinder quay of the cylinder pile wall type is investigated through numerical calculation.

Effect of sediment on vertical dynamic impedance of rock-socketed pile with large diameter

Based on the fictitious soil pile model, the effect of sediment on the vertical dynamic impedance of rock-socketed pile with large diameter was theoretically studied by means of Laplace transform technique and impedance function transfer method. Firstly, the sediment under rock-socketed pile was assumed to be fictitious soil pile with the same sectional area. The Rayleigh-Love rode model was used to simulate the rock-socketed pile and the fictitious soil pile with the consideration of the lateral inertial effect of large-diameter pile. The layered surrounding soils and bedrock were modeled by the plane strain model. Then, by virtue of the initial conditions and boundary conditions of the soil pile system, the analytical solution of the vertical dynamic impedance at the head of rock-socketed pile was derived for the arbitrary excitation acting on the pile head. Lastly, based on the presented analytical solution, the effect of sediment properties, bedrock property and lateral inertial effect on the vertical dynamic impedance at rock-socketed pile head were investigated in detail. It is shown that the sediment properties have significant effect on the vertical dynamic impedance at the rock-socketed pile head. The ability of soil-pile system to resist dynamic vertical deformation is weakened with the increase of sediment thickness, but amplified with the increase of shear wave velocity of sediment. The ability of soil pile system to resist dynamic vertical deformation is amplified with the bedrock property improving, but the ability of soil-pile system to resist vertical vibration is weakened with the improvement of bedrock property.

嵌岩桩水平承载力地基反力Matlock法分析

嵌岩桩在海上风电、跨海大桥等结构中的应用十分广泛,但在嵌岩桩水平承载特性方面的研究仍有较多不足。弹性地基反力法中的Matlock法在中国是用于计算水平承载桩承载力时应用最多的方法,但地基反力Matlock法针对嵌岩桩缺少合理的取值方法。基于现场试验数据建立并验证有限差分数值模型,通过数值模拟与参数分析,研究了岩体力学参数和桩基参数等因素对桩岩相互作用的影响,提出了Matlock法中地基反力系数比例系数的拟合计算公式。通过现场试验数据对提出的方法进行了验证,结果表明计算结果与实际情况较为相符,与其他方法比较,所提出的修正Matlock法相对非线性的p-y曲线法具有取值计算较为简便的优势。

中风化花岗岩中嵌岩桩承载性能原位试验与极限承载力预测

为深入探究中风化花岗岩中嵌岩桩的竖向抗压承载特性,对12根嵌岩桩进行了单桩竖向抗压静载原位试验与ABAQUS有限元数值模拟,通过多种方法对嵌岩单桩极限承载力进行评价,明确中风化花岗岩中嵌岩桩竖向抗压承载性状。研究表明:12根中风化花岗岩中嵌岩桩并非表现出完全端承桩,而是呈摩擦型桩或摩擦端承桩的性状;中风化花岗岩地基中的嵌岩桩竖向抗压极限承载力较高,桩顶沉降小,满足工程对基础的承载要求;有限元模拟荷载-沉降曲线与实测荷载-沉降曲线走势吻合度较高,桩顶沉降误差较小;本试验条件下,桩端阻力占桩顶荷载的56.9%,桩侧摩阻力占比为43.1%,桩侧摩阻力在荷载传递过程中发挥较充分;有限元模拟得到的单桩极限承载力与指数函数模型的预测结果较为吻合,可用于嵌岩桩单桩竖向抗压极限承载力的预测,以及嵌岩桩承载性状和荷载传递规律的分析。

嵌岩单桩水平静力加载现场试验及 p-y 曲线研究

为研究风化花岗岩地质条件下嵌岩单桩的受荷响应和p-y曲线规律,本文基于现场试验,开展了水平静力荷载作用下嵌岩单桩的荷载-位移关系、弯矩、桩身变形及p-y曲线响应研究。试验表明:在所研究的相对深度范围内,随着z/D的增加,岩土阻力和相应位移都减小,上部荷载很难传递到深部岩层;桩身最大弯矩在3~4倍桩径之间,极限荷载主要取决于桩身强度而不是岩土体。将p-y曲线分别与一般双曲函数和双曲正切函数进行拟合,评估现有p-y曲线模型在风化花岗岩地基中的适用性,修正了模型在风化岩层中的参数取值。结果表明:一般双曲函数在较浅区域拟合良好,相对深度较大的区域数据离散性较强;双曲正切函数在各深度处拟合优度均较好。分析结果简化了现场p-y曲线的预测程序。

大直径嵌岩灌注桩承载特性试验与有限元模拟

基于青岛某工程的4根大直径嵌岩灌注桩,在现场开展了单桩竖向抗压静载试验和桩身完整性测试,以明确大直径嵌岩灌注桩在竖向荷载下的承载特征,拟揭示不同荷载水平下嵌岩灌注桩的承载力发挥机制。结合不同嵌岩深度的单桩承载性能有限元模拟,重点分析了单桩在不同嵌岩深度下的竖向抗压承载特性和桩土位移分布特征。研究表明:在笔者试验条件下,大直径嵌岩灌注桩单桩竖向抗压承载力具有一定离散性,桩头部位的损坏会极大影响单桩承载力的有效发挥;加载完成后,数值模拟得到的桩顶沉降量为31.56 mm,约为现场实测值的1.1倍,模拟结果与实测结果较为吻合;通过不同嵌岩比的模拟结果对比发现,嵌岩深度越大桩端阻力占桩顶荷载的比例越小,且桩端阻力占比的变化速率随着嵌岩比的增加逐渐减缓;嵌岩深度取2.5倍桩径为宜。

移动充放电设施技术及其规划与运营研究综述

目前,充放电需求区域性、时段性短缺,固定充电设施存在总量不足、扩容难、利用率低等问题,移动充电设施因其移动便捷性,受到广泛关注。阐明移动充放电设施的8种典型应用场景,阐述了“智能插座+移动充电桩”、不带储能装置的移动充电车、带储能装置的移动充放电车3种移动充放电设施类型。分析规划布局、调度运行、运营模式与价格机制、关键组件以及安全等关键技术。针对移动模式选取等7个关键方面对移动充放电设施的发展模式进行总结和展望。

嵌岩桩承载性能对比分析及优化措施探讨

在实际工程中,岩土体参数取值及基础设计方案对工程造价存在较大影响。该文依托重庆秀山地区某工程嵌岩桩相关技术资料,通过有限元方法及经验参数法对基桩承载性能进行对比分析,分析表明:在相同工程条件下,经基桩有限元方法及经验参数法计算的侧摩阻及端阻占比差值有正有负,基桩承载力特征值计算结果差距大,有限元方法比经验参数法大20%以上,提出应从地质参数及桩型方面对其进行优化。通过对嵌岩桩承载性能对比分析及优化措施的探讨,以期为类似工程实践提供一定的参考及借鉴。

高桩码头承插式T形桩帽安装灌浆工艺

在传统高桩码头结构中,桩芯、桩帽常采用现浇工艺。受潮位变动区影响,现浇过程中钢筋、混凝土受海水浸泡侵蚀,难以控制结构质量。并且海上作业需要赶潮施工,人员风险性高。依托福建宁德18~20号泊位工程,介绍一种高桩码头承插式T形桩帽施工工艺。通过将T形桩帽承插式安装至钢管桩内,并利用UHPC材料灌浆与钢管桩形成整体。T形桩帽为一种新型结构,通过研究其安装、灌浆工艺,解决了高桩码头直桩装配化技术问题。应用结果表明,该工艺可以提高码头的装配化率和施工质量,应用效果良好。

基于岩溶三维地质模型的桩基承载力特性研究

本文依托中铁十九局集团有限公司岑大公路YTHJ4标桥梁桩基项目,通过Civil 3D软件建立了三维地质模型;并介绍了桩基作用下溶洞两种不同的破坏模式;然后采用基于FLAC 3D数值分析软件的单因子变量法分析了不同溶洞顶板厚度、顶板跨度、洞高、溶洞中心偏离桩轴线距离等对嵌岩桩承载力特性(极限承载力、极限侧摩阻力、桩土相对滑移距离等)的影响。研究结果表明:溶洞顶板是影响桩基极限承载力的主要因素;溶洞极限状态下的破坏模式强烈依赖于溶洞顶板厚度、顶板跨度和岩体力学性质;当溶洞顶板厚度达到三倍的桩径时,桩侧摩阻力可完全发挥;溶洞顶板跨度和偏心距离对桩基承载力特性的影响存在一个稳定点。这些研究结论为岩溶地区的嵌岩桩设计提供了一定的参考依据,进一步丰富了岩溶地区桩基设计理念。

基于内聚力模型的嵌岩双斜桩水平承载特性分析

基于已有的对桩-岩界面剪切特性的研究,建立了界面几何参数和材料特性与内聚力模型参数间的转换关系,与现场试验和理论研究对比,验证了接触模型的准确性;结合室内嵌岩双斜桩模型试验,建立了对应有限元数值计算模型,对比分析了桩基荷载-位移曲线与弯矩规律,验证了模型的可靠性;进而建立不同倾角的足尺嵌岩双斜桩模型,分析在不同竖向定荷载下的水平承载特性。研究表明:嵌岩双斜桩系统是多因素协同作用的承载系统,对受多向组合荷载的嵌岩双斜桩而言,存在一最优竖向设计荷载,使得嵌岩双斜桩的水平承载力大大提高,但过大的竖向荷载和过小的倾角反而提高桩承台失稳的风险。

桩端采空区对嵌岩桩承载力的影响

针对桩端采空区对嵌岩桩的设计(如承载性能和长期服役性能)提出的挑战,以杜家山特大桥采空区嵌岩桩为原型,进行缩尺模型试验,研究采空区到桩端不同距离以及采空区是否注浆的单桩承载力。计算比例参数,并选择合适的试验材料进行模型构建;通过多级荷载试验,获得采空区到桩端不同距离以及注浆后桩顶沉降、桩基础轴力、桩端阻力和桩侧摩阻力的变化特征;并对比分析了无采空区嵌岩桩的承载特征。结果表明,随着采空区到桩端距离的减小,桩端持力层的承载能力减小,不利于模型桩的承载力;注浆后,桩端持力层的承载能力明显增加,导致模型桩的桩顶沉降显著减少,承载能力显著提高。

非挤土嵌岩预应力高强度混凝土管桩的桩端承载性能研究

施工装备和工艺的不断创新使得非挤土嵌岩预应力高强度混凝土(prestressed high-strength concrete,简称PHC)管桩逐渐得到推广和应用。为揭示嵌入中微风化岩PHC管桩的桩端承载机制,以随钻跟管工法桩为背景,基于泥质粉砂岩地区5组桩径为500 mm的PHC管桩桩端现场静载破坏性试验,分析了不同条件下嵌岩PHC管桩的桩端承载性能及宏观破坏模式,并提出桩端承载力计算方法。试验表明:对于采用敞口桩靴的PHC管桩,未封底时,敞口桩靴削弱了PHC管桩桩端承载性能,呈现刺入岩基的破坏,极限荷载下桩端沉降为11~15 mm;混凝土封底后,显著提高了桩端承载性能,极限承载力较非封底时提升340%,封底混凝土和桩靴的桩端阻力分担比分别为78%和22%,桩端呈整体剪切破坏。基于Hoek-Brown强度准则,提出了嵌岩PHC管桩桩端承力简化计算方法,计算精度得到了试验验证,可供非挤土嵌岩PHC管桩的设计与施工参考。

碎石土填方场地嵌岩桩负摩阻力性状分析

以西南地区土石混合体为研究对象,通过单桩室内模型试验,研究了素填土和土石混合料地基中桩周土体沉降、桩土位移、桩身轴力、桩侧负摩阻力、中性点位置等。结果表明:土石混合料填土地基中桩周土体与桩身沉降较素填土地基中更小;在堆载及加载作用下,中性点位置随着荷载等级提高而下移,且土石混合料地基的中性点位置高于素填土地基,其中性点位置距桩顶0.36 l~0.52(l l为有效桩长)内;桩身轴力在土石混合料和素填土中均随深度先增后减,但土石混合料填土地基中桩身轴力小于素填土地基。

水平循环荷载下嵌岩单桩基础受力特性试验研究

为保障嵌岩单桩基础海上风机的长期安全运行,试验研究了嵌岩单桩基础与土质地基单桩基础的受力特性差异,通过室内1g模型试验分析了地层性质、荷载条件对桩基承载力与受力特性的影响规律。结果表明:对于长径比较小的单桩基础,底部嵌岩时桩基水平刚度和承载力较无嵌岩情况提升显著;水平单调循环加载作用下,桩顶累积位移在开始的数十个循环中快速发展,后期逐渐趋于稳定;底部嵌岩时,桩顶的累积位移存在平衡状态;循环加载初期,桩基刚度均随循环荷载作用次数增加而增大,主要表现为砂土的振密效应,砂土密实后,结构刚度基本稳定;在循环荷载幅值较大时,强风化地基中的桩-岩界面在加载后期损伤脱离,桩基刚度有所下降;水平加载试验中,底部嵌岩单桩桩身弯矩最大位置始终高于无嵌岩情况;无论嵌岩与否,桩身最大弯矩位置均随荷载循环加载次数增加而有所下降;对于嵌入不同风化程度岩石的单桩,循环加载后再静力加载至桩基破坏,其最终破坏模式存在明显差异。

山区机械化成孔的大孔径硬岩嵌岩桩承载能力

为揭示硬质岩石的承载能力与荷载传递机制,结合保定西某500 kV输电线路的山区机械化成孔项目,对山区大孔径嵌岩桩承载性能的影响因素进行了研究.首先利用准静态压缩试验得到岩石地质参数.然后,采用显式非线性有限元方法对山区大孔径硬岩嵌岩桩的抗拔与抗剪承载特性、失效模式和受力机理进行数值研究,具体分析桩体在上拔和水平荷载作用下的力学性能,讨论了覆土层增加钢套筒对桩体水平极限承载力的影响.研究结果表明:在上拔荷载下,承载力主要由桩体侧摩阻力和桩体自重来承担,硬质岩层桩侧摩阻力占主导地位,约为总侧摩阻力的90%;在水平荷载下,桩身较大位移区域在桩身4 m内,弯矩最大值出现在距桩顶2~3倍桩径,覆土层增加钢套筒可明显提高桩体的水平承载极限.本文研究结果将对岩石地质山区大孔径嵌岩桩结构设计和机械化施工提供理论指导.