3D finite element analysis on pile-soil interaction of passive pile group

The interaction between pile and soft soil of the passive pile group subjected to soil movement was analyzed with three-dimensional finite element model by using ANSYS software. The soil was assumed to be elastic-plastic complying with the Drucker-Prager yield criterion in the analysis. The large displacement of soil was considered and contact elements were used to evaluate the interaction between pile and soil. The influences of soil depth of layer and number of piles on the lateral pressure of the pile were investigated, and the lateral pressure distributions on the (2×1) pile group and on the (2×2) pile group were compared. The results show that the adjacent surcharge may result in significant lateral movement of the soft soil and considerable pressure on the pile. The pressure acting on the row near the surcharge is higher than that on the other row, due to the "barrier" and arching effects in pile groups. The passive load and its distribution should be taken into account in the design of the passive piles.

A simplified approach for negative skin friction calculation of special-shaped pile considering pile-soil interaction under surcharge

A simplified approach was proposed to analyze the negative skin friction calculation of special-shaped pile considering pile-soil interaction under surcharge. Based on the concentric cylinder shearing theory, considering the changes of pile shape(such as, taper angle and diameters of pile base, etc.), the load-transfer of special-shaped pile was built. The accuracy of the developed simplified approach was verified by numerical simulation model with the same condition. Then, the influence factors, such as, taper angles, the diameter of pile base, surcharge, and pile-soil interface parameters were analyzed and discussed. The results show that the developed simplified approach can calculate NSF of special-shaped pile under surcharge effectively. A limited parametric study indicates that in many practical situations special-shaped piles(such as belled wedge pile shown in this work) offer a design option that is more economical than traditional uniform cross-section piles.

Pile-soil stress ratio in bidirectionally reinforced composite ground by considering soil arching effect

To discuss the soil arching effect on the load transferring model and sharing ratios by the piles and inter-pile subsoil in the bidirectionally reinforced composite ground, the forming mechanism, mechanical behavior and its effect factors were discussed in detail. Then, the unified strength theory was introduced to set up the elastoplastic equilibrium differential equation of the subsoil under the limit equilibrium state. And from the equation, the solutions were derived with the corresponding formulas presented to calculate the earth pressure over and beneath the horizontal reinforced cushion or pillow, the stress of inter-pile subsoil and the pile-soil stress ratio. Based on the obtained solutions and measured data from an engineering project, the influence rules by the soil property parameters (i.e., the cohesion c and internal friction angle φ) and pile spacing on the pile-soil stress ratio n were discussed respectively. The results show that to improve the load sharing ratio by the piles, the more effective means for filling materials with a larger value of φ is to increase the ratio of pile cap size to spacing, while to reduce the pile spacing properly and increase the value of cohesion c is advisable for those filling materials with a smaller value of φ.

Comparison of Pile-Soil-Structure Interaction Modeling Techniques for A 10-MW Large-Scale Monopile Wind Turbine Model Under Wind and Wave Conditions

Considering the large diameter effect of piles,the influence of different pile-soil analysis methods on the design of monopile foundations for offshore wind turbines has become an urgent problem to be solved.Three different pile-soil models were used to study a large 10 MW monopile wind turbine.By modeling the three models in the SACS software,this paper analyzed the motion response of the overall structure under the conditions of wind and waves.According to the given working conditions,this paper concludes that under the condition of independent wind,the average value of the tower top x-displacement of the rigid connection method is the smalle st,and the standard deviation is the smallest under the condition of independent wave.The results obtained by the p-y curve method are the most conservative.

The Boundary Element Method for Pile-Soil Interaction

In this paper, several mathmatical models for the pile- soil interaction are outlined. The Boundary Element Method is one of the very effective methods for the reasonable models of elasticity and elastoplasticity. The major of this paper is concerned with the Boundary Element Method for the pile-soil interaction, including general methods and calculating formulation of static and dynamic analysis of the pile and pile groups. Some results of analysis are also given.

Optimum Design of Jacket Platforms Considering Structure-Pile-Soil Interaction

This paper proposes an optimum design model for the offshore jacket platform considering multidesign criteria, multi-design constraints and the structure-pile-soil interaction, and gives an optimum design procedure in which the proposed optimum design model is used together with structural analysis software SAP91 and optimum algorithm software OPB1. The Chengbei (#)11 offshore platform, which lies in the Shengli oilfield, is designed by use of the above optimum design model. The results show that the optimum design model is stable, and it depends on neither the optimization algorithm nor initial values of design variables. All values of the objective function converge to the same minimum value, and the speed of convergence is high, showing that the proposed optimum design model is reasonable.

Comparative Analysis of Seismic Response Characteristics of Pile-Soil-Stnicture Interaction System

The study on the earthquake-resistant performance of a pile-soil-structure interaction system is a relatively complicated and primarily important issue in civil engineering practice. In this paper, a computational model and computation procedures for pile-supported structures, which can duly consider the pile-soil interaction effect, arc established by the finite clement method. Numerical implementation is made in the time domain. A simplified approximation for the seismic response analysis of pile-soil-structure systems is briefly presented. Then a comparative study is performed for an engineering example with numerical results computed respectively by the finite clement method and the simplified method. Through comparative analysis, it is shown that the results obtained by the simplified method well agree with those achieved by the finite element method. The numerical results and findings will offer instructive guidelines for earthquake-resistant analysis and design of pile-supported structures.

The mechanical response of piles with consideration of pile-soil interactions under a periodic wave pressure

The pile-soil interaction under wave loads is an extremely complex and difficult issue in engineering. In this study, a physical model test is designed based on the principle of the gravity similarity to obtain time histories of wave forces of unsteady regular waves, and to measure the magnitude and the distribution of wave forces acting on the piles. A numerical model and relevant numerical methods for the pile-soil contact surface are adopted based on the principles of elastic dynamics. For a practical project, the time histories of wave forces on the piles are obtained through physical model tests. The deformations of the piles in the pile-soil interactions and the distribution of the bending moment on the piles are studied. It is shown that, with the increase of the period of wave pressures, the absolute value of the horizontal displacement of the piles increases, the embedment depth of the piles increases, and the scope of influence of soils increases. The change of the bending moment on the piles is consistent with that of its theoretical results, and the proposed numerical method can very well simulate the properties of the piles.

A simplified method for the determination of vertically loaded pile-soil interface parameters in layered soil based on FLAC3D

The numerical analysis of pile-soil interaction commonly requires a lot of trial works to determine the interface parameters and the accuracy cannot be ensured normally. Considering this, this paper first conducts a sensitivity analysis to figure out the influence of interface parameters on the bearing behavior of a single pile in sand. Then, a simplified method for the determination of pile-soil interface parameters in layered soil is proposed based on the parameter studies. Finally, a filed loading test is used for the validation of the simplified method, and the calculated results agree well with the monitoring data. In general, the simplified method proposed in this paper works with higher accuracy and consumes less time compared with the traditional trial works, especially on the determinations ofinterfacial cohesive and interracial friction angle.

基坑开挖对管桩竖向承载性状影响研究

针对基坑开挖引起管桩挤土效应的弱化,以及挤土效应弱化对管桩承载性质影响问题,开展了室内模型试验,并通过对模型试验进行数值建模,验证了数值模型的可靠性。在此基础上,从桩长、桩间距、桩侧摩阻力系数对开挖卸荷影响下管桩基础承载性状的影响展开研究。结果表明:开挖卸荷对管桩承载特性造成较大影响,极限承载力对应桩顶沉降量提高54.5%;数值计算发现,卸载前后极限荷载所对应最大沉降差率为9.52%,满足工程精度要求,验证了所提数值模型的可靠性;数值计算结果表明,随桩长提高,最大桩身轴力位置不断上升,而中性点位置却不断下降;桩间距越小,开挖卸荷对桩身轴力影响越大,而对负摩阻力影响越小;摩阻力系数为0.3时,摩阻力系数对桩身轴力及桩侧摩阻力发挥敏感度最高。

Finite element prediction on the response of non-uniformly arranged pile groups considering progressive failure of pile-soil system

A uniform arrangement of individual piles is commonly adopted in the conventional pile group foundation,and basin-shaped settlement is often observed in practice.Large differential settlement of pile groups will decrease the use-safety requirements of building,even cause the whole-building tilt or collapse.To reduce differential settlement among individual piles,non-uniformly arranged pile groups can be adopted.This paper presents a finite element analysis on the response of pile groups with different layouts of individual piles in pile groups.Using the userdefined subroutine FRIC as the secondary development platform,a softening model of skin friction and a hyperbolic model of end resistance are introduced into the contact pair calculation of ABAQUS software.As to the response analysis of a single pile,the reliability of the proposed secondary development method of ABAQUS software is verified using an iterative computer program.The reinforcing effects of individual piles is then analyzed using the present finite element analysis.Furthermore,the response of non-uniformly arranged pile groups,e.g.,individual piles with variable length and individual piles with variable diameter,is analyzed using the proposed numerical analysis method.Some suggestions on the layout of individual piles are proposed to reduce differential settlement and make full use of the bearing capacity of individual piles in pile groups for practical purposes.

加固软土地基路堤分层填筑数值模拟分析

以江苏某高速公路为研究背景,采用水泥土搅拌桩、土工格栅以及0.5 m砂垫进行地基处理,运用有限元软件PLAXIS分析分层填筑施工过程后路基土竖向沉降、水平位移变形规律。研究结果表明:采用水泥土搅拌桩处理后的竖向沉降量降低了45.6%;处理后的水平位移为未处理前的39%,且最大水平位移出现的位置由路堤脚趾处向下移动至水泥土搅拌桩底部位置;分层填筑施工过程中,每填筑一层水平位移和竖向位移均出现一定程度的增长,离路堤中心距离越远,竖向位移影响越小,水平位移呈现先增大后减小的变化趋势。

拉森钢板桩在软土地层深基坑支护中的应用

拉森钢板桩作为一种低碳环保、可回收的建筑材料,在各类建筑中发挥着重要的作用。以蕲春县某河道整治项目为例,选取了基坑支护工程中2个典型剖面,介绍了拉森钢板桩在软土地层中的应用,并将天汉软件设计计算结果、MIDAS GTS NX数值模型分析结果与基坑监测结果进行对比分析,三者得到的支护结构位移、受力数值较为一致,表明天汉深基坑设计软件的客观合理性及可靠性非常高,施工前可以用MIDAS GTS NX数字模拟来预测及引导施工。

深厚软土且空间受限条件下桩板结构现浇梁支架方案设计

桩板结构具有结构简单、受力明确等优点,能够减少材料用量,降低工程造价,在跨越小面积的河流、道路或其他交通设施时,得到广泛使用。莲鹤大道项目与珠肇高铁并行段,设计采用桩板结构桥梁,共计3100m,地质条件复杂,淤泥质软土深厚,梁底距离地面空间受限,现浇梁施工难度大。设计方建议采用贝雷梁+工字钢结构形式支架方案,由于部分梁底距离地面净空不足,该方案向下反开挖最多达3.0m,施工工效低,投入大。本文针对不同净空条件,研究了三种支架结构,满足共线段3.1km桩板结构现浇梁施工,提高了施工工效,降低了施工成本,为后续类似工程提供了参考。

温度影响下能量桩-土接触面剪切特性试验研究

能量桩工作过程中,桩体受温度变化影响会产生热变形,进而引起桩周土体的循环剪切作用,弱化地基承载力,给桩基的正常使用带来风险。由于传统直剪仪无法模拟能量桩工作过程中的温度变化,因此对桩-土接触面力学特性受温度影响的变化规律研究较少。对传统直剪仪进行改造,使其可以改变剪切试样温度;所用土体从重庆某施工现场取样,开展不同温度变化下桩-土接触面的室内土工直剪试验,分析单次温度变化和循环温度变化对桩-土接触面力学性能的影响,并对温度影响下桩-土接触面力学特性与土体力学特性的差异进行比较。结果表明,能量桩-土接触面的抗剪强度受温度影响较大;随着温度的升高,能量桩-土界面摩擦角和黏聚力先减小后增大;低法向应力下温度循环对桩-土接触面力学特性影响较大,而高法向应力下温度循环对桩-土接触面力学特性影响不显著;土体的抗剪强度、黏聚力和摩擦角随温度变化规律与桩-土界面类似。

杂填土地基中螺杆桩竖向承载特性研究

为了研究杂填土地基中螺杆桩竖向承载特性,基于极限平衡理论分析了桩-土咬合机理,结合桩-土之间的相互作用得到螺纹段等效侧阻力增大系数,在此基础上建立了单桩竖向承载力计算公式,并对杂填土地基中螺杆桩单桩进行缩尺模型试验。结果表明,螺杆桩在竖向荷载作用下,荷载-沉降曲线经历了弹性、弹塑性、塑性破坏3个阶段。根据模型试验所得桩身轴力和桩侧等效侧阻力沿深度的分布规律,总体上螺纹段等效侧阻力高于直杆段。当桩体达到极限承载力时,试验所得等效侧阻力扩大系数与理论分析结果基本一致。

Fiber optic monitoring of an anti-slide pile in a retrogressive landslide

Anti-slide piles are one of the most important reinforcement structures against landslides,and evalu-ating the working conditions is of great significance for landslide mitigation.The widely adopted analytical methods of pile internal forces include cantilever beam method and elastic foundation beam method.However,due to many assumptions involved in calculation,the analytical models cannot be fully applicable to complex site situations,e.g.landslides with multi-sliding surfaces and pile-soil interface separation as discussed herein.In view of this,the combination of distributed fiber optic sensing(DFOS)and strain-internal force conversion methods was proposed to evaluate the working conditions of an anti-sliding pile in a typical retrogressive landslide in the Three Gorges reservoir area,China.Brillouin optical time domain reflectometry(BOTDR)was utilized to monitor the strain distri-bution along the pile.Next,by analyzing the relative deformation between the pile and its adjacent inclinometer,the pile-soil interface separation was profiled.Finally,the internal forces of the anti-slide pile were derived based on the strain-internal force conversion method.According to the ratio of calculated internal forces to the design values,the working conditions of the anti-slide pile could be evaluated.The results demonstrated that the proposed method could reveal the deformation pattern of the anti-slide pile system,and can quantitatively evaluate its working conditions.

黄土地基中能量桩群桩承载变形性状模型试验

基于室内缩尺试验研究了含能量桩群桩在4次冷热循环过程中的桩身热力学特性及桩基承载变形特性变化规律,分析冷热循环对桩土温度、承台沉降、桩顶荷载及桩身摩阻力的影响。试验结果表明:冷热循环过程中能量桩较浅位置处桩身及桩侧土温度始终高于较深处,热循环过程中能量桩的传热效率高于冷循环过程。冷热循环会使承台顶面的工作荷载及群桩中各基桩的桩顶荷载发生往复变化,相应地引起承台发生往复倾斜,热循环引起的承台倾斜稍大于冷循环。热循环引起的能量桩桩身上部摩阻力为负,下部为正,冷循环时则相反。

玛多7.4级地震野马滩大桥桥台纵桥向破坏机理分析

针对2021年青海玛多7.4级地震中野马滩大桥的桥台震害,开展基于Pushover分析的桥台纵桥向破坏机理研究。提出土-桩-桥台精细化有限元模拟方法,以及基于地勘资料的模型土体参数确定实用方法,建模方法和加载模式要点为:(1)适用于土-桥台相互作用的分布式p-y弹簧修正模型;(2)可识别背墙弯曲、剪切或弯-剪多种破坏模式的背墙非线性梁柱单元-墙底非线性剪切单元串联模型;(3)土-搭板和土-翼墙摩擦弹簧;(4)基于分布式间隙单元的可捕捉地震中主梁与背墙接触位置变化的Pushover加载模式,从而实现了桥台纵桥向地震损伤破坏全过程模拟。结果表明:野马滩桥台在水平地震作用下,背墙底截面先发生屈服,随后背墙剪力达到抗剪能力峰值,桥台整体水平承载力开始退化,直至背墙底完全剪断,而桩基础并不发生明显损伤。总体而言,桥台破坏模式为背墙弯-剪破坏,数值分析结果与桥台实际震害相符。

上覆土层对倾斜液化场地-桩基-结构地震反应的影响研究

倾斜液化场地桩基的地震动力响应是岩土抗震工程领域关注的重要问题。本文依据振动台模型试验,基于OpenSees软件平台建立了倾斜液化场地-群桩-结构相互作用二维整体化数值模型,模型中考虑了桩-土接触的非线性以及土层的剪切局部化,并通过与振动台试验结果进行对比,验证了本文数值模拟方法的合理性和有效性。在此基础上,建立了针对实际场地的典型倾斜液化场地-群桩-结构相互作用有限元模型,讨论了不同上覆土层参数对场地及结构体系地震反应的影响。计算结果表明:随着上覆土层厚度的增大,饱和砂土层中的孔压比减小,土体的水平残余位移减小,同时桩身位移以及桩基曲率均有所减小;上覆土层强度对桩基动力反应的影响更加显著;上覆土层厚度的增加可以降低土层的液化程度并提高桩基的受力性能。