Displacement and deformation analysis for uplift piles

On the assumptions that the shear resistance increases linearly with increasing shear displacement between the uplift pile and surrounding soil, that the axis force is distributed as parabola along the pile length, that elastic distortion occurs when the pile is loaded, that the displacement of pile is in accord with that of the soil, and that the uplift pile failure is regarded as the soil failure, a rational calculation method was proposed for calculating the deformation, ultimate displacement and shear resistance of piles. The distributions of frictional resistance and the shear displacement along the pile length were obtained with the method. The comparisons were made between the measurement results and the present results. The present theoretical results agree well with the measurement results, with the average difference being less than 12% before failure. The comparisons show that the proposed method is reasonable for uplift design and engineering construction of piles.

Deformation and failure modes of composite foundation with sub-embankment plain concrete piles

With the development of high-speed railway in China, composite foundation with rigid piles has become a stamdard solution of meeting the high requirements of stability and post-construction settlement of embankment on soft subgrade. Among several im- provement pattems, plain concrete piles have been extensively used to treat soft ground supported embankment. To investigate the deformation and failure modes of unimproved soft ground and soft ground reinforced by sub-embankment plain concrete piles, and to learn the influences of track and vehicle load, the effect of pile spacing, as well as the compression moduli of soil layers and upper load condition on the failure modes, a series of centrifuge model tests were performed. Test results indicate that the dis- placement of unimproved soft ground under the embankment increases continuously as embankment, track and train loading, and slip circle failure takes place. The deformation law of soft ground reinforced by sub-embankment plain concrete piles depends on pile spacing, compression modulus of the soft ground, and loading conditions. It was also found that plain concrete piles show displacement and failure patterns depending on its location, compression modulus of soft soil around the pile, and loading condi- tions. Furthermore, the evaluation of improved ground stability as well as the model test procedure is also presented.

Analysis of dynamical response to large deformation of piles with initial displacements

In this paper, a nonlinear mathematical model for analyzing dynamical response to the large deformation of piles with initial displacements is firstly established with the arc-coordinate, and it is a set of nonlinear integral-differential equa- tions, in which, the Winkeler model is used to simulate the resistance of the soil to the pile. Secondly, a set of new auxiliary functions are introduced. The differential-integral equations are transformed into a set of nonlinear differential equations, and the differential quadrature method （DQM） and the finite difference method （FDM） are applied to discretize the set of nonlinear equations in the spatial and time domains, respectively. Then, the Newton-Raphson method is used to solve the set of discretization algebraic equations at each time step. Finally, numerical examples are presented, and the dynamical re- sponses to the deformation of piles, including configuration, bending moment and shear force, are graphically illuminated. In calculation, two types of initial displacements and dynamical loads are applied, and the effects of parameters on the dynamical responses of piles are analyzed in detail.

Study on the Effect of Occlusion Rate on the Deformation of Non-Vegetarian Occlusal Piles

In order to investigate the force characteristics of the occlusal pile, this paper takes the underground garage support project of Nanchang Bayi Square as the research background and studies the bending moment of the occlusal pile after the excavation process of the foundation pit through the model test. The test results show that the bending moment of the pile increases and then decreases with the increase of soil depth under horizontal load, and the bending moment reaches the maximum near the excavation surface of the foundation pit;the test results can provide a reference for the design of occluded pile body in practical engineering.

Effects of liquefaction-induced large lateral ground deformation on pile foundations

The pile-soil system interaction computational model in liquefaction-induced lateral spreading ground was established by the finite difference numerical method.Considering an elastic-plastic subgrade reaction method,numerical methods involving finite difference approach of pile in liquefaction-induced lateral spreading ground were derived and implemented into a finite difference program.Based on the monotonic loading tests on saturated sand after liquefaction,the liquefaction lateral deformation of the site where group piles are located was predicted.The effects of lateral ground deformation after liquefaction on a group of pile foundations were studied using the fmite difference program mentioned above,and the failure mechanism of group piles in liquefaction-induced lateral spreading ground was obtained.The applicability of the program was preliminarily verified.The results show that the bending moments at the interfaces between liquefied and non-liquefied soil layers are larger than those at the pile＇s top when the pile＇s top is embedded.The value of the additional static bending moment is larger than the peak dynamic bending moment during the earthquake,so in the pile foundation design,more than the superstructure＇s dynamics should be considered and the effect of lateral ground deformation on pile foundations cannot be neglected.

Stereo particle image velocimetry measurement of 3D soil deformation around laterally loaded pile in sand

A developed stereo particle image velocimetry(stereo-PIV) system was proposed to measure three-dimensional(3D) soil deformation around a laterally loaded pile in sand.The stereo-PIV technique extended 2D measurement to 3D based on a binocular vision model,where two cameras with a well geometrical setting were utilized to image the same object simultaneously.This system utilized two open software packages and some simple programs in MATLAB,which can easily be adjusted to meet user needs at a low cost.The failure planes form an angle with the horizontal line,which are measured at 27°-29°,approximately three-fourths of the frictional angle of soil.The edge of the strain wedge formed in front of the pile is an arc,which is slightly different from the straight line reported in the literature.The active and passive influence zones are about twice and six times of the diameter of the pile,respectively.The test demonstrates the good performance and feasibility of this stereo-PIV system for more advanced geotechnical testing.

Study of seismic behavior of PHC piles with partial normal-strength deformed bars

Nine PHC piles with partial normal-strength deformed bars were prepared in present study,and cyclic loading tests were implemented to evaluate these piles’seismic performance.The influence of the axial compression ratio and the amount of normal-strength deformed bars on failure modes,crack patterns,strength,stiffness,and ductility were examined.The test findings indicate that the change of axial compression ratio has a noticeable influence on the failure mode of PHC piles.A larger axial compression ratio results in a higher cracking bending resistance,ultimate bending resistance,and initial stiffness,but the propagation heights of flexural cracks decrease as the axial compression ratio increases.Furthermore,increasing the amount of normal-strength deformed bars causes a slight decrease in ductility.Finally,a calculation formula was proposed to predict the flexural capacity of PHC piles with partial normal-strength deformed bars.

Research on Deformation and Force of Bridge Pile Foundation on High and Steep Slope in Mountainous Area

With the rapid development of my country’s economy, the demand for infrastructure construction is also increasing. However, in most areas of China, the terrains are mountainous and hilly. Some projects have to be built on steep slopes. Choosing viaducts or half-bridges on high-steep slopes is not only conducive to the protection of the surrounding environment, but also conducive to the stability of the slope. Bridges usually choose the form of pile foundation-high pier bridge. This paper uses numerical simulation to study and analyze the bridge pile foundation of the slope section. Relying on actual engineering, use the finite element software ABAQUS6.14 to establish a three-dimensional finite element model to study the bearing mechanism and mechanical characteristics of the pile foundation under vertical load, horizontal load and inclined load, discuss the influence of the nature of the soil around the pile and the stiffness of the pile body on the deformation and internal force of the bridge pile foundation in the slope section. The analysis results show that the horizontal load has a great influence on the horizontal displacement of the pile, but has a small influence on the vertical displacement, and the vertical load is just the opposite. Inclined load has obvious “p-Δ” effect. The increase in soil elastic modulus and pile stiffness will reduce the displacement of the pile foundation, but after reaching a certain range, the displacement of the pile foundation will tend to be stable. Therefore, in actual engineering, if the displacement of the pile foundation fails to meet the requirements, the hardness of the soil and the stiffness of the pile can be appropriately increased, but not blindly.

Mechanical Behaviors and Deformation Properties of Retaining Wall Formed by Grouting Mould-Bag Pile

The simplified mechanical model and finite element model are established on the basis of the measured results and analysis of the grouting pile deformation monitoring,surface horizontal displacement and vertical displacement monitoring,deep horizontal displacement(inclinometer)monitoring,soil pressure monitoring and seepage pressure monitoring in the lower reaches of Wuan River regulation project in Shishi,Fujian Province.The mechanical behavior and deformation performance of mould-bag pile retaining wall formed after controlled cement grouting in the silty stratum of the test section are analyzed and compared.The results show that the use of controlled cement grouting mould-bag pile technology is to strengthen the soft stratum for sealing water and reinforcement,so that it can rock into a retaining wall,which can both retain soil and seal water with excellent effect.The control of cement grouting technology not only makes the soft soil rock in the range of retaining wall of mould-bag pile,but also makes a wide range of soil around the mould-bag pile squeeze and embed to compaction;and its cohesion and internal friction angle increased,so as to achieve the purpose of reducing soil pressure and improving mechanical and deformation properties of retaining wall.

A case study on behaviors of composite soil nailed wall with bored piles in a deep excavation

A complete case of a deep excavation was explored. According to the practical working conditions, a 3D non-linear finite element procedure is used to simulate a deep excavation supported by the composite soil nailed wall with bored piles in soft soil. The modified cam clay model is employed as the constitutive relationship of the soil in the numerical simulation. Results from the numerical analysis are fitted well with the field data, which indicate that the research approach used is reliable. Based on the field data and numerical results of the deep excavation supported by four different patterns of the composite soil nailed wall, the significant corner effect is founded in the 3D deep excavation. If bored piles or soil anchors are considered in the composite soil nailed wall, they are beneficial to decreasing deformations and internal forces of bored piles, cement mixing piles, soil anchors, soil nailings and soil around the deep excavation. Besides, the effects due to bored piles are more significant than those deduced from soil anchors. All mentioned above prove that the composite soil nailed wall with bored piles is feasible in the deep excavation.

Field Test Study on Cantilever Circular Occluded Pile Supporting Structure

In order to explore the deformation of the pile body of the circular occluded pile retaining structure under earth pressure, this paper carries out on-site monitoring in combination with the actual project, and obtains the deformation characteristics and change rules of the occluded pile by measuring the strain and displacement of the pile body. The research conclusion can provide a certain reference value for the pile body design of bite pile in similar projects.

盾构隧道近接斜交侧穿桥梁桩基变形计算方法

以圆形截面桩为例,基于修正后的Loganathan公式,利用文克尔弹性地基梁模型、m法计算理论和荷载传递法,建立盾构隧道近接斜交侧穿既有桥梁桩基的变形计算方法.通过现场监测结果验证计算方法的工程适用性,并利用该方法分析侧穿桥梁桩基施工引起桩身水平挠曲变形的主要影响因素.结果表明:桩身水平位移和桩顶竖向位移的理论计算结果与监测结果之间的最大误差分别不超过14.6%和2.7%.与现有方法相比,所提方法的计算结果更接近实测值.入土段桩身水平挠曲程度与隧道轴心和桩基中心轴线之间的水平距离、隧道侧穿斜交角呈负相关;最大水平挠曲位移与隧道侧穿斜交角呈负相关.当水平侧穿距离为6.0 m时,最大水平挠曲变形为7.4 mm;当隧道盾构侧穿斜交角为70.0°时,入土段桩身最大水平挠曲位移为15.4 mm.

洞桩法地铁车站边桩结构受力机制的模型试验设计

为了方便学生更形象地理解洞桩法地铁车站边桩结构的受力机制,该文以广州地区某洞桩法地铁车站工程为依托,设计了一种简化的洞桩法车站边桩结构模型试验。基于该试验方法,演示分析了边桩结构在洞桩法车站开挖过程中的施工力学行为规律,并对比研究了不同桩型布置参数下的桩后土压力、边桩结构的力学和变形规律。通过该试验,为学生展示了洞桩法边桩结构模型的设计、制作、试验具体操作及数据监测的全过程,从而让学生更好地掌握洞桩法车站边桩结构力学行为演变规律,以及采用不同边桩布置型式的力学行为差异。

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。

成都地铁基坑围护桩大变形原因分析及对策研究

[目的]周边环境及地质条件复杂的地铁基坑施工稍有不慎易导致基坑事故的发生。需分析基坑围护桩大变形原因,并提出针对性加固措施。[方法]以成都某近接老旧建筑物的桩锚支护结构地铁车站基坑为工程背景,分析了基坑施工过程中围护桩体发生大变形的原因,提出控制围护桩变形的加固措施。通过Harding-soil二阶高级本构模型研究了围护桩发生变形后,坑内采用反压堆载、基坑坑外坡体采用钢管桩及再次开挖前加强两道锚索措施的可行性。[结果及结论]模拟计算结果及现场实测结果表明,围护桩累计位移为77.77 mm;围护桩产生大变形后采用加固措施,可将围护桩水平位移控制在53 mm以内;根据模拟计算结果及现场实测结果,二者桩体水平位移曲线变化规律一致。实际施工结果表明,采取加固措施后,基坑变形控制效果明显,后续施工过程中未发生大范围变形。

黄土地区洞桩法地铁车站边桩和中柱的受力变形机理

[目的]为了确保黄土地区洞桩法车站施工过程中重要竖向承重构件的稳定性,需要对施工过程中边桩和中柱的受力变形机理进行研究,并对最不利受力阶段边桩和中柱提出变形控制措施。[方法]以西安地铁2号线何家营站为研究背景,通过数值模拟与现场监测的方法,对施工过程中边桩的水平位移、钢筋内力、水平土压力及中柱应变展开研究。[结果及结论]扣拱施作以及站厅层和站台层土体开挖是边桩水平位移最不利的三个阶段,在这些关键阶段施工时,应在结构内部架设钢支撑并适当加固已扰动的地层;在桩梁和扣拱施作中,边桩主筋承受轴向压力,而在站内剩余土方施工阶段,边桩背土侧的钢筋由轴向压力逐渐转化为轴向拉力,且随着边桩埋深的增大,钢筋的轴向拉压力增长变缓;在扣拱初期支护施作中,土压力在边桩埋深6.6 m处达到最大值34.5 kPa,且随着边桩埋置深度增大,边桩的桩侧压力增长速率显著,因此车站内侧的土方开挖是控制边桩迎土侧土压力大小的关键阶段,必要时对桩后土体进行注浆加固有利于提高桩基的承载力;中跨扣拱施工时,中柱的应变呈现出先减小、后增大的趋势。

综合管廊深基坑支护结构变形分析及优化研究

基于某综合管廊深基坑工程,运用Midas有限元软件,通过改变支护桩桩径、型钢布置形式、型钢尺寸、冠梁尺寸、内支撑间距的参数对支护桩水平位移变化规律进行了分析,并选取最优的支护方案。结果表明:通过增加桩径可有效抑制支护桩变形;型钢布置形式和型钢尺寸的改变对支护桩的影响较小;冠梁主要对支护结构的顶部变形起约束作用;内支撑水平向不等间距布置时增大了工作空间从而方便施工。最终方案为Φ850@600 SMW工法三轴水泥土搅拌桩,内插HN700×300×13×24型钢,型钢插一跳一布置;桩顶设置钢筋砼冠梁,内支撑为钢筋砼撑,支撑在冠梁上。模拟结果与实测结果基本一致,符合工程要求。

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。

静压桩残余应力对极限承载力影响

为研究静压桩回弹特性,明确静压桩残余应力性状,使静压桩承载力能够得到有效发挥,通过静压桩沉桩及静载荷试验,结合有限元模拟方法,对不同沉桩速率和卸荷速率作用下静压桩的回弹特性进行分析,总结桩端残余应力对静压桩极限承载力的影响规律。结果表明:卸荷过程中桩体回弹量占桩体总沉降量的80%,卸荷完成桩体回弹位移逐渐稳定;沉桩结束后,桩周土体应力最大达到被动土压力的4.5倍,卸荷后浅部土体桩周侧压应力消散程度大于深部土体;桩端土体应力消耗越多,桩端残余应力越小,卸荷后桩端土体回弹量越多;沉桩速率和卸荷速率增加都会导致桩端残余应力减小,从而桩端土体能够提供的承载力降低,致使桩体承载力降低。研究认为静压桩残余应力是影响承载力的主要因素,卸荷速率对静压桩残余应力的影响最为明显。

非挤土桩对于砂土地层地震液化的影响机制研究

如何通过工程措施实现地基抗液化能力的有效提升,是岩土工程领域近年来研究的热点问题之一。非挤土桩作为地基处理的常用措施,其加固后地层的抗液化能力能否得到提升,在学术界还存在着一定争议,主要原因是其对于砂层地震液化的影响机制尚未明确。针对该问题,本文开展了干砂及饱和砂土原状场地与非挤土桩加固场地的超重力模型试验,通过对比不同试验中地层的动力响应与超静孔隙水压力的发生发展规律,首次发现非挤土桩对于地层的作用机制并非仅有“刚度效应”,还有因振动过程中桩-土变形不协调而产生的附加作用力,该作用力将显著提升浅层土体的应力及应变水平,加大其液化的可能性,且随着埋深增加,该附加作用力逐渐变小,“刚度效应”将逐渐占据主导地位,相关研究成果可为进一步揭示非挤土桩抗震加固机理、评估其加固效果提供一定的基础和支撑。