Vertical bearing capacity of pile based on load transfer model

The load transfer analytical method is applied to study the bearing mechanism of piles with vertical load in this paper. According to the different hardening rules of soil or rock around the pile shaft, such as work-softening, ideal elasto-plastic and work-hardening, a universal tri-linear load transfer model is suggested for the development of side and tip resistance by various types of soil (rock) with the consideration of sediment at the bottom of the pile. Based on the model, a formula is derived for the relationship between the settlement and load on the pile top to determine the vertical bearing capacity, taking into account such factors as the characteristics of the stratum, the side resistance along the shaft, and tip resistance under the pile tip. A close agreement of the calculated results with the measured data from a field test pile lends confidence to the future application of the present approach in engineering practice.

Evaluation of ultimate bearing capacity of Y-shaped vibro-pile

Based on Mindlin stress solution, a numerical computational method was proposed to calculate the stresses in the ground induced by side friction and the resistance of Y-shaped vibro-pile. The improved Terzaghi's and ЪерезанцевВГ's methods for ultimate bearing capacity evaluation were proposed by considering the stress strength induced by friction resistance at pile head level of Y-pile. A new method to calculate the ultimate bearing capacity of Y-pile was also proposed based on the assumptions of soil failure mode at the tip of Y-pile and the use of Mohr-Coulomb soil yield criterion and Vesic compressive correction coefficient with the induced stresses in the ground. Based on the comparisons with the field static load test results, it is found that the improved Terzaghi's method gives higher ultimate capacity, while the other two methods shows good agreement with the field results.

Research on Vertical Bearing Capacity of Pile Foundation under Wave Scouring

In order to analyze the influence of wave scouring on the vertical bearing behavior of the pile foundation, the finite element software ABAQUS was used to simulate the force of the pile foundation under the action of wave scouring. A three-dimensional finite element calculation model of the pile foundation was established according to the actual working conditions, and the calculation results were compared with the field test results to verify the correctness of the built model. Then, the influence of wave scouring depth and pile embedding depth on the vertical bearing behavior of pile foundation was analyzed through calculation examples. The analysis results showed that the greater the depth of wave erosion, the greater the impact on the vertical bearing behavior of the pile foundation. Meanwhile, the smaller the buried depth of the pile body, the greater the impact on the vertical bearing capacity of the pile. Thus, the reduction rate of the vertical bearing capacity under different scouring depths was obtained.

Experimental Study on Horizontal Bearing Characteristics of Screw Pile

The horizontal bearing capacity of the screw pile and monopile was analyzed by model tests.Results showed that the horizontal bearing capacity of the screw pile was significantly greater than that of the monopile under the same loading conditions.With the increase in horizontal loading speed,the ultimate horizontal bearing capacity of the two piles also increases,and the difference decreases gradually.Moreover,the influence of vertical loading on the horizontal bearing capacity of screw pile and monopile is studied at the horizontal loading speed of 2 mm s-1.The findings indicate that vertical load evidently affects the horizontal bearing capacity of common piles,but slightly influences the horizontal bearing capacity of screw piles.

Stability Analysis of Piles Subjected to Lateral Load in Static and Seismic Conditions

It is disclosed a method for the stability analysis of foundation piles and piers subjected to lateral loading, both static and seismic conditions. The stability analysis for stratified soil is based upon the models of foundation soil-structure interaction and the Rankine＇s theory of earth passive pressure. In addition, its application is simpler and it can be solved using a spreadsheet. The procedure described in this work can be used in homogeneous soils as in stratified soils, considers the horizontal drag forces exerted by the soil mass against the foundation during an earthquake, can be used easily in the four pile and piers boundary cases, and considers the pore pressure generated in a fine saturated soil during an earthquake or during a rapid application of the horizontal load. The solution of two examples are shown, one in static condition and one in seismic condition, detailing the procedure step by step.

A new method for testing pile by sin- gle-impact energy and P-S curve

By studying the pile-formula and stress-wave methods (e.g., CASE method), the authors propose a new method for testing piles using the single-impact energy and P-S curves. The vibration and wave figures are recorded, and the dynamic and static displacements are measured by different transducers near the top of piles when the pile is im- pacted by a heavy hammer or micro-rocket. By observing the transformation coefficient of driving energy (total energy), the consumed energy of wave motion and vibration and so on, the vertical bearing capacity for single pile is measured and calculated. Then, using the vibration wave diagram, the dynamic relation curves between the force (P) and the displacement (S) is calculated and the yield points are determined. Using the static-loading test, the dynamic results are checked and the relative constants of dynamic-static P-S curves are determined. Then the sub- sidence quantity corresponding to the bearing capacity is determined. Moreover, the shaped quality of the pile body can be judged from the formation of P-S curves.

基于ABAQUS的桩端含多溶洞对桩基承载力的影响研究

岩溶区地基中往往含有多个溶洞,当前对含多溶洞桩基-地基承载机理的研究落后于工程实践。因此,针对含多溶洞地基-桩基承载机理,依托某岩溶桩基工程,应用大型有限元分析软件ABAQUS建立模型,通过对桩基荷载-位移曲线的分析,探讨不同溶洞顶板厚度下溶洞形状、溶洞几何特性及溶洞间距对桩基极限承载力的影响。结果表明:相同工况下,方形溶洞对桩基承载力的不利影响大于圆形溶洞;随着溶洞单一尺寸的增大,溶洞对桩基极限承载力的不利影响逐渐增大。桩端存在双溶洞时,侧溶洞洞高对桩基极限承载力的影响大于洞跨对其的影响;随着溶洞间距的增大,侧溶洞对桩基承载力的影响降低,当间距达到5倍桩径时,侧溶洞对桩基承载力的影响可忽略。

基于ABAQUS的灌注桩竖向承载力模拟分析

作为一种常见的地基处理方式,灌注咬合桩在深基坑领域中应用广泛。为了评估和预测灌注咬合桩的竖向承载力,结合中国铁建华南总部大厦基坑工程咬合桩情况,提基于ABAQUS数值模拟方法进行灌注桩竖向承载力模拟分析。通过混凝土桩与钢筋混凝土桩的交叉连接,对灌注桩的竖向承载力进行分析。研究结果表明:在地应力和周围土压力的作用下,咬合桩主要应力分布在钢筋混凝土桩中部和交叉连接处。通过工程桩基承载力与预测值进行对比,检验了咬合灌注桩模拟结果的可靠性。

基于Midas对桥梁桩基础竖向荷载-位移影响规律研究

为了优化桥梁桩基础的承载特性,文中以某三跨连续刚构桥为例,通过Midas模拟分析不同桩间距以及桩长度对桩基础荷载-位移曲线的影响规律。结果表明,加载初期,桩间距为5、6、7 m条件下的桩基础位移基本一致,桩间距对桩基础的位移无影响;随着荷载水平的增加,桩基础的位移随着桩间距的增加桩基础位移越来越小;桩长度为35 m比桩长为30 m的桩基础位移低了34.2%;桩长度为40 m比桩长为30 m的桩基础位移低了44.9%。桩长越长,桩间距越大,桩基础的位移越小,桩基础的承载特性越强。

基于RAGA的指数曲线模型预测基桩承载力

预测挤扩支盘桩单桩极限承载力指数曲线模型的函数表达式是一个超定非线性方程。采用传统的最小二乘法对该模型参数进行回归处理时,往往由于计算复杂和人为因素的影响使预测结果存在较大的误差。为此,用实数编码加速遗传算法(RAGA),对指数曲线模型的参数和理论极限承载力进行优化,并基于MATLAB环境下编写了模型的计算程序。结合工程实例,应用指数曲线模型对挤扩支盘桩静载荷试验实测数据进行了拟合分析。结果表明,基于RAGA的指数曲线优化模型能够更好地拟合实测数据和有效地预测单桩极限承载力,且基于RAGA的指数曲线优化模型具有求解速度快、计算精度和自动化程度高、人为干扰因素小、通用性强等优点。

基于GA-BP神经网络的单桩承载力预测

针对BP神经网络易收敛慢、易陷入局部极小等不足,引入遗传算法处理了BP的初始权值和阈值,并在此基础上建立了长螺旋压灌混凝土桩复合地基单桩极限承载力预测模型。利用该模型通过对现场工程数据进行了学习、训练以及预测检验。预测结果精度高,表明此模型是有效的,并在单桩承载力预测方面具有较好的应用价值。

小子样下基于Bayes推广理论的单桩竖向承载力研究

为了更有效地确定小子样下单桩承载力的设计值,利用勘探阶段的静力触探资料,结合《建筑桩基技术规范》中的经验参数法,先使用Grubbs方法剔除基桩参数数据中的疏失误差数据,得到单桩竖向承载力的验前信息,然后根据静载荷试验结果对先验信息进行调整,得到关于单桩竖向承载力的验后信息。经比较分析,利用Bayes方法估算的单桩极限承载力更加精确,置信区间更加集中,从而为小子样条件下单桩竖向承载力设计值提供了理论参考依据。

基于ANFIS的单桩竖向极限承载力预测模型

人工神经网络已应用在岩土工程的各个方面。针对常用的 BP 网络的不足之处,建立了基于自适应神经模糊推理系统(ANFIS)的单桩竖向极限承载力预测模型。利用文献中桩的载荷试验数据来训练 ANFIS 网络,确定了网络参数。研究结果表明。同常用的 BP 网络相比,ANFIS 预测模型具有学习速度快。拟合能力较好,训练结果唯一等优点,该方法是一种有效地预测单桩极限承载力的方法。

单桩极限承载力的ANFIS预测分析

为了提高单桩极限承载力的预测精度,利用ANFIS较强的学习能力和模糊逻辑推理功能,建立了单桩竖向极限承载力预测的自适应网络模糊推理系统.通过静载荷试验成果的学习与预测检验,系统的预测误差在-10.5%～15.5%,绝大部分误差都在10%以内,表明该系统预测精度良好、适用性较强.

预测钢筋混凝土预制桩竖向极限承载力的ANN方法研究

传统的钢筋混凝土预制桩极限承载力预测方法,难以考虑单桩极限承载力影响因素的模糊性和相互作用关系.本文提出并建立了预测钢筋混凝土预制桩极限承载力的人工神经网络方法,收集了某地区的41例钢筋混凝土预制桩,利用其中37例的实测数据建立了预测单桩极限承载力的ANN模型,另外的4例检验了模型的预测性能.研究结果表明,所建立的ANN方法的预测精度能够满足工程应用要求.

基于ANFIS的单桩极限承载力预测及可靠度分析与设计

利用ANFIS较强的学习能力和模糊逻辑推理功能,建立了单桩竖向极限承载力预测的自适应网络模糊推理系统。该系统通过对静载荷试验成果的学习与预测检验,证明其预测精度良好、适用性强,因而具有较大的工程应用价值。基于该预测方法,采用无量纲随机变量的极限状态方程,结合宁波市桩基静载试桩资料进行单桩竖向极限承载力可靠度分析,利用最优化方法计算单桩承载力可靠指标,并提出了单桩可靠度设计方法。

基于Ansys的带侧向支撑桩的稳定性

为分析既有建筑物增设地下空间托换桩的稳定性,利用Ansys建立增设侧向支撑的钢筋混凝土桩的三维有限元模型,通过改变桩周土水平抗力系数的比例系数、桩周土开挖深度、桩身截面边长、桩身配筋率和载荷偏心距等参数,分析桩的受压极限承载力和相应支撑轴力的变化规律。结果表明:桩受压极限承载力和相应支撑轴力随载荷偏心距和桩周土开挖深度的增大而减小,随着桩周土水平抗力系数的比例系数、桩身配筋率和桩身截面边长的增大而增大。根据虚拟嵌固点法提出带侧向支撑钢筋混凝土桩承载力和侧向支撑轴力的计算公式,并将公式计算值与数值模拟结果进行对比,两者吻合较好,验证计算公式的可靠性。

ALE方法评估黏土场地的自升式平台桩靴承载力

为研究自升式平台桩靴在黏土场地中的极限承载力,建立Abaqus桩靴-土模型,采用任意拉格朗日-欧拉(Arbitrary Lagrangian-Eulerian,ALE)方法对桩靴的贯入过程进行模拟,提出大值法、中值法、小值法等3种数据处理方法,并拟合桩靴承载力估算公式。将模拟计算结果与SNAME规范公式计算结果进行对比分析,对比结果证明ALE方法模拟桩靴贯入的可行性。为提高工程的安全性,提出对SNAME公式计算结果进行折减的具体公式,以使其与ALE小值法处理结果更吻合。

不同灌浆效果下黏土海床导管架桩基础的竖向承载特性离心试验

在40~60 m水深海域,海上风力发电机多使用导管架基础作为主要支撑结构.导管架通过水下高强灌浆与桩基础顶部连接,形成顶端密封段,共同承载竖向荷载.针对桩基顶部灌浆正常、灌浆不足、灌浆不良存在通孔3种不同灌浆效果开展离心模型试验,分析极限状态下基础的竖向承载力及灌浆段与桩身段的承载力分担比,并与现有理论计算方法进行对比.结果表明,灌浆密封顶盖的承载力取决于密封效果.对于灌浆密封顶盖灌浆正常和灌浆不足的基础,灌浆密封顶盖的承载力约占基础总承载力的25%~30%;灌浆不良存在通孔时,基础灌浆段承载力发挥较早且很快达到极限,其分担比远低于其他两者承载力.试验结果可为导管架桩基础设计中的灌浆段承载力计算提供参考依据.

斜拉桥易损性及极限承载力分析

以某独塔斜拉桥为研究对象,基于拉索的参数振动理论,计算分析了拉索的基频、拉索在单对断索损伤场景下的拉索应力传递系数和主梁应力安全系数;采用Pareto多目标评价方法,按结构最小损伤比例造成性能残余强度最小的优化原则,研究单对断索损伤场景下拉索的易损性,确定了易损的拉索次序和拉索对结构极限承载力的影响。分析结果表明:该斜拉桥外侧拉索更容易发生参数共振;单对拉索损伤场景下,易损拉索为主跨的Z6,Z8,Z9索;边跨单对拉索断裂对结构极限承载力影响在2%以内,主跨拉索Z6发生断裂使结构极限承载力降低14.5%。研究结果可为研究独塔斜拉桥拉索易损薄弱部位,桥梁健康监测的关键索号选取和提高结构安全性提供理论依据和参考。