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.

Finite element analysis of effect of soil displacement on bearing capacity of single friction pile

Effect of soil displacement on friction single pile in the cases of tunneling,surcharge load and uniform soil movement was discussed in details with finite element method.Lateral displacement of the pile caused by soil displacement reached about 90% of the total displacement,which means that P-Δ effect of axial load can be neglected.The maximum moment of pile decreased from 159 kN·m to 133 kN·m in the case of surcharge load when the axial load increased from 0 to the ultimate load.When deformation of pile caused by soil displacement is large,axial load applied on pile-head plays the role of reducing the maximum bending moment in concrete pile to some extent.When pile is on one side of the tunnel,soil displacements around the pile are all alike,which means that the soil pressures around the pile do not decrease during tunneling.Therefore,Q-s curve of the pile affected by tunneling is very close to that of pile in static loading test.Bearing capacities of piles influenced by surcharge load and uniform soil movement are 2480 kN and 2630 kN,respectively,which are a little greater than that of the pile in static loading test(2400 kN).Soil pressures along pile increase due to surcharge load and uniform soil movement,and so do the shaft resistances along pile,as a result,when rebars in concrete piles are enough,bearing capacity of pile affected by soil displacement increases compared with that of pile in static loading test.

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.

Bearing capacity and mechanical behavior of CFG pile composite foundation

CFG pile (i.e., pile constructed by granular materials of cement, fly-ash and gravel) composite foundation is applied in subsoil treatment widely and successfully. In order to have a further study of this kind of subsoil treatment technology, the influencing factors and calculation methods of the vertical bearing capacity of single CFG pile and the CFG pile composite foundation were discussed respectively. And based on the obtained solutions, effects by the cushion and measurements to reduce negative friction area were analyzed. Moreover, the developing law of settlement and bearing capacity eigenvalue controlled by the material strength with the increase of load were given for the CFG composite foundation. The in-situ static load test was tested for CFG pile. The results of test show that the maximum test load or half of the ultimate load is used from all the points of test, the average bearing capacity eigenvalue of single pile is 390 kN, and slightly greater than the design value of bearing capacity. The bearing capacity eigenvalues of composite foundation for 3 piles are greater than 300 kPa, and the mechanical properties of CFG pile composite foundation are almost identical in the case of the same load and cushion thickness. The pile-soil stress ratio and the load-sharing ratio can be adjusted through setting up cushion thickness.

Bearing Behaviors of Stiffened Deep Cement Mixed Pile

一系列调查被进行学习适用的能力和混合的使硬的深水泥(SDCM ) 的负担转移机制堆积。实验试验包括六个标本被进行调查在具体核心和 thecement 土壤之间的摩擦抵抗。二模型堆积和 24 照原尺寸的堆积被测试检验单个堆积的适用的行为。实验室和模型测试结果显示连贯的力量足够大保证在核心堆积和外部水泥土壤之间的相互作用。full-scaletest 结果证明 SDCM 堆积展出类似的适用的行为到无聊并且 cast-in-placeconcrete 堆积。一般来说，与合理合成结构， SDCM 堆积能有效地播送应用负担，并且由于更生硬的核心的增加， SDCM 堆积拥有高适用的能力。基于这些试验性的调查和理论分析的调查结果，一个实际设计方法被开发预言 SDCMpile 的垂直适用能力。

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。

New Method for Prediction Pile Capacity Executed by Continuous Flight Auger (CFA)

A study of piles is quit complex and the estimation of carrying capacity is calculated from theoretical formula and load test results. The design resistance may be calculated using conventional static pile design theory. The pile founding depths should be predetermined before installation from a site geotechnical investigation. To ascertain the field performance and estimate load carrying capacities of piles, in-situ pile load tests should be conducted. In this study, field pile load test data is analyzed to estimate the ultimate load for end bearing piles. The investigated site is about 100 × 110 m located in Alexandria, Egypt. Geotechnical investigations at the site are carried out to a maximum depth of 45 m. Four borings have been done in field. The tests are conducted at the site for two skelton structure buildings to be constructed on raft foundation rested on piles executed by continuous flight auger. Four pile load tests are performed on 600 mmdiameters and 27 mlengths. Ultimate capacities of piles are determined according to different methods. It is concluded that the percentage of friction load carried by the shaft along the pile length is about 46% of total load while the percentage of load carried by the end bearing is 54% of total load. A new proposed method by the author is presented to calculate the ultimate capacity of pile from pile load test. The proposed method depends on the settlement of pile without taken into consideration the elastic deformation. An empirical formula is presented from the relationship between stress and settlement of pile due to friction and end bearing only after deducting the elastic deformation. However, the obtained results for the ultimate capacity of end bearing piles are considered to be more accurate than other methods. The proposed method appears to give bitter results that agrees well with the theoretical predictions. The proposed method is easier, quicker and more reliable.

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。

Bearing capacity and load transfer mechanism of a static drill rooted nodular pile in soft soil areas

The static drill rooted nodular pile is a new type of pile foundation consisting of precast nodular pile and the surrounding cemented soil.This composite pile has a relatively high bearing capacity and the mud pollution will be largely reduced during the construction process by using this type of pile.In order to investigate the bearing capacity and load transfer mechanism of this pile,a group of experiments were conducted to provide a comparison between this new pile and the bored pile.The axial force of a precast nodular pile was also measured by the strain gauges installed on the pile to analyze the distribution of the axial force of the nodular pile and the skin friction supported by the surrounding soil,then 3D models were built by using the ABAQUS finite element program to investigate the load transfer mechanism of this composite pile in detail.By combining the results of field tests and the finite element method,the outcome showed that the bearing capacity of a static drill rooted nodular pile is higher than the bored pile,and that this composite pile will form a double stress dispersion system which will not only confirm the strength of the pile,but also make the skin friction to be fully mobilized.The settlement of this composite pile is mainly controlled by the precast nodular pile;meanwhile,the nodular pile and the surrounding cemented soil can be considered as deformation compatibility during the loading process.The nodes on the nodular pile play an important role during the load transfer process,the shear strength of the interface between the cemented soil and the soil of the static drill rooted pile is larger than that of the bored pile.

Experimental Study on Concrete Columns Confined by BFRP-PVC Tubes Under Uniaxial Loading

This paper presents an experimental study on the behavior of circular concrete columns reinforced by BFRP-PVC tubes under uniaxial loading.A total of six specimens were prepared and tested under uniaxial loading.The main parameters varied in the tests were strengthening ratio and strengthening approach of BFRP.The performance,such as failure modes,ultimate bearing capacity and stress-strain curves,was investigated in details and a formula was proposed to predict the compressive ultimate strength.The results show that this kind of confined columns obviously improves the ultimate bearing capacity,and the ultimate bearing capacity increases with the strengthening layers.The formula proposed is applicable and efficient for prediction of the ultimate bearing capacity as well.

Mechanical performance of shear studs and application in steel-concrete composite beams

This work experimentally investigates the effects of shear stud characteristics on the interface slippage of steel-concrete composite push-out specimens. ABAQUS is used to establish a detailed 3D finite element(FE) model and analyze the behavior of push-out specimens. The modeling results are in good agreement with the experimental results. Based on parametrical analysis using the validated FE approaches, the effects of important design parameters, such as the diameter, number, length to diameter ratio, and yield strength of studs, concrete strength and steel transverse reinforcement ratio, on the load-slip relationship at the interface of composite beams are discussed. In addition, a simplified approach to model studs is developed using virtual springs with an equivalent stiffness. This approach is demonstrated to be able to predict the load-displacement response and ultimate bearing capacity of steel-concrete composite beams. The predicted results show satisfactory agreement with experimental results from the literature.

Experimental Investigations on Web Crippling Failure Modes of Aluminum Hollow and Composite Tubes

In order to study the web-crippling behavior of aluminum hollow sectionsubjected to concentrated load, sixteen aluminum hollow tubes with different loadingconditions, bearing length and web slenderness ratios were tested. This paper alsodiscussed a method to improve the web crippling strength of the aluminum hollowsections by infilling the mortar as composite section, and four aluminum compositesections were tested. The literature has reported lots of web crippling tests, but there isfew reports on web crippling behavior of aluminum composite sections. Interior-Ground(IG) and End-Ground (EG) loading conditions were adopted, with the specimens placedon the ground to simulate the load of floor joists. Specimens were also placed on abearing plate with end (ETF) or interior (ITF) bearing load. The influence of supportingconditions, loading positions, bearing length and web slenderness ratios on web cripplingultimate bearing capacity and ductility of aluminum hollow sections was studied. Theenhancements of infilling mortar were also evaluated. The results obtained from theexperiments show that infilling the mortar in aluminum hollow tubes is an effectivemethod for enhancing the ultimate capacity of the web, especially for specimens underInterior-Ground (IG) condition. Based on the results of parameter research, this paperproposes a series of design formulas for well predicting web crippling ultimate capacityof aluminum hollow and composite tubes under four different loading and boundaryconditions.

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.

Experimental Research on Large Diameter Cast-in-Place Piles Embedded in Rock

This paper expatiated the field test of large diameter cast in place piles embedded in soft rock, including static loading test, high or low strain dynamic test, measurement of stresses and strains of pile body, and pressure measurements between pile tip and soft rock. The relative in situ test problems are discussed. Based on the limit equilibrium theory and the load transfer equation, a synthesis method of analyzing the ultimate carrying capacity of single large diameter pile is put forward. The research results show that the key to determining the ultimate carrying capacity of single pile with a large diameter is the analysis of the intensity of soft rock.

基于改进BAS-BP模型的水平受荷桩承载力预测方法研究

水平受荷桩在高速道路、桥梁和抗震等工程中广泛使用,其设计中存在的重要问题之一为承载力的预测。影响水平受荷桩承载力的因素较多,而现有的相关计算理论未能考虑岩土参数的变异性,难以反映实际使用时的工程情况,从而使得承载力的预测误差较大。采用自适应惯性权重和最小步长策略改进了BAS算法,优化了神经网络模型参数,建立了水平受荷桩承载力预测模型。预测结果表明,改进BAS算法可以显著改善神经网络的泛化能力、收敛速度和预测精度,预测模型对水平受荷桩承载力预测具有良好的适用性。采用连接权重法对水平受荷桩承载力进行了敏感性分析。结果表明:Su为最重要输入参数,其次为e,而L和D对单桩水平承载力的影响较小。该预测方法计算简便、高效,预测精度相对较高。且此方法可进一步考虑荷载、桩体和土体类型等相关因素的影响,适用范围广、包容性较强。

上砂下黏地层中桩-筒复合基础V-H承载特性

海上风机基础不仅受自重等竖向力V作用,也因水流、波浪和风等影响而承受水平荷载H。为探讨上砂下黏地层中一种由单桩和吸力筒组成的新型海上风机桩-筒复合基础受V-H组合作用时的承载特性,自主设计完成了一系列室内桩-筒复合基础V-H组合加载模型试验,获得不同组合参数下桩-筒复合基础的荷载-位移曲线和桩身弯矩分布曲线,并绘制出V-H承载力包络线。在此基础上,采用ABAQUS建立了上砂下黏地层中桩-筒复合基础三维数值分析模型,经模型验证与参数分析,进一步讨论了砂土厚度、筒径、筒高以及加载高度等参数对桩-筒复合基础承载特性的影响曲线,并拟合出桩-筒复合基础承载力简化计算公式,分析结果表明:桩-筒复合基础能显著提高桩身水平承载力,增幅达30%~90%,且增加筒径比增加筒高更有利于提高基础水平承载力;上部砂土层较厚时,桩-筒复合基础存在一个使复合基础水平承载力达到最大的预加竖向荷载最佳值,其值随不同载荷工况在(0.4~0.7)Vult范围内变化。

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。

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。