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1.
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。 相似文献
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Ameer A. Jebur William Atherton Rafid M. Al Khaddar Ed Loffill 《Geotechnical and Geological Engineering》2018,36(5):2893-2906
This investigation aimed to examine the load carrying capacity of model piles embedded in sandy soil and to develop a predictive model to simulate pile settlement using a new artificial neural network (ANN) approach. A series of experimental pile load tests were carried out on model concrete piles, comprised of three piles with slenderness ratios of 12, 17 and 25. This was to provide an initial dataset to establish the ANN model, in attempt at making current, in situ pile-load test methods unnecessary. Evolutionary Levenberg–Marquardt (LM) MATLAB algorithms, enhanced by T-tests and F-tests, were developed and applied in this process. The model piles were embedded in a calibration chamber in three densities of sand; loose, medium and dense. According to the statistical analysis and the relative importance study, pile lengths, applied load, pile flexural rigidity, pile aspects ratio, and sand-pile friction angle were found to play a key role in pile settlement at different contribution levels, following the order: P?>?δ?>?lc/d?>?lc?>?EA. The results revealed that the optimum model of the LM training algorithm can be used to characterize pile settlement with good degree of accuracy. There was also close agreement between the experimental and predicted data with a root mean square error, (RMSE) and correlation coefficient (R) of 0.0025192 and 0.988, respectively. 相似文献
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楔形桩与圆柱形桩复合地基承载性状对比研究 总被引：3，自引：0，他引：3
基于剪切位移法,引入Mylonakis & Gazetas桩-土相互作用及Winkler地基模型,导出了复合地基中桩-桩、桩-土及土-土相互作用柔度系数;在此基础上,提出了一种综合考虑桩-土-垫层共同作用的复合地基分析方法,并利用Matlab软件编制了相应的计算程序。为了验证该方法的可行性,对楔形桩和圆柱形桩复合地基进行了模型对比试验,并利用该方法对两个模型试验进行了计算分析,试验及理论结果均表明,桩顶平面处的桩间土反力保持着类似天然地基的马鞍形分布,圆柱形桩复合地基的承载力明显低于楔形桩复合地基的承载力,同时,圆柱形桩复合地基的桩土平均应力比明显高于楔形桩复合地基的桩土平均应力比,楔形桩对缓解复合地基中桩顶应力集中,充分利用天然地基的承载能力具有良好的调节作用。 相似文献
4.
In the present study, the end bearing capacity of screw and straight pipe pile under similar pile tip area and ground conditions were investigated. The effect of increasing overburden pressure was also considered in this research. Pile load tests on close-ended screw and straight pipe piles were conducted in the small scale. Dry Toyoura sand was used to develop the model ground. The sand was compacted at relative density of 70, 80 and 92 %. It was observed that in case of straight pipe pile, load settlement curve plunges downward without increase in load around settlement equals to 10 % of pile tip diameter, whereas in case of screw pile, the load settlement curve plunges around settlement equals to 15 % of pile tip diameter. Moreover, the screw piles having helix-to-shaft diameter ratio 2–4.1 showed 2–12 times higher end bearing capacity than straight pipe piles with similar pile shaft diameter. It was also observed from the test results that the end bearing capacity of single-helix screw pile was in average 16.25 % less than straight pipe pile with similar pile tip area and ground conditions irrespective of the effect of increasing overburden pressure. 相似文献
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Coupled deformation–seepage analysis of dynamic capacity tests on open-ended piles in saturated sand
Open-ended piles such as tubular piles or I-beams are used as foundations for offshore and nearshore construction. After the pile installation a load test to estimate the bearing capacity of these open-ended piles is necessary. Due to the offshore conditions and the high bearing capacity of the installed piles a static load test is not normally feasible. Therefore, dynamic load tests are carried out where the wave propagation due to an dynamic impact at the pile head is measured. The methods to estimate the bearing capacity from the measured signal of the dynamic tests were derived for solid pile profiles. It is questionable whether these evaluation techniques are applicable for open-ended piles. Hence, the influence of various important system parameters as well as the differences between static and dynamic load tests on open-ended piles is investigated in this paper. 相似文献
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在大桩径、小桩距的群桩条件下,不仅有来自桩侧、桩端和承台传递的多重应力叠加,还有群桩对桩间土的夹持作用影响,桩-土-承台之间作用更加复杂。用有限差分软件模拟固定桩距、桩径,变化竖向荷载下桩-土-承台的相互作用。从各层土的侧摩阻力、不同位置桩的桩顶荷载、荷载-沉降关系、桩间土体位移等方面的计算结果分析桩-土-承台之间的相互影响。结果表明,荷载超出117.8 MN（略大于Pu/2,Pu为群桩极限承载力）后,群桩对上部桩间土的夹持作用开始减小,桩侧上部侧摩阻力增大;桩侧下部侧摩阻力在多重应力叠加作用下呈减小趋势,不同位置的桩侧摩阻力影响范围有差异;用群桩沉降达到5%倍桩径时的荷载作为群桩的竖向极限承载力是可取的;当沉降与桩径的比值超出1%后,承台分担荷载的比例逐渐增大,群桩分担荷载的比例减小。 相似文献
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不同成桩工艺条件下冻结粉土中基桩承载性状试验研究 总被引：1，自引：1，他引：0
桩基础作为冻土工程中最适宜的基础形式,主要采用插入桩、静压桩和灌注桩三种桩型,因其成桩工艺不同对冻土地基及桩基自身造成的差异不一。为研究不同成桩工艺对冻土地基及基桩承载性状的影响,通过开展室内-1.5 ℃条件下单桩静载模型试验,分析在冻结粉土中不同成桩工艺对地温场、桩基极限承载力、桩身轴力以及桩侧摩阻（冻结力）的影响规律。试验结果表明：灌注桩对桩周地温场扰动剧烈,桩侧温度较高,地温变化幅度大。随着桩周土体的回冻,地温逐步降低,其中灌注桩桩侧降温速率最大;在承载力方面,2根灌注桩的极限承载力约为12.8 kN,静压桩为11.6 kN,插入桩极限承载力最小,仅为钻孔灌注桩的2/3。并对比4种不同成桩工艺的基桩在不同荷载条件下对应的沉降量,体现出成桩工艺对基桩沉降造成的差异性;随着桩顶荷载的逐级增加,桩侧摩阻（冻结力）和桩端阻力逐渐发挥作用,桩身上部1/3由于温度较低,致使桩侧摩阻（冻结力）较大,在10 cm深度附近温度最低,使桩侧摩阻（冻结力）达到最大值;并对比4种不同成桩工艺的基桩在荷载5.6 kN下轴力沿桩身的传递情况,发现静压桩更易把荷载传递到冻土区深层地基。 相似文献
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为了研究软岩地基桥桩的荷载传递性状、破坏机理,并获取在该地质条件下更为可靠的桩基计算参数,对秦巴山区软岩地基3根钻孔灌注试桩进行竖向静载试验。结果表明：秦巴山区软岩地基桥桩试桩荷载沉降曲线呈陡降型,实测竖向极限承载力为20 500kN,桩的破坏方式为桩身材料强度破坏;淤泥质亚黏土地层中的碎石起到一定的骨架作用,增强了此地层桩极限侧阻力,发挥极限侧阻力所需的桩土（岩）相对位移为4～8mm;强风化砾岩表现为加工软化型,发挥极限侧阻力所需的桩土（岩）相对位移为3～8mm;中风化砂砾岩表现为明显的加工硬化型,所需的桩岩相对位移大,且桩极限侧阻力的特征点不明显;淤泥质亚黏土地层桩侧阻力占总荷载的60%～70%,随着桩顶荷载的逐步加大,该地层桩侧阻力所占比例不断下降,而嵌岩段桩侧阻力所占比例逐渐上升,达到55%～65%,嵌岩段桩侧阻力沿桩深的分布曲线表现出非线性的特征;试桩为端承摩擦桩,桩端阻力约占桩顶荷载的20%左右,且未充分发挥,在上部结构允许的沉降范围内,适当增加桩端的沉降有利于端阻力的发挥;桩侧阻力先于端阻力发挥,建议单桩承载力设计时分别采用不同的端阻力和侧阻力安全系数。 相似文献
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BP神经网络预测嵌岩桩承载力 总被引：1，自引：0，他引：1
确定嵌岩桩承载力的最可靠最直接的方法是静载试验,但是由于嵌岩桩承载力大,静载试验耗工费时,并且很难做到破坏,因此工程界希望能在不影响结果精度的前提下尽可能少做静载试验。利用以往的嵌岩桩静载试验资料,在BP神经网络理论的基础上,运用Matlab中的神经网络工具箱进行编程分析,总结出嵌岩桩的各种可控参数对其承载能力的影响,从而确定最终比较合理的嵌岩桩的设计参数。对比分析前人的研究成果,得出的结论具有一定的实用性。 相似文献
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以桩的长径比l/d、桩间距与桩径之比s/d、注浆加固体厚度h为因素,以单桩极限承载力Qu与某一荷载下的桩顶沉降Sp为评价指标,设计L9(34)正交试验方案,采用有限元法进行了桩端后注浆对单桩承载性状的作用效应研究,得出各因素作用效应的重要性次序和作用规律。研究表明,无论对桩基承载力还是对桩基沉降,桩间距与桩径之比都是最重要的影响因素,s/d较大时采用桩端后注浆来提高桩基承载力,减小桩基沉降,效果更显著;桩端后注浆使桩的端阻增大,承载性状改变,由摩擦桩逐渐过度为端承摩擦桩、摩擦端承桩或端承桩。 相似文献
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J. R. Omer 《Geomechanics and Geoengineering》2015,10(3):223-233
A new computer program “PILESET” is developed for use in predicting the bearing capacity and load-settlement behaviour of axially loaded single piles. The program can analyse almost any soil profile and accommodates (a) displacement piles (b) replacement (c) friction piles, (d) end-bearing piles, (e) under-reamed piles and (f) partially sleeved piles. A variety of soil input data can be used, including: (i) standard penetration tests, (ii) cone/piezo-cone tests, (iii) pressure-meter tests and (iv) laboratory tests. The above data types can be combined, if desired, for pile analysis by PILESET. The program calculates the shaft and base capacities of a pile based on 23 methods published in design guides in over 10 European countries. PILESET also predicts the pile load-settlement curve using five published methods, which include two modified load transfer (t-z) approaches formulated by the author. To demonstrate the capabilities of the program, analysis is carried out for case study involving seven full-scale screw piles formed in sand and tested to failure. In each case, the load-settlement curve computed using the author’s modified method in PILESET is found to be in excellent agreement with the actual pile test results. 相似文献
14.
轴向荷载对斜桩水平承载特性影响试验及理论研究 总被引：1，自引：0，他引：1
斜群桩受水平荷载作用时,群桩中的基桩受到径向荷载、轴向荷载和弯矩的共同作用。为研究轴向荷载对斜桩水平承载特性的影响,完成了3根单桩以及1组1×2斜桩的大尺寸模型试验。试验结果表明：轴向拉力作用会降低斜桩的水平刚度和极限承载力;而轴向压力作用则会使其水平刚度和极限承载力提高。基于桩侧浅层土体楔形破坏假定,推导了考虑轴向荷载影响的斜桩水平极限土抗力计算公式,提出了桩侧土抗力的p-y曲线方法,并通过模型试验及现场试验验证其合理性。 相似文献
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高速铁路超长桥桩承载特性试验研究 总被引：2，自引：0，他引：2
超长桩广泛已应用于土木工程各个领域,但黄土地区超长桩的承载性状和变形特性尚不十分清楚,需要进一步研究。通过对郑西铁路客运专线某特大桥的4根超长桩现场测试项目的资料分析,得出了超长桩桩身轴力及侧阻力的变化规律,对超长桩的承载特性有了更为清晰的了解。试验结果表明,在桩顶竖向荷载作用下,桩身轴力随荷载的增加发生了局部调整,砂性土层的桩侧摩阻力具有增强效应,黏性土层的桩侧摩阻力具有退化效应;单桩竖向刚度随桩顶荷载的增加而减小,单桩竖向刚度降低40 %～70 %。 相似文献
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针对刚性筏板下群桩基础优化设计问题进行分析,通过改变桩长分布来调整各桩的荷载分担,群桩分析采用基于弹性理论的积分方程方法,并通过cut-off方法来反映桩的弹塑性特性,实现群桩基础的弹塑性优化分析,改进了常规弹性分析方法的缺陷。算例分析表明,随着外荷载的不断增加,角桩首先达到极限荷载,对角桩超出极限荷载的部分进行重新分布,继而使得边桩逐渐达到极限承载状态,继续加载直至内桩也达到极限承载状态,从而引起桩筏基础的整体破坏。采用cut-off方法可以改进基础变刚度优化设计,使之与实际情况更为吻合。 相似文献
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湿陷性黄土地区基桩承载力检测中桩顶荷载是在土体沉降后施加的,桩基使用条件下是桩顶荷载施加之后再出现土体沉降。简要分析了这两种加载次序之间桩土相互作用差异的机制。采用有限元方法分析了这种差异。计算结果表明,在这两种加载次序中,桩顶荷载的增加都会引起沉降增加,中性点下降,下拉力减小。结果还表明,与桩顶荷载先施加的相比,桩顶荷载后施加得到的中性点的位置比较低,桩基沉降比较小,下拽力也较小,这些差异随着桩顶荷载的增大而更加明显。在两种加载次序的各个加载阶段,桩周摩阻力的分布与发挥也会出现细微的变化。这会使湿陷性黄土地区桩的承载力检测结果略微偏于不安全 相似文献
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针对纵截面异形桩（扩底桩和楔形桩）、等混凝土用量常规等直径桩的水平向承载特性进行对比模型试验研究,测得不同水平荷载等级下扩底桩和楔形桩的内力、变形、极限承载力和桩侧土压力分布等变化规律特性;初步探讨3种桩型的水平极限承载特性和桩侧土压力分布规律。考虑纵向截面异形效应,基于水平土抗力与水平位移（p-y）曲线法建立纵截面异形桩水平向承载特性理论计算方法,进一步分析弯矩分布规律,并开展影响因素分析。研究结果表明,在当前试验条件下,等混凝土用量楔形桩的水平向承载力比等直径桩的高,砂性土和黏性土中楔形桩水平向极限承载力约分别为等直径桩的1.25倍和1.33倍。相关研究成果可为今后类似土层下水平受荷纵截面异形桩的设计与计算提供参考依据。 相似文献
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主要介绍了压桩力与单桩竖向极限承载力的关系,以及利用压桩力估算单桩竖向极限承载力的方法。在试桩阶段,位于饱和软土的摩擦桩,压桩力较低,桩的承载力主要来自土体恢复后桩侧的摩阻力。根据静载荷试验检测结果,用单桩竖向极限承载力除以压桩力,引出一个系数,称为压力比,通过分析比较,得出在昆明地区的正常压力比,静压预制管桩在1.3～2之间,静压预制方桩在2.5～5之间。用压桩力乘以压力比,可以估算单桩竖向极限承载力。还简要介绍了挤土效应和超孔隙水压力对桩的承载力的影响。在工程桩施工时,地层中的土体和孔隙水被挤压,形成孔隙水压力,会产生一个向上的浮力,导致已施工的桩上浮,单桩承载力显著降低。 相似文献
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Bearing capacity calculation method and field static load test (SLT) program were carried out simultaneously to study the bearing characteristics of individual Plastic Tube Cast-in-Place Concrete Pile (TC pile), which are increasingly being employed for support of embankments in southeast China. The bearing capacity calculation method considering pile setup (i.e., setup calculation method) was built up according to the cylindrical cavity contraction and horizontal consolidation theories. A series of SLTs on different dates were applied to study the bearing behavior of TC pile and to verify the validity of the established setup calculation method. During TC piles installation, there is about 45% contraction in cylindrical volume due to the extraction of steel casing. Both theoretical and experimental results show that the calculated outcomes considering cylindrical cavity contraction agree well with measured ones. The difference value between them is not more than 12%. On the other hand, if the cylindrical cavity contraction is ignored, the calculated bearing capacities of TC piles are overestimated by 160–300%. The setup of TC pile is mainly due to the increment of pile shaft resistance with time elapsed. Cylindrical cavity contraction accompanied by TC pile installation causes much loss of pile shaft resistance. 相似文献