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1.
循环荷载下饱和粉土地基单桩水平承载特性试验研究 总被引：3，自引：0，他引：3
在饱和粉土地基中进行了单桩水平静力和循环加载室内模型试验,实测得到静载和循环荷载下桩身弯矩与深度的关系、桩身最大弯矩与循环次数之间的关系等,推导出静载和循环荷载下粉土的p-y曲线,并结合API规范给出了针对粉土地基的相关参数。单桩循环加载试验结果表明,在一定深度内随着循环次数增大,粉土极限抗力显著减小,文中给出了不同循环次数和深度下粉土地基极限抗力的折减系数建议值。 相似文献
2.
自升式钻井平台插桩是地基土在桩靴荷载作用下发生连续的塑性破坏的动态过程,当地基极限承载力等于桩靴荷载时插桩完成。经典土力学极限承载力理论对土体潜在滑动面做了假设,无法有效分析土体内部的破坏过程。本研究应用有限元法（FEM ）对插桩过程进行了模拟,得到地基土的破坏机制以及中间荷载下土体的应力、应变情况,通过和各理论公式计算的极限承载力进行对比分析,分析影响地基极限承载力的因素。研究表明,基础宽度与硬土层厚度的比值 B/H越大,下卧软土层越容易发生塑性破坏,极限承载力明显下降,当B/H＜0．286时,可以忽略下卧软土层对地基承载力的影响。 相似文献
3.
江苏海岸辐射沙洲是江苏重要的海上风电规划区域,该海域的地层资料和试桩资料极为缺乏。通过钢管桩的现场静荷载试验,对江苏海岸辐射沙洲地层中大直径钢管桩基础承载性能进行研究,以揭示各地层的主要承载性能参数。试桩结果表明,江苏海岸辐射沙洲地层中钢管桩实际的轴向极限承载力明显小于高应变动测结果,只有高应变动测结果的79.09%。总侧摩擦阻力占总承载力的95.61%,而桩端阻力只占总承载力的4.39%。桩内土对管壁的侧摩阻力作用很小,主要是桩外土对管壁的侧摩阻力在发挥作用。辐射沙洲地层中粉土夹粉质黏土的承载性能一般,不适应作为钢管桩的持力层。轴向抗压静载试验得到的极限侧摩阻力高于静力触探的测试结果和API法的计算值。浅部砂层实际的极限水平土体抗力高于API法计算值,在水平荷载作用下上部砂层的p-y曲线具有明显软化效应,土体的软化效应在设计时需进行考虑。 相似文献
4.
p-y 曲线法常用于水平静力受荷桩的分析，但海洋工程中的桩基除静力外还承受波、流等循环荷载作用，将静力 p-y曲线直接用于循环荷载下桩基的设计研究时，往往会产生误差。本文梳理了水平循环荷载作用下 p-y 曲线模型的研究成果，
按照得到循环 p-y 曲线的不同方式，将其分为总体调整法和参数修正法。在参数修正法中，根据修正时考虑的因素不同，分为考虑荷载特性的修正和考虑桩土相互作用的修正。最后通过对循环荷载作用下 p-y 曲线研究现状的总结对比，评价了不同方法的特点，讨论了当前研究存在的问题并给出了建议。 相似文献
5.
以浙江舟山大陆连岛工程宁波连接线项目为依托,选择1根典型摩擦桩开展了自平衡试桩法在沿海软弱地层中的试验研究,并对自平衡测试后的试桩进行了传统桩顶堆载验证试验。介绍了自平衡试桩法从设计、现场试验及数据分析的全过程及各阶段的设计要点,并对容易引起测量误差的现有位移测量方法进行了改进,避免了易发缺陷的荷载箱处虚位移的影响。试验测得了试桩的负摩阻力系数值及单桩承载力值,其结果符合试验设计要求,试桩承载力满足设计要求,相关试验设计及测得的参数可以作为此类地层中自平衡测试的参考。经与传统桩顶堆载验证试验对比可知,自平衡试桩法在工程上的应用具有合理性与准确性。 相似文献
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采用有限元软件ABAQUS建立了海上风电单桩基础与土相互作用数值计算模型,将波浪、洋流及风荷载等效成双向对称循环荷载,研究了水平循环荷载作用下不同因素对桩身水平位移、剪力和弯矩的影响规律。研究表明,随着循环荷载比的增加,桩身位移零点和桩身剪力反弯点沿埋深逐渐下移,桩身弯矩最大值点位于浅层土体;不同荷载频率时桩身位移在零点以上变化较大,桩身弯矩随着频率的增加逐渐增大;单向循环荷载作用下桩身位移最大,双向对称循环荷载作用下桩身位移最小;壁厚较小时对桩身水平位移影响较大;在位移零点之上范围内可以考虑设计"上厚下薄"的钢管桩,以减小桩身水平位移;不同桩壁厚时桩身剪力曲线在埋深约6D处出现交点,且泥面处桩身弯矩变化不明显。 相似文献
8.
《中国海洋大学学报(自然科学版)》2020,(Z1)
通过ABAQUS建立海上风电单桩基础的数值模型,并与室内模型桩试验的结果作对比,验证模型的可靠性。根据实际桩土参数建立数值模型,并对桩土模型施加循环波浪荷载,分析波浪荷载作用下桩周土体的水平应力和水平位移随时间的变化特性,以及土体水平位移在空间分布上的差异。结果表明在波浪荷载作用下桩周土体的水平应力和水平位移在一定范围内循环波动,且极端海况下土体所受的扰动远大于正常海况下土体所受扰动。海床表面桩周土体在距桩体10 m范围内受桩体影响显著,竖直方向上桩身以泥面以下大约2/3桩身入土深度处的一点为基点做循环摆动,且这一旋转基点的位置与波浪力的大小无关。 相似文献
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结合在钱塘江盐官河段对涌潮作用下桩式丁坝动力特性进行的现场测试,首次将有限差分法应用于求解桩式丁坝框架结构受涌潮瞬态荷载作用时的动力响应。其桩周土模型采用Winkler假定,应用有限差分法将桩式丁坝框架结构的各梁柱单元离散后联立起来,从而求得整个结构的动力响应。通过参数研究揭示了结构的形式、结构的刚度、土的剪切波速(即反映桩土相对刚度)对桩式丁坝框架结构横向振动的影响。通过与现场测试结果比较可知,理论计算值与实测值基本吻合,验证了该方法的精度和稳定性。该方法计算过程简单,克服了传统的静力法不能考虑结构的惯性力以及土的粘滞阻尼和动刚度的缺点,对工程实际具有一定的指导意义。 相似文献
11.
—In the designing of the flexible fender pile,M-method is usually adopted.But M-method isusable only in the case that the value of the force(moment M and shear force Q)exerted on the pile abovethe soil is known.In practical cases,only the percussive energy of the ship can be found,while the exactvalue of the percussive force cannot be computed directly.In this paper,a method is introduced which canbe used to calculate the inner force of flexible fender piles by a computer in these cases.First,according tothe known docking dynamic energy of a ship,the absorbed energy can be found from the deformation ofthe pile and the rubber fender respectively,at the same time the value of the force acting on the fender pilesand the reaction of fenders can be calculated.Then the inner force and displacement of the fender piles canalso be calculated further by M-method.The whole computing process is realized by a computer programand the results obtained are reasonable.In this paper,the computation,the iteration method a 相似文献
12.
ABSTRACTThe strain wedge model effectively performs nonlinear analyses of the lateral response of piles by using a nonlinear stress-strain relationship to describe soil behavior in the strain wedge. In this study, a state-dependent plasticity model has been implemented in the strain wedge model to calculate the stress-strain relationship for sand in the strain wedge. To complement this implementation, the effect of dilatancy on the shear strain is considered in the strain wedge. A full-scale test and a 45 g centrifuge model test on laterally loaded piles are used to validate the proposed method. The results show that the deflections and moments predicted by the proposed method accord well with those measured from full-scale and centrifugal model pile tests. Moreover, the combination of the state-dependent plasticity model and the strain wedge model allows for analyzing the lateral response of single piles using a unique set of model parameters for different relative densities of sands. In addtion, the stress-strain response in the strain wedge, not the dilatancy, dominates the soil resistance in the strain wedge and thus the lateral response of piles. 相似文献
13.
小尺度群桩应用广泛,一直是学者研究的重点,小尺度有别于大尺度桩柱,由于桩柱周围存在漩涡的脱落,使得受力特性复杂。以往的研究过程中,波浪主要采用单向不规则波浪,并且试验模型多以两桩或三桩组成的群桩结构为主,桩数相对较少。多向不规则波与群桩结构的作用特点有别于单向不规则波且研究较少。通过物理模型试验,针对多向不规则波对于9桩桩排群桩结构的作用进行了研究。首先综合考虑KC1/3数和相对桩径的影响,提出以参数KCLD 1/3数来衡量群桩的效应,并分析了正向力与横向力随着参数KCLD 1/3数和相对桩距的变化关系,研究了群桩中不同桩位桩柱波浪力的变化规律和方向分布宽度对于群桩波浪力的影响。研究结果表明,群桩中各桩的正向力随着方向分布标准差的增大而减小,而横向力在相对桩距较大时随着方向分布标准差的增大而增大,同时群桩中不同位置桩上的波浪力具有较大的差异。 相似文献
14.
This study has evaluated the vertical bearing capacity by conducting static load tests for noise-free and vibration-free screw pretensioned spun high-strength concrete (PHC) piles installed using two different methods (end-squirting shoe and pre-boring methods). Vertical bearing capacity differences seem to occur due to the displacement of soils near the external circumference of a pile, depending on the installation method. A method by which to evaluate the bearing capacity of screw concrete piles is suggested by considering the equations that already have been used to calculate the bearing capacity of piles. Based on static load tests and analysis, the pile installed using the end-squirting shoe method was assumed to be a bored pile and it was reasonable to use the equation proposed by the Japanese Geotechnical Society. At the same time, the pile installed using the pre-boring method was deemed a low soil displacement pile and so it was reasonable to apply the equations proposed for calculating the bearing capacity of the driven pile suggested by the Architectural Institute of Japan. 相似文献
15.
Liqiang Sun Yandi Wang Shuwang Yan Jian Chu Xiaoqiang Liu 《Marine Georesources & Geotechnology》2018,36(6):709-721
The super-long and large-diameter steel pipe piles are often adopted for the construction of offshore oil platforms in deep sea. One constructability issue related to driving heavy pipe piles is the pile running. The term pile running refers to the quick penetration of a pile into the seabed as a result of its high self-weight and low resistance from the seabed. The unexpected pile running can cause the steel wire of the hammer to break or even the loss of the hammer. A case study of pile running at an oil platform is introduced in this paper. A simplified theoretical method is proposed to explain the mechanisms of the pile running in this case. A factor of friction degradation is proposed to calculate the dynamic skin friction from the static ultimate skin friction of surrounding soil. The comparisons between the predictions to the case history show that the proposed simplified method can be used to predict the pile running condition. 相似文献
16.
FSRU在恶劣环境条件下的作业和安全停靠性能与系泊缆张力、靠垫挤压应力、船体6自由度运动等参数有关。针对FSRU码头处海洋环境条件,进行FSRU不同装载状况的模型实验,获得FSRU的6自由度运动及其系泊载荷的动力特性。基于三维辐射和绕射理论,使用Sesam软件进行频域计算,以此为基础在相应海洋环境条件下进行时域耦合分析,获得FSRU 6自由度运动、系泊载荷、靠垫应力等参数的响应时历。结果表明:30%装载、横浪条件下FSRU的运动响应最大,系泊缆张力未达到破断值,靠垫压力超过其压缩60%时的载荷;模型实验对FSRU运动响应和系泊缆张力的预测结果可信,靠垫受力情况需要数值仿真进行辅助研究。 相似文献
17.
This paper presents a series of full-scale load tests on long bored piles instrumented with strain gauges along the shafts, including eight field tests of piles loaded to failure and one non-destructive pile load test. The load-displacement response, skin friction, end resistance, and the threshold of the pile-soil relative displacement for fully mobilizing skin resistance were discussed. A simple softening model was proposed to describe the degradation behavior of the skin friction along the pile-soil interface and the load-displacement relationship developed at the pile base. It is found that the shaft resistance degradation investigated in the non-destructive load test only occurs at a shallow depth, and the skin friction of deeper soil is not fully developed. However, unlike the results of the non-destructive load tests, the softening is accompanied by a reduction in skin friction and observed to be along the whole pile depth. The thresholds of pile-soil relative displacement for fully mobilizing skin resistances in different soils have been found to be in the range 0.6% to 2.4% of the pile diameter. Moreover, in practical applications, a bilinear model is assumed to be feasible in analyzing the load-settlement relationship developed at the end of non-destructive pile, whereas the load transmission curve of the soils below the pile base corresponds to a softening model in the field tests of piles loaded to failure. 相似文献
18.
-The hydrodynamic coefficients for each of two piles and three piles in both side-by-side arrangement and tandem arrangement under the action of irregular waves are experimentally investigated. These coefficients vary with the KC number, the relative pile spacing, the number of piles and the pile location, and their relationships are presented in this paper. They can be used in Morison Equation and other equations to calculate directly the in-line wave forces and the transverse forces on each pile in array. 相似文献
19.
Study of the Bearing Capacity at the Variable Cross-Section of A Riser-Surface Casing Composite Pile
Reducing the cost of offshore platform construction is an urgent issue for marginal oilfield development.The offshore oil well structure includes a riser and a surface casing.The riser,surface casing and oil well cement can be considered special variable cross-section piles.Replacing or partially replacing the steel pipe pile foundation with a variable cross-section pile to provide the required bearing capacity for an offshore oil platform can reduce the cost of foundation construction and improve the economic efficiency of production.In this paper,the finite element analysis method is used to investigate the variable cross-section bearing mode of composite piles composed of a riser and a surface casing in saturated clay under a vertical load.The calculation formula of the bearing capacity at the variable section is derived based on the theory of spherical cavity expansion,the influencing factors of the bearing capacity coefficient Nc are revealed,and the calculation method of Nc is proposed.By comparing the calculation results with the results of the centrifuge test,the accuracy and applicability of the calculation method are verified.The results show that the riser composite pile has a rigid core in the soil under the variable cross-section,which increases the bearing capacity at the variable cross-section. 相似文献
20.
The pile group with elevated cap is widely used as foundation of offshore structures such as turbines, power transmission towers and bridge piers, and understanding its behavior under cyclic lateral loads induced by waves, tide water and winds, is of great importance to designing. A large-scale model test on 3×3 pile group with elevated cap subjected to cyclic lateral loads was performed in saturated silts. The preparation and implementation of the test is presented. Steel pipes with the outer diameter of 114 mm, thickness of 4.5 mm, and length of 6 m were employed as model piles. The pile group was cyclic loaded in a multi-stage sequence with the lateral displacement controlled. In addition, a single pile test was also conducted at the same site for comparison. The displacement of the pile cap, the internal forces of individual piles, and the horizontal stiffness of the pile group are presented and discussed in detail. The results indicate that the lateral cyclic loads have a greater impact on pile group than that on a single pile, and give rise to the significant plastic strain in the soil around piles. The lateral loads carried by each row of piles within the group would be redistributed with loading cycles. The lateral stiffness of the pile group decreases gradually with cycles and broadly presents three different degradation patterns in the test. Significant axial forces were measured out in some piles within the group, owing to the strong restraint provided by the cap, and finally lead to a large settlement of the pile group. These findings can be referred for foundation designing of offshore structures. 相似文献