共查询到17条相似文献，搜索用时 109 毫秒
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近年来海上工程的规模越来越大,为了满足工程需要,桩基设计常常采用大直径,大长度的钢管桩。打桩过程是个相当复杂的过程,不仅涉及到几何非线性、材料非线性、边界非线性,而且是个动力过程。有限元法在处理打桩分析方面具有很强的优势,采用PLAXIS对不同条件下的打桩问题进行了动力模拟分析。分析显示在打桩过程中,桩端土体会产生较大的水平位移和竖向位移,桩端土体和靠近桩端的部分土塞内会产生较大的超孔隙水压力。在砂土中,停锤较短时间也会使孔压迅速消散,这也是打桩中间的停锤会造成后续打桩困难的主要原因。 相似文献
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自升式平台桩基土体变形规律与破坏机理分析 总被引：2，自引：0，他引：2
张其一 《中国海洋大学学报(自然科学版)》2012,(11):111-116
研究自升式平台桩基土体的变形规律与失稳机理,对合理评价平台桩基的稳定性具有十分重要的意义。本文基于Galerkin数值分析方法,采用网格重绘与插值技术,利用Abaqus/Stand的牛顿求解方法对平台插桩过程进行大变形分析,较为准确地研究了边界非线性对土体变形规律与破坏机理的影响。通过Abaqus二次开发接口,合理地模拟了桩土界面摩擦特性,以及海床土层剪切强度沿深度非均匀变化特性对海床极限承载能力和破坏机理的影响。揭示了插桩过程中桩周土体的变形规律与失稳模式,给出了插桩入泥深度与极限承载力曲线,并将计算结果同Skempton、Hansen等计算公式进行了合理对比。结果表明:本文给出的桩基土体变形规律与破坏机理,能够较为合理地揭示自升式平台插桩过程中海床土体的大变形特性,以及较为合理地评估自升式平台桩基极限承载能力。 相似文献
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三种不同管土相互作用模型在触地区立管运动模拟中的比较研究 总被引：3，自引：3，他引：0
选择恰当的管土相互作用模型,对于准确描述海洋悬链线立管在触地区的动力响应至关重要。首先总结分析了国内外已有的三类典型管土作用模型,并基于三种模型计算模拟了触地区管道的竖向运动过程,计算结果与试验数据进行了对比验证。选用的三类模型均包括四个管土作用状态,即未接触、初始贯入、上拔和再贯入。研究发现:RQ模型对管道远端管道埋深的预测结果远比试验值小,明显低估了管道的触地区范围;AB模型可以考虑管道的开槽效应,但对于土体强度弱化估算不准,预测的管道埋深远低于试验值;ABY模型能够考虑土体强度的循环弱化,但在模拟管土相互作用时会严重低估土体的强度,预测的管道远端的埋深远大于试验值,这可能导致对管道疲劳寿命的估计错误,需对其进行必要的修正。 相似文献
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海上风电工程主要受到风、波浪及洋流等产生的水平循环荷载作用，本文研究楔形单桩基础在水平循环荷载作用下的变形规律，并探讨不同循环荷载对变形规律产生的影响，以确保风电设施正常运行。通过数值模拟建立海上风电单桩-海床模型，考虑土体超孔隙水压力的演变规律及土体致密规律，土体采用UBC3D-PLM本构模型。本文重点讨论并分析在不同水平循环荷载作用下楔形单桩基础与等截面单桩基础的桩周土体位移、塑性应变及桩基累计转角位移之间的差异。研究结果表明：楔形结构会降低桩周土体位移及塑性应变，使得楔形单桩基础旋转中心位置更低，产生倾覆的可能更小，当循环荷载比为0.7时，累计转角位移能减少41.86%；循环荷载越大，楔形单桩基础水平受荷特性越好，累计位移减少量的增长率越高。研究成果可为今后海上风电基础的选择与设计提供参考。 相似文献
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《海洋湖沼通报》2018,(6)
海底管道一旦受到坠物撞击损伤,会造成严重的环境污染及经济损失,为保证管道在运行期间的安全性,常对其进行埋深处理。对于有埋深的海底管道,坠物的撞击会造成管道上覆土体的大变形,在数值模拟中会导致网格畸变,甚至无法收敛。耦合欧拉-拉格朗日法(CEL法)可有效处理土体大变形问题,本文基于此方法建立了坠物-管道-土体有限元模型,分析了坠物撞击速度、质量、形状、海床土体性质(弹性模量、内摩擦角、黏聚力)、埋深对海底管道塑性变形的影响。结果表明,管道的凹痕深度随坠物撞击速度和质量的增加而增加;坠物与海床土体及管道接触面积越小,管道的凹痕深度越大;管道的埋置深度及海床土体的性质对吸收坠物的撞击能量有直接关系:海床土体的强度越高、埋深越大,管道所受到的损伤程度越小。分析结果可为管道的设计与防护工作提供科学依据,且与现行规范比较,本文方法更加经济、合理。 相似文献
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由于作用荷载复杂,沉入式大圆筒码头结构设计计算需要考虑不利情况下的各种荷载组合,难以应用现有的有限元加载系数法进行稳定性分析。有限元强度折减法目前已广泛应用于土体边坡稳定性分析。沉入式大圆筒结构的抗滑、抗倾稳定性是靠地基土的嵌固作用来维持的,可通过弱化土体强度来实现对结构极限破坏状态的模拟。在此假设基础上,建立沉入式大圆筒码头稳定性分析的有限元强度折减法。结合某工程实例,利用有限元强度折减法分析沉入式大圆筒码头结构的稳定性。强度折减法只需对土体的强度进行弱化,操作方便,克服了加载系数法的缺点,适用于码头等作用荷载复杂的结构物稳定性分析。 相似文献
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针对我国南海某岛礁珊瑚砂地基上的圆形桩基础,采用N-S方程K-s模型、双向耦合方式跟踪流场中颗粒运动轨 迹的方法,对桩周珊瑚砂的冲刷规律进行了求解,分析了桩体周围流体的速度场以及桩体表面剪应力场的分布规律,同时对桩周珊瑚砂冲刷坑的形成过程进行了模拟。计算结果表明,在桩体周围形成的马蹄形漩涡和桩柱后方的尾涡作用下,桩周土体出现了较为明显的冲刷现象,涡旋的释放显著地影响着珊瑚砂地基上桩基的冲刷坑形状;而且,由于珊瑚砂颗粒密度较石英砂小,水动力作用下桩周冲刷坑更容易形成,所以实际工程中需要考虑有效的防护措施。 相似文献
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《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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水射流破坏桩内土塞辅助动力沉桩是一种有效处理土塞问题使桩达到标准贯入深度的辅助沉桩方法,而该项技术的关键是水射流对桩内土塞的破坏。借助理论分析、数值模拟和模型实验进行水射流破坏桩内土塞辅助动力沉桩研究。首先进行射流破坏土塞理论分析,定性地说明水射流破坏土塞能力与水射流压力、流量等参数有关;然后对不同形状喷嘴形成的射流的破坏土塞能力进行数值模拟,得到六种喷嘴射流作用下土塞内的最大、最小应力;再通过模型实验对有无射流辅助沉桩的沉桩锤击数进行对比,结果表明水射流辅助沉桩的锤击数少于无射流辅助沉桩的锤击数,说明水射流可用于辅助动力沉桩。最后设计出水射流破坏桩内土塞辅助动力沉桩工艺步骤。 相似文献
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Stability of many ocean structures is affected by seabed scour induced by under-currents. The depth of scour is an important parameter for determining the minimum depth of foundations as it reduces the lateral capacity of the foundations. A review of the literature reveals that there is not much information available in the field of scour in cohesive soils. Hence, a detailed laboratory testing programme on model piles of diameters 50 mm to 110 mm embedded in soft silty clay soil was carried out in a wave flume of 30 m long, 2.0 m wide and 1.7 m deep, which has the capability of simulating steady currents. Scour around the pile due to steady streaming is monitored by using special instrumentation. A procedure has been suggested to predict the ultimate scour depths based on the observed variation in scour depth over a limited time period. The study indicates that the ultimate scour depth is controlled by diameter of obstruction, current velocity, model Reynolds number, flow Froude number, shear stress, and soil characteristics. Based on these results, a few functional relationships are suggested between scour depth and other parameters like Reynolds number, Froude number, and strength of the soil bed. 相似文献
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The static drill rooted nodular (SDRN) pile is a new type of precast pipe pile with equally spaced nodes distributed along the shaft and wrapped by the surrounding cemented soil. In this paper, the longitudinal dynamic response of the SDRN pile embedded in layered soil is investigated with respect to the complexity of the pile body structure and the pile–soil contact condition. First, the shear complex stiffness transfer model is used to simulate the radial inhomogeneity of the surrounding soil. Then, the governing Equations of the pile–soil system subjected to longitudinal dynamic loading are established. The analytical solution for the dynamic response at the pile head is obtained by the shear complex stiffness transfer method and the impedance function transfer method. The degenerate case of the present solution is compared with the published solution to verify its reliability, and the complex impedance of the SDRN pile is compared with that of the precast pipe pile and the bored pile. Finally, a parametric study is conducted to investigate the influence of pile–soil parameters on the complex impedance at the pile head within the low frequency range concerned in the design of the dynamic foundation. 相似文献
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Zhen-Ya Li 《Marine Georesources & Geotechnology》2017,35(2):256-265
The vertical dynamic impedance of the large-diameter pile is theoretically investigated considering the construction disturbance effect. First, the Rayleigh–Love rode model is introduced to simulate the large-diameter pile with the consideration of its transverse inertia effect. The shear complex stiffness transfer model is proposed to simulate the radial inhomogeneity of the pile surrounding soil caused by the construction disturbance effect. Then, the pile–soil system is divided into finite segments, and the governing equation of the pile–soil system subjected to vertical dynamic loading is established. Following this, the analytical solution of vertical dynamic impedance at the pile head is obtained by means of the shear complex stiffness transfer method and the impedance function transfer method. Based on the present solution, a parametric analysis is conducted to investigate the influence of the transverse inertia effect on the vertical dynamic impedance at the pile head and its relationship with the pile–soil parameters. Finally, comparisons with published solutions are carried out to verify the reliability of the present solution. 相似文献
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单向流条件下单桩桩周冲刷过程特征试验研究 总被引：2，自引：1，他引：1
水流引起桩基周围地基冲刷是海洋工程中的经典课题,由于问题涉及流体动力学和土力学的交叉内容,加之试验技术和计算能力的限制,这一冲刷过程仍有很多方面尚待进一步厘清。开展10组室内水槽试验,研究了不同水深情况下定床和动床冲刷时单桩桩周局部冲刷深度的发展过程。在试验过程中,通过模型桩内放置摄像机实时监测桩周冲刷深度变化,得到桩周冲深边界及最大和最小冲深方位随时间的变化曲线。试验研究发现这一冲刷过程主要特征为:局部冲刷首先发生在桩(侧)前方并逐渐向桩周扩展,而桩后则先发生淤积后再冲刷;水深越大,流速越大,桩后淤积现象持续时间越短,桩周冲刷发展迅速、均匀,但达到稳定所需时间越久;桩周最大、最小冲深点首先分别位于桩的侧前方、桩后区域,随着试验进行会发生转变或波动。 相似文献
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AbstractWith the large-scale development and utilization of ocean resources and space, it is inevitable to encounter existing submarine facilities in pile driving areas, which necessitates a safety assessment. In this article, by referring to a wharf renovation project as a reference, the surrounding soil response and buried pipe deformation during pile driving in a near-shore submarine environment are investigated by three-dimensional (3D) numerical models that consider the pore water effect. Numerical studies are carried out in two different series: one is a case of a single pile focusing on the effect of the minimum plane distance of the pile–pipe, and the other is a case of double piles focusing on the effect of the pile spacing. 相似文献
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AbstractThe ground vibrations during pile driving operation have a drastic potential to undermine the surrounding structures both in land and reclaimed land. Particularly, reclaimed land necessitates ample application of pile driving due to the weak land condition. To prevent the structural damage, attenuation of the ground vibrations to an allowable level through active isolation of circular open trench is the scope of this study. In this research, finite element simulations of continuous impact pile driving process from the ground surface was executed with particular attention to the pile-soil interaction, and thereby, the efficiency of open trench application in attenuation of the unsafe distance of different structures was surveyed using the vibration sensitivity degree. Regarding the crucial parameters of an open trench (depth, width, and location), it was concluded that a sufficient high depth can attenuate the unsafe distance up to 68%, the trench width variations are less effective, and an average pile-trench distance is the most efficient option. The excavation volume was also concluded as another crucial parameter in open trench design which takes all three parameters into account. The trench depth equal to the pile’s maximum critical depth of vibration was inferred for an optimum design. 相似文献