Transition from wavelets to ripples in a laboratory flume with a diverging channel   总被引：3，自引：1，他引：2  

William B. RAUEN  Roger A. FALCONER 《国际泥沙研究》2008,23(1):1-12

An experimental investigation on the initiation and development of bed forms on a bed of fine silica sand was conducted under alluvial flow conditions in a laboratory flume with a diverging channel. The main aims of the study were to assess： i） the steepness of bed forms in the transition stage of development; and ii） the threshold height of wavelets （ηt） that triggered the start of ripple development. Detailed bed profile measurements were carried out using an acoustic Doppler probe, traversed longitudinally over the sediment bed at various experimentation times. The bed form dimensions were extracted from such bed profile records and analysed for the wavelet, transition and equilibrium stages. It was found that the steepness of ripples in the transition and equilibrium stages were similar, confirming predictions of previous mathematical model simulations. A lognormal distribution fitted the wavelet length data. The wavelet threshold height was estimated as ηt ≈ 7 mm, or ηt≈ 80 in wall units. Such a height magnitude suggested that ripple development could be triggered by the wavelets reaching the outer flow zone of a turbulent boundary layer. The ηt value obtained corresponded generally to the intersection point between two predictive equations for bed form dimensions. A formulation was developed to predict ηt as a function of the sediment grain size, which was confirmed for the fine sand used in this study.  相似文献   

筒仓与地基相互作用对支承柱端弯矩的影响   总被引：3，自引：0，他引：3  

王命平  孙芳  刘伟  王瑞萍 《世界地震工程》2008,24(2)

对钢筋混凝土柱承式筒仓动力时程分析表明,场地类别对支承柱端弯矩的变化有重要影响,在软弱场地上柱顶弯矩绝对值大于柱底弯矩绝对值;整体性较好的基础可以明显改善支承柱的受力,支承柱合理增设赘余杆也可以改善柱顶受力;文中提出了柱端弯矩增大系数及取值,以考虑地基与结构的相互作用.  相似文献   

Study of vibrating foundations considering soft-pile-structure interaction for practical applications     

Han Yingcai 《地震工程与工程振动(英文版)》2008,7(3)

  相似文献   

Study of vibrating foundations considering soil-pile-structure interaction for practical applications   总被引：1，自引：0，他引：1  

Yingcai Han 《地震工程与工程振动(英文版)》2008,7(3):321-327

An investigation of soil-pile-structure interaction is carried out, based on a large reciprocating compressor installed on an elevated concrete foundation （table top structure）. A practical method is described for the dynamic analysis, and compared with a 3D finite element （FE） model. Two commercial software packages are used for dynamic analysis considering the soilpile-structure interaction （SPSI）. Stiffness and damping of the pile foundation are generated from a computer program, and then input into the FE model. To examine the SPSI thoroughly, three cases for the soil, piles and superstructure are considered and compared. In the first case, the interaction is fully taken into account, that is, both the superstructure and soil-pile system are flexible. In the second case, the superstructure is flexible but fixed to a rigid base, with no deformation in the base （no SSI）. In the third case, the dynamic soil-pile interaction is taken into account, but the table top structure is assumed to be rigid. From the comparison beteen the results of these three cases some conclusions are made, which could be helpful for engineering practice.  相似文献   

双层散体材料桩复合地基固结理论   总被引：1，自引：0，他引：1  

孙举  谢新宇  谢康和 《岩土力学》2008,29(2):321-326

研究了考虑涂抹效应和应力集中效应的双层散体材料桩复合地基固结解析解及其工程应用,分不同情况讨论了特征根的可能变化规律,也讨论了解析解转化为双层竖井地基以及双层天然地基的普遍适用性。研究发现,固结速率随井径比的减小、水平向渗透系数比的增大和桩体刚度的增大而增加;底面排水条件对双层散体材料桩复合地基的固结影响,在井径比不是很大的情况下影响不大;是否考虑应力集中效应对计算结果影响较大。  相似文献   

不排水不可压缩条件下两相介质的两重网格算法     

牛志伟  李同春  赵兰浩 《岩土力学》2008,29(3):800-804

对于不排水、不可压缩饱和软土地基的固结问题的有限元分析,可以用Biot固结方程来考虑土体颗粒与孔隙水间的相互作用。由于受Babuska-Brezzi稳定条件的限制,用常规的等插值u-p混合有限元法求解将导致孔隙压力出现紊乱的结果。提出了基于位移和压力线性等插值函数的两重网格,但位移独立变量总数大于独立压力变量总数的计算方法,可以满足Babuska-Brezzi稳定条件,使得位移场和压力场单元插值阶数保持一致。通过几个简单算例验证了提出方法的正确性。  相似文献   

含圆柱形弹性夹杂地基沉降量的解析解     

王明斌  李术才  李树忱  王兆清 《岩土力学》2008,29(6):1575-1579

研究各向同性地基中含一个圆柱形弹性夹杂的地基沉陷问题。考虑全场的应力、变形特征,运用复变函数的罗朗级数展开技术,构造合适的应力函数,结合夹杂的边界条件和无穷远的性态,获得了全场复势的解析表达。数值结果显示：由于两相材料剪切模量之比的不同,在某个范围内沉陷量大于基底中点沉陷;在这个范围之外,则小于基底中点沉陷。当夹杂埋深为夹杂半径的5倍以上时,就可以运用所得结果,而不致引起太大误差;含圆形隧洞和刚性夹杂的问题可作为特殊情况得到。  相似文献   

刚-柔性桩复合地基变形特性有限元分析   总被引：2，自引：0，他引：2  

朱奎  徐日庆  郭印  周鹏飞 《岩土力学》2008,29(4):937-943

在现场试验基础上对条形基础下刚-柔性桩复合地基进行有限元模拟分析。着重讨论了褥垫层、承台、刚性桩、柔性桩等的参数变化对刚-柔性桩复合地基沉降特性的影响。结果表明,复合地基沉降随着褥垫层厚度减小而减小,随着褥垫层模量增加而减小,承台厚度增加有利于减少差异沉降,刚性桩是控制沉降的主要构件,柔性桩桩长增加可以减少差异沉降。分析结果为刚-柔性桩复合地基的优化设计提供理论基础。  相似文献   

临近基坑既有建筑物地基的抗剪强度指标取值问题     

王红雨 《岩土力学》2008,29(8):2215-2220

基坑开挖不仅改变了半无限空间体边界条件,卸载时还会引起周围地层移动,导致既有建筑物地基承载力的附加损失。在临近基坑既有建筑物地基承载力计算中,其抗剪强度参数的选取有别于斜坡上地基计算参数的常规取值方法。通过探讨临近基坑既有建筑物地基抗剪强度指标的取值问题,建议以地基土的完全软化强度与残余抗剪强度的平均值作为临近基坑既有建筑物地基抗剪强度指标,并据此估算了临近基坑既有建筑物地基承载力。所得结果与斜坡上地基承载力的试验值和理论解对比分析后显示出其具有一定的合理性。所建议的抗剪强度指标取值方法,还有待于试验的进一步验证。  相似文献   

现浇混凝土薄壁管桩复合地基桩土应力比影响因素分析   总被引：3，自引：2，他引：1  

刘汉龙  张波 《岩土力学》2008,29(8):2077-2080

桩土应力比是复合地基设计计算中一个重要参数。基于盐―通高速公路单桩复合地基静载试验,通过有限元模拟,研究了褥垫层模量和厚度、桩体模量、桩长、基础刚度等影响因素对现浇混凝土薄壁管桩复合地基桩土应力比的影响。结果表明所建立的模型是合理的。褥垫层模量增大或厚度减小导致桩土应力比增大,桩体模量、桩长和基础刚度的增加可使桩土应力比增加。  相似文献