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Analysis of wave-induced liquefaction in seabed deposits of silt 总被引：1，自引：0，他引：1
The dynamic stress introduced in half elastic space by wave loading is characterized by the equation between the magnitude of half cyclic axial stress and cyclic torsion shear stress and the principal stress,whose direction rotates continuously and compression stress on seabed can be calculated by the use of small amplitude wave theory.With relationship curves of saturated silt of liquefaction cycles and cyclic stress ratios obtained by cyclic triaxial-torsional coupling shear tests and curve fitting method to different data points of relative density,it is suggested that the cyclic stress ratio corresponding to constant liquefaction impedance be taken as the critical cyclic stress ratio which implies liquefaction.There exists a linear relationship between critical cyclic stress ratio and relative density under different relative densities.Empirical formula for critical cyclic stress ratios of seabed liquefaction induced by wave loading under different relative densities is established.The possibility of seabed silt liquefaction and its influence factors are analyzed based on the small-amplitude wave theory and the data acquired in laboratory tests. 相似文献
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Sediment incipient motion is a fundamental issue in sediment transport theory and engineering practice. Silt has transitional behavior between cohesive and non-cohesive sediment and its incipient motion is still poorly understood. This study aims to find an expression for incipient motion from silt to sand from a unified perspective and analysis. From the analysis of forces, using the derivation method for the Shields curve, an expression for sediment incipient motion is proposed for both silt and sand under conditions of combined waves and currents. The differences and similarities in the sediment motion threshold were analyzed under the effects of waves and currents, and fine and coarse sediment. The Shields number was revised by introducing the cohesive force and additional static water pressure, which indicates that this study could be seen as an extension of the Shields curve method for silt. A number of experimental datasets as well as field data were used to verify the formula. The effect of bulk density on fine sediment was discussed and tested using experimental data. 相似文献
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现代黄河三角洲沉积物临界剪切应力研究 总被引：2，自引：1，他引：1
为研究现代黄河三角洲沉积物临界剪切应力空间分布特征及其影响要素,本文在现代黄河三角洲不同沉积区域,垂直海岸线布设测线,采用黏结力仪进行沉积物临界剪切应力测试,并在相应测点开展沉积物物理力学性质与粒度成分测量工作。研究结果表明高潮滩沉积物临界剪切应力最高,在1.1~4.02Pa之间,沉积物不易发生侵蚀,含水量低、干容重大、黏粒与粉粒含量高、平均粒径小、不排水剪切强度大是高潮滩沉积物临界剪切应力偏高的重要因素;中潮滩沉积物受生物活动影响显著,临界剪切应力在0.10~1.90Pa之间,生物活动扰动、生物排泄及遗体遗迹的程度与数量是造成不同区域测试差异的重要原因;低潮滩沉积物临界剪切应力很低,在0.08~0.80Pa之间,沉积物极易发生侵蚀,含水量高、干容重偏低、砂砾含量高、平均粒径大、不排水剪切强度小是其典型的沉积物物理力学性质,也是造成低潮滩沉积物临界剪切应力普遍低于高潮滩的重要原因;现代黄河三角洲沉积物临界剪切应力区域特征表现为北部沉积物临界剪切应力水平最低,在0.11~0.4Pa之间,东部最高,在2.8~4.55Pa之间,南部与东北部居中,分别在0.63~0.84Pa与0.83~2.99Pa之间,东北部空间非均匀性分布显著,粒度组分的分异是导致沉积物临界剪切应力区域差异显著的重要因素,黏粒含量高的沉积区域沉积物临界剪切应力普遍高于砂砾含量高的沉积区;与世界其他大型河口三角洲相比,现代黄河三角洲沉积物临界剪切应力水平偏低但非均匀程度较高。 相似文献
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The characteristics of dynamic stress in the seabed under wave loading are constant principal stress and continuous rotation of the principal stress direction.Cyclic triaxial-torsional coupling shear tests were performed on saturated silt by the hollow cylinder apparatus under different relative densities,deviator stress ratios and vibration frequencies to study the development of pore water pressure of the saturated silt under wave loading.It was found that the development of pore water pressure follows the trend of "fast～steady～drastic".The turning point from fast to steady stage is not affected by relative density and deviator stress ratio.However,the turning point from steady to drastic stage relies on relative density and deviator stress ratio.The vibration cycle for the liquefaction of saturated silt decreases with increasing deviator stress ratio and increases with relative density.The vibration cycle for the liquefaction of the saturated silt increases with vibration frequency and reaches a peak value,after which it decreases with increasing vibration frequency for the relative density of 70%.But the vibration cycle for the liquefaction of saturated silt increases with vibration frequency for the relative density of 30%.The development of pore water pressure of the saturated silt is influenced by relative density and vibration frequency. 相似文献
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Incipient Motion of Sediment Under Currents 总被引：4，自引：3，他引：4
DOU Guoren 《中国海洋工程》2000,14(4):391-406
Summarized in the paper are the author's studies on incipient motion of sediment in recent 40years.In addition to the forces of gravity,drag and lift,the cohesive force and the additional static pres-sure are important for fine particles.The relations between three stages of incipient motion are defined byuse of instantaneous velocity.Formulas for initial velocity and critical shear stress are given and overallverified by the author's and others'experimental data. 相似文献
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通过黄河三角洲埕北海域表层沉积物的粒度资料、实测潮流数据以及50 a一遇的波浪要素,分析了埕北海域表层沉积物的分布类型以及粒度参数特征,并计算了表层沉积物的临界起动应力、日平均单宽输沙通量以及波流共同作用下的单宽推移质输沙率。结果表明:研究区表层沉积物主要是粉砂质砂、砂质粉砂、粉砂和泥四种,分选中等偏差,近对称到正偏,中等尖锐到尖锐峰态;对大潮期间埕北海域潮流底应力和表层沉积物的临界起动应力的计算说明潮流在大部分区域具有起动和输运泥沙的作用;秋季潮流作用下的日平均单宽输沙通量均值为372.32 kg/（m·d）,方向为涨潮流向。利用贝克尔（Bijker）和经典的Van Rijn公式计算出的50 a一遇的波流共同作用下单宽推移质日平均净输沙率结果近似相等。 相似文献
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动荷载作用下海底粉土的孔压响应及其动强度 总被引：5，自引：0，他引：5
本文选用近海分布较广的粉土为研究对象 ,利用室内动三轴试验结果 ,找出动荷载作用下粉土的动应力应变关系 ,分析模拟波浪荷载作用下粉土中的孔压响应、临界循环次数 ,确定波浪作用下粉土的应力状态、破坏临界循环次数 ,判断不同深度处的粉土发生液化的可能性及发生液化所需要的时间 ;研究粉土在动荷载作用下的强度降低 ,为海上工程设计和施工提供科学依据。 相似文献
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Rheological Properties and Incipient Motion of Cohesive Sediment in the Haihe Estuary of China 总被引：2，自引：1，他引：2
The Haihe cohesive sediment, which is typical in China, is studied systematically for its basic physical and incipientmotion properties. Following the requirements of dredging works in the Haihe Estuary, cohesive sediment samples weretaken from three locations. Laboratory experiments were conducted to determine the rheological properties of these sam-ples and to examine the incipient motion of the cohesive sediment. It is found that the cohesive sediment has an obviousyield stress τb, which increases with the mud density in a manner of an exponential function, and so does the viscosityparameter η. The cohesive sediment behaves like a Bingham fluid when its density is below 1.38 ～ 1.40 g/cm3, andwhen denser than these values, it may become a power-law fluid. The incipient motion experiment also revealed that theincipient velocity of the cohesive sediment increases with the density in an exponential manner. Therefore, the incipientmotion is primarily related to the density, which is different from the case for non-cohesive sediment in which the incipi-ent motion is correlated with the diameter of sand particles instead. The incipient motion occurs in two different ways de-pending on the concentration of mud in the bottom. For sufficiently fine particles and a concentration lower than1.20 g/cm3, the cohesive sediment appears as fluidized mud, and the incipient motion is in the form of instability of aninternal wave. For a higher concentration, the cohesive sediment appears as general quasi-solid-mud, and the incipientmotion can be described by a series of extended Shields curves each with a different porosity for newly deposited alluvial mud. 相似文献
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Prediction of threshold conditions and incipient motion is the essential issue for the study of sediment transport. This work compares existing empirical threshold curves proposed for Shields diagram, a method based on the concept of probability of sediment movement, and an empirical method based on movability number. These methods are used to predict the incipient motion conditions for experimental runs taken from various studies. Most of the experimental data, used in this work, have not been used before in derivation of alternative formulations for Shields diagram and other methods. The empirical threshold curves based on the Shields entrainment function was the least successful at predicting the measured incipient motion conditions, while the use of the movability number gives good predictions of critical shear velocity compared with experimental data. 相似文献
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We consider steady, slowly varying water waves propagating on a steady current over a gently sloping bed, so-called current depth refraction. All expressions are correct to second order in wave amplitude. Formulating the energy equation for the fluctuating motion in terms of wave action (wave energy divided by intrinsic angular frequency) results in an expression, where the dissipative term is strikingly similar to wave action itself. It is simply the ‘extra’ dissipation (per unit area) caused by the fluctuating motion (i.e. total dissipation minus the effect of current acting on total mean bed shear stress) divided by the intrinsic angular frequency. We call it ‘wave action dissipation’. An inconsistency in Phillips' (1977) book is pointed out. A new formula for the calculation of wave amplitudes along rays is set forth. 相似文献
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本文基于OpenFOAM建立三维波浪数值水槽,模拟计算植被水域波浪作用下的床面切应力,分析了入射波高、植被密度、植被淹没高度、水流对植被水域波浪作用下床面切应力的影响。结果表明:纯波时,由于植被的阻水作用,植被水域床面切应力沿程衰减,其衰减程度与入射波高、植被密度及植被淹没高度呈现正相关;与纯波时相比,在波浪和同向流共同作用下正向床面切应力幅值增大,负向床面切应力幅值减小;弱水流对植被水域床面切应力的大小及分布无明显影响;强水流时,床面切应力在植被水域先增大后逐渐减小并在植被水域后显著降低。 相似文献
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使用波潮仪、流速计以及浊度计现场测量记录海堤前的波高、潮高、流速和浊度值,与室内测定的浊度和水中悬浮颗粒物含量对应值比较,分析计算浊度与现场测量波高、潮高、流速水动力因素间的相关性,得出堤前泥沙起动的决定性水动力因素。在悬移质运移为主情况下,由于海堤的阻挡,波浪破碎产生的旋涡和紊动是泥沙起动的主要动力因素,泥沙起动量与波高值呈现较高相关性;海堤前复杂水动力条件中,波浪破碎前的流速值与悬移质泥沙起动量相关系数较小,启动流速的主要组成部分是破波产生的旋涡和紊动的流速。 相似文献
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为准确把握新鹤海湾的演变特征和水动力条件,采用现场观测和GIS技术对其地形变化、冲淤分布和冲淤量进行探讨,并利用数值模拟分析波浪、潮流和泥沙共同作用对海湾演变的影响。结果表明:海湾演变对连续台风的响应不同,表现为先冲后淤,其中苏拉作用下的冲刷量为台风过境后全年的2倍左右;受东南季风的影响,春夏冲淤幅度较大,海湾冲淤分布为南冲北淤,波高分布不均与涨潮流入湾时的向北偏转是其主要原因;波流共同作用下的底床切应力约为潮流单独作用时的10倍,波浪是导致海湾冲刷的主要因素,常浪下底床切应力小于临界冲刷应力,泥沙不易起动,因此海湾冲刷主要是由极端天气时的大浪所导致的。 相似文献
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The behaviors of granular material and influencing factors under complex dynamic loading are studied by more and more researchers with particle flow method. Only the strain-controlled loading has been generally used in the current study, although this method was not consistent with the practice of engineering in many situations. In this article, stress-controlled dynamic simulation tests were carried out with particle flow method, which were used to study the collapse characteristics of silt under mutation of principal stress orientation. The tests were performed by PFC2D. The simulation results and the laboratory real tests’ results had a high degree of similarity, particularly in the collapse strain and vibration times. It was very useful to forecast the silt's critical failure state. Based on the verification data, the effects of confining pressure and cyclic shear stress ratio on the collapse characteristics of silt were studied further. With the increase of cyclic shear stress ratio, the deviator strain amplitude increased and the required vibration times gradually reduced to achieve the same strain level. Under the same dynamic shear stress ratio and vibration times, the initial dynamic elastic modulus slightly increased with the increase of initial confining pressure, and the variation range of final collapse deviator strain was small. In the analysis of micro-structural evolution, the redistribution of internal stress of sample was revealed during cyclic loading. With the increase of vibration times, the development of distribution gradually stabilized, and then the high shear stress appeared in some connected regions. On that stage, the particle system developed to instability and failure. The PFC simulation results confirmed that the collapse state was the critical stage to trigger the liquefaction of silt. 相似文献
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Gil Y. Kim Hong J. Yoon Jin W. Kim Dae C. Kim Boo K. Khim Seok Y. Kim 《Marine Georesources & Geotechnology》2007,25(1):37-51
This study was undertaken to investigate the implication of geoacoustic behaviors in the shallow marine sediments associated with the changes in geotechnical index properties. Two piston cores (270 cm and 400 cm in core length) used in this study were recovered from stations 1 and 2, the western continental margin, the East Sea. Scanning electron microscopy (SEM) was employed to illustrate the effects of microstructure on shear properties. The direct SEM observation of sediment fabrics is inevitable to understand the correlation of the changes in geoacoustic properties to the sediment structure. The consolidation of sediments by overburden stress resulting in the clay fabric alteration appears to play an important role in changing shear properties. Water contents and porosity of sediments gradually decreases with increasing depth, whereas wet bulk density shows a reverse trend. It is interesting to note that shear wave velocities increase rapidly from 8 to 20 m/s while compressional wave velocities significantly fluctuate, ranging from 1450 to 1550 m/s with depth. The fabric changes in sediment with increasing depth for example, uniform grain size and well oriented clay fabrics may cause the shear strength increase from 1 to 12 kPa. Shear wave velocity is, therefore, shown to be very sensitive to the changes in undrained strength for unconsolidated marine sediments. This correlation allows an in-situ estimation of shear stress in the subsurface from shear wave velocity data. 相似文献