An analysis of the factors contributing to the settling potential of fine fluvial sediment

The settling potential of fine sediment is known to be influenced by particle size, shape, density and porosity, and is commonly predicted using Stokes's law, despite its known limitations for modelling the behaviour of natural particles. In order to develop an improved understanding of the potential for fine sediment to settle out of suspension or undergo transport by hydraulic processes, it is important to examine the role of particle structure in detail. In this study, stepwise regression was used to identify which structural properties of particles exert an important control on fine sediment behaviour in river systems. The presence of composite particles and their associated particle size, porosity and fractal dimension were shown to be the most important controls on settling potential. Composite particles that form in the aquatic environment (flocs) were shown to have significantly different form and behaviour from composite particles of terrestrial origin (aggregates). Importantly, it was demonstrated that particle structure and behaviour exhibited consistencies between contrasting river catchments in different locations. An understanding of the mechanisms responsible for the formation of composite particles is viewed as providing a valuable input to efforts to model the mobilisation, transport and fate of fine sediment. Copyright © 2008 John Wiley & Sons, Ltd.     

掺细料砾石土的动孔压特性探讨

地震荷载作用下发生滑坡的滑动带通常由粗颗粒与细颗粒组成。滑带土的动力性质及动孔隙水压力的发展对边坡的稳定性至关重要。对掺细料砾石混合土进行动三轴试验来探讨细料(粒径小于0.5mm)含量对砾石(粒径6~20mm)混合土的动孔压特性的影响,进行细料含量为0%、20%和40%的三组试样的动三轴试验,采用固结围压为100kPa、固结应力比为1.0、频率为1.0Hz,施加轴向动应力分别为0.50、0.55、0.60和0.65kN,得到动孔压的变化规律。试验发现:(1)相同激振力作用下,随着细料含量的增加,动孔隙水压力增长速度逐渐变缓;相同细料含量时,随着激振力的增大,动孔隙水压力增长速度变快。(2)激振力较大和细料含量较少时,动孔隙水压力在较少的振次下达到较大值并趋于稳定。(3)细料含量为20%的砾石混合土试样在试验终止时的振动次数最大,细料含量为40%的砾石混合土在试验终止时的振动次数最小。(4)当细粒含量为0%和20%时,试验终止时最终的孔压都可以接近固结围压;当细粒含量为40%,激振力较大时,试验终止时最终的孔压才接近固结围压,而激振力较小时最终的孔压远远没有达到固结围压。     

荆江大堤下伏饱和粉细砂动力特性试验研究

针对荆江大堤江陵段下伏地层广泛分布的饱和粉细砂,参照原位试验成果重塑粉细砂试样,按估算的固结应力比(Kc约为1.6)对试样动剪模量、阻尼比及总应力动强度进行测试,结果表明:(1)试样应力-应变骨干曲线与Hardin-Drnevich双曲线模型假设高度吻合,Hardin公式可很好地拟合动模量/阻尼比与动应变的关系。在研究试样密实度范围内,最大动模量随围压和密实度的增加而增加,但围压对动模量的敏感性更高,且相同围压下动剪模量比与动应变关系曲线近乎重合。围压增大或密实度升高均会引起阻尼比的降低,1%应变对应的阻尼比分布在0.15~0.21之间;(2)偏压状态下以累积轴向应变5%作为液化判别标准进行抗液化强度试验,随特征振次及测试围压的增大,液化动剪应力比相应减小,试样振动孔压比最高仅能达到0.8~0.9;(3)由总应力法求取的动内摩擦角与黏聚力均随设定特征振次的增加而下降,且内聚力并非约等于0,表明动力作用下该试样具有一定的黏滞性。     

3D主动源地震折射/反射联合快速波前成像研究

基于深地震测深震相记录特征及最新发展起来的快速波前追踪方法,利用理论合成的3D主动源地震折射/反射数据,对强速度对比及复杂Moho结构的重建进行数值模拟计算。结果表明,折射震相Pg对上地壳细结构有较高的分辨,宽角反射震相PmP可较好地约束中下地壳及Moho界面的细结构特征,但对浅部结构的分辨力较差,折射和反射地震的联合成像可有效恢复深浅部3D空间的强速度对比结构及Moho界面形态特征。     

An evaluation of visual and measurement-based methods for estimating deposited fine sediment

A wide range of methods are commonly used to measure deposited fine sediment and quantify substrate quality in rivers as part of bioassessment or monitoring programmes. In this laboratory-based experi-ment known amounts of three sediment types (sand, topsoil, peat) were added to mesocosms and four methods of measuring deposited fine sediment;turbidity, estimation of released sediment, Turner–Hillis deposited sediment sampler (DSS) and visual estimation of%surface cover were evaluated. The objective of the study was to evaluate which of these methods for estimating deposited sediment best dis-criminates between levels of deposited fine sediment added and assesses the effects of inter-observer variability between % surface cover estimations. While turbidity measurement and the resuspension method were strongly related to levels of added sediment, it proved difficult using the two methods to resolve differences between adjacent levels of added sediment e.g. 50 g and 100 g. Surface cover esti-mations were also strongly related to added sediment levels and were better able to distinguish between adjacent levels of added sediment. Furthermore, we found no significant differences between the %surface cover estimations between observers. Results from this laboratory experiment strongly endorse the use of visual estimation of surface cover in field studies. Further work evaluating the turbidity and re-suspension methods under field conditions would also be beneficial.     

X射线断层扫描投影图像背景不一致的校准

在X射线断层扫描(X-ray CT)成像过程中,经常会出现射线源、样品和探测器三者之间的相对移动,导致采集的投影图像(Projection image)以及亮场图像(flat field image)的空间位置配准关系出现偏差。这直接影响了投影图像背景的正常扣除,以及后续的CT图像重建。本文利用互相关方法,求出各投影图像背景与探测器原始采集位置之间的不一致量。然后将投影图像和亮场图像作相应变换,最后扣除背景得到校准后的图像。由于该方法对图像灰度较为敏感,所以在对实际样品校准之前,本文先对该样品投影图像及亮场图像进行了照度归一化。实验结果表明,该方法能够有效校正由射线源、样品和探测器之间相对移动造成的CT投影图像背景不一致,获得较好的CT投影图像和重建切片。      

太北开发区井震结合精细构造描述及应用

太北开发区河道砂体发育规模小,钻遇率低,井网控制程度低,现井网条件下砂体预测精度低,断层认识精度低,单砂体注采关系不完善,开发效果差,开展井震结合精细油藏描述研究.井震结合构造认识成果表明:断层较以往认识结果相比变化较大,利用各类动静态资料分析断层的描述精度,认为井震结合断层描述精度高;井震结合微幅度构造描述更加精细,通过油水井的生产动态变化,研究微幅度构造对开发效果的影响;应用井震结合成果及多学科油藏研究成果,分析断层变化井区的剩余油,指导断层变化井区的补充井布井、注采系统调整及油田外扩调整,均取得较好效果.     

基于图像测量的饱和细砂排水剪切试验研究

将计算机数字图像测量技术应用于土工静力三轴试验的土样变形测量,实现了土样变形的非接触测量。针对南宁饱和细砂,采用干装敲击法和控制不同初始成样含水率的湿装夯实法制备松砂和密砂试样,联合采用数字图像测量技术与常规三轴变形量测方法,在不同围压下进行了固结排水剪切试验。着重探讨了成样方法、初始成样含水率、密实程度、固结围压对两种量测方法所获得的应力-应变关系与邓肯-张模型中的切线模量5参数的影响。试验结果表明：成样方法、初始成样含水率、密实程度和围压决定土样的剪切破坏形式,影响应力-应变关系;剪切破坏的形式以及剪切带位置的不同,导致图像测量和常规三轴试验获得的轴向应变和偏应力数值均存在不同程度的差异;邓肯-张模型5参数不仅受到试样的成样方法、初始成样含水率、密实程度的影响,而且受到量测方法的影响。     

细粒含量对粉土动孔压发展模式影响的试验研究

采用多功能静动液压剪切仪进行了粉土动荷载下的孔压试验,探讨了黏粒含量和粉粒含量对重塑粉土动孔压发展的影响。试验模拟大震时细粒含量影响的孔压发展规律,对已有的指数形式孔压模式进行修正,以便模拟初始液化发生后达到一定液化程度的实际情况,该模式包含2个参数a和b。研究结果表明,细粒含量对粉土动孔压发展影响较大,其影响主要体现在孔压发展模式参数b上。粉土中粉粒含量与孔压参数b的关系呈单调的线性关系,而黏粒含量与孔压参数b的关系则不是单调的线性关系,是在黏粒含量为8 %时孔压参数b达到的最大值,试验数据验证该修正的动孔压模式有更广泛的应用性。     

用反射地震方法研究物理海洋—地震海洋学简介

地震海洋学是通过传统反射地震勘探方法研究物理海洋学的一种新方法.相对于传统的接触式温盐深测量方法,该方法具有较高的横向分辨率和能快速对整个海水剖面成像等优点,是一种非常有前途的新方法.本文将详细阐述反射地震方法在探测海洋锋温盐细结构、刻画水团边界、海洋内波、黑潮等方面的研究进展.目前海水层温度差异主要通过叠加剖面的反射轴振幅计算得到,但是叠加剖面并没有做真振幅处理.为了解决计算过程中的误差,最后提出在地震海洋学仲利用真振幅偏移结果可以使计算更加合理的设想.