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Monitoring and characterisation of sand-mud sedimentation processes

机译：砂泥沉降过程的监测和表征

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Estuaries and tidal inlets are often characterised by the presence of both cohesive and non-cohesive sediments. Knowledge of the sedimentation behaviour of sand-mud mixtures is therefore crucial to the understanding and prediction of the time-dependent structure (i.e. mixed or segregated), composition and erodibility of sediment bed deposits developing within these environments. In the current study, a series of settling column tests are conducted to investigate the hindered settling and initial bed consolidation phases of a range of sand-clay mixtures to determine the parametric conditions under which bed segregation occurs. A new, non-invasive, electrical resistivity measurement technique is employed to capture both temporal and spatial changes in the density, porosity and composition of the evolving sand-clay bed deposits, complimented by time-lapsed images of the sedimentation process within the column. The results show that the formation of segregated (sand-clay) bed layers with bed deposits is largely controlled by the initial fractional composition (i.e. relative sand and clay concentrations). Specifically, mixtures with low clay contents are shown to form well-defined (sand-clay) layer segregation within the resulting deposits, while higher clay contents result in more transitional segregation patterns or no layer segregation (for very high clay concentrations). The physical mechanisms under which these different segregation types can be generated are illustrated through predictions from an existing polydisperse hindered settling model. This model indicates that the degree of bed segregation, and time scale over which this occurs, correlates well with the difference in predicted hindered settling characteristics and upward displacements associated with the sand and clay fractions, respectively. In this regard, the new experimental dataset provides validation for the polydisperse model (for the first time), with the combined data and model predictions providing new insight into mixed (sand-clay) sedimentation processes.
机译：河口和潮汐口的特征通常是同时存在粘性和非粘性沉积物。因此，了解泥浆混合物的沉积行为对于理解和预测随时间变化的结构（即混合或分离的结构），沉积物在这些环境中的沉积物的组成和易蚀性至关重要。在当前的研究中，进行了一系列沉降柱测试，以研究一系列沙土混合物的受阻沉降和初始床固结阶段，以确定发生床偏析的参数条件。一种新的，非侵入性的电阻率测量技术被用来捕获正在演化的砂粘土床沉积物的密度，孔隙度和组成的时间和空间变化，并辅以该柱内沉积过程的延时图像。结果表明，具有床沉积物的分离的（砂土）床层的形成很大程度上受初始分数组成（即相对的沙子和粘土浓度）控制。具体而言，低粘土含量的混合物显示出在所形成的沉积物中形成明确的（砂土）层偏析，而较高的粘土含量导致更多的过渡偏析模式或无层偏析（对于非常高的粘土浓度）。通过对现有多分散受阻沉降模型的预测，说明了可以生成这些不同隔离类型的物理机制。该模型表明，层分离的程度及其发生的时间尺度，分别与预测的受阻沉降特征和与沙子和粘土组分相关的向上位移的差异具有良好的相关性。在这方面，新的实验数据集首次验证了多分散模型，并结合了数据和模型预测，为混合（砂土）沉降过程提供了新的见识。

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