ON THE STABILIZING INFLUENCE OF SILT ON SAND BEDS
ON THE STABILIZING INFLUENCE OF SILT ON SAND BEDS
复制标题
DOI：
10.2110/jsr.2013.57
复制
发表时间：
2013-07-01
影响因子：
2
通讯作者：
Huhn, Katrin
中科院分区：
文献类型：
--
作者：
Bartzke, Gerhard;Bryan, Karin R.;Huhn, Katrin
在海洋环境中，来自不同来源的沉积物被搅拌和分散，形成由不同粒度的混合和层状沉积物组成的床。然而，用于预测侵蚀阈值的传统工程公式通常是针对单峰沉积物分布的，因此可能不适用于常见的沿海沉积物。我们在实验室环形水槽中测试了由简化的两粒级(粉砂(D-50=55微米)和沙(D-50=300微米))组成的淤积和混合泥沙床的输移特性，目的是研究控制泥沙床稳定性的参数。为了模拟最近大型风暴事件后颗粒的沉积以及细颗粒在粗沉积物中掺入的长期结果，我们设计了两套实验：(1)“分层实验”：在沙床上覆盖一层不同厚度的薄粉砂(0.2-3毫米；0.5-3.7wt%，在10厘米深的一层干重)；(2)“混合实验”，床层由沙子和少量粉砂均匀混合(0.07-0.7wt%，干重)。为了在两种情况下引发侵蚀并检测可能的稳定效果，我们将流速递增至0.30m/S。结果表明，沉积物床(或在分层实验中的下垫层砂床)随着粉砂成分的增加而稳定。泥沙稳定性增加的定义是，初始门槛条件向更高的水流速度转变，在混合床的情况下，结合侵蚀速率的降低。我们的结果表明，即使是极低浓度的泥沙也起到了稳定作用(10厘米厚的层状沉积床上的泥沙含量为1.4%(wt%))。在混合沉积物床的情况下，0.18%的泥沙(重量%，在10厘米深的样品中)稳定了床。这两种情况都表明，沉积物组分的沉积历史可以改变海床的侵蚀特征。这些观察结果在一个概念模型中进行了总结，该模型表明，除了对表面粗糙度的影响外，粉砂还通过堵塞孔隙空间和减少床层中的流入来稳定砂层，从而增加了床层的稳定性。对相似床组合的渗透系数的测量定性地支持了这一结论，表明在层状床的情况下，泥沙可以使渗透率降低22%，在混合床的情况下，可以使渗透率降低70%。
In marine environments, sediments from different sources are stirred and dispersed, generating beds that are composed of mixed and layered sediments of differing grain sizes. Traditional engineering formulations used to predict erosion thresholds are however, generally for unimodal sediment distributions, and so may be inadequate for commonly occurring coastal sediments. We tested the transport behavior of deposited and mixed sediment beds consisting of a simplified two-grain fraction (silt (D-50 = 55 mu m) and sand (D-50 = 300 mu m)) in a laboratory-based annular flume with the objective of investigating the parameters controlling the stability of a sediment bed. To mimic recent deposition of particles following large storm events and the longer-term result of the incorporation of fines in coarse sediment, we designed two suites of experiments: (1) "the layering experiment": in which a sandy bed was covered by a thin layer of silt of varying thickness (0.2-3 mm; 0.5-3.7 wt %, dry weight in a layer 10 cm deep); and (2) "the mixing experiment" where the bed was composed of sand homogeneously mixed with small amounts of silt (0.07-0.7 wt %, dry weight). To initiate erosion and to detect a possible stabilizing effect in both settings, we increased the flow speeds in increments up to 0.30 m/s. Results showed that the sediment bed (or the underlying sand bed in the case of the layering experiment) stabilized with increasing silt composition. The increasing sediment stability was defined by a shift of the initial threshold conditions towards higher flow speeds, combined with, in the case of the mixed bed, decreasing erosion rates. Our results show that even extremely low concentrations of silt play a stabilizing role (1.4% silt (wt %) on a layered sediment bed of 10 cm thickness). In the case of a mixed sediment bed, 0.18% silt (wt %, in a sample of 10 cm depth) stabilized the bed. Both cases show that the depositional history of the sediment fractions can change the erosion characteristics of the seabed. These observations are summarized in a conceptual model that suggests that, in addition to the effect on surface roughness, silt stabilizes the sand bed by pore-space plugging and reducing the inflow in the bed, and hence increases the bed stability. Measurements of hydraulic conductivity on similar bed assemblages qualitatively supported this conclusion by showing that silt could decrease the permeability by up to 22% in the case of a layered bed and by up to 70% in the case of a mixed bed.