现代黄河三角洲沉积层压实下沉的计算分析
The computation and analysis of compactional subsidence of sediments in the modern Huanghe River Delta
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摘要: 1855年以来形成的厚度为15 m的现代黄河三角洲分流叶瓣在遭废弃后的最近30 a内的沉积压实幅度为2.28～3.87 m,年平均压实量达0.1 m,其中黏土质粉砂被压实了25.8%,粉砂沉积地层被压实了15.2%,黏土质粉砂的沉积压实量是粉砂沉积压实量的1.7倍,在此期间基本上完成了三角洲压实下沉过程。下伏沉积地层的压缩量有限,不同沉积年代的沉积压实下沉量相差小,如厚度为20～30 m的沉积压实量仅有0.2～0.28 m,其中黏土质粉砂被压实了0.91%,粉砂被压实了1.19%,沉积地层平均被压实了1%。无论是黏土质粉砂还是粉砂,孔隙度与沉积地层深度呈负指数函数关系,黏粒含量愈高,孔隙水则愈难以排出,覆盖在下伏沉积地层上面的表层沉积物对压实下沉贡献愈大。Abstract: The abandoned lobes of the modern Huanghe River Delta since 1855 have reached 15 m in thickness if not compacted. And the sedimentary compaction subsidence in the abandoned delta lobe varied between 2.28 and 3.87 m after passing 30 a, and the average compactional degree reached about 20.5%. The compactional subsidence of clayey silt is about 1.7 times than that of the silt.The compactional proportion of clayey silt is about 25.8% and silt is about 15.2%. which indicates that the compaction processes have been basically completed. On the other hand, the compaction subsidence of the underlying layer was quite limited. Theoretically, the compactional subsidence of the layer differed insignificantly with each other. For example, in the depth range of 20～30 m, the compaction subsidence varied between 0.2 and 0.28 m, namely, for the 24.4 m thickness underlying sedimentary layer, the compaction subsidence was 0.24 m and the average annual compaction subsidence was only 0.008 m. The average compaction ratio of clayey silt was 0.91%, while that of silt was 1.19%, and hence the average compaction ratio of the whole sedimentary layer was about 1%. During the process of compaction in both of types, there was a negative exponential function relationship between the porosity and depth of sedimentary layer, and the higher the clay content, the harder the pore water was drained or discharged. The sediments on the underlying sedimentary layer contributed more value to the compactional subsidence.
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Key words:
- Huanghe River Delta /
- compactional subsidence /
- sedimentation /
- porosity
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