The computation and analysis of compactional subsidence of sediments in the modern Huanghe River Delta

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.