Stratigraphic Sequence and Deposition-affected Compressibility of Fine-grained Sediments in the Ancient Yellow River Delta during the Late Pleistocene and Holocene

To investigate the stratigraphic sequence in the ancient Yellow River Delta and further discuss the correlation of compressibility of undisturbed soils with depositional environments, two boreholes were drilled at Liyao test site in Cangzhou, Hebei Province, China. Some basic tests regarding to index properties were performed on sediments from one borehole, and oedometer test was conducted for the “undisturbed samples” collected from the other. The stratigraphic sequence in the study area is classified into four depositional systems in terms of sedimentation environment. Evaluation of sample disturbance shows that the “undisturbed samples” for oedometer test are just slightly disturbed in the sampling process. Since overall compressibility can be divided into intrinsic compressibility and additional one, the environmental factors that can affect soil microstructure are closely correlated with additional compressibility. Thus, the influencing mechanism of depositional rate on additional void index ΔI, was investigated quantitatively. Moreover, the relationship between floating range of yield stress and buried depth is established. Then, the additional compressibility of undisturbed samples can be evaluated with depositional rate and buried depth. Finally, the predicted overall compression curve with the proposed method in this study is compared with the measured curve to verify the reasonability and feasibility.