Effect of Quaternary transgression and regression on the engineering properties of Shanghai soft clays

The engineering properties of marine clays are closely related to its depositional environment. However, the correlation between the chemical properties and depositional environment and their effect on engineering properties of upper Shanghai marine clay are still pending. The sedimentary processes of upper Shanghai marine clays from the Quaternary transgression, the correlation between the chemical properties and its depositional history are investigated in this study based on a series of laboratory experiments. The distribution of chemical indicators (e.g., pH value, oxidation-reduction potential and salt content) with depth showed that the depositional environment directly affected the chemical properties of the soil layer. The correlation of salt content with sensitivity, liquid limit and liquidity index in upper Shanghai layers represents a unique two-stage distribution, with the boundary at the bottom of the Layer-4 clay. The two-stage distribution is caused by the Quaternary transgression and regression, which is confirmed to have different effects on the salt content, sensitivity, liquid limit and liquidity index. The quantitative approaches used to evaluate the correlation between depositional environment, chemical and mechanical properties can provide valuable references for investigating the engineering properties of soft clays.