Abstract: With the increasing congestion of underground space facilities, the depths of underground structures are increasing. And the study of deep soils is becoming more and more important. The sedimentary environment of deep soil (the 6th—9th layer clays) in Shanghai was analyzed by studying the sea level and atmospheric temperature changes in the East China Sea since the late Pleistocene. The sedimentary environments of the 6th to the 9th layer clays were found to be lakes, rivers-marinas, lakes and rivers-marinas, rivers. By using the Becker energy method to analyze the results of the high-pressure consolidation test, the over-consolidation ratio of the 8th layer clay was about 3.0. Through the triaxial consolidated undrain test, it was found that the pore pressure coefficient while soil sample failure was negative, showing the characteristics of strong over-consolidated soil. From the perspective of stress and non-stress, the causes of over-consolidation of the 8th layer clay were analyzed. With the groundwater level decreasing, the pore water in the soil dissipated. And the increase of effective stress in the soil was the cause of stress. The long-term secondary consolidation and cementation were the reasons of non-stress.

Key words: deep soil, depositional environment, over-consolidation, high-pressure consolidation