Depositional environment and geotechnical properties of Shanghai clay: a comparison with Ariake and Bangkok clays

Shanghai soft clay was deposited in the Yangtze River Delta in the Late Pleistocene and Holocene eras. The general engineering properties of this clay have been studied in the last few decades. However, limited research on its depositional history and impact on geotechnical properties is available. In this paper, the depositional history of Shanghai clay was reproduced based on sea level changes and other geological information. The unique depositional environment was compared with two other Asian clays, Ariake clay in Japan and Bangkok clay in Thailand. The physical, mineralogical and mechanical properties of different strata were investigated by a series of laboratory tests. It was found that silt-sized grain particles dominated the clay materials and illite is the major clay mineral, while clay-sized grains and smectite are predominant in Ariake and Bangkok clays. The liquid limit, plastic limit and activity are lower than the Ariake and Bangkok clays. Oedometer tests and undrained triaxial tests indicated a less sensitive structure. Stronger hydraulic conditions (faster stream velocity) and the origin of material in the middle and lower reaches of the Yangtze River account for the large amount of silt-sized particles and illite. A less saline depositional environment is the main reason for the weaker structure in Shanghai clay than the two other Asian clays.