Behaviour and engineering implications of recent floodplain soft soil along lower reaches of the Yangtze River in Western Nanjing, China

Recent floodplain soft soil is widespread along the lower reaches of the Yangtze River in western Nanjing, China, an area of new residential development and underground space utilisation such as subway lines and tunnels under rivers in Nanjing city. Construction experience in this area in the last two decades shows that ground and underground engineering are susceptible to accidents. The accidents are fundamentally due to the lack of a clear and detailed understanding of the geotechnical and geological properties, in particular the differential consolidation settlement of the soft soil. In this context, this paper studies the behaviour and engineering implications of such soil. First, we present the soil's geological background and sedimentary features, test its geotechnical properties, and identify its material composition by X-ray diffraction and SEM. Then, we investigate changes of microstructure at different depths and under different applied loadings, and corresponding engineering implications under consolidation and compression. Finally, by referring to a microstructure classification system for marine sediment, we suggest a combined type of microstructure for the floodplain soft soil.