Based on the laboratory and in situ seismic piezocone tests (SCPTU), comprehensive analyses of soils sampled from the Yangtze River floodplain at the Nanjing Fourth Bridge site were conducted, including the fine division of the soil layer, permeability evaluation of clayey soils and hydraulic conductivity prediction. It is shown that the measured parameters of SCPTU (qt、fs、u2) can be used effectively for profiling the highly layered and heterogeneous deposits in the Yangtze River floodplain, especially for identifying the soil interfaces, thin permeable or impermeable interlayers. Based on the dissipation of excess pore pressure in the process of SCPTU testing, the permeability of the complicated mixed soils can be evaluated. Based on SCPTU, the predicted kh values show significant discreteness. It is observed that the lab measured kh values are generally lower than those estimated from SCPTU within 1-2 orders of magnitude. The results from Burns & Mayne method (2002) can be used in the planning phase of civil engineering works. It is suggested that such an enhanced seismic piezocone test should be considered to be a new tool for the dewatering design of foundation pit engineering.