DEPOSITION HISTORY AND ENGINEERING CHARACTERISCS OF THE HUGE THICK SOFT SOIL IN OUJIANG ESTUARY

Oujiang is the second largest river in Zhejiang province, and Oujiang estuary is a typical area where soft soil is distributed in China. Oujiang estuary has experienced three transgressions in Quaternary Period, and three layers of soft soil was formed ever since. The transgression which happened in Holocene Epoch is the largest in scale, Yetthe deposition history and engineering characteristics of the three layers of soft soil formed duringtransgressions have not been compared or studied. On the basis of studying the deposition history and distribution characteristics of soft soils formed in different deposition stages, the physical and mechanical properties of the soft soil were studied and compered. It was found:as the stratum become newer, the physical properties and the struct of the soft soil become weaker, the sensitivity of the soil become more remarkable. In the relationship between physical and mechanical indexes, the water content of the silty soft soil which is formed in Holocene Epoch is in good linear relationship with wet density, compressibility coefficient and void ratio. As the deposition history extended, the linear relationship between indexes was no longer remarkable, the discreteness enhanced. Specially, as the deposition history extended, the horizontal permeability coefficient enhanced remarkably and the vertical permeability coefficient decreased gradually, the multiple can be up to 10 times.