It is important to investigate the rheological properties of soft muds in considering the transport process of bottom materials in sea area or estuaries. In this study, rheological properties of muds under various conditions were investigated by using a coaxial-type rotary vise-meter.
　In the field, bottom mud suffers a shear stress under the action of ocean waves. In this case we can make a rough estimate of a strain velocity D(=du/dz) in mud as D<10s-1. In this study, the strain velocity D was set less than 10s-1 in measuring a flow curve. In the first place, several kinds of muds were used to get flow curves and compared each other. Various factors which affect the rheological properties of muds such as temperature, salt concentration and changing rate of strain velocities were also examined.
In this study, we obtained the following conclusions:
1)Soft muds can be treated as Bingham fluid in the range of very low strain velocities (D<1s-1).
2)Yield stresses and plastic viscosities of muds are dependent on the rate of water content and decrease with a power of water content.
3)Bentonite clay is strongly affected by salinity. The increase in salinity makes bentonite more fluidity.