Experimental study on rheological properties of soft mud in Yangtze River Estuary

In order to clarify the soil mechanical properties of soft mud in the Yangtze River Estuary under shear loads, experimental study by using Anton Paar MCR302 rotary rheometer was conducted to examine the rheological responses of the mud to shear forces, especially on the basic rheological property of the mud with bulk density ranging from 1.16 to 1.72 g/cm³, as well as the associated influences of bulk density, salinity, pH value and temperature. The results showed that under the action of shear loads, the mud in the Yangtze River Estuary exhibits Bingham fluid characteristics, and the relationship between shear stress and shear rate can be quantitatively described based upon the Dual-herschel-bulkley rheological model. With the increase of shear rate, the complex phase transformation process from solid to liquid of the mud was observed which can be classified into three typical stages:solid-like stage, solid-liquid transition stage and liquid-like stage, corresponding to the elastic, viscoelastic and plastic material respectively. The shear strength of the mud increases with the increase of bulk density, salinity and pH value, and decreases with the increase of temperature. Finally, with the measured results, an empirical constitutive equation was established to describe the rheological behaviors of the mud, that can be applied for quantitative analysis of the mud movement under hydrodynamic forces such as tides and waves.