Thixotropic and anti-thixotropic behaviors of fine-grained soils in various flocculated systems

• Thixotropic behavior of low- and high-activity clays is dependent on the time of shearing.
• Larger grain sizes produce larger hysteresis loop areas.
• Low-activity clay experiences a decrease in viscosity with shearing time.
• High-activity clay experiences an increase in viscosity with shear time.

Time-dependent yield stress fluids display hysteresis with respect to reversible and irreversible structural changes. We report an experimental study of the rheological behavior of clay-rich soils (i.e., Mediterranean Sea and bentonite clays) and clay-poor material (i.e., iron mine tailings) that includes steady state, dynamic response, and hysteresis measurement. The Mediterranean Sea and bentonite clays are low- and high-activity clays, respectively. For the materials examined, different thixotropic behaviors are observed as a function of the time of shearing. These materials typically exhibit strong thixotropic behavior for a given shear rate in the limited time of shearing. In general, larger grain sizes produce larger hysteresis loop areas. However, the bentonite clay experiences an increase in viscosity with shear time, regardless of the salinity effect, for sufficiently long shearing times under continuous shear conditions at the shear rate of 1200 s− 1 (the maximum value in the present study). As a result, the flow behavior of clayey soils is strongly influenced by the imposed shearing time.