Time dependent stress–strain behavior of bentonite slurries; effect of thixotropy

• Shear strength increase with time of bentonite slurries is measured and discussed.
• Also for the shear wave velocity of the slurries
• This behavior is attributed to the thixotropy phenomenon.
• Matric suction during the process of thixotropy is also monitored.
• An original and unique adiabatic cell is developed for the experimental program.

Thixotropy phenomenon in soils is usually defined as the gain of shear strength with time developed by some fine grained soils after remolding. This work reports the results of a study focused on the thixotropic phenomenon developed in sodium bentonite slurries saturated with sodium chloride solutions at different electrolyte concentrations. Changes in fabric and structure of the soil during the thixotropic process were monitored indirectly by measuring wave velocity, matric suction, electrical resistance and capacitance, and shear strength. The slurries were placed in a water bath to keep the samples at constant temperature during remolding and subsequent thixotropic hardening. The obtained results show that there is no variation in water tension during thixotropic behavior. Results also suggest that fabric changes occur during the process, which reveals the influence of unbalanced electrical forces at double layer levels. Rising in temperature and lowering in electrical resistance during remolding is attributed to the effect of breaking of bonds between particles. Increase in salt concentration makes double layer shrinks and particles tend to accommodate closer in a more parallel structure. The effect of salt concentration, and consequently the soil structure, becomes relevant in the shear strength of the pastes but it has negligible effect on stiffness.

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