Experimental Rheological Characterization And Viscous-Plastic Behavior Modelling Of Rock Salt From Slănic Prahova Under Uniaxial Loading

Abstract The time-dependent behaviour specific to geological formations, known as creep, was investigated through a series of multi-stage uniaxial creep tests, applying six increasing stress increments until reaching the failure stage. The analysis confirmed the presence of the three distinct creep stages: primary, secondary (steady-state or stationary), and tertiary. Based on the strain-time data, it was demonstrated that the relationship between the ultimate axial strain (ε f ) and the final time (t f ) aligns with a power-law model. For modelling secondary creep, Norton’s power law was applied, yielding a stress exponent of n≈1.57 and ln(C)≈−10.74. This relatively low exponent value suggests that diffusion-based creep mechanisms may be dominant. However, the magnitude and non-monotonic variation of the secondary creep rate with respect to stress indicate the limitations of this simplified model, highlighting the microstructural complexity of the salt. In the tertiary creep stage, under the highest applied load (117.6 daN/cm 2 ), a pronounced acceleration of the strain rate was observed. Exponential extrapolation of this phase led to an estimated service life of approximately 123 days before reaching a critical strain of 5 %. The results are significant for calibrating constitutive damage models and for forecasting the long-term stability and lifespan of underground structures within Slănic Prahova salt deposit.