New Insights Into Poisson's Ratio Variability in Rocks Under Load

ABSTRACT Poisson's ratio is a fundamental parameter in rock mechanics, traditionally often treated as a constant. This study challenges that notion by developing a universal empirical model that captures its significant stress‐dependency from initial loading to failure. The model was rigorously calibrated using 42 uniaxial compressive tests on granite and successfully generalized to limestone, marl, sandstone, and saltstone, representing a wide spectrum of mechanical behaviors from brittle to ductile. Its predictive accuracy was quantified using root mean square error (RMSE), mean absolute error (MAE), and mean absolute percentage error (MAPE). The model demonstrated high fidelity, particularly at the critical crack initiation stage ( σ / σ c = 0.5), where errors were minimized. Across all five rock types and three calculation methods (secant, average, tangent), the MAPE ranged from 1.4% to 3.7%, RMSE from 0.007 to 0.012, and MAE from 0.005 to 0.010. Performance was superior for ductile rocks like marl (MAPE ≈ 1.9%) and saltstone (MAPE ≈ 1.4%) due to their homogeneous deformation, while effectively capturing the more complex, crack‐dominated response of granite and sandstone. The research conclusively demonstrates that Poisson's ratio is not a fixed material property but a dynamically evolving parameter. This work provides a practical and robust framework that moves beyond the assumption of a constant Poisson's ratio, offering a significant improvement for accurate deformation analysis in numerical modeling, underground excavation design, and reservoir geomechanics.