Nonlinear Rock Creep Constitutive Model Based on Energy Entropy Increase Theory

Triaxial creep tests were conducted on sandstone at 25°C–100°C under three‐dimensional stress to investigate temperature‐dependent creep behavior. An entropy‐dependent nonlinear dashpot was developed by relating entropy production to the evolution of viscous resistance, and a local fractal‐order time‐scaling formulation was introduced to improve the representation of nonlinear time‐dependent deformation. The one‐dimensional formulation was further extended to three dimensions using a pressure‐dependent yield function and plastic potential function. Model parameters were identified using the Levenberg–Marquardt algorithm. The calculated curves showed good agreement with the experimental data, with R 2 values above 0.90, and provided a closer representation of accelerated creep than the classical Nishihara model. The proposed formulation can describe instantaneous, primary, steady‐state, and accelerated creep under the investigated stress and temperature conditions.