Shale creep equation based on chemical pH value characterization

Taking the shale sample in Tangkou coal mine in Shandong province, China, the creep characteristics of different chemical pH values are tested with a triaxial creep tester.Aiming at the influence of chemical pH on the key characteristic parameters of shale creep and combined with the force-chemical coupling effect in creep process, a new force-chemical coupling rheological element is proposed.The creep equation of shale under different pH values is established by nonlinear processing of the creep empirical equation of power exponential and the viscosity coefficient of the viscoplastic body in Burgers model.By analyzing the test results and using the least squares method, the creep equation parameters are determined and the influence law of chemical pH value on the key parameters of shale creep is obtained.Through the sensitivity analysis of the key parameters of the equation, the influence law of the key parameters (including elastic modulus, viscosity coefficient etc.) on the creep characteristics of shale is explored.The model theory curve is in accord with experiment curve in three phases, which indicates that creep equation based on chemical pH value characterization proposed above is capable to describe the whole creep process of corrosion shale, especially the third creep phase.The stronger the chemical acid base is, the larger the exponent β which is related to the properties of shale materials is, the shorter the steady phase of creep is, and the more prone to unstable creep until the rock is unstable and fractured.The acidic condition at pH=3 is stronger than the alkaline condition at pH=10.Based on the fitting analysis of creep test results, the change curve of key parameters of the model with chemical pH value is obtained, and the influence trend of different chemical pH values (acidity and alkalinity) on the key parameters of shale creep is obtained.The results provide a reference and basis for the long-term stability evaluation of rock engineering in underground water corrosive environment in coal mines.