Creep property and model of red sandstone under low temperature environment

In order to study the long-term stability of rock mass engineering in low temperature environment,multi-level loading and unloading uniaxial creep tests were conducted on Shaanxi saturated red sandstones at different temperatures (20,-10,-20 ℃ ) using MTS810 rock mechanics testing machine. The creep property of red sandstone under different temperature conditions and the effect of temperature on rock creep properties were studied. According to the creep tests results,the total strain of the rock sample was divided into instantaneous strain and creep strain,the instantaneous strain consists of instantaneous elastic and instantaneous plastic strains,and the creep strain consists of viscoelastic and visco-plastic strains. The results show that the instantaneous strain increases with higher stress level,and the relationship between the instantaneous elastic strain and the stress can be described by approximate linear expression. The visco-plastic strain keeps increasing with time,and the proportion of visco-plastic strain in the total strain also tends to increase when the stress is higher. The instantaneous deformation and creep deformation of the rock sample decreases with the temperature drop. The creep duration is prolonged. The damage strength of rock is increased. Based on the deformation characteristics of rock and the creep test results,a fractional calculus was introduced to establish a nonlinear creep model considering the influence of low temperature. The Universal Global Optimization algorithm and Levenberg-marquarat algorithm were taken to identify the model parameters of creep test results in different temperature environments. The theoretical curve agrees well with the experimental results,especially in the accelerated creep stage. It indicates that the model can well describe the creep behavior of red sandstone in a low temperature environment. The model parameters under different temperature conditions were analyzed. As the temperature drop,the elastic modulus E3(T) increases parabolically,while the elastic modulus E1(T),E2(T) and viscosity coefficient η1(T) increase exponentially. The study provides a theoretical basis for the long-term stability analysis of freezing method construction and rock mass engineering in cold regions.