Sandstone Unloading Rheological Test and Model Parameters Study

Rock rheology is common in engineering practice, which has an effect on long-term security and stability of the project. In order to understand the rheological mechanical properties under the condition of unloading sand, automatic servo apparatus of triaxial creep of rock was used to have a rheological mechanical unloading triaxial test on sandstone, which got typical flow complete curves of rock. Rheological test results showed that rheological phenomena occured in sandstone, and its rheological properties were significant with large rheological deformation, especially in high-stress conditions, When the external load exceeded the long-term strength of rock samples, specimen deformation went through three typical rheological stages with time increasing, and ultimately speed up the flow breakdown. Based on the experimental results, analyzed and studied the rheological parameters that were obtained, and discussed unsteady character law of rheological parameters. defined rheological damage of rock in the accelerating flow process as the unloading capacity and time-related exponential function, and proposed corresponding damage evolution equation, brought damage evolution equation into Burgers rheological model, and obtained nonlinear unloading model of rheological damage of rock, used accelerating rheological test curve of sandstone samples under the condition of 15MPa confining pressure and 135MPa stress level to verify nonlinear unloading model of rheological damage of rock, and the results showed that the fitting results of rheological test data and the improved rheological model had good consistency, and the rheological model can reflect the three stages of nonlinear rheology of rock, which can reflect the rheological characteristics under the condition of unloading sandstone more accurately.