Rheological behavior of sandstone under unloading

摘要

Engineering practice shows that the instability and destruction of rock excavation does not occur immediately after the completion of the excavation, and unloading is a time-related concept, including the instantaneous unloading, as well as long-term unloading. It is quite necessary to carry out rheological test of rock mass under unloading for the study of the rock mass long-term stability, which has an important engineering significance. By using of rock servo-controlling rheology testing machine, triaxial compression rheological experiments were carried out, the variation laws of rock deformation with time increasing was analyzed under different confining pressure, the deformation properties of rocks in the rock triaxial rheological process were studied, and the development trends and characteristics of rock deformation in stage of accelerated rheology were discussed. At the same time, the rupture forms and mechanisms were analyzed. It can be seen from tests that, the rheological phenomena of sandstone samples took place significantly over time in the long-term external loads, the rheological deformation characteristics of sandstone samples became more and more obvious under the condition of unloading confining pressure sequentially and maintaining stress level and confining pressure constant, and sandstone rock samples, when in the final level of confining pressure levels, rocks came into rheological destruction of non-linear accelerating. Assume that at the rheology accelerating stage the evolvement of rheology damage represent a exponential function of the unloading degree and time, and the damage evolving functionwas deduced. In order to improve classic Burgers linear rheological model of rockwhich does not reflect the nonlinear rheological properties of rock enough, the damage factor was added to the burgers rheological model. The corresponding damage rheology model was proposed. In order to verify the adaptation and rationality of the rock nonlinear rheological model, used accelerating rheological test curve of sandstone samples under the condition of 15MPa confining pressure and 135MPa stress level to verify nonlinear rheological damage model 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 accurately reflect the sandstone rheological characteristics under the condition of unloading.