Unloading Rheological Test and Model Research of Hard Rock under Complex Conditions

Abstract

In order to study the unloading rheological properties of hard rock under complicated conditions, the proposed Mengdigou hydropower station with a granite dam foundation was taken as the research object. This paper studied the unloading rheological properties of the granite by testing means, and it obtained the unloading rheological deformation characteristics and deformation rules of the granite under complex stress conditions. The granite unloading rheological characteristics of the whole stress-strain curve were analyzed, and the nonlinear unloading rheological model (FOD-HKVP) was proposed based on the fractional-order derivative. When certain conditions are satisfied, it is possible to degrade this model into the classical Nishihara model, but it should be noted that the FOD-HKVP model is a more reasonable way to determine the long-term strength of the granite and to consider also the rock unloading rheological damage effect. It introduced the fractional-order viscous body of combination components with a different fractional-order derivative to describe the nonlinear creep characteristics of the granite unloading, which provides an adequate description of steady-state creep and accelerated creep properties. Following the analysis of test data and parameter identification for the FOD-HKVP model, the rationality of the model was validated. Compared with the Nishihara model, the fitting accuracy of FOD-HKVP model was more accurate.