Experimental study of creep characteristics of gypsum mine rock in triaxial compression

Gypsum minings use room and pillar method frequently; the creep characteristics of gypsum mine have an important impact on the stability of mined-out area. In this paper, Jinghua gypsum mine is taken as the background, using RC-2000 microcomputer to control triaxial creep test machine to carry out experiments with Jinghua gypsum mine rock under confining pressures of 0, 2.5, 5.0, 7.5 MPa respectively. Creep test data obtained are analyzed, selecting the appropriate model for the test curve, and utilize the stress-strain curves method to obtain long-term strength under different confining pressures. The analytical results elaborate that the gypsum mine rock creep contains attenuation creep and constant creep; attenuation creep appears when the axial stress is small; constant creep and attenuation creep appear when the axial stress is big enough; using Nishihara model to fit the test curve. Results show that Nishihara model can describe the creep mechanical properties of gypsum mine rock nicely; the correlation coefficient R is more than 0.9. The ratio of long-term strength to creep strength is within 0.89-0.95 under different confining pressures, which means that the confining pressure has little effect on the long-term strength. The results findings will provide a basis for studying stability of gypsum mine mined out areas.