Study of creep characteristics of gypsum rock in natural and saturated states

The saturated and softening creep characteristics of gypsum rock have important impacts in the safety evaluation of gypsum mine goaf. Taking Jingmen gypsum mine as the research object, the saturated and softening creep characteristics of gypsum rock are analyzed by carrying out single sample step by step increment load experiment in natural or saturated conditions; the constitutive relation of gypsum rock has been described by Nishihara model. The results show that the total creep deformation of saturated states is large than the natural; the average strength (11 MPa) of saturated samples is 0.54 times of the natural samples (21.5 MPa), the average long-term strength of saturated samples (10 MPa) is 0.49 times of natural samples (19.5 MPa); using the Nishihara model to fit the creep curve and analyze the creep parameter; the fitting results show that the creep parameter E-1 is 0.1-0.5 times of natural sample; eta(1) is 0.2-0.7 times; E-2 is 2-10 times. The above results indicate that the creep characteristics of saturated samples are more obvious than the natural ones. By analyzing the mechanism of creep characteristics of water-softening gypsum rock, we can draw the conclusion: the water-softening of gypsum rock includes the hole-pressure effect under hydrostatic pressure in physical layer aspect and recrystallization in chemical layer aspect. The resulting findings can provide basis for safety evaluation of gypsum rock goaf, which has important actual engineering significance.