To investigate the water-induced ageing effect on gypsum rock

different water environment conditions were simulated in the laboratory

including different air humidity conditions and saturated groundwater conditions which may exist in the gypsum mines. Mechanical parameters of gypsum rock specimens were obtained under the pre-set conditions for different times. Meanwhile

the variation of pore structure in gypsum rock specimens was measured by nuclear magnetic resonance equipment. Then

the water-induced ageing mechanism of the gypsum rock was revealed. The results showed that the effect of water on the ageing of gypsum rock was obvious. Firstly

the ageing extent of gypsum rock increased with time

whereas mechanical parameters including uniaxial compressive strength

Brazilian tensile strength and elastic modulus decreased with time in a negative exponential relation. However

the Poisson’s ratio of gypsum rock had no clear relation with time. Secondly

the ageing extent and ageing rate of gypsum rock were closely related to the state of water. The higher the relative humidity was

the more pronounced the ageing extent was and the faster the ageing rate was. In particular

the ageing extent of gypsum rock was the most significant and its ageing rate was also the fastest when fully submerged in water. Generally

the water-induced ageing mechanism of gypsum rock was caused by the coupling of physical and chemical effects of water

and the chemical effect was the primary cause for the ageing effect. When the gypsum rock was exposed to water

the continuous dissolution and recrystallisation of the gypsum rock changed the mineral composition of the gypsum rock. As a result

the rock structure became loose

the porosity increased

and mechanical properties gradually weakened. The research results provide references for designing the gypsum mining and the evaluation of the long-term stability of gypsum goaf.