Abstract: In China, rock salt deposits are typically characterized by interlayers, which are mostly distributed in Yunying and Pingdingshan areas. In the construction and operation processes of salt caverns, gypsum interlayers are soaked in corrosive solutions (e.g., brine and oil). To investigate fracture toughness and weakening mechanisms of gypsum interlayers under corrosive environment, we conducted a series of cracked chevron-notched Brazilian disk (CCNBD) tests. The CCNBD specimens suggested by ISRM were prepared in the laboratory and were soaked in four different liquids (i.e., water, half saturated brine, saturated brine and acidic oil) under three different temperatures (i.e., 20, 50 and 80 ℃). The soaking time for specimens was one month. Moreover, the results of soaked specimens are compared with those of dry ones. The results indicate that fracture toughness of gypsum significantly decreases with the increase of temperature when soaked in a given liquid. By contrast, the fracture toughness of gypsum approximately remains constant at the same temperature. The degree of fracture toughness of gypsum after water and brine immersion is greater than that of acidic oil. The weakening of gypsum soaked in water and brine is attributed to the combined effects of water, temperature, and chlorine ions. Specially, the effect of water-temperature contributes to a severe weakening, but the chlorine ions have little effect. The weakening mechanisms of gypsum soaked in acidic oil are chemical reactions and dehydration. Petroleum acid (naphthenic acid) reacts with gypsum to produce calcium naphthenate, which can be dissolved in the oil phase. During this process, the dissolution of calcium naphthenate in the oil phase promotes the forward reaction. Consequently, the study is significant for the evaluation of the leakage risk of storage caverns in bedded salt deposits.

Key words: bedded rock salt, gypsum interlayer, fracture toughness, chloride ions