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Abstract In the laboratory，uniaxial compression experiments are carried out under monotone and cyclic loading states with gypsum specimens in dry，saturated and half-saturated states. The test results demonstrate that the peak strength of dry gypsum by cyclic loading is 12.3 MPa，strength decreasing of 15.8% at 14.6 MPa under monotone uniaxial compression. The strain of the specimens at peak strength also decreases from 0.39% under cyclic loading to 0.19% of monotone uniaxial compression. Both the peak strength and the corresponding strain of gypsum decrease when loaded in cyclic state. However，the elastic modulus keeps unchanged. Compared with that of dry specimens，the peak strength of the wet gypsum specimens，either saturated or half-saturated in brine，does not decrease. It demonstrates that brine corrosion effect on gypsum strength is minor. However，the elastic modulus decreases from 6.6 GPa of dry state to 4.5 and 2.8 GPa of saturated and half-saturated states，respectively. It means that the deformation ability of gypsum is enhanced greatly after saturated in brine. Due to tightness in structure and low porosity of gypsum，chemical solution can not easily immerge into it. In addition，the brine solution is acidic in chemical component in the test and no chemical reactions can happen with gypsum even less brine moving inside. Consequently，the strength of gypsum can keep undamaged when saturated in brine. However，the deformation ability will be enhanced and a softening trend will emerge because of long-term soakage in brine. It is suggested that this mechanical property should be taken into account in construction and operation of oil and gas storage in bedded salt deposit containing thick gypsum interlayers.
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Received: 31 December 2009
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