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| EXPERIMENTAL STUDY OF MECHANICAL PROPERTY OF GYPSUM ROCK SOAKED IN HOT SATURATED BRINE |
| (Institute of Mining Technology，Taiyuan University of Technology，Taiyuan，Shanxi 030024，China) |
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Abstract Gypsum rock is commonly found as an interlayer in bedded salt deposits which are solution mined for the purpose of salt mining or oil and gas storage construction. To investigate the related mechanical properties of gypsum rock under the situation，series tests of uniaxial compression，tensile and shear strength are carried out in the laboratory with gypsum specimens soaked in brine of different temperatures and concentrations. It is demonstrated that the strength of gypsum rock is weakened to different extents with brine temperature and concentration increasing and soaking time lasting. The strength softening coefficient can be as low as 0.10 to 0.73 after being soaked in hot and concentrated brine for 60 d. The elastic modulus of the gypsum rock is also linearly decreased with the temperature and concentration of brine increasing. The elastic modulus of gypsum rock is 5.92 GPa after being soaked in half saturated brine of 40 ℃ for 60 days，however it suddenly decreases to 0.21 GPa when being soaked in saturated brine of 70℃ for the same time. Similarly，the tensile strength also decreases from 0.64—0.66 MPa soaked in brine of 40℃ to 0.27—0.47 MPa of 70 ℃. After being soaked in saturated brine of 70 ℃ for 60 d，a regressed equation for Mohr-Coulomb shear strength of the gypsum rock is obtained as . Two similar strength equations are also regressed as ， when the soaked time is 30 and 80 d respectively. It demonstrates that both the cohesion and inner friction coefficient of gypsum rock decrease with soaking time lasting. A parameter of failure rigidity is defined to illustrate the difference of gypsum failure at different situations. According to the calculated results and the geometry of stress-strain curves of the gypsum rock under uniaxial compression，the failure style of gypsum rock changes from brittle to ductile damage obviously with increase of the temperature and the concentration of soaked brine. The study is significant not only for the investigation of hydromechanical property of gypsum rock，but also for guidance for solution mining or storage cavern construction in bedded salt deposits.
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Received: 12 November 2010
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2011, Vol. 30 
