Mechanical properties of bedded rock salt and creep failure model

Taking the Sodium Chloride rock salt specimens containing mudstone interbed, located at 600～700 m level of Yunying salt-mine in Hubei Province as the research objects, the conventional mechanical tests on the specimens and uniaxial compression creep tests on the specimens under multi batch stress levels were performed. The conventional mechanical tests obtained the result that the bedded rock salt is a kind of special combined soft rock, its elastic modulus is comparative little, but lateral deformation of the rock salt is great under uniaxial compression stress state. Through creep experiments, the results were obtained as follows: (1)If the duration of creep is enough long, the attenuation creep stage, the steady creep stage and the accelerative creep stage are appeared during the bedded rock salt creep, with the accelerative creep stage last longer compared with other rocks. (2)The phenomenon of invagination of interlayer and bulge of rock salt is found at the steady creep stage. Uncoordinated creep deformation may lead to shear dislocation in the interbed. Creep failure model of bedded rock salt is also established in which the damage variable is viewed as the ratio of the ring tensile strain of specimens and ultimate tensile strain. Mechanism of creep failure in the rock salt strata induced by the differences in creep characteristics of the interlayer and that of rock salt theoretically is revealed. The experimental phenomena that the interlayer splits failure firstly, then the failure of interlayer driving tension cracks propagating in interbedded rock salt is reasonably explained.