Creep properties and constitutive model for salt rock subjected to uniaxial trapezoidal cyclic loading

Abstract

Uniaxial trapezoidal cyclic loading creep tests with different loading and unloading rates are performed on salt rock to study its creep properties. The results indicate that the axial strain produced by salt rock under trapezoidal cyclic loading occurs mainly in the 1st cycle, and other cycles generate less axial strain. The existence of constant high pressure stage leads to an obvious horizontal segment in the stress-strain curve, while constant low pressure stage has little effect on its stress-strain curve. The stress-strain curve in the 1st cycle includes elastic stage, plastic stage, creep stage and deformation recovery stage. The axial strain generated at plastic deformation stage gradually tends to 0 with increasing cycle numbers, then the curve in a single cycle includes only elastic stage, creep stage and deformation recovery stage. When the cycle numbers is small, the irreversible deformation produced by salt rock in a single cycle mainly consists of plastic deformation produced at the loading stage and creep deformation generated at the constant high pressure stage. After several cycles, the irreversible deformation in a single cycle mainly consists of creep deformation generated at the constant high pressure stage. With increasing cycle numbers, the minimum value of creep rate in a single cycle basically does not change, and the maximum value of creep rate decreases firstly and then keeps constant. Moreover, with increasing loading rate, the mean value of minimum creep rate basically remains unchanged and the mean value of maximum creep rate gradually increases. With increasing unloading rate, both the mean values of minimum and maximum creep rate decrease gradually. Finally, the creep equation for the Burgers model subjected to trapezoidal cyclic loading is deduced, and the reasonableness of which is checked.