Experimental creep curves of bischofite rock in a complex stressed state

In the work, rheological tests of samples of bischofite rock in a complex stressed state were carried out. The tests were carried out on cylindrical specimens according to the Karman scheme on a hydraulic all-round compression unit. During long-term deformation of samples of bischofite rock, the area of the samples changed during the experiment, and the axial stress was a function of the transverse deformations of the sample. This was taken into account in subsequent calculations. All tests were carried out at room temperature and humidity. The values of the principal stress differences were taken equal to 2, 5, 8, 11, 14, and 17 MPa with the sum of the principal stresses unchanged. The tests were carried out at average stresses of 45 and 59 MPa. Phenomenological rheological models of creep processes with various combinations of elastic and viscous elements in such samples were used for a visual mathematical description of the properties of bischofite rock. The model is presented as a sum of mathematical expressions describing elastic deformation, as well as damped, steady-state and progressive creep.
In practice, it becomes necessary to obtain rheological curves for arbitrary values of the principal stress differences that are in the range between their minimum and maximum values. Therefore, an algorithm and a computer program were developed for obtaining the desired curves for any given difference in the principal stresses that are between the minimum and maximum values specified in the experiment. The program can be sent upon request.