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.

本研究针对水氯镁石岩（bischofite rock）试样开展了复杂应力状态下的流变试验。试验采用圆柱形试样，依托液压式全围压压缩试验机，按照卡曼（Karman）试验方案进行。在水氯镁石岩试样的长期变形过程中，试样的截面积会随试验进程发生变化，且轴向应力为试样横向变形的函数，该情况已在后续计算中予以充分考虑。所有试验均在室温及恒湿环境下开展。本次试验选取的主应力差分别为2、5、8、11、14及17 MPa，且保持主应力和恒定；试验的平均主应力设为45 MPa与59 MPa。为实现对水氯镁石岩流变特性的可视化数学描述，本研究采用了包含多种弹性元与黏滞元组合的蠕变过程唯象流变模型（phenomenological rheological models），该模型由描述弹性变形、衰减蠕变、稳态蠕变及累进蠕变的数学表达式叠加组合而成。实际应用中往往需要获取介于试验最小与最大主应力差之间任意取值下的流变曲线，为此本研究开发了可生成指定范围内任意主应力差对应流变曲线的算法与计算机程序，该程序可应请求提供。