Fractional viscoelastic constitutive equations have been extensively used for describing the creep and relaxation behaviors of geomaterials. Their value and efficiency for fitting the creep or relaxation curves of geomaterials have been validated by many researches. In order to study the physical meaning of fractional order, creep curves of shale, rock salt, and mudstone under different confining and deviatoric stresses, temperatures, and water contents have been fitted and compared. We found that samples from the same layer have similar fractional orders and they are almost constant during the steady creep. Increasing confining stress will increase the elasticity of the rock and a larger deviatoric stress will lead to a stronger viscosity. The most interesting phenomenon is that the fitted parameters will have a mutation, when the deviatoric stress acting on the sample is larger than the long-term strength of the rock. Both the temperature and water content, which is the ratio of water mass and dried simple mass, have significant impacts on the creep curves. However, the fractional order is more controlled by temperature than water content. This is because that temperature has a more significant influence on the property of the minerals and the cementing property between the mineral grains is more likely to be determined by water content.

分数粘弹性本构方程已被广泛用于描述土工材料的蠕变和松弛行为。它们对拟合土工材料的蠕变或松弛曲线的价值和效率已被许多研究证实。为了研究分数阶的物理意义，拟合并比较了不同围压和偏应力，温度和含水量下的页岩，岩盐和泥岩的蠕变曲线。我们发现来自同一层的样本具有相似的分数阶，并且在稳定蠕变期间它们几乎是恒定的。围压的增加将增加岩石的弹性，较大的偏应力将导致较强的粘度。最有趣的现象是，拟合参数将发生突变，当作用在样品上的偏应力大于岩石的长期强度时。温度和水含量（即水量与干燥的简单量之比）对蠕变曲线都有重要影响。但是，分数阶比水更受温度控制。这是因为温度对矿物的性质具有更大的影响，并且矿物颗粒之间的胶结性质更可能由含水量决定。