Rheology characteristic is an important property of engineering soft rock. During that process, rock mass parameters decay with time. As one of the commonly used constitutive models, the Nishihara rheological constitutive model can comprehensively reflect the elastic-viscoelastic-plastic viscous rheological properties of rock. However, the parameters of its components are usually assumed to be constant, and the state description of the Nishihara model during the accelerated creep phase is not accurate enough, which is quite different from the actual one. Based on the Nishihara model and the parameter attenuation caused by damage, the parameters are regarded as variables over time, this paper proposes a Nishihara rheological model that considers damage and a method combines triaxial compression test to determine the damage threshold. Then, according to the proposed model, the second development of the custom model is carried out on the FLAC^3D platform, and a numerical simulation experiment with the same conditions as the existing literature is calculated. By comparing the results of the triaxial test in the existing literature and data of the numerical simulation of the improved constitutive model, it is concluded that the improved Nishihara model is in good agreement with the actual situation; in the experimental loading curve, the volume strain has an obvious inflection point, and then the damage increases sharply, which can be determined as the damage threshold.

In order to explore the meso damage and degradation law of jointed sandstone under the dry-wet cycles, the particle flow software was used to carry out the meso numerical simulation of jointed sandstone, and the meso mechanical properties and energy evolution mechanism of jointed sandstone under different dry-wet cycles were studied. The results show that the contact force between particles and the maximum value of parallel adhesion force decrease linearly with the increase of the number of dry-wet cycles; The crack evolution of jointed sandstone under dry-wet cycle mainly experienced four stages: slow increase, uniform increase, step increase and abrupt increase, and the number of cracks (total cracks, tensile cracks and shear cracks) was positively correlated with dry-wet cycles; The meso boundary energy, parallel cohesive strain energy and linear cohesive strain energy decrease gradually with the increase of dry-wet cycles. The dissipation energy in jointed sandstone is positively correlated with the number of microcracks; The dry-wet cycles action leads to the weakening of the fracture resistance between particles and the reduction of the energy storage capacity of rock samples, which is the energy mechanism that causes the dry-wet damage and deterioration of jointed sandstone.