Nishihara Rheological Model of Soft Rock Considering Damage and FLAC^3D Implementation

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.