Creep property and damage constitutive model of dioritic porphyrite under cyclic loading-unloading

The hierarchical loading compression creep test fails to fully consider the viscoplastic strain in a stable creep. Thus, the triaxial cyclic loading compression creep test is adopted to realize the separation of viscoelastic and viscoplastic strain to fully consider the two strains in each stage of the creep. With the development of hydropower project construction in China being moved towards the mountain valley, the geological conditions and engineering environment faced by geotechnical engineering become more complex. Moreover, in the process of geotechnical engineering design, engineering construction, and safe operation, the effect of the rheological, mechanical properties of rock becomes more difficult to ignore. This engineering problem is becoming more significant for the staff involved. Therefore, rheological, mechanical properties of rock have become a very important research content. This study took the diorite porphyry of one hydropower station as an example to discuss the creep characteristics of this type of rock. Before the failure, the instantaneous elastic strain and instantaneous plastic strain increase linearly as the deviator stress gradually increases. With increased deviator stress, the viscoelastic strain and viscoplastic strain exhibit a nonlinear increase. The fractional Abel viscous pot and Kelvin model were introduced to form a new viscoelastic model. The fractional Abel viscous pot was used to replace the linear Newtonian fluid in the traditional viscoplastic model, and a viscoplastic damage model was established based on the damage variables. The new viscoelastic plastic model and viscoplastic damage model were then connected in series with the transient elastic model and transient plastic model to form a new rock creep damage model. Finally, the model is fitted with the rock creep curve to prove the applicability of the model.