Experimental study on creep deformation and long-term strength of unloading-fractured marble

Abstract

In order to take account of the unloading fractures in rocks due to the excavation, unloading-fractured marble specimens were obtained by the triaxial unloading tests. Then, creep tests on the unloading-fractured marble specimens under different stress levels and confining pressures were performed. Based on the creep tests, the creep deformation characteristics were studied and the results show that the creep curves exhibit the three stages of the idealised creep curve. Special attentions were paid on that the creep deformation and creep rate in lateral direction are far greater than that in axial direction and the lateral creep reaches the accelerated stage earlier than the axial creep. There are stress thresholds correspond to the inflection point of stress–strain relationship in lateral and axial directions, respectively, and the lateral threshold is less than the axial one. The creep failure is mainly caused by the strong expansion in lateral direction. Moreover, both the creep rate and deformation have positive relationships with the axial stress but decrease as confining pressure increases. The failure strain increases with increasing confining pressure. Then, the long-term strengths determined by the axial and lateral isochronous stress–strain curves, respectively, are discussed. Through the comparative analysis, the lateral creep reflects the creep characteristics of unloading-fractured marble more clearly and the long-term strength determined by the lateral isochronous stress–strain curves is safer for engineering applications.