VARIABLE PARAMETERS NONLINEAR CREEP DAMAGE MODEL OF ROCK WITH CONSIDERATION OF AGING, DAMAGE AND DETERIORATION

The loss in bearing capability of partial bearing elements, which are subjected to the loads in the long-term, will be induced by the accumulation and development of internal damage. Because of the above phenomenon, the actual stress strength in internal parts of rocks is usually higher than the apparent stress strength. Based on rheology theory, the damage factor is introduced into the elastic and viscous elements. The creep equations of elastic-damage and viscous-damage element, which are used to depict the time-depending nonlinear characteristics of creep caused by damage accumulation in the process with constant loading, is proposed. Then, based on the characteristic creep equations of elastic-damage and viscous-damage elements, the creep equation of state of the classical combined model, where damage effects have been considered, is proposed. According to component characteristics of creep in the steady creep state, the nonlinear creep-damage model, which is characterized by five-element parameters, has been established and used to depict the steady creep of soft rock. At the same time, the characteristic equation of the combined model, which is characterized by creep damage, has also been established. Finally, based on the experimental data in steady creep stage conducted on the sandy shale from the Dongxiang copper mine in Jiangxi, analysis of the accuracy and feasibility of the combined model, which is used to depict the nonlinear creep characteristics of soft rocks, is conducted. The results of curve-fitting show that the aging-nonlinear characteristics can be depicted satisfactorily by introducing the damage factor into the creep elements.