An Improved Creep Model for Granite Based on the Deviatoric Stress‑to‑Peak Strength Ratio

摘要

Time-dependent behaviors of rocks can be attributed to long-term applied stress, which occurs in most underground engineeringprojects. The creep behavior of granite from the Shuangjiangkou underground powerhouse in western Sichuan Province,China, was investigated via creep tests. It is shown that granite has an obvious creep behavior under different confiningpressures and deviatoric stresses. The new dimensionless parameter DPR, which is defined as the ratio of the deviatoricstress to the peak strength, is proposed for experimental analysis. The relationships between the instantaneous strain andfinal visco-elastic creep strain of granite with DPR are established under different confining pressures. It is shown that whenDPR is equal to 0.63, the final visco-elastic creep strain of rocks will reach a minimum value. Based on DPR and the secondarycreep strain rate, a unified method for defining the long-term strength of rocks is proposed, and the granite will enterin secondary creep with a nonzero strain rate when DPR > 0.9501. The Nishihara model is improved, and the relationshipsbetween the parameters of the improved model with confining pressures and DPR are obtained. The improved creep modelcan satisfactorily represent the primary creep strain of granite and secondary creep strain of granite with time under a givenconfining pressure and deviatoric stress.