[This article belongs to Volume - 53, Issue - 05]
Gongcheng Kexue Yu Jishu/Advanced Engineering Science
Journal ID : AES-14-11-2021-73

Title : Time-dependence of Generalized Rheological-compliance and Rheological-modulus About Rock
ZHANG Hailong, TANG Yang, REN Ting, OKUBO Seisuke,

Abstract :

Creep deformation and stress relaxation are two properties of rock mass in underground engineering, but in many construction practices, rock mass is neither pure creep deformation nor pure stress relaxation, with stress and strain of rock masses simultaneously changed with time, which is time-dependent, and may ultimately cause failure. It’s hard to explain the phenomenon simply by creep deformation and stress relaxation, so it is a challenge for rock mechanics researchers. To ensure the long-term stability of underground engineering and its structures, it is necessary to further study the properties of rock mass in the generalized theory of rheological mechanics. In the linear viscoelastic theory, the creep compliance was obtained by creep deformation test while the relaxation modulus by stress relaxation test, and the two values were showing linear rheological features, in a reciprocal relationship with each other, and could be converted in each other under certain conditions, so they were no essential difference. But in non-linear viscoelastic theory, their relationship was not clear, and the generalized rheological theory by the stress-feedback controlling method provided the possibility to study mutual relationship. The generalized rheological tests of Tage tuff at 50%, 85% of the peak stress level, Sanjome andesite at 50%, 65% and 80% of the peak stress level were carried out by using the stress-feedback testing method, the generalized rheological direction coefficient for two rocks were 3.0, ±∞, –3.0, –1.0, –0.3, 0, 0.3, respectively. The experimental results showed that the generalized rheological law for two rocks was similar, and the variation of stress and strain obeyed the logarithms law. Based on the definitions of creep compliance and relaxation modulus in the linear viscoelastic theory, the generalized related strain and stress were defined, the calculating method for generalized rheological-compliance (GRC) and generalized rheological-modulus (GRM) was proposed. According to the testing results analyses, the proposed method was general, and creep compliance and relaxation modulus were two special forms of generalized rheological properties. It was found that GRC and GRM were relevant to viscoelastic deformation, had obvious characteristics of time-dependence, direction coefficient-dependence and non-linear rheology, and the ratio between GRC and GRM slightly decreased with time, which showed that the rock rigidity gradually reduced, and deformation quickly increased in pre-failure region. Consequently, the proposed method in this paper can further analyze the quantitative relationship between rock rigidity and plastic deformation, it is very valuable for further investigation of time effect and assessing the long-term stability of underground structures.