A constitutive equation of variable compliance type had been proposed by Okubo in 1987. The equation is simple and its parameters are relatively easy to obtain. The equation can be applicable to creep of rock, however, experimental result in primary creep region in which strain rate is decreasing with time does not conform well to the calculated result.
Recently Okubo and Fukui (2002) proposed a constitutive equation especially focusing on low stress level creep. In this study, old one proposed in 1987 and new one proposed in 2002 are combined to extend an applicable range of the constitutive equation of variable compliance type.
For validation of the proposed constitutive equation, calculated results are compared with the experimental data by Okubo and Nishimatsu (1986) and Fukui et al. (1992, 1993), and it can be said that experimental results in uniaxial compression can be well simulated by the proposed equation. The equation is also tested against the creep performed in uniaxial tension and possible applicability of the equation to tensile stress field is discussed.