Shigen-to-sozai, Vol.116, No.2, pp.91-96.
Multistage Creep Test of Inada Granite and Estimation of Long-term Life Time under Confining Pressure
Tsutomu YAMAGUCHI1, Seisuke OKUBO2, Enrico MARANINI3 and Takashi NARITA1
| 1. Department of Geoengineering, National
Institute for Resources and Environment,
Tsukuba-shi 305-8569 2. Department of Geosystem Engineering, The University of Tokyo 3. Department of Engineering, University of Ferrara, Italy |
| During a multistage creep test (MSCT), a
rock specimen is stepwise loaded until failure.
Several loading phases are followed by creep
periods at regular time intervals, during
which free viscous deformations are observed
in the sample. The MSCT is very useful to
examine the visco-elastic behavior of rocks
: when the stationary creep state (or steady
state) is observed during a creep stage,
the creep rate is revealed as a function
of the applied constant stress level. In
case of hard rock like granite, a logarithmic
creep relation is commonly identified to
explain the visco-elastic behavior during
a given creep stress level. One of the authors
(Okubo) proposed a visco-elastic constitutive
equation for a rock. This law can explain
correctly the time dependent behavior of
rocks, both during creep behavior, relaxation
behavior, and dependence of strength level
associated to different loading rates. In this work, MSCTs were performed in triaxial compression on Inada granite specimens, at a confining pressure varying from 0 to 40 MPa. The data were analyzed adopting the above said constitutive equation. The results of both the experimental and the analytical characterization give the following conclusions ; (i) the Janach failure criteria fits correctly the strength level variations of Inada granite, at confining pressure up to 40 MPa; (ii) a logarithmic relation can explain the creep rate during each step of the MSCTs ; (iii) the proposed constitutive equation predicts correctly the visco-elastic behavior of the rock ; (iv) the same formulation can be used to estimate the life-time dependency of this rock. |
| KEY WORDS: Rock, Failure Criteria, Multistage Creep, Time-dependent Behavior, Life Time, Constitutive Equation |