Long-Term Stability of a Circular Roadway Subjected to Inner Pressure

Seisuke OKUBO and Katsunori FUKUI

J. of MMIJ, Vol.115, No.1, pp.9-15 (1999)

It is the purpose of this study to clarify long-term stability of a circular roadway subjected to inner pressure σr(ri) together with rock pressureσr(ro). Circumferential stress at the wall σθ(ri) obtained by the elastic analysis is equal to {2σr(ro) - σr(ri)} . Therefore, it is natural to consider that tensile failure possibly develops into the surrounding rock starting at the wall if σr(ri) is larger than 2σr(ro). A question arises whether it can be properly applied to a circular roadway where large visco-elastic deformation is expected.

A non-linear rheological model proposed by this authors was used to simulate time-dependent behaviour of rock around a circular roadway. It was assumed that inner pressure gradually increases. Results of computer simulation indicate that ,at first, the failed region develops and the roadway converges. As time goes by, inner pressure gradually increases, then convergence ceases and finally the roadway diameter starts to increase. We obtained interesting results as follows;

1.	Even if σr(ri) is larger than 2σr(ro), σθ(ri) is still remained in compression provided that Poisson's ratio increases with failure of rock.
2.	Post-failure characteristics of rock, that is, slope of descending portion of stress-strain curve in the post-failure region is not so important.
3.	Time-dependency of rock is very important, and affects long-term stability of a circular roadway.

Right now, we have only limited information concerning time-dependent behaviour of rock. It is especially important to obtain accurate knowledge concerning Poisson's ratio and behaviour of rock in tension.

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