In many practices of underground engineering

rock mass is subjected to neither pure creep nor pure relaxation.In fact

both stress and strain change with the lapse of time

and thus rock mass has time-dependent property

which eventually lead to fracture of rock mass.It is hard to exhaustively explain this phenomenon by creep and relaxation.This study comprehensively describes the characteristics of generalized stress relaxation and the significance of engineering practices.Non-linear Maxwell model is applied to solve the exact solutions of variable compliance type constitutive equation under the generalized relaxation condition.In particular

we obtain

the accurate value of parameter-n

1

which governs the time-dependent behavior in the pre-failure region by alternately loading rate and loading-unloading tests.Generalized relaxation tests are carried out under 70%and 90%stress levels

and the time-dependent behavior under different stress levels and different direction coefficients are also discussed.Finally

experimental results of generalized relaxation under 70%and 90%stress levels are numerically simulated by the variable-compliance-type constitutive equation based on the non-linear Maxwell model.Calculated results are good agreement with experimental data

and the properties of generalized relaxation of Kawazu tuff are well explained.