Index of time-dependency for rock and its application for the assessment of the long-term stability of underground structures

摘要

Previous experimental and theoretical studies showed that rock strength was proportional to the 1/(n + 1)-th power of loading-rate and creep lifetime was inversely proportional to the n-th power of creep stress, where n was the constant value depending on rock type and testing environment. This paper introduced the n values of various rocks and analyzed the relation of the n value to the loading condition, testing environment and other mechanical properties. The n values were almost constant in unconfined various loading conditions if rock type and testing environment were same. The n value decreased in water-saturated condition and increased under confining pressure in proportion to strength. The effect of time was incorporated into Rock Mass Rating (RMR) with the aid of the n value. A formula representing the reduction of RMR due to time was proposed.