The creep-seepage characteristics of rock under true triaxial compressions

Carbon storage, nuclear waste disposal, tunnels, and other underground engineering have a long service life and require accurate permeability control. The surrounding rock is subjected to a true triaxial stress state because of tectonic stress and engineering disturbance. Previous studies have found it difficult to reproduce the in situ stress state, which affects disaster prediction and assessment. In the present work, with the help of the true triaxial apparatus, the creep-seepage tests have been performed on sandstones under true triaxial conditions with the loading type of constant intermediate stress coefficient, bσ. Experimental results show that strain and strain rates are in three stages. There is a functional relationship between anisotropic creep strain and bσ. The stable creep strain rate in three principal stress directions is mainly affected by the creep stress ratio, Sr. The permeability decays in the low creep stress ratio stage, and the permeability tends to increase when Sr is 0.95. The anisotropic characteristics of permeability show a trend of first increasing, then weakening, and increasing again in the accelerated creep stage.