Abstract: Triaxial rheology tests under different confining pressures and osmotic pressures were carried out on the silty mudstone from the Badong formation in Three Gorges Reservoir area to study the effect of osmotic pressure and confining pressure on the rheological properties of rock mass. The collection and preparation of rock specimens as well as the test scheme are introduced in detail. Through analyzing the creep curves of silty mudstone, the osmotic pressure and confining pressure’s influences on the rheological process and mechanism of silty mudstone are discussed. Furthermore, creep long-term strength of silty mudstone under different confining pressures and osmotic pressures is obtained according to the stress-strain isochronal curves and the steady-state creep rate. Results show that: 1) the instantaneous elastic modulus of silty mudstone decreases as the stress level increases; 2) pore water pressure could reduce the axial strain in the initial stage of creep, but increase the axial strain in the later stage of creep because of crack extension; 3) osmotic pressure shortens the time of creep damage and causes some characteristics of brittle failure; 4) osmotic pressure is conducive to the expansion and coalescence of rock fissures, which yields the reduction of the creep long-term strength of rock; whereas confining pressure increases the creep long-term strength. The results provide important experimental and theoretical references to understanding the creep characteristics of silty mudstone in the Three Gorges Reservoir area.

Key words: silty mudstone, triaxial rheology, osmotic pressure, confining pressure, long-term strength, Three Gorges Reservoir area