Abstract: To explore the creep mechanical behavior of mudstone under different temperature and stress fields, we carried out triaxial step-loading creep test on mudstone at room temperature (25 ℃), 60 ℃ and 120 ℃, and built a constitutive creep model in consideration of damage and temperature effect according to the obtained creep curves and creep parameters under different temperature and stress fields. Results show that high temperature promoted the internal molecular motion of mudstone, weakened the mutual cementitious force between particles, and made the creep characteristic more obvious; confining pressure inhibited the internal damage development of mudstone to some extent. Steady creep rate increased in an exponential function with the rising of deviatoric stress and temperature; but reduced linearly with the increase of confining pressure. Under each temperature field, the long-term strength and the long-term shear strength parameters of mudstone increased in a good linear relationship with the increase of confining pressure; under the same confining pressure, however, the long-term strength weakened with the rising of temperature. The constitutive creep model coupling heat-mechanical effect on the basis of classic Nishihara model could well simulate the creep behaviors of mudstone under temperature and stress fields. Fitting results suggest that the elastic modulus and viscosity of mudstone reduced linearly with the rising of temperature, while α increased with the rising of temperature.

Key words: mudstone, temperature and stress field, triaxial stepped creep, steady creep rate, long-term strength, constitutive model