Abstract: In the aim of obtaining the creep mechanical properties of mudstone under different stress environments, stepped loading creep test under confining pressure of 0.5 MPa, 1 MPa, 2 MPa, and 5 MPa was carried out on augergine mudstone from a project under construction. Results revealed that strength, plastic deformation ability and rheological properties of aubergine mudstone were greater and more significant with the increase of confining pressure; steady-state creep rate increased exponentially with the increase of deviatoric stress under the same confining pressure, and reduced with the increase of confining pressure under the same deviatoric stress. According to isochronous stress-strain curves, the long-term strength of aubergine mudstone was 11 MPa, 16 MPa, 22.5 MPa, and 29 MPa respectively, reduced approximately 40%~45% compared with the short-term strength under corresponding confining pressures; the long-term cohesion and internal friction angle were 3.09 MPa and 34.8° by Mohr strength criterion, decreasing by 20.6% and 25.9% compared with the short-term parameters. Furthermore, a fractional creep constitutive model with strain trigger was given to simulate the whole process of mudstone creep, and the theoretical curves fit well with experimental curves.

Key words: aubergine mudstone, triaxial creep, steady-state creep rate, long-term strength, creep constitutive model