Tri-axial creep test was carried out on borehole sampling basis in order to reveal the creep characteristics of purple silty mudstone in the Upper Silurian in the center and west of North Tianshan, and provide the basis for the designing, construction and long-term stability evaluation of the proposed deep and long tunnel. Test was performed on five rock tri-axial creep test machines with the confining pressure of 0, 5, 10, 20 and 30 MPa, respectively. Through the study, the following resulted were achieved. Rock creep characteristics was proved to be describable by the Xiyuan Model and a creep constitutive equation was establish for this kind of mudstone. The creep parameters were gained by calculating them based on creep curves. Long-term rock strength was obtained by superposition theorem and isochronous curve method, and the confining pressure effect was revealed on the long-term strength. The creep parameters increased with the increase of confining pressure, and the difference between long-term rock strength and instant rock strength increased by 25% under uni-axial pressure and 52% under tri-axial pressure of 30 MPa as the confining pressure increased. The long-term shearing strength decreased by 60%(cohesion) and 36% (internal friction angle) compared with the instant shearing strength.These results provided a scientific basis for the engineering construction, and the test and result collation methods were available for other similar construction and research. Meanwhile, physical and mechanical property of silty mudstone was also obtained through routine tests, which helps to apply creep test result to other similar projects.
