Stress relaxation tests on green schist specimens under multi-axial compression

The biaxial stress relaxation tests on green schist under different stress levels from the auxiliary tunnel at Jinping Second Stage Hydropower Station are carried out by using biaxial creep machine, and an empirical fitting equation is put forward. The research results show that the axial stress descends in step form with fixed axial strain under uniaxial compression, which is the result of new crack occurrence and pre-existing crack propagation. The axial stress descends and the lateral stain ascends in step form when the axial stress relaxation tests under biaxial compression are carried out, and the lateral stress descends and the axial stain ascends in step form when the lateral stress relaxation tests under biaxial compression are carried out. Meanwhile, the axial and lateral stresses have much influence on each other when the axial and lateral stress relaxation tests are carried out simultaneously. The curves of the empirical equation agree with the test ones; therefore the empirical equation is available and reasonable.