Abstract: Previous studies show that with increasing pressure level, the critical state stress ratio M of some clays decreases remarkably within a narrow range of Δe. In other words, "steep decrease" in M of clay occurs. However, stress path, end restraint and second saturation after consolidation were not taken into account in these studies, which could lead to erroneous test conclusions. For further validation, taking measures including the use of lubricated ends and second saturation by back pressure after consolidation, triaxial undrained compression and extension tests on remolded clay from deep strata in East China are performed under stress levels of 0.3~2.5 MPa. It is shown that the above "steep decrease" in M exists for both triaxial compression and extension tests, and that second saturation has a far more significant effect on the measured critical state stress ratio of clays under high consolidation pressure than does alleviating the end friction restraint. Then, comparative analysis indicates that the existing nonlinear strength theories of geomaterials cannot reasonably describe the observed pressure- and stress-path-dependent nonlinear M of the studied clays. Finally, it is preliminarily revealed that the "steep decrease" in M of clays is closely related to the predominant face-to-face contacts between parallel clay particles at critical state under high pressure.