Effect of Initial State and Intermediate Principal Stress on Noncoaxiality of Soft Clay–Involved Cyclic Principal Stress Rotation

Abstract

This paper presents an experimental study of the influences of initial major principal stress direction (ξ) and intermediate principal stress coefficient (b) on noncoaxial behavior of soft clay involved pure principal stress rotation. The noncoaxiality discussed in this paper was defined as the difference between the major principal stress direction and the corresponding principal strain increment direction. The results from a series of undrained tests for soft clay consolidated with different initial major principal stress directions (ξ) conducted by a hollow cylinder apparatus (HCA) are presented. The influences of intermediate principal stress coefficient (b) and initial major principal stress direction (ξ) on the variation of noncoaxiality were investigated. The experimental results provided clear evidence for soft clay noncoaxiality–involved cyclic principal stress rotation. The noncoaxiality showed segmentation characteristics. At the beginning of the test, the deviation degrees were also similar in all three tests, equal to approximately 4°. Also, with the same initial major principal stress direction, the degree of noncoaxiality under b = 1 was lower than that under b = and b = .5; with the same intermediate principal stress coefficient (b), different variation trends occurred with different initial major principal stress directions. It can be concluded that the degrees of noncoaxiality of clay specimens were affected by both intermediate principal stress coefficient and initial major principal stress direction. The results can provide an experimental basis for constitutive modeling of clays under complex stress path–involved principal stress rotation in future work.