The Influence of Principal Stress Direction on the Deformation and Failure of Red Clay

Red clay is widely distributed in Southwest China. Restricted by the preparation technology of remolded clay hollow cylindrical sample, the phenomenon and mechanism of the influence of the change of principal stress direction on the mechanical properties of red clay are still not clear. In this paper, saturated remolded red clay hollow cylindrical samples were prepared by the self-developed sample preparation device using the layered under compaction method. Pure principal stress axis rotation tests and shear tests with fixed principal stress axis were carried out. The results show that macro-mechanical behaviors of the specimen, such as deformation, strength, and morphology, are closely related to the rotation angle around the second principal stress, and these macro-mechanical behaviors show obvious segmentation characteristics. The calculation of stress paths shows that the loading direction of the extra load plays a decisive role in the tension and compression state of the sample. It results in the phenomena of "compression and swelling", "pure torsional failure" and "tensile and necking" and determines the macroscopic deformation. The reason for the above phenomenon may be that the compaction of the remolded specimen along the axial direction is stronger than that in the radial and circumferential directions. Therefore, the modulus, strength and other parameters of the specimen along the axial direction are different from those in the horizontal direction. It means that specimens have obvious cross-isotropy. The stress applied in different directions "activates" such difference, which in turn makes the specimen exhibit different mechanical properties in macro. Therefore, the research on the influence of stress direction on soil deformation and failure should comprehensively consider the stress direction and specimen anisotropy.