Influence of principal stress direction on the stressstrain behaviour of completely decomposed granite

The measurement and study of the stress-strain-strength behavior of soils in general stress states involving principal stress rotation are necessary and valuable. To investigate the strength behavior under principal stress rotation, a series of undrained tests on compacted hollow cylinder specimens of completely decomposed granite (CDG) was carried in hollow cylinder apparatus. Tests were conducted at constant inside and outside pressures and maintained a fixed angle of rotation of principal stress with the vertical (?). Seven different angles of major principal stress orientations were used to cover the entire range of major principal stress directions from vertical to the horizontal. Two different confining stresses were also used. It is observed that the deviator stresses as well as excess pore pressures decrease with the angle ?. It is also observed that specimens were getting softer with the increase of ?. The results also show a significant influence of principal stress direction angle on the strength parameters. It is found that the angle ? is related to the occurrence of cross-anisotropy and the localization which resulted in a pronounced influence on the strength parameters of the CDG specimens