Experimental study of deformation behaviour of sand under rotation of principal stress axes

A hollow cylinder apparatus (HCA) was used to study the deformation behaviour of sand under rotation of principal stress axes. A series of drained tests were carried out with two types of stress path. The first one was pure rotating stress axes without changing the deviator stress, while in the other one the deviator stress was increased with the rotation of principal stress axes. Various constant deviator stresses were used to study the effects of stress level on the deformation and non-coaxial behaviour of sand. Specimens with two relative densities were prepared to investigate the influence of density on non-coaxiality. Meanwhile, study was carried out to validate the previous viewpoint that non-coaxiality was induced by the initial fabric anisotropy of material by comparing results from two different materials, which were Portaway sand and Leighton Buzzard sand. The results show that the deformation would accumulate with the rotation of principal stress axes. And the non-coaxial behaviour of soil was found in the study. It was also indicated that the non-coaxiality would be affected by the stress level, density and the initial fabric anisotropy of material.