Abstract: Under engineering loads such as traffic and seismic loads, granular soil is often subjected to complex 3D stress paths. Most existing constitutive theories and models for granular soil have been proposed based on results from laboratory tests conducted under relatively simple loading conditions. Therefore, the existing constitutive theories and models need to be verified under more realistic stress paths if they are to be applied to engineering practice. However, due to limitations in mechanical control, conducting laboratory tests with complex 3D loading is often very difficult or even impossible. In this study, a new numerical test method is proposed to provide the means to investigate the mechanical response of granular material under complex 3D loading. Spherical numerical specimens are adopted along with high precision stress-controlled boundaries, allowing for the application of any arbitrary stress state, forming the basis for complex 3D loading. Combined with a set of stress and strain measurement techniques, most existing physical tests can be quantitatively and numerically reproduced. Then, the 3D rotation of principal stress axes is achieved, exhibiting the advantages to use this method in the investigation of the mechanical response of granular material under complex 3D loading.

Key words: granular material, numerical test, discrete element method(DEM), complex 3D stress path