Abstract
This paper presents a numerical investigation on the behavior of three dimensional granular materials during continuous rotation of principal stress axes using the discrete element method. A dense specimen has been prepared as a representative element using the deposition method and subjected to stress rotation at different deviatoric stress levels. Significant plastic deformation has been observed despite that the principal stresses are kept constant. This contradicts the classical plasticity theory, but is in agreement with previous laboratory observations on sand and glass beads. Typical deformation characteristics, including volume contraction, deformation non-coaxiality, have been successfully reproduced. After a larger number of rotational cycles, the sample approaches the ultimate state with constant void ratio and follows a periodic strain path. The internal structure anisotropy has been quantified in terms of the contact-based fabric tensor. Rotation of principal stress axes densifies the packing, and leads to the increase in coordination numbers. A cyclic rotation in material anisotropy has been observed. The larger the stress ratio, the structure becomes more anisotropic. A larger fabric trajectory suggests more significant structure re-organization when rotating and explains the occurrence of more significant strain rate. The trajectory of the contact-normal based fabric is not centered in the origin, due to the anisotropy in particle orientation generated during sample generation which is persistent throughout the shearing process. The sample sheared at a lower intermediate principal stress ratio $$(b=0.0)$$ has been observed to approach a smaller strain trajectory as compared to the case $$b=0.5$$ , consistent with a smaller fabric trajectory and less significant structural re-organisation. It also experiences less volume contraction with the out-of plane strain component being dilative.
Highlights
The sample sheared at a lower intermediate principal stress ratio (b = 0.0) has been observed to approach a smaller strain trajectory as compared to the case b = 0.5, consistent with a smaller fabric trajectory and less significant structural re-organisation
Soil laboratory testing and numerical simulations have mostly been carried out to study proportional loading with a stress history in which the deviatoric stress components are kept in constant ratio to each other, and the soil, if it has an anisotropic fabric, does not rotate with reference to the frame of the principal stresses [1]
The virtual experiment procedure proposed by Li et al [33] has been implemented in the commercial software PFC3D to reproduce the behavior of three dimensional granular materials subjected to continuous rotation of principal stress axes
Summary
Soil laboratory testing and numerical simulations have mostly been carried out to study proportional loading with a stress history in which the deviatoric stress components are kept in constant ratio to each other, and the soil, if it has an anisotropic fabric, does not rotate with reference to the frame of the principal stresses [1]. Arthur et al [4] applied controlled changes of principal stress axes with the Directional Shear Cell and studied sample behaviour to shearing after a pre-loading to a high stress ratio and a rotation of principal stress axes. The introduction of an additional deformation mechanism associated with loading orthogonal to the current stress state is often the practice [1,18,19]. This implies a large number of model parameters which are often difficult to calibrate. The list of boundary particles needs to be regularly updated, in particular at large strain levels This requires additional computational power, and may cause local force redistribution. The summation convention over tensor indices is followed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
