  In this article, we investigate the creep mechanism of clay at the nanoscale.
We conduct the molecular dynamics (MD) modeling of clay samples consisting of
hexagonal particles under compression and shear. The MD simulations include
oedometer creep, shear creep, direct shear tests, and stress relaxation. The
numerical results show that the nanoscale creep mechanism of clay is related to
particle rotation, translation, and stacking under different loading
conditions. The clay sample under creep shows two types of particle
arrangements, i.e., the shifted face-to-face configuration and the face-to-edge
configuration. The orientation angle of clay particles is computed to track the
rotation of individual particles due to creep. The fabric variation of the clay
under creep is characterized by the dihedral angle between the basal particle
plane and the x-y plane and the order parameter. It is found that the factors
affecting the microstructure variation of the clay aggregate include stress
levels, loading rates, and particle sizes. In the nanoscale shear creep test,
the creep process comprises three stages, i.e., primary, secondary, and
tertiary. The microstructure change during creep depends on the initial
alignment of clay particles. The clay creep under a more significant stress
level results in a more considerable order parameter and a more orientated clay
structure.
