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The interparticle friction behavior of saturated clay controls its mechanical properties, but remains unclear at nanoscale. As one of major clay minerals, the hydrated montmorillonite (MMT) is selected to investigate the nanoscale friction characteristics using Molecular Dynamics simulation method. Two portions of MMT representing two particles with a water film in the middle are created to simulate an undrained system. A virtual spring is applied on the upper MMT portion to provide the sliding with a constant velocity relative to the bottom portion. The effects of normal load and sliding velocity on the frictional behavior are then investigated. The friction coefficients of hydrated MMT at different cases were measured and compared with other experimental and simulation results for the validation. The evolution of normal load with the number of hydrogen bonds for hydrated MMT was finally analyzed. All simulation results indicated that the friction load fluctuated periodically with a cycle of about 9.10 A at sliding velocity inferior 0.001 A•fs−1, which was nearly equal to montmorillonite's lattice constant along the sliding direction; the fluctuation amplitude of the friction load increased with the decreasing sliding velocity; the relationship between the average friction load and the logarithm of sliding velocity followed a power function; the friction coefficient and the cohesion were found to increase approximately linearly with sliding velocity.

Nanoscale mechanical behavior of kaolinite as a fundamental failure mechanism has been investigated under uniaxial tension and compression using Molecular Dynamics (MD) simulation methods. External deformation has been applied on kaolinite with a strain rate of 5 × 10−7fs−1 for tensile and compressive tests in the directions parallel (x-, y-direction)/perpendicular (z-direction) to clay mineral layers. Results showed that better mechanical performance was presented in the directions parallel to clay mineral layers than the other direction due to its continuous lattice in this plane. However, the elastic modulus of kaolinite in the z-direction was almost half of that in the other directions, which nearly equals the overall elastic modulus of kaolinite with a value of about 72.6 GPa. Compression in the x- and y-directions resulted in the separation of clay mineral layers then bending toward the octahedral sheet till crack. Compression in the z-direction resulted in slippage of clay mineral layers at the first fracture then resistance till the second fracture at the strain of about 0.2. Tension would cause cracks in the direction perpendicular to the strain direction, which may be a cleavage fracture or cracks in clay mineral sheets. Different failure modes under tension and compression were originated from the layered structure of kaolinite.