Deformation and failure processes of Na-montmorillonite under uniaxial compressive strain condition via molecular dynamic method

Abstract

It is crucial to understand the compressive mechanical properties of bentonite for nuclear waste burial engineering while existing theories and methods are difficult to predict the mechanical properties and failure mechanisms of hydrated montmorillonite in the small strain scope. The structural evolution and mechanical behavior of different hydrated montmorillonite under compressive strain had been investigated through molecular dynamics simulation. Results indicated that the characteristics of deformation and failure in three directions were as follows. Compression in the X-direction led to the bending of the clay mineral planes, and rapid crack nucleation causing brittle failure. Y-direction compression caused the orientation of the clay mineral to tilt, local chemical bonds broke and dislocations occurred. Z-direction deformation was characterized by interlaminar compression, then stacking of layers, disordered distribution of atoms, and finally the collapse of the structural system. The mechanical properties of montmorillonite had a strong dependence on water content. There was a negative correlation between the ultimate compressive strength, Young’s modulus, and water content in the X- and Y-directions. Meanwhile the bilayer hydrated state had a higher ultimate compressive strength than the other two ones in the Z-direction.