Influence of Water on Tensile Behavior of Illite through the Molecular Dynamics Method

Illite is a type of clay mineral that forms rocks. It plays an important role in the mechanical properties of the red-bed soft rock, which is significantly influenced by water. However, it remains unclear how water affects the mechanical properties of illite. An axial tensile test of illite with water content is performed using molecular dynamics (MD) simulations. Uniform tensile velocity is applied in the directions parallel (x) and perpendicular (z) to the illite. The slip and shear of this clay mineral sheet are the main cause of the softening of the red-bed soft rock because stretched illite is difficult to disturb when soaked in water. The density distribution of the interparticle solution shows that only the inner-sphere surface complexes exist in illite when it has a low water content. While in the cases of high water content, outer-sphere surface complexes exist in illite as well. The existence of water can greatly reduce the tensile strength of illite, by as much as 14%-25% (along x-direction) and 54%-84% (along z-direction) than those of the dehydrated cases, respectively, with different water film thicknesses. The destruction of tension along the x-direction is first caused by the tension fracture of the substituted tetrahedral covalent bond (At···Ob), which finally leads to the crack coalescence of the clay mineral sheet. While the tensile failure along the z-direction is mainly due to the pull off of the interparticle solution.