The role of boundary normal stiffness in the micromechanical behavior of geomembrane-sand interface: A numerical study

Three-dimensional discrete element method (DEM) is employed to investigate how boundary normal stiffness influences the shearing behavior at the soil-geomembrane interface. A robust and efficient algorithm was developed and implemented into direct shear numerical models, effectively capturing the key aspects of the sand-geomembrane interface behavior across a wide range of boundary normal stiffness values. The numerical model was validated by comparing the bulk responses of interface shear stress and volume change versus shear displacement with experimental data. At the microscale, particle displacements, rotations, contact network evolution, coordination number, redundancy factor and elastic stiffness tensor were investigated to shed light on the impact of normal stiffness on the interface response. The micromechanical insights, such as the development of higher level of geometrical and mechanical anisotropy, stronger interface interlocking to resist sliding and rolling of sand particles, and increased local density and bulk stiffness, are connected to the macroscopic response, explaining how higher boundary normal stiffness enhances interface shear strength and normal stress during shearing.