Numerical modeling of dip-slip faulting through granular soils using DEM

Abstract

A GPU-based DEM modeling methodology with rolling resistance is employed to study comprehensively dip-slip faulting through granular soils from both engineering and fundamental viewpoints. From engineering viewpoints, the results of engineering significances, including the ruptures path, the fault outcropping location, the ground surface distortion zone, the near surface stress path within the rupture and the fault outcropping strain are studied. From fundamental viewpoints, the orientation of the ruptures (shear bands) is discussed using the Roscoe theory. The analyses show that the fault ruptures deviate from the fault projection surfaces as propagating up toward the ground surface; the deviation depends on the faulting type, faulting angle and soil density. The reverse ruptures may deviate from the fault projection surfaces toward the hanging wall or foot wall, depending on the fault dip angle; however, both primary and secondary normal ruptures refract at the soil-bedrock interface, deviating toward the hanging wall. In addition, the analyses show that by increasing the fault dip angle, the slopes of the near surface stress paths within the reverse ruptures increase from about the slope of the biaxial compression stress path to about that of the p-constant stress path (compressional regime); conversely, these slopes within the normal ruptures decrease from about the slope of the biaxial extension stress path to about that of the p-constant stress path (extensional regime). Moreover, the analyses show that the fault outcropping strains of reverse faulting are comparatively higher than those of normal faulting. In addition, the fault outcropping strains are proportional to the soil ductility. From fundamental viewpoints, the analyses show that all of the reverse and normal fault ruptures through the denser and looser sands do propagate in parallel with zero-extension lines of the localized areas located along the ruptures paths, provided that the variations of the maximum principal strain directions and dilatancy rates along the ruptures are taken into account; this is in accord with the Roscoe theory.