Small-scale size effects on the shearing behavior and sliding stiffness reduction-displacement curves of rock-plastic gouge simulant under low normal stresses

Assessment of the influence of laboratory specimen size (and scale effects) is critical to be obtained in the study of geological structures. The present work examines the influence of the small-scale size of specimens (in the range of a few tens of millimeters) on the behavior of analogue discontinuities with highly plastic clay filling material using a custom-built apparatus. The results showed that the displacement required to reach the peak friction increased with the specimen size, while the shearing stiffness showed an opposite trend. A slight increasing tendency of peak friction with increasing specimen size was also observed, but it needs further testing to be assertive. The weakening behavior in the gouge layer increased at larger normal stresses leading to significant post-peak softening, which was intensified as the gouge layer size increased. Application of pre-consolidation to the gouge layer intensified the weakening behavior. The degree of non-linearity in the stress-displacement curves and rigidity of the specimens were also quantified, and a hyperbolic-type model was implemented to measure the shear stress mobilization rate based on the stress-displacement curves. The data were further integrated with that from previously published works on experiments at smaller and larger scales to enhance the findings from this work on scale effects on the mechanical behavior of geological structures.

Automated summary

The influence of laboratory specimen size on the mechanical behavior of geological structures is examined in this study. The results show that specimen size affects the peak friction and shearing stiffness, with larger specimens requiring more displacement to reach the peak friction and exhibiting lower shearing stiffness. The weakening behavior in the gouge layer is also intensified at larger normal stresses and increasing gouge layer size.