Hydro-mechanical coupling characteristics and weakening mechanisms of filling joint resulting from water injection

The injection of fluids into fault gouges in rock formations disturbs the in situ stress conditions, leading to fault slip and increasing the risk of inducing earthquakes. The weakening effect and the permeation of the injected fluid can be influenced significantly by the presence of fault gouges. To investigate this issue, the hydro-mechanical characteristics of fault gouges were evaluated using physical tests to study the combined effects of coupling injecting water and shear deformation. We propose a new experimental apparatus that allows us to measure the spatial distribution of the thickness of a gouge layer sample under combined conditions of shearing and water injection, using 3D scanning technology to evaluate the primary flow path. The test results showed that injecting water had a significant effect in reducing the maximum shear strength, but the degree to which the strength was affected varied with the gouge fill material. The effect of shear deformation is that it will increase the inhomogeneity of the thickness distribution and therefore the distribution of injected water along the fault is not uniformly radial. Additionally, the properties of gouge fill material have an important influence on flow characteristics during fault slipping.