Fractal model of shear-induced rough fracture flow by cross-scale description of its geometry

The Beishan area in Gansu province is the main pre-selected site for deep geological disposal of high-level radioactive waste, it therefore bears implications for the study of fracture seepage characteristics of granite caused by shear failure. This paper investigated the fractal modeling of the geometric and seepage characteristics of granite fracture sections under shear conditions, with the aim to explore the effect of the geometric characteristics of multi-scale rough fractures on the evolution of nonlinear seepage field in Beishan granite. Results show that the roughness height and aperture of rough fractures have complete self-similarity in the process of model scale change, whose distribution are always consistent in the process of spatial scale change. The seepage velocity field, gradient field and divergence field only demonstrate the continuation of local characteristics, in particular, the corresponding quantity fields at different scales are subject to normal distribution. As the observation scale increases, the spatial fluctuation in the field gradually decreases, the sharp mutations in the three fields gradually disappear and are smoothed. This indicates that the larger the observation scale, the greater the probability that the seepage of rough fracture is misjudged as the seepage of parallel plate, therefore the seepage characteristics of rough section would be more accurately described by taking the geometric scale into account.